Originally Posted by JER
Its been my general feeling for quite a while now that for many people reception problems are usually related more to signal quality than signal strength.The above post by FoxTV indicates how complicated the signal environment can be and how difficult it can be to resolve these kinds of problems without a truck load of test equipment.
Probably the simplest way to avoid a lot of these problems is to get the antenna outside and to avoid amplifiers.
Putting the antenna outside helps reduce the impact of household noise sources. It also dramatically increases signal level and reduces the effect of indoor multi-path.
While amplifiers increase signal level, they always add something (e.g. noise, harmonic distortion, and inter-modulation distortion) that’s not actually on the air. A cheap amp can easily saturate on a strong in-band or even out-of-band signal and generate a wide spectrum of “crud” that makes it impossible to detect anything with the receiver. By starting off without an amp, you can make a better determination of what your true signal situation is like. Then, if you’re missing some weak stations you can add the amp and see if it really helped.
JER, I agree with your thoughts on amplifiers. I think they are overused to the point of causing problems instead of solving them. An amplifier is the last thing I would recommend to try and solve reception issues. This is based on my last 3 or so months doing field strength tests in our market that has very mountainous terrain. I have received signals from ours, and other transmitters in this rough reception terrain at 75 miles out, and still had plenty of signal head room for good reception using a Clear Stream C2 or in some cases a C4 at only 20 feet elevation.
I have seen this same scenario at many different locations in our rigorous signal testing project. I use a Rhode & Swartz FSH-3 TV Analyzer for RF signal analysis, along with a Sencore DTU 236 transport stream analyzer to look for echo strength and amplitude, and for echo timing to see how far out on the time line the echos are in highly problematic areas. It seems that most of the multi path issues are from reflective objects that are relatively close to the receive location instead of miles out as in analog.
I have not seen one location at that distance that if enough signal strength was there that I could not receive the signal, and have not really seen a situation where an amplifier would solve any reception problems. We have even seen situations on the Rhode & Swartz Analyzer where the signal was almost near the SNR of the tuner that we were using, but the gain of the C2 would still allow reception of weaker signals WITHOUT an amplifier.
You have also hit on a point that I have noticed on my Sencor TS analyzer that the BER (Bit Error Rate), EVM (Error Vector Magnitude), and SNR (Signal To Noise Ratio) changes drastically when an antenna is not aimed optimally. There is also a great variance in the BER, EVM, and SNR of various signals between different stations in the same market, and this can affect viewers reception of signals due to the signal quality between different stations in a given market.
The EVM and SNR are factors that determine the quality and receivability of a signal, especially out in the fringe areas of any given DTV signal. The viewer has no control over these aspects of the signal, and Broadcast Engineers are the ones responsible for ensuring that there is a quality signal being broadcast from their transmitter site.
If a viewer is having problems receiving a certain station, but all or most other stations can be received well, and the predicted signal levels are close to each other in strength, they may be fighting a loosing battle if the EVM and SNR of the transmitted signal is out of spec, or near the lower limits of legality in regards to FCC minimum specs. This is where the truckload of test equipment is needed in order to evaluate a Broadcast DTV signal for quality, which can effect reception of that signal.
Simply saying that an amplifier will solve these problems is not accurate in the real world. I can envision a day when spectrum analyzers for DTV could be built into receivers, and the terminology changed in order for the consumer to gauge the quality of the received signal themselves. I think this improvement would greatly enhance OTA viewing for the average viewer.
Test gear can show a lot of problems with a signal that are not known to the viewer and cannot be evaluated by any other method. Low signal IS NOT ALWAYS THE CAUSE OF RECEPTION PROBLEMS, as can be seen on test gear. I have seen situations where the RF signal levels were very strong, but multi path echos which could have been caused by the high signal levels in the first place would still kill quality reception of signals in highly reflective signal areas causing breakup and pixelazation of the signals. (RF signal levels and signal quality are measured on a completely different devices on a separate antennas so they can be evaluated simultaneously)
In closing, I do not recommend amplifiers at all, but they may have a use in the far field areas that do truly have a weak or low signal issue, but those situations are not all that common in our market, and evaluating different brands of antenna amplifiers with test gear is not on my agenda any time soon due to cost and time restraints.
I believe its fairly well known that amplifiers can overload on strong FM signals. The ensuing harmonics and intermod products can easily wipe out reception in high VHF television and higher bands. For those that must use the amp, a FM trap placed ahead of the amplifier can help reduce the overload and improve TV reception. The problem nowadays is that FM stations are only one of many possible strong signals that may enter the amplifier and cause overload and distortion.
I have a hunch (no data at this time) that at least some reception problems being observed may be traceable to cell phone towers. The lower cell bands are easily passed by most TV antennas. Since the cell towers are often very close to homes its easy to envision them saturating a cheap TV preamp since most of them have pass bands extending out to about 1 GHz.
Has anyone conclusively observed such a situation? If so, I’d be interested to hear about it.
Interesting, your post from the other day suggested that you supported some amplification to overcome large distribution loses. Why the change of heart? In my case, I lose one station due to distribution losses not poor reception. What do you suggest in my situation? See: http://www.dtvusaforum.com/dtv-hdtv-reception-antenna-discussion/12366-pre-amplifiers-usage-reviews.html#post35817
Antenna amplifiers and distribution amps are not the same animal. The only type of amplifier I would ever recommend would be a distribution amp to feed multiple sets, or to get the signal up enough to satisfy a multitude of splitters in multiple set installations. Possibly an antenna amp may help in fringe areas as long as there are no other strong sources of RF energy that are also amplified and can saturate the front end of a receiver while being amplified along with the DTV signal.
Distribution amps get installed after the signal is decoded in order to amplify the demodulated DTV signal for distribution to multiple sets, and have no relation to amplifying the 8-VSB digital data stream that makes up the DTV broadcast signal.
A lot of people are trying to overcome signal issues who’s quality may be in question by amplifying the signal, but a digital signal is not like analog where reception quality was simply an issue of more brute force power, either at the transmitter or at the receive antenna.
I have not heard any mention of signal quality except from JER, and if you look at different signals in any given market, you will see that signal quality can vary greatly among different broadcasters in the same market, and all of the high gain antennas and amplifiers you can buy and and erect will never overcome this problem if that is what is actually causing reception issues in the first place.
Signal quality refers to the signals parameters themselves, and not RF signal levels or power levels. The only way to gauge the quality of a signal is with a transport stream analyzer, and they are fairly expensive items that most people cannot afford, or will not use enough to justify its costs.
In regards to your channel 47 issues, since you are using a homebrew antenna, you could possibly replace the driven elements, or half of the driven elements with a physical size that favors the upper end of the UHF band. I am assuming that these channel numbers are the actual RF channels and not virtual channel numbers.
Since you have plenty of signal on the other channels, you could possibly afford to change the antenna to favor 47 without to much loss on the rest of the band.
I just hit upon this the other day, in my ponderings and ruminations as well.
I wonder if a new product would be successful, a low pass filter just above UHF Ch. 51. (or 55 for MediaFlo broadcasts).
Perhaps bandpass filters should be more commonly used, in general?
Hi Fox TV,
Sorry, didn’t see your reply earlier… I do my testing with an Apex 502 converter box that provides signal strength and signal quality readings. An example graph of my testing with attenuators is attached. Note signal strength has a strong linear relationship with margin to dropout indicating that the Apex is measuring signal strength rather than some other measure. Also note, signal quality was 100% until the margin decreases down to 5 dB or less. A good picture was observed until margin to dropout fell to 2 dB or below. However, recordings on my HTPC have many video/audio errors when signal quality is less than 100%. For that reason, I need to achieve a margin to dropout of least 10 dB for all my channels.
I did try a 4-bay with shorter spacing between bays and shorter elements (supposed tuned higher than my original DIY). Margin to dropout was only 1 to 2 dB higher with the new antenna, not enough to solve the problem.
Adjusting antenna aim to favor ch 47 has merit. I have attached a graph that shows the effect of aiming off axis on margin to dropout. Aiming directly at ch 47 tower saves 4 dB for that station but whacks ABC, PBS, and CBS by 14 dB. That’s too large of a whack, given that my distribution losses equal 20 dB and I need to maintain at least a 10 dB margin for each channel.
IMO, a pre-amp or distribution amp is the better choice.
Best,
Rick
All i know is i need two in-line (those cheap ones you buy at K-mart, signal amp) to pick up half of what i pick up. it doesn’t hurt the normal 15 or less i get any time, but without those two i’d have zero access to channels such as WPSD-DT. WAZE-DT (still watching George Lopez on that one 🙂 ), WSIL-DT and of course my new favorite, WBKO-DT
No one can say that there are no situations where an amplifier will not work, but if you live anywhere near a source of RF energy that is capable of saturating a DTV receiver, that Rf energy is also amplified along with the desired signal as well. Most DTV receivers were not built with FM harmonic filtering like the old tuners in almost all of the analog sets were. That was a requirement of FCC part 15 acceptance of the tuners if they were submitted for testing under part 15 at all, and not all were submitted for this approval process.
A lot of reception issues also come down to how much power a transmitter is running, and the assigned radiation pattern of their antenna. There are many scenarios that affect reception that the general public is not aware of. Not all stations are running the same power levels as all of the others in a given market. That could be due to limiting factors at the transmitter site, or for financial reasons, or for interference reasons. A lot of broadcasters were assigned directional antennas that have deep nulls in their signal pattern, and that could have been done to protect another channel such as an analog signal that is no longer on the air, or to protect an adjacent channel etc.
There are still financial and technical repercussions of the DTV transition that are not all worked out as of now for a lot of stations. A lot of items such as transmitter power, antenna patterns and many other limiting factors that are a repercussions of the FCC having to accommodate digital and analog channels at the same time that will take years, and many millions of dollars to fix.
At my station, we were assigned a directional antenna at one of or two transmitter sites in order to protect an analog channel that now is no longer on the air. In order to gain that coverage area back, we are now facing the task of raising our tower another 50 feet, and buying another $150,000 antenna, and scrapping the directional antenna that is only 3 years old that cost $100,000 dollars and it will be headed to the scrap yard in the near future. This is in addition to the current top mounted analog antenna that is also destined for the scrap yard.
The transmitter sites of many broadcasters are not optimized at the current time. There are many other factors involved in TV broadcasting that can effect reception that the general public will never know about, and it will take many years and many dollars to fix. I think that TV broadcasters should be eligible for a bail out too, or at least given tax breaks for the forced change over that many of them could not afford in the first place. The Government only said that you had to do DTV, and the Broadcasters were forced to do so, or lose their license to broadcast, with no financial incentives or tax considerations given.
Just another example of the heavy handed tactics of Government, when some business are considered “To BIG to Fail” and they get to rob the taxpayers of their hard earned dollars while some smaller broadcasters had to file for bankruptcy or mortgage their stations to the max to comply with the DTV transition. The DTV transition is not complete for a lot of stations, and there are many of these scenarios taking place even now.:angry:
Once the new 700 MHz cell towers come on line and FloTV already has, all of that RF is designed into all the equipment everyone is using.
There are filters that stop everything above 700 MHz but they are about $25 plus shipping, or say about $35 by the time it’s all said and done.
We have only begun to see interference from cell towers.
But if Congress and FCC gives them UHF TV, the interference problem will go away…
There will definitely be times when an amplifier will help reception. The problem is that the average Joe has no idea when to use one or what kind to buy. The fact that there are a lot of bad ones on the market with incomplete specifications doesn’t help.
I think the biggest problem is that there are a lot of cheap indoor antennas with amps that have too much gain (I’ve seen as much as 55 dB advertised) and that have terrible linearity and overload characteristics. Note that roughly 80% of the TV antenna market is for indoor antennas.
This problem is two fold. First it gives people the notion that they can receive TV with an indoor antenna even though the DTV system was developed assuming outdoor antennas. Second, it leads people to believe that its essential to have an amplifier with an antenna. Because of this, its nearly impossible to sell an indoor antenna nowadays that does not include an amplifier. Consumers incorrectly assume that the amplifier somehow magically makes up for the antenna being small and indoors. If this forum did nothing else but dispel this myth then we would be doing a great service to the public.
Now, lets talk about how and when an amp may help.
Please correct me if I’m wrong, but I believe the average DTV receiver has a noise figure of around 7 to 10 dB or so depending on band. Given this, its reasonable to expect that a well designed amplifier with a noise figure lower than that of the receiver will help reception by improving the signal to noise ratio.
For example if you have an amp with a noise figure of 2 dB and the receiver has a noise figure of 7 dB then you will likely see an increase in noise margin of roughly 5 dB (actually a bit less depending on gain, cable and mismatch losses). In SOME circumstances adding the amplifier is just as good as getting an antenna with 5 dB more gain. IN SOME CIRCUMSTANCES!
The problem is that the amplifier and receiver both have limited dynamic range. This fact automatically sets you up for problems.
If you buy a cheap amp (most likely scenario) it will likely overload on something (either in or out of band). When its overloaded, it will generate harmonic and Intermodulation signals that are not on the air. These distortion signals can easily ruin reception on some or all channels. Note that distortion phenomena aren’t captured in the noise figure number! Noise figure only looks at random noise added by the amplifier when its not in an overload or even strong signal situation.
If you buy decent amp with good linearity and overload resistance (high OIP3 and P1dB) you will find that the signals out of the amp are clean but now possibly too strong for the receiver. If the receiver overloads you’re back in the same situation as above with the cheap amp. You might see reception improved on some channels and ruined on others depending on how the distortion products pile up. A variable attenuator, trap or equaliser after the amp may help at this point but it will be a trial and error type of thing unless you have a truck load of test equipment.
So, the basic recommendation should be to start off with no amp and see what you get. If you get everything then you’re done. If not then you can try an amp and see what happens. The amp you want may depend on what problem you’re trying to solve.
If you’re deep fringe rural with nothing but weak signals (either in or out of band) then buy one with low noise figure (lower the better) and enough gain to overcome your losses.
If you’re in urban or suburban area where signals are strong, but you have lots of cables and splitters you want something different. Here, you should opt for an amp with good linearity and overload as measured by OIP3 and P1dB (higher the better on both). The noise figure will only need to be a modest 3 to 5 dB or so. This will ensure that you have clean signals with bit of a bump in sensitivity from the amp to help noise margin on the very weakest stations.
Again, the basic rule is to use outdoor antennas and to only use amps if and when you find problems that can’t be solved by other means.
I’ve got three properties in different rural areas, i.e. central New York, Adirondack Mountains, New York, and northern Michigan. A large antenna at any of these places will not yield even one channel. With a preamp, I get many. Night-and-day difference. Note also that I test-run all antennas on site with a max of 20′ of coax.
Here in central New York, where I’ve had a home for 30 years, I used to get one snowy VHF channel on RF 6 with a huge Wade VIP-307, as long as a good preamp was hooked it. With no amp, no TV.
Since the digital changeover, I put up three antenna sites on my property. I’m on the side of mountain, surrounded 360 degrees by more mountains. So, three sites gives me the best shots at three different city-targets – all 50-60 miles away and all in different directions. Again, big antennas e.g. Winegard HD8200, Winegard 9032, Wade-Delhi VIP-307, DB8, and 91XGs – all get absolutely nothing until a preamp gets hooked to them. Now, I get over a dozen channels consistently, many HD, and almost 30 subchannels.
As I said, in all the rural areas I’ve worked on TV reception, using a good preamp is a “no brainer.” Also, for my furthest antenna site that is 550 feet from my house, a 30 dB lineamp is also being used, along with the 28-30 dB preamp at the antenna, with RG11 coax buried in conduit.
I’ll also note, that with the preamps, I’ve observed very little difference in performance between those rated at noise levels of 4 dB (Antenna Craft 10G212) and those rated at low and ultra-low noise. I have a British Research Communications amp rated a .6 dB noise on UHF, and it works no better when it comes to locking and holding a weak channel, then my 4 dB amp.
Had a similar experience working on my wife’s parents house in northern Michigan. They are fairly close to two TV transmitters, both 30-40 miles away – and Michigan has virtually no mountains like here in New York. Lots of trees, though. They used to get two channels with rabbit ears until the digital change, then they lost both. Ends up their loss was due to #1, a change from VHF to UHF, and #2 a move to a more distant transmitter tower by one station. I installed a moderate size VHF/UHF antenna for them (90″ boom Yagi), and it was able to pull in one channel, off and on, with no amp. I added a good preamp, and they know get both fine. Now, maybe there was some other most costly remedy, like a bigger antenna, multiple antennas, tower, etc. Why bother when we know a $27 amp fixed the problem?
If you are not near any other sources of RF energy (FM transmitters, Cell phone towers etc) then I am not saying that amps will NEVER help reception problems. Amps have their place, and yours is a perfect example of a situation where they are actually useful, but they are the absolute last thing I would try after all other aspects have been exhausted. I would only recommend them in situations like yours where the problem is obviously low signal levels due to the distance away from the transmitters.
There is currently research ongoing into this very topic by industry experts. I am providing some useful links below to reception articles written in TV Technology magazine by Charlie Rhoades, who is an industry renowned expert on DTV reception and his opinions on amplified antennas are in the first link provided, along with a list of all of his reception articles written by him in the the last few years in the second link.
http://www.tvtechnology.com/article/88282
http://www.tvtechnology.com/section/digital-tv
Maybe some insight from experts into reception issues in general, and amplifiers specifically will help viewers along these lines. The first link addresses amplifiers specifically, but the research is not complete as of now. One last note is that their site is sometimes slow to load.
You did state that you “do not recommend amplifiers at all . . . ” and also that issues like mine are not “common” in your market. I’m not trying to pick a word-fight here but . . . to not recommend at all is just as silly as me recommending everybody use an amp.
I admit I don’t know what your “market” is. If you have something to do with Fox TV (going by your username), I can say that I get several Fox channels at all my rural properties. There are people who read these forums trying to make decisions on equipment, and such a negative statement can cause as much confusion as a blanket pro-amp statement.
The USA has around 300,000,000 people in it. At least 60,000,000 are in rural areas, and another 140,000,000 live in suburban or quasi-rural areas. That’s a lot of people who may not get TV at all, or very well, without some sort of signal amplification. I’ll add that I’ve met many people who tried to get digital TV reception and gave up – without even trying an amp due to some misinformation they read somewhere – or even worse – advice received at the local Radio Shack store. I’ve heard and read, often, about how amps cannot make a small antenna behave as if it’s bigger – yet many times a preamp can do just that. Also read about the digital cliff at 65 miles which is also untrue. Also about digital, or UHF digital only working with line-of-sight transmissions – again, not true. For somebody who’s been working with this stuff over the years, they can sift through such conflicting statements. But, somebody with no experience trying to read up first, and then do things right? That can be tough.
I still maintain that preamps and lineamps can be very useful and not just to an esoteric few. My in-laws live in the City of Alpena, Michigan and lost their only two TV channels after the digital change. A $27 preamp and a $45 antenna fixed their problem. The only other option (and I tested) was to install a 40 foot tower and antenna 450 feet from their house on a hill. Then the antenna gets those two channels with no preamp when tested on-site – but with a 450 foot run, a line-amp would be needed, even with RG-11 coax.
Seems the $72 invested was much more cost-effective than the tower and long line-run.
I like most of what you’ve said here, but this…
…cannot go without challenge. What you offer as proof is anecdotal evidence that only applies to the rural areas with which you’re familiar. For suburban and urban viewers — areas which include nearly 70 percent of the nation’s population, BTW — your axiom is a recipe for reception-robbing amp or tuner overload. It may also mislead rural readers into thinking that they can skimp on the antenna and get the same results.
The only way an amp can possibly make “a small antenna behave as if it’s bigger” is by counteracting cable and splitter losses. Please review the discussion here, under the heading “Signal Amplifiers, Preamplifiers,” for details. Money quote:
If amps were capable of doing as you suggest, lots of us could have saved a great deal of money by connecting bent paper clips to them instead of antennas!
No on several counts. I offered nothing as “proof.” I offered my experiences, based on just that. “Experiences” that I’ve had installing many antennas for 40 years in many suburban and rural areas. An individual event is certainly anecdotal. Many anecdotal events is more of a pattern. I’ll further add that many times I’ve fixed problems that defied book-logic by using anecdotal-based suggestions.
Sorry but not true. A good LNA can take a signal at the antenna that is present but too weak for the TV tuner to acknowledge, and make it so a picture appears on the screen. A line amp can make up for line-loss and keep signal strength strong enough so the TV tuner takes it. Main difference is that the noise caused by the first amp matters much more (LNA at the antenna). The line-amp noise matters little since it only has a small effect on final signal-to-noise ratio. Go to an area where some signals are known to be weak. Then, install the highest gain antenna you can find. Then tune into a fringe channel that the antenna can just barely get with no help from a preamp. Chances are, in that exact spot, an antenna with much lower gain and a much smaller size will pull in that same channel with a good preamp as long as it’s able to get some signal. Is it always that simple? Of course not. A preamp cannot make a signal out of nothing. It can, however, take a weak signal and make it strong enough to work on your TV. Just as a high-gain antenna can make the difference over a low-gain antenna. To reduce this to the paper-clip argument is silly. Using a small antenna will often result in being too far below the threshold of getting any signal at all. Then the amp does nothing but make noise. Note that I never said anything like a small antenna is as GOOD as a large antenna, nor did I say a small antenna and amp will ALWAYS get what the larger antenna gets. I did say that sometimes a small antenna certainly can behave like a much bigger antenna – and that is very easy to verify. Sounds to me like you’ve never camped or road-travelled with a small portable antenna and amp. I test potential antenna sites with a 24″ antenna and amp on a 20′ pole, and can list many experiences I’ve had – taking that 24″ amplified antenna and then installing a Winegard HD8200, or a DB8, or twin 91XGs etc. I assume my results would be regarded as impossible, going by your comments. Today, I can go up the hill behind my house and hook up that 24″ antenna and get 6-7 stations. I can hook a Winegard HD8200 in the exact same spot and height – with no amp – and get nothing. If I then hook a good amp to that Winegard I get over a dozen TV channels. So, what does that all mean? In means – in this anecdotal circumstance – the small two foot antenna with amp is outperforming the fourteen foot antenna without an amp, and the converse is true when the big antenna gets an amp. I suspect you’ve never tried these sorts of comparisons.
Note again – you commited the formal-logic flaw of “reducing to the rediculous.” I suggested that small antennas with amps can sometimes behave like much bigger antennas with no preamps. I said nothing about anything paperclip sized, nor did I say small antennas are logical replacements for large high-gain antennas. Not all is discrete reasoning here – there are shades inbetween “all” or “nothing.”
I started my DTV experience with a Wineguard HD-1080 antenna on a 20 ft pole. I could only get 4 channels at maybe 20% to 40% signal strength. I added a Wineguard AP-8275 pre-amp and now I get 12 channels, 3 range from 60% to 70% and the other channels at 80% to 90%. I have about 100ft of coax. I’m 32.1 miles from the transmitters.:huh:
I used to live in down town Salt Lake City. There, the transmitters are on a 9500 ft ridge about 18 miles SW of town. The elevation at my house was about 4200 ft with line of sight to the towers.
At the time, I was using a typical chimney mounted Radio Shack combo antenna. I had a Radio Shack distribution amp in the attic to drive several jacks in the home. The system worked great! My analog reception was beautiful and absolutely problem free.
Then came the day when I brought home my first DTV receiver. I was excited to see what digital was all about and I immediately pluged the receiver into the living room jack with a short coax jumper cable. I quick did a channel scan and waited patiently expecting to see amazing digital pictures on the screen. I waited and waited, and when the scan was finally done do you know what I saw? ABSOLUTELY NOTHING! No channels were found whatsoever!
I thought I did something wrong so I went back and read the manual! I checked the cabling and scanned again. Still nothing. I rotated the antenna and still nothing. I was beginning to think that the receiver was DOA, but I found that hard to believe. Even harder to believe was that I wasn’t getting anything even though my analog reception from the same jack was perfect. I replaced the jumper cable and still got nothing after several more scans. In a fit of desperation I pulled a small indoor antenna I had stuffed deep in the closed and hooked it up. Just like that I had a couple of digital channels. While I didn’t get all of them at least I knew it wasn’t the receiver and so I kept on investigating.
Eventually, after playing some games with traps and attenuators and getting filthy dirty climbing into the attic crawl space to adjust the distribution amp I was finally able to determine that I was getting signal overload and that the main rooftop antenna would work just fine if I dialed the gain of the amp all the way back or removed it entirely. While this didn’t help the analog reception it was essential for digital.
At the time I was astonished to see that an antenna, amp and cable setup that worked superbly for analog, was simply not “out of the box” ready for digital. Had I not been an engineer and trained to look and diagnose such problems I’m pretty sure that I would have been taking that receiver back to the store or I would have punted and called the cable guy.
So while amps can and do help in rural and deep fringe areas, they can also be disastrous in urban and suburban areas. With the proliferation of strong signal sources into even remote areas, my basic recommendation remains “try without an amp first and then add one only if you find its necessary”.
My hunch is that FoxTV’s viewers in the mountains of Roanoke, VA are probably in a more similar situation to what I saw in Salt Lake than to what others have seen in rural areas in Michigan and elsewhere. In areas with big mountains and lots of “height gain” its probably comes down to a signal quality more than a signal strength issue. in those situations amps are more likely to do harm than good, so his recommendation of no amplifiers is probably the right call for his market.
In the final analysis there will be situations where amps help and some where they hurt. The trick I think is to get people thinking about what problem they are trying to solve rather than just blindly buying and installing one.
I’d like to hear specifics about exactly what made your “analog” system not “digital ready.” That is something I have yet to encounter. I have however, found many VHF only antennas that would not pick up a UHF signal, and many TV stations changed from VHF to UHF. Also, the converse. Also removed several amps that were too limited in the frequency range, and were only meant for VHF bands. None of the aforementioned has anything to do with analog or digital. Just the frequency, signal strengths, etc.
That I agree with. I always test an antenna first – on site, no amp. And then, work from there. By testing on site, long wire runs don’t become part of the equation. If an antenna, hooked up on site only gets two channels with no amp, and gets twenty channels with an amp – that is kind of a no-brainer to me. That is, unless you don’t want the extra channels. On the other hand, if hooking in an amp gains nothing, I don’t use it. I’ll that many people only test at the TV site, and not at the antenna. That leads to a lot of guess work and/or calulating since you don’t really know, for sure, what kind of reception difference there is – between on site and at the TV.
I agree with that also. But, there is a huge difference between someone saying he “never recommends and amp” to recommending to “use as needed.”
If I bought a diesel powered car and the engine blew, would it then make sense to warn others to never buy a diesel car?
Thanks for posting the links!
Interesting comment in the first one: “If there’s an active indoor antenna, temporarily replace it with a good passive indoor antenna. If that doesn’t solve the problem, add a really linear low noise amplifier such as the Channel Master 7777. “
I agree that many issues have been resolved by switching to passive indoor antenna. However, following that up with recommending a CM 7777 for indoor use is way over the top…. Pre-amp and tuner overload are *very* likely…
Remember that he was talking about his particular location, and not speaking generically or in general. This author is well renowned as one of the top RF and reception experts in the nation, and possibly the world. To me, what he says is gospel, and his reception testing including the use of amplified antennas is ongoing.
His intent was to show that a low gain indoor antenna with an amplifier can in some cases be an advantage, but again, this is location specific, and would not apply in every case. He was also looking at gain and linearity of that specific amp, and in his situation, he saw a definite improvement. You also need to note that he has access to all types of test equipment, and this area of broadcasting has been his life’s work, he is definitely one to be listened to. When Charlie speaks about RF and DTV reception, I listen and learn.:cheer2:
The expert should have qualified the use of the CM7777. Pre-amp and tuner overload are very likely in an urban environment with the CM7777. Check the forums and you’ll see many examples with overload with roof mounted antennas and the CM7777 in urban areas. Granted there is attenuation with an indoor antenna over a roof mount, still the overload risk is too high for anyone under 35 miles from the towers. I would expect an expert to qualify his statement when he is leaping well away from accepted practice.
JMO
I do work as a broadcast engineer for a FOX affiliate in South West Virginia. One point that I made in another post that seems to be forgotten about is one of SIGNAL QUALITY, and that is a BIG factor involved in ease of, and the reliability of reception. The transition is not complete for a lot of stations due to multiple reasons that are to numerous to mention again here.
Signal quality and signal strength are issues that simply cannot be ignored, but also cannot be determined by the average viewer. SIGNAL QUALITY is a huge factor and it just cannot be assumed that it is good. Even though the FCC sets minimum standards for the EVM (Error Vector Magnitude) and SNR ( Signal to Noise Ratio). If a stations signal quality parameters are near the minimum specs, but RF levels are high, you are still likely to experience reception issues even with high RF signal levels, and all of the high gain antennas and amplifiers in the world will not improve your reception of a poor quality signal.
This is just not something that can be determined by the viewer, or anyone who does not have the proper equipment to do so. A transport stream analyzer will tell you about signal quality, and in the real world, signal quality is a BIG issue. Remember that DTV is as new to Broadcast engineers as it is to consumers, and due to all of the money spent on transmitters, antennas, HD equipment for master control etc, some stations simply do not have the test equipment needed to gauge the QUALITY of their own signal.
Here is a real world example: there is a VHF low station in our area that has fought signal level and signal quality for several years, and they are finally getting things corrected, even though they have had a DTV signal on the air since 2002. When the transmitter was set up by the factory technicians, all was well for a several years, and their VHF low signal could even be received on a UHF antenna at 15 miles out, but their signal quality began to deteriorate to the point of not being receivable on virtually any antenna or receiver.
I looked at their signal with a transport stream analyzer, and it was way out of spec, with a non linear signal being sent out, and it was just a poor quality signal, even though the RF levels were good. If you are unknowingly fighting a poor quality signal issue, you will never solve the reception issues with amplifiers, and to simply say “Add an Amplifier” is not a cure all to SOME reception problems, SIGNAL QUALITY matters greatly, and has the most negative effect the further away you are from the transmitter. These signal quality issues along with RF signal levels actually determine where the CLIFF is located. (The cliff is where a DTV signal is no longer strong enough or of a high enough quality to be received reliably)
If the data levels of the DTV signal are not linear, and the Pilot Carrier is not high enough in relation to the data levels, reception will suffer.:gossip:
Often a consumer certainly can determine a good signal. Not in a scientific sense – more in the general sense. If a consumer can consistently get a good picture on the TV screen -it is likely that is all that matters to him or her.
Yes, and they are the ones that need the specialized equipment along with a comprehensive knowledge of all the possible pitfalls. When on the broadcast end – there are many issues to deal with along with many alternatives to try.
To the converse, take the consumer on the receiving end. There is not a tremendous amount of highly varied equipment and choices. Things are more simple. If a person is wondering what is available over the air – $120 can be invested in the highest gain antenna available (within reason) – and he/she can quickly tell what is available coming from the air. A $120 investment in an antenna, a $30 investment in an amp, and maybe $80 for a portable AC power supply along with a portable TV is basically all that’s needed. Not a huge investment. Obviously, there are issues with bogus claims for all equipment that muddy the water. But, everything on the consumer market is like that. At a professional lever, I’ve experienced just as much bad information from professionals that are overly myopic.
My point is that not much has changed on the consumer-end since TV first became popular. My uncle built the first TV in our town, and he had to stand behind it fiddling with controls to keep a picture on the screen while others watched. So, yeah – that sort of thing has changed since TVs are now cheaper then ever and few consumers build their own. But as to the rest? There’s not much new under the sun, although many ads selling TV equipment would like the consumer to think otherwise.
I agree and it’s not something I’d ever tell anybody. What I have said many times is . . . that it might be worth spending $30 on an amp and see what happens if dealing with a problematic channel. If it works . . . it may not matter much why.
I’ll comment on my own situation. I was advised by two broadcast engineers about what would be best for me to get their channels in my area. One was from the oldest TV station in the USA. Their help was free, well meaning – and dead wrong on several counts. I fixed my problem the old-fashioned way. I spent some money and actually tried just about everything that is popular and available to the average consumer. I got good results along with some real-world perspective on digital mostly UHF transissions in rural and hilly areas. I admit I went a bit overkill. I did so out #1 from frustation caused by bad-information overload, and #2 just as an interesting experiment.
Just in the past six months, I worked on five antenna installs in three areas in Otsego County, NY, two in the Hamilton County (Adirondacks) NY, one on the Tug Hill Plateau NY (Jefferson County), and three in northern Michigan in Presque Isle and Alpena Counties. Two in city limits and the rest extreme-fringe rural. I experimented with: Antennas – Wade VIP 307 VHF, Winegard HD8200 VHF/UHF, Antennacraft Y10-7-13 hi-band VHF, Winegard YA-1026 low-band VHF, Antennas Direct DB8 bowtie UHF, Winegard 9032 Yagi UHF (single, stacked, and ganged), 91XG (single, stacked,and ganged), Channel Master 3671 VHF/UHF combo, Antenna Craft HD850 VHF/UHF, and a Radio Shack 15-264 VHF/UHF . Also tested amps: Channel Master CM 7777, Winegard AP-8275, Research Commications 9262 (ultra low noise), Antenna Craft 10G212 and 10G202. Also tested some small amplifed antennas that I won’t bother listing. With most of the equipment I just listed, I installed on same-sites to compare. Every amp and every antenna was tested this way. I wonder how many engineers who write about reception at the consumer level have done the same?
And yes, what I’ve done does not provide useful information across the board for everyone – no more than some of the esoteric high tech stuff does to the average consumer.
I would like to see a “Signal Quality” function in all DTV receivers, along with the “No Signal” message. The “No Signal” message automatically leads some to make the wrong assumption that they actually have a “No Signal” situation, which sometimes starts a mad scramble to improve signal levels with amps and outrageously high gain antennas, when in fact it could be one of several issues causing the dreaded “No Signal” message.
Everything form Multi Path, Poor Signal Quality, FM Harmonics, extremely high a signal levels causing receiver overload, and actual low signal level issues can all threaten DTV reception, but with the current technology of DTV receivers ( Except for the one you mentioned) do not actually give you a clue as to the real problem. Bit stream analyzers are now basically now on a chip set that could be included in DTV receivers to help determine signal levels and signal quality, and echo intensity, and echo timing and amplitude that all can cause DTV reception issues.
I wish I had access to all of the antenna models you have listed so I could run them through some tests that would tell the actual reception characteristics of different antenna designs in regards to forward gain, rear rejection, and susceptibility to multi path issues.
I am in a difficult DTV reception area, and all of my knowledge comes from dealing with Multi Path issues, and my main concern is for this area is Ghost killing antennas for UHF that are actually effective at canceling enough of the ghost signal to allow reliable reception. I have found that the UHF designs that use a backplane reflector are the most effective at nulling out enough of the ghost signal for reliable signals to be received.
Funny, “ghosts” are something I hadn’t thought about for years – until recently. When installing an antenna at my in-laws in Michigan, we got one analog channel that was perfect pointing at 100 degrees, and triple-ghosting when pointed at the opposite direction. With digital, I guess we don’t don’t get to see them anymore. Might lose the picture instead, but won’t see ghosts or snow.
Back around 1979 I’d given up on over-the-air TV. We were getting one VHF channel full of snow and ghosts with a high-gain Archer preamp and huge Wade VIP-307 antenna.. Then I heard of a place in Montana that specialized in rural TV reception – called “Ghost Fighters.” Called them up and wound up buying plans to build my own 14 foot huge satellite dish out of wood and chicken wire. They supplied the LNA and receiver. I built the dish and the winch to move it, satellite to satellite. Had to tune the parabolic curve of that dish at least once every year. That was the end of over-the-air TV for me, until this past June. After the digital change, I get close to 20 channels – including three from Fox. No more ghosts, but do get two very snowy analog channels.
Which UHF antennas have been the best ghost killers in your area?
Thanks!
Best,
Rick
I almost hate to answer that question because of all of the angst about Clear Stream antennas on this forum, but the C series, and specifically the C2 and C4 have received signals that conventional yagis, combos, or log periodics will not receive due to multi path.
I do mostly concentrate on the UHF signals because I work for a UHF station, but it is also good to keep an eye on the VHF competitors, and I use a C5 for that, as we only have one VHF commercial station on channel 13 in our market, and the C5 works well in that band. We do have a VHF low station on 3, but it is a PBS station, and is not considered as competition to a commercial station due to the lack of advertising.
I do like the design of the DB series stacked bow ties with the backplane reflector, but even they are not as effective at ghost canceling as the C series with its tapered driven element design.
The antenna that impresses me the most is a re-make of the Gray-Hoverman antenna, but it is physically large, and that instantly drives most people away because of its large size. I think the Gray-Hoverman should make an excellent fringe area antenna
Not only in the Gainesville market but in the Vero Market (they are split between Orlando and W. Palm). The long boom yagis with corner reflectors kill ghosts the best and seem to have the longest range.
I had ghosts on WOGX 31 and WUFT 36, which oddly enough are the two strongest stations to me on a 4221A. I replaced it with a VERY old U-75R, Radio Shack and the ghosts went away (analog was still on the air). The digital also obviously stopped rapid dropouts. http://www.rabbitears.info/dxlocation.php?id=18
I really believe in them, even short boomed ones for killing multipath.
The only things that come close are the side by side collinear bow-ties and such like the DB8, but actually depending on definition, those are 2 antennas stacked side by side. So with that definition, the corner reflector yagi to me wins hands down for front to side rejection. Remember very few ghosts / multipath are from the rear. And actually most come to the antenna at an acute angle (less than 90 degrees). So the antenna also needs to drop off fast after say 45 degrees from center of beam width to be effective.
I do agree that signal quality is important. I test our signal with my APEX 502 converter box because it has both signal quality and signal strength measures. When it reads 100% signal quality, the video/audio are great on all my tvs, the capture card on my htpc displays no errors while recording, and my video editor finds no errors when editing. Does it mean the our local signals are perfect? No, just means they’re “good enough” that our tuners can effectively handle any imperfections in the video. IMO, the APEX 502 is an excellent consumer grade tool for evaluating signal quality.
Also, my first concern with any pre-amp is the potential for overloading either the pre-amp and/or the tv tuner. There needs to a be an assessment rather than a generalized recommendation to use a top shelf, fringe pre-amp.
Have a great day, Fox TV! Our local Fox and CBS engineers have been very helpful to me in my OTA planning.
Right, and that’s why I raised the red flag over your expert’s recommendation to use a CM 7777 in an urban environment.
Excellent answers, thanks Fox TV and Piggie! 🙂
Fox, I was surprised by your comment relative to the C-2. I think it is a good antenna and it gets props on the HDTV primer (see: Comparing some commercially available antennas). I was thinking that it may have issues with multipath…
Surprisingly, that curmudgeonly author has probably never looked at the signal from that antenna on specialized test equipment to see just what is happening.
Just one of the hazards of bloviating based on simulations but without hands-on experience…
I don’t think you are talking about me, as all of my reception data is based on almost 4 months of field strength testing using a Rhode & Swartz FHS 3 DTV spectrum analyzer, along with a Sencor DTH 236 bit stream analyzer. That seems like it qualifies as “specialized test equipment” to me.
What types of “specialized test equipment” do you have access to, and which antennas have you tested in real world field conditions in a very mountainous terrain where there are more ghost signals then there are rain drops in a summer thunder storm?
I am not worried about gain as much as the ability of a given antenna to perform in a high multipath situation, and that is the goal of the field tests I have been involved in that were intended to find weak spots in our stations coverage, as well as finding an antenna that would work well in this area..
And why do you have to get on here and use words like curmudgeonly (An ill-tempered person full of resentment and stubborn notions) when you have no idea of who that person is or what you are talking about. What ever happened to RESPECT?
It seems to me like you may be the curmudgeon and the bloviater, simply based on the definition of the words when this was a friendly exchange before you chimed in with derogatory words like curmudgeon and bloviate (To discourse at length in a pompous or boastful manner).
That is the problem with a public forum, as it lets in people with no respect for others when the majority of us are trying to be civilized, and have an intelligent conversation about our personal and real world experience in regards to a new technology that still has issues to address.
Here we go again..I have been through this on the AVS FORUM, and it is happening here too. So long folks, I have no need for smart a__ comments from instigators, when people are offering their opinions and EXPERIENCE to others who want to know more about DTV reception issues they may be having from people with REAL WORLD knowledge on the topic at hand.
If I was the moderator, I would ban anyone who disrespects another user for absolutely no logical reason. Disagreement and disrespect are two completely different issues, and one of them has no place here..Can you guess which one that is?
Thanks for your untimely and disrespectful input!!
Well, it does make sense that a wider beam antenna would have more problems with multipath than a narrower beam antenna… Of course, the real anectodotal stories can be very revealing as well, particularly if one can show issues of multipath with antenna A, replace it with antenna B, and then find no multipath. Those are the type of stories I would like to read about… I suspect Fox TV has some…. Come on Fox, give em up… 😀
Fox TV,
ProjectSHO was directing venom at Ken Nist, author of the HDprimer link from post 33 in this thread. Please stay, you are a valuable contributer to the forums! Plus, I would like to read some of your success stories.
Best,
Rick
Who ever it was directed to, it is uncalled for and DISRESPECTFUL still. If he is going to shout out hate and discontent, he should at least put the name of the person he is blasting so someone (LIKE ME) doesn’t take is out of context
Good point.
Take care, Fox!
Robert,
My apologies! My remarks were NOT directed at you but, at the writings of the person that Rick indicated. I’m sorry if you mistook them as being directed at you. Your previous comments regarding your hands-on testing with pro-grade test equipment are the kinds of reports that are invaluable to end users and hobbyists alike.
My intent was to highlight that there is a huge difference between running computerized simulations and then posting opinions based on those simulated tests vs. field tests based on real antennas, real equipment, and real world environments. Mr Nist’s opinions are very widely quoted on this and other forums but he is seldom, if ever, challenged to see if his simulations and posted opinions match up with real-world testing and experiences. In other words, his reviews and opinions are taken and re-quoted without any challenge as to their relative merits.
I was definitely feeling “curmudgeonly” and crabby last evening and it showed. Mea culpa.
PS89
Maybe I did not read far enough back in the previous posts to see what the fuss was about. I have seen some of Mr Nist’s writings, and have no opinion either way. I guess I am a little touchy on the topic of respect, for I went through a Flame War on my local AVS forum just recently, and it all started out the same way with some people throwing around remarks out of context, and with a huge lack of respect.
I am not here to argue with anyone about anything. I only want to share my insight into the reception issues that plauge DTV, and each market or reception area is different, and it seems that an antenna that performs well in one area, may not get the job done as well in other areas of the country. I only try to comment on topics where I have had real world experience, and that is mainly in a mountainous area that would have been a great test bed for Distributed Transmission.
I have been building antennas for many years, and the advent of DTV, plus my employment in the industry is fuel for the antenna fire, and I enjoy building and diagnosing their performance, especially since I now have access to test equipment whenever I need it.:eek:
JER, You may have an interest in this link in regards to antenna modeling.
Antenna Design, 3D Electromagnetic Antenna Simulation Software
@FoxTV. Thanks for the link to the simulator!
CST makes really good stuff but like most good EM simulators its also very expensive so I’ve not yet had the opportunity to try it out.
I’ve used NEC-4, OSU BSC (Basic Scattering Code), Remcom X-FDTD and FEKO extensively in my work of the years. Using them is as much an art as it is a science, and the results vary from one simulator to another, and even from run to run, depending on what choices are made in approximating the real structure.
Each simulator has its good and bad points. The NEC codes are very efficient for wire structures but aren’t very good at including the effects of dielectric materials. The BSC code is great for electrically large structures like an airplane, but isn’t suitable for analyzing a typical TV antenna. X-FDTD is really can handle just about any material or structure you throw at it, but the run times are really long even with a GPU capable of 1 TeraFLOP throughput! In the end, you have to make judgement calls and use the right tool for the job. Sometimes you need two combine tools to get an answer. As an example, its possible to use NEC to solve for the pattern of a communications antenna in free space and then push the pattern data into BSC to see what’s happening when the antenna is on an airplane or ship that would be too large to solve otherwise in NEC.
No matter what simulator you use you still need to back it up with some measured data if you’re going to have confidence in it. There are so many things that can go wrong in both measurements and simulation that the only way you really know you’re right is if both match up. I’ve spent a fortune on computers, software and lab gear through the years (see my website and you’ll know what I mean) and I’ll probably spend a few more fortunes before I retire just to be able to stay relevant and competitive in this field.
I have a friend who used to run the R&D portfolio at Boeing. He told me that Boeing has spent an enormous sum of money over the years perfecting Computation Fluid Dynamics Codes so they could accurately simulate an airplane’s performance before its ever built. The codes are apparently so good that they can now skip many of the flight tests that they used to do saving them a lot of money on flight testing. At the same time the company was also developing EM codes for analyzing antennas and other EM structures on airplanes. Even though they spent a similar amount of money, they were not able to reduce their antenna test budget one bit. Moral: Antennas and EM are harder to do than jets.
BTW: This thread was about amplifiers. If we’re going to continue to discuss antennas and simulators and such then I suggest someone (one of the moderators perhaps) start a new thread. Thanks!
Classy post PS89! Hat tip…
To properly understand what an antenna is doing we need to use every tool at our disposal. In addition to the classical analysis and design knowledge we have in text books and journals, the main tools we use to develop new antennas are embodied in computer simulations, lab tests, and field tests.
Modern computer simulators are amazing and they allow us to see things that would be nearly impossible to measure or account for using classical analysis methods. They also allow us to do enormous numbers of design iterations. For the most part, simulators allows companies and engineers to do more with less, and do it faster. With a simulator we no longer have to build and test a physical device to get some idea of a what a device might do. This takes years and huge sums of money out of the design cycle and we end up with better products faster.
Laboratory testing in controlled conditions, such as an anechoic chamber or outdoor range, is essential. It allows us to assess how well we’ve transitioned a design from the virtual world of the simulator to a physical device. This step is important because there are often components of the device that cannot be easily and / or accurately included in the simulator. The lab tests allow us to quantify those items without being concerned with the complicated signal environment you would have in a field test situation.
Also, depending on what you’re doing, its still sometimes faster to mock up something quick in the lab than it is to run a simulation.
Field testing of course is the final final validation that what we’re doing in the simulator and lab are actually making a difference. Doing good repeatable field tests is difficult and requires a lot of time, money, and equipment. Most of all, it requires people with the experience, to properly interpret what works and what doesn’t and why!
In a perfect world the insights obtained from field testing get fed back into the design loop so that subsequent generations of a product are improved. This is the main reason why I am on the forums. We can only afford to do so much field testing, but its important nonetheless to find out what people are seeing in a lot of different situations. Feed back from people like FoxTV is the most valuable to me since he has the test gear, the experience, and the motivation to do good, repeatable, meaningful tests.
In summary, it is my feeling that its not sufficient to have only simulation data or only lab data or only field data to understand and quantify an antenna. Instead, you really need to have all of it! Then, if you see strong correlations between what you see in the simulator, the lab tests, and the field tests you might really know what you’re doing. If you don’t have all the data or if you don’t have correlation across the data sets then you likely have some serious work ahead of you before you realy know what’s happening.
Excellent post JER! I admit that I’m a fan of the hdprimer because I find Ken’s modeling efforts to be very helpful. His modeling of the CM 4221 has matched my field tests with a DIY four bay. Although, Ken’s work needs to viewed cautiously… Hopefully his work matches the performance of the antenna under consideration. I found Ken’s comments on the C-2 very helpful and it now makes my list of antennas to recommend for posters that have a wide spread between broadcast towers. Fox’s comments yesterday were also helpful in regards to C-2 performance under multipath conditions.
Thanks guys…..I live in a bad reception area. Trying hard to receive the NYC locals from Port Jervis NY. The mountain in the way is causing my problem. I receive low signal on the channels I want and have had limited reception at night. Wish I knew someone with your expertise.