Question: Channel Master CM4221-HD - performance data

#22
That's right on the spec sheet, both on the front in writing and in the graph on the back. If, however, you were referring to Ken's work, that information can be obtained from his comparison page at Comparing some commercially available antennas first plot, trace R.
Both raw and net gains are graphed for each antenna. Which of the two is on the individual scatter diagrams in the links? We don't know. And what are the numbers at various angles from the peaks? No way to tell. No dB labels appear on the scatter diagrams above -10, and the labels that are there are irregular, which makes the more pertinent labels hard to extrapolate. Do the dB ratings refer to dBi or dBd? I suppose they're probably dBi, since that's what they use on the main page, but why make a mystery? Why produce a ton of charts, then withhold the simple labels required to make them useful??

I know they didn't do it on purpose. I'm sure a lot of work went into the project, and it's nice they put it out for the public. I just think there needs to be some work on communication skillz. No signatures on any of those pages either. No way to know if the scatter diagrams were a group project, or if they were all done by the same person.

Yes, I was referring to Ken's work, if that's who put up all the charts. I imagine the manufacturers' numbers are all different. They usually are.

Rick
 

DW-77

DTVUSA Member
#23
Thanks Rick. I like his comments too, and I believe you are right: the charts do look like the result of Sw simulations that did not take the balun into account. (UHF PCB baluns do not work well at VHF frequencies).

So, you think that AD is exaggerating the numbers, when it comes to the DB4e?


(Thank you RFSteve and ProjectSHO89. I made the correction in the balun related statement above, based on your feedback).
 
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#24
(PCB baluns do not work well at VHF frequencies)
That is too broad of a statement to make about all PCB baluns, but to the best of my understanding does apply to the AD baluns in use on the CS antennas.
Steve
 
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#25
Both Nist's charts and AD's tech data sheets are the results of software simulations. AD lists, in the notes, that the balun is not included.

PCB baluns do not work well at VHF frequencies)
It would be accurate to say that UHF PCB baluns do not do well at VHF frequencies and that VHF PCB baluns do not well at UHF frequencies. There are VHF PCB baluns that do quite well for their design frequencies.

So, you think that AD is exaggerating the numbers, when it comes to the DB4e?
There is zero evidence or indication that would suggest such. The specifications are similar to the M4 which as similar dimensions.
 
#26
So, you think that AD is exaggerating the numbers, when it comes to the DB4e?
You know, forty+ years ago I got a minor in math from a music conservatory, (don't even know if they still do that these days. :rolleyes:), but I don't have as much faith in numbers as you do. Did you know that years ago, many magazines stopped allowing gain figures in antenna ads? They are just way too easy to skew. You can make up ALMOST any number, then figure out a way to justify it.

Anyhow, I don't have any conclusive evidence they exaggerated any numbers, but I'd honestly be shocked out of my gourd if they haven't! Why would they be unique among all the English speaking companies on the globe?? No. I don't expect that. What I do object to is hyperbole like this:

AD's site: said:
Antennas Direct® doubles the power of traditional bow tie designs. A breakthrough in performance and reliability. We have created an antenna the size of our traditional DB4, with the performance of the DB8. The DB4e is light years ahead of our competition. No other bow tie antenna can match the DB4e's combination of power, gain and value. The new extreme range bow ties - only from Antennas Direct®. The most powerful compact antennas on the planet! ... It has 3X the power and half the size - making it ideal for indoor and outdoor.
They can't even make up their mind if there's two or three mints in one! I almost made the mistake of buying a DB4e, because of all the hype. I would have had to cut three inches off my desk, or totally rearrange my living room SOMEhow. Meanwhile, the 4221HD, which was already out when the above was written, has very comparable gain figures (slightly higher peak gain -- I remember a misleading AD brag about peak gain also), with a larger beam width, and it fits perfectly on top of my desk. (I'm stuck indoors due to an obstinate landlord.)

There's nothing revolutionary about the DB4e design. They just retuned the old DB4 design to the new 14-51 UHF channel range, and added some cute orange baubles. Every antenna nut knew they should have done it three years before they did.
 
#27
The tech data sheets read as if written by a professional engineer; just numbers, graphs, and data.

The ad copy reads like over-the-top hyperbole, fluffery, and puffery. Obviously written by two very, very different types of individuals. One was conveying factual information, the other was seeking to stir an emotional response so as to create a purchasing reaction or interest.

If you have any actual data that would suggest that the technical data provided is incorrect, then please share it. Otherwise, your opinions and suspicions are your own.

AD's engineer posted here a few years back. His user name was JER something, IIRC.

[edit] Okay, I went back and dug up some old threads. You can read all his posts by following this link: http://www.dtvusaforum.com/search.php?searchid=1366472 He introduced himself in this post: http://www.dtvusaforum.com/antenna-...ltimate-measure-better-antenna.html#post32694
 
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DW-77

DTVUSA Member
#28
Did you know that years ago, many magazines stopped allowing gain figures in antenna ads? They are just way too easy to skew...
Rick, I did not know, and if they stopped showing gain figures, only to replace them with "range" figures, I suspect that was not because "gain was too easy to skew", but because of ... quite the opposite: gain is precisely defined, measurable, can be verified, and if claims are found to be untrue, the manufacturer might be accused of false advertising. On the other hand, "range" is meaningless, cannot be verified, disclaimers are already there, therefore anyone can claim whatever "range" they want. Could it be that those magazines were protecting the antenna makers the same way "the FDA protects food industry" (quoting what you said in a different thread) ?
 
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#29
If you have any actual data that would suggest that the technical data provided is incorrect, then please share it. AD's engineer posted here a few years back. His user name was JER something, IIRC.
Didn't say anything about JER. Didn't even say anything about a technical data sheet. I merely said I'd be "shocked out of my gourd" if they haven't "exaggerated any numbers." "They" is the entire company, not just one man. 3 is a number. "3X the power and half the size" is an exaggeration. Q.E.D.

BTW, it's very possible for a number to be an exaggeration and still be technically correct. And if JER made one extra dime due to exaggerated marketing claims, he has to take some of the blame -- but I'd still be thrilled to see him back here at DTVUF.

your opinions and suspicions are your own.
Indubitably.

R.
 
#30
Rick, I did not know, and if they stopped showing gain figures, only to replace them with "range" figures, I suspect that was not because "gain was too easy to skew", but because of ... quite the opposite: gain is precisely defined, measurable, can be verified,
No, no, no, no. You still have too much faith in numbers.

comparing.html on hdtvprimer.com said:
A few years ago QST, which is the principal publication of the HAM radio community, announced that they would no longer accept advertising for antennas if the ads contained gain figures that were measured experimentally. Henceforth any such gain figures would have to be the result of computer simulations. There were two big problems with the experimental data:

1. The experimental antenna is affected by its surroundings. Computers can do true “free space” modeling.

2. The process of choosing the surroundings encouraged overly favorable choices. Most of us would call it cheating, but they justified it to themselves by the belief that their competitors were doing it.
You want to put your faith in simulations? Here's what JER, an antenna inventor that Proj likes, who works for Antennas Direct, says about simulators:

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.
Shoot, you could put an antenna on a patio that happens to have reflecting material on three sides before you do a measurement, then simulate that same situation. It's still the gain of that antenna (in that particular circumstance). And who says the beam width charts have to come from the same tests as the gain charts?

Look, I think the major manufacturers are generally sort of close in the docs they put out, but I wouldn't bet my life on it! And if you get a hold a salesman -- forget it.

Rick
 

DW-77

DTVUSA Member
#31
"Faith in numbers" I have, provided that the numbers add up and make sense. I took RF classes in college, and I spent enough hours in the lab (many of them making measurements on antennas) to know that, when done right, such measurements can give very accurate and consistent results.

Yes, numbers can be faked; yet, most of the times, someone who has the right knowledge and experience can see through that. Yes, one can put a good antenna in a place where surrounding objects will alter its performance, but that is not the antenna's fault, it is a location / installation specific issue. When it comes to the antenna itself, gain, radiation pattern and impedance are about the only things one can count on.

When salesmen decided to stop talking about gain in favor of "range", of course they said they made that change "for our sake", because "everybody understands distance, while many of us don't even know what gain or dB mean". While that claim may have been legit, at the same time, they gave themselves the freedom to put any numbers they want in the product literature.

Therefore, at least for me, measured data is best; simulated data is good (when the numbers "add up" :)); "maximum gain" is like selling cars based on "maximum speed"; and "range" is BS.
 
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DW-77

DTVUSA Member
#32
...3 is a number. "3X the power and half the size" is an exaggeration. Q.E.D.
R.
We seem to agree that marketing statements are usually exaggerated. Some documents are pure marketing fluff, while others are a combination of marketing fluff and relevant data. It is the relevant data part that I am interested in, and I am talking about here.

If you want, we can target marketing exaggerations separately, and I am sure there is plenty of material out there one could talk about (and laugh at). :)
 
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#33
3X the power and half the size" is an exaggeration
More likely, it's a fat-fingered typo since the verbiage in the Overview section says "doubles [emphasis added...] the power of traditional bow tie designs. ...".


I don't have any conclusive evidence they exaggerated any numbers,
What that means, is you don't have ANY evidence at all of such.

Did you know that years ago, many magazines stopped allowing gain figures in antenna ads?
Actually, you've exaggerated that one. Back in the 80s, the ARRL set as editorial policy that all advertisements in their publications for antenna gain be derived from computer modelling rather than "range" or similar testing since the testing could be cooked to enhance results. OTOH, anyone with the antenna's physical measurements could run the same simulation and should produce almost identical results. That means that you could get an antenna for measurements and run the simulations yourself with one of the publicly available simulators like 4NEC2 and you'll then be able to comment knowledgeably about the antenna's performance.

Shoot, you could put an antenna on a patio that happens to have reflecting material on three sides before you do a measurement, then simulate that same situation. It's still the gain of that antenna
Nonsense. Simulations are performed in "free space". OTOH, "testing" could be done on that same real patio and the antenna performance may well be affected by that location and its surroundings.
 
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#34
I don't get where you guys are coming from. Are we now supposed to promote LESS skepticism when it comes to claims from an antenna manufacturer? Who profits from that attitude?

When I wrote that post, I didn't have any "conclusive evidence" of exaggeration, because I simply failed to look. I just assumed you guys knew that every antenna mfr makes stuff up. The evidence is abundant and it's incontrovertible.

Project, you defend an exaggeration by hoping it's a typo of another exaggeration?? In what sense is "doubles the power of traditional bow tie designs" remotely accurate at one-half the size for the DB4e? Name a traditional bow tie that compares that poorly with the DB4e! I've looked at the C4, the old DB4, the old 4221, the 4221HD, the old DB8, the DB8e, the old 4228 and the 4228HD. The closest is the old DB8, but its average dBi is NOT 3 dB under the DB4e, and it's not anywhere near twice as big in either square or cubic inches. What are you talking about?? If they didn't mean half the size, it can't be a typo.

More evidence AD cooks the books:

From the DB-8 page on hdtvprimer.com: "AntennasDirect calls the DB-2, DB-4, and DB-8 “Multi-directional antennas”. There is good justification for calling the DB-2 and DB-4 multi-directional, but the DB-8 is one of the most directional antennas you can buy. AntennasDirect is simply flat wrong about this."

From the AD web site: "The ClearStream™ 4 extreme range antenna offers the power and efficiency normally found in antennas up to 10 times its size."

The ClearStream 4 specifications page states flatly: "Gain of 12.2 dBi." The average person reading that would take it as a guarantee of 12.2 dBi on any station. A skeptic might think it was an average. In fact, it's the peak dBi -- i.e. an exaggeration. The average runs around 11.7 .

My favorite from Antennas Direct: "The Micron XG represents the most powerful indoor antenna one can buy." (unless you get an Eagle Aspen 2 bay at about one-third the price!)

I don't understand the need to separate "Specification" pages on their web site from PDF spec sheets. I hate to shake up anyone's dreamland, but I won't become a shill. If they said it, they said it. The evidence is overwhelming, and it's conclusive every time you look at an ad from Antennas Direct -- or any antenna mfr.

Rick
 
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#35
The most powerful indoor antenna I can buy is a set of rabbit ears. Where I live all full power broadcasters are VHF. Nearest full power UHF broadcast signals are over 100 miles away.
Steve
 

dave73

DTVUSA Member
#36
I never fully understood the numbers that the manufacturers provide. I will however say for UHF antennas, my Antennas Direct DB8 (original DB8 ) has worked well for me, as it has allowed me to pick up some LPTV stations that I didn't get at all, or not as well. When I went with separate VHF & UHF antennas, I originally got the Winegard HD9032 UHF yagi, & that mainly worked best for full power stations, & only 1 LPTV station with pre-amp, while the other 3 LPTV stations sent enough signal to make it come in like a local. That antenna was rather weak with stations in the RF 40 - 49 range. My VHF only antenna is an Antennacraft CS600, & that's because I bought it for a VHF-LO Class A station, & need a pre-amp to get it. If it weren't for the subchannels to the Class A VHF-LO station, I would have bought the Antennacraft Y5-7-13 antenna, since I have 1 full power VHF-HI station, & no full power VHF-Lo stations. If that Class A station can get moved to UHF, then my current VHF only antenna will only be good for RF 12 & FM radio.

As for Antennas Direct, their antennas aren't exactly the cheapest, but the quality is there on their UHF antennas. For the DB8, I only wished the directions would have been clearer on how to install it. It took 2-3 hours for me to install, because the reflectors weren't that easy, or attaching the balun & the metal strips from the balun, to each part of the 4 bays that they attach to, to make it work as an 8 bay. I've had that antenna for about a year & a half now, while I've had the Antennacraft CS600 for over 3 years.
 
#37
Thanks Dave. I agree Antennas Direct antennas "aren't exactly the cheapest, but the quality is there."

I understand the desire to exaggerate claims. I read once that, as a child, Rachmaninoff would play pieces written by Chopin and claim he was the composer. So I played things written by Rachmaninoff and claimed **I** was the composer! heh, heh. I was maybe 13 or 14 at the time.

I never had to exaggerate my talent as an adult, because I really had WAY too much work without a marketing effort. In fact, I woke up today after a dream rekindling my guilt at missing a concert with a Junior High School Choir. I was supposed to be the accompanist. I forgot about it -- too busy, :Cry: That was about 15 years ago. Maybe after 20 years, I'll let myself off the hook. But I guess I'm not the best man to drag antenna mfrs through the muck.

Steve, I thought it over, and I can see how "The most powerful indoor antenna I can buy is a set of rabbit ears" might really be accurate!

Rick
 

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