DTV reception issues explained and some possible solutions !!
This article written by me for our stations website. It is rather lengthy, but it has a place in this forum. It also contains references to our broadcast area and its terrain, but it applies to other areas of the country as well.
Digital TV reception problems explained with some possible solutions
TV broadcasting history and some basic facts
The era of analog TV broadcasting has finally come to an end. Analog TV broadcasting in itself has enriched our lives in terms of education, entertainment, public safety, and in many other areas of our lives, and we take this convenience for granted on a daily basis. Analog TV broadcasting had changed little in the 60 or so years it had been used.
Digital TV broadcasting is a new technology that is still in its infancy, and reception of digital TV signals still has some issues that need to be addressed. The first issue is that until recently, there had been very little research into new antenna designs that try to address some of the inherent reception issues of broadcast digital TV signals. The older antenna designs worked very well for analog TV reception on both broadcast bands, be it VHF or UHF. Almost 90% of digital TV Broadcasting will take place in the UHF TV band on average, but that fact does not apply in the Roanoke-Lynchburg broadcast market, as there will be 2 broadcasters that will be using VHF channels.
In the past, broadcasters preferred the VHF channels to UHF channels for several reasons, which will be outlined here. The VHF signal is more desirable for analog due to its propagation properties, which in essence, made it easier to receive, along with the lower costs involved in operating a VHF TV transmitter versus a UHF TV transmitter. It takes less transmitter power in the VHF TV band to reach your target audience, which equates to lower power bills. Calculate this power savings over the lifespan of a typical TV transmitter of 20 to 25 years or more, and the cost savings over time are substantial, but recently discovered reception issues with some VHF channels indicates that the UHF band is the desirable band for digital TV broadcasting in contrast to the past where VHF was the desired band.
Digital TV reception issues explained
The reception of digital TV signals has several minor issues that are now being addressed by the broadcast industry. The first issue that effects digital TV signals is a phenomenon known as multi-path signals, which are more commonly referred to as ghost signals. The effects of ghost signals in analog broadcasting were shadows, or multiple images on the screen. Ghost signals are basically just signals that take a longer path to your antenna than the main signal by reflecting off of a distant object, and arriving at your antenna slightly lagging in time when compared to the direct path signal.
This timing difference between the direct path and the ghost signals is the main cause of the reception problems we are seeing for digital TV receivers, as it actually causes them to become confused since they cannot determine which is the main or direct path signal, so viewers see the dreaded “No Signal” logo on their screens. The “No Signal” indicator is actually misleading to viewers, as it is not always a “No Signal” issue that is causing the problem, but is actually a ghost signal that causes most of the reception problems that we are seeing.
The ghost signal phenomenon has a much greater, and very detrimental effect on digital TV reception, and this area of digital TV reception is now being addressed by several new antenna designs currently on the market. There have been very few innovations in regards to TV reception antennas for many years, as the old designs were very effective at receiving analog signals, so no one wanted to invest time and money into new designs that were intended to address the ghosting issue.
One additional issue that makes digital reception even more difficult is the mountainous terrain in our broadcast area, and in densely populated areas around bigger cities that have lots of high-rise buildings such as New York City.
There have been many misconceptions in regards to promoting the concept of digital TV broadcasting that in my personal opinion have misled many viewers in the wrong direction in regards to choosing reception equipment such as indoor versus outdoor antennas, and the need for an antenna rotor.
The fact that broadcast TV signals are now digital, does not change the actual physics of a transmitted radio signal. The actual electrical properties of a radio signal are the same in regards to reception, regardless of the information that radio signal contains, even if that information is in a digital format. As in everything that is manipulated by man, we are now discovering that there are exceptions to this basic rule in regards to reception of digital TV signals.
Some antenna myths revealed
You may see it stated that your existing antenna and cabling will work for digital TV, and you may also see antennas being sold as HDTV, or digital ready, and as a general rule, both statements are true, but this is where the exception to the rule mentioned above comes into play. In areas where the terrain is basically flat, an existing antenna that receives both the VHF and UHF band should work fairly well. The issue of ghost signals comes into play in areas such as ours that have irregular, or mountainous terrain such as southwestern Virginia.
The irregular, or mountainous terrain of our region calls for some additional considerations when choosing the correct antenna for your location. Some of the issues that affect reception can be dealt with very effectively if some planning and research is done before purchasing an effective antenna system for this area. A TV signal receiving system is a complete system, and is not just the antenna itself. A properly chosen antenna can enable you to receive TV signals that were not available to you before the digital transition, but in some very extreme cases, you may not be able to receive signals that you had before the transition took place due to technical changes that may have been necessary at the transmitting site, or to prevent interference to other broadcasters
There are other signal issues to consider besides ghost signals in our area that present additional challenges to reliable TV reception, with the first being that not all stations will be using the UHF TV band to broadcast their signals. A few stations will still be using VHF channels, along with the placement of several transmitters that are not located along side of the rest of the transmitters in this area, and since digital TV signals require the antenna to be aimed directly at the broadcast tower, the different location of those transmitters requires the antenna to be rotated or aimed using an antenna rotor or a “Smart Antenna” to accomplish this task.
Smart antennas allow the digital TV tuner to control the gain and reception characteristics of an intelligent antenna, but this is a relatively new concept that has not been fully adopted by equipment manufacturers to date. Another option that has been used in this area in the past is the use of two separate antennas combined together using an antenna combiner, with the antennas aimed in different directions to accomplish the same results as an antenna rotor or a “Smart Antenna”.
Outdoor Antennas will always work more efficiently
I will state from many years of experience that outdoor antennas will normally outperform an indoor antenna in almost all cases. Even mounting your digital TV antenna inside the attic can lead to poor reception, as a lot of building materials such as roofing shingles, plumbing, and even some types of attic insulation can reflect the incoming signals away from the antenna, and an attic mounted antenna can be expected to lose well over 50% of the received signal strength versus an outdoor installation.
If you live reasonably close to the location of the broadcast antennas, indoor antennas can work in some cases, but in general, they are not recommended for most locations. Some viewers may live where they may have restrictions about outdoor antennas such as those that may be imposed by a public housing authority, or some other restrictions such as managed subdivisions or homeowners association restrictions that may try to hinder or impede your outdoor antenna installation, but you do have some federally mandated laws that can help you in this area.
Antenna installation restrictions explained
Here is a short summary of the rules regarding antenna placement on property you own or rent, and these federal laws normally take precedent over local laws regarding antenna installations. The rule (47 C.F.R. Section 1.4000) has been in effect since October 1996, and it prohibits restrictions that impair the installation, maintenance or use of antennas used to receive video programming. The rule applies to video antennas including direct-to-home satellite dishes that are less than one meter (39.37″) in diameter (or of any size in Alaska), TV antennas, and wireless cable antennas. The rule prohibits most restrictions that: (1) unreasonably delay or prevent installation, maintenance or use; (2) unreasonably increase the cost of installation, maintenance or use; or (3) preclude reception of an acceptable quality signal. You may read the rest of these rulings at the following web link, FCC Fact Sheet on Placement of Antennas.
Amplified antenna myths revealed
Another big misconception that is a carry over from analog broadcasting is the use of amplified antennas. A large majority of antenna amplifiers are of low quality, and they can sometimes contribute to the reception issues that plague digital TV signals. The vast majority of reception issues can be directly traced back to the ghosting phenomenon, and amplified antennas only aggravate the problem even more by amplifying the ghost signal as well as the main signal that you are trying to receive. In this situation, the amplifier will never solve the problem; instead, it will only make it worse.
The use of amplified antennas for viewers close to the transmitters will normally not solve reception issues. I only recommend amplified antennas for viewers who actually have a low signal problem, and they are usually located in the far outer reaches of our coverage area. Another area where amplifiers may be helpful would be for viewers who require long cable lengths from the antenna to reach their receiving equipment.
It is even possible with digital TV signals to have too much signal. The modern efficient circuitry used in digital TV reception devices can actually suffer from too much signal, and antenna amplifiers can again contribute to this problem for viewers who may live very close to the transmitters. If you are using an amplified antenna, and you still suffer from reception issues, the first thing to try would be to remove any amplifiers you may be using to see if that helps the problem.
Signal Splitters and cabling
The use of “Signal Splitters” and the wrong type of cabling, or too long of a cable run can all contribute to reception issues. Signal splitters can be useful for supplying a signal to multiple TV sets from a single antenna, but they do have a negative effect of lowering the signal level that all of the connected sets will receive. How many sets a splitter will serve depends on how strong the received signal is at your location. A general rule would be 2 TV sets maximum, but this can vary based on signal levels. If you intend to feed more than two sets, a signal distribution amplifier may be useful in this situation.
A signal distribution amplifier is not the same device as an antenna amplifier. The use of good quality cable is also a factor in quality TV reception. All digital TV receivers have a 75-ohm F-Type cable input jack, and the recommended cable type used in this application is known as RG-6 coaxial cable. It is available at many electronics stores and home improvement centers. It is also advisable to use waterproof connectors, or some type of coaxial cable sealant to ensure against water getting inside the cable at the antenna connector, as this can greatly degrade your reception and possibly block it altogether.
Proper grounding and lightning protection required
A properly installed outdoor antenna requires adequate grounding and lightning protection, and a lot of antennas are not considered as being properly installed if this area of extreme importance is ignored. First of all, make sure all of your reception gear is plugged into a high quality surge protector, preferably one that’s guaranteed for at least the amount of your equipment replacement costs. There are surge protector models available that allow you to connect your coaxial cable to it for additional protection.
You also need to make sure that it is plugged into a properly wired and grounded receptacle. Any receptacle that does not have the third or center-grounding prong is not properly wired or grounded, and they will not protect your equipment, as they use the third grounded prong of the receptacle to send voltage surges to ground. Pictured below is the basic grounding diagram suggested by the National Electrical Code in section 810-20 regarding proper antenna grounding. You can sometimes find the exact applicable code at your local library.
You should also be aware that a coaxial cable grounding block is not adequate lightning protection, and that a coaxial cable gas discharge device is the best lightning protection method currently available, even though a good gas discharge device can be rather pricey, this is the best method available to protect your expensive digital TV, and any other connected components such as stereo receivers or audio amplifiers.
Antenna recommendations by the ____ engineering staff
Due to all of the issues mentioned in the above text, the engineering staff of ____ presents the following general antenna system recommendations. In order to receive all of the stations in this market requires the use of some type of VHF / UHF combination antenna, or 2 separate antennas as previously mentioned. If using a single antenna, you must be able to steer or aim the antenna, which would require the use of an antenna rotor, or the use of a “Smart Antenna” is another good option, but your receiving equipment MUST support this new type of antenna.
Some models of converter boxes, and especially high end digital TV’s are compatible with the “Smart Antenna” concept. Check your owner’s manual to see if your receiving equipment supports this option, as this antenna concept is very effective at resolving the ghosting issue explained above, and once it is installed and operating properly, the receiver does all of the work from there on.
One last fact to include that is very important to remember is this excerpt from the official FCC website; The Federal Communications Commission (FCC) recommends the following guidelines in regards to TV antenna installations, “In order to receive broadcast TV signals reliably, the antenna should be installed 30 feet above the ground”.
When the concept of digital TV was under development and testing, the 30-foot receive antenna rule was the basis for all of the testing done on digital TV reception, and the logic behind promoting indoor antennas or rabbit ears is still confusing to broadcast engineers everywhere. This concept of promoting indoor antennas as viable for digital TV use has led to a lot of the confusion among consumers over the digital TV reception issues they may now be experiencing, and about choosing the correct antenna for your location.
Some additional tips for satellite viewers
Have you looked at the costs you are paying for satellite TV lately? Did you know that you could save the monthly charges for your local channels, which can average around 6 to 8 dollars per month? If you would like to reduce your TV entertainment costs, you may want to consider dropping your local channels from your monthly satellite fees and consider installing an outdoor antenna. The installation of a properly selected and installed antenna can pay for itself in a short time when compared to the continual monthly charges incurred with your local channels being delivered by satellite.
If you are looking for the highest quality picture to match your glorious new wide screen HD TV, then off air reception may be your best choice. The picture quality of broadcast high definition signals is far superior to those sent to you via satellite or cable. In order for those providers to squeeze all of those channels onto their delivery systems, they actually “steal” a little picture quality from each signal they send out in order to have room for all of the channels they carry. It is a proven fact that the picture definition of broadcast high definition TV signals is much better than those alternate signal delivery methods such as cable or satellite.
It is my hope that this article will help you in your quest for receiving the wonderful new digital and High Definition TV signals that we broadcast for our viewers. We constantly strive to provide the highest quality broadcast signals available to our audience. Please remember that digital TV broadcasting is a new concept that is still in the development stages in regards to reception issues