Antenna Amps, Do they help or hurt reception?
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.