Originally Posted by holl_ands
I wouldn't worry about the mediocre Noise Figure numbers, because the large, 20 dB attenuator on the input is reducing sensitivity by a HUGE amount in order to prevent "Overload" (desensitization on weak channels)....which is probably needed due to the extremely high 48-52 dB Gain in the Preamp (which is needed to overcome the high Loss in the RF Splitter chains).
This is a primitive MATV system which, if there is no filtering and mixing network, was only capable of roughly balancing the VHF low, VHF high and UHF band levels. If all the VHF stations were in the same direction and "full powered", then your two VHF low band channels (CBS-2 and NBC-5) came off the antenna at nearly the same level as one another, as did your two VHF high band stations (ABC-7 and indepenent/WB/CW-9), so all the "system designer" cared about was driving the amplifier to its max without causing excessive sync compression. UHF signals from one market sometimes varied a little more in strength.
TA-52 Spec Sheet is rather vague re Overload Specs....they appear to be saying that input levels should be below 8 dBmV for THREE strong signals, which corresponds to 50 dBmV OUTPUT after 48 dB Gain.
The 8dBmV figure is the minimum input
level needed to enable the amplifier to be driven to full output level. 8 dBmV in plus 52 dB gain develops 60dBmV out. Those specs for three channels are for one low band, one high band and one UHF channel.
The thermal noise floor is about - 59dBmV, so if this relatively noisy amplifier has an input of even a little under 0dBmV, it will be able to sustain an NTSC analog S/N ratio of 46dB, which is what old fashioned analog MATV system designers used to shoot for.
Most distribution amps from that era didn't even have IMD figures in their original specs. They only had a maximum output level for 5% sync compression.
If you have access to a Signal Level Meter, you should adjust the input attenuation to determine the "best" value that allows reception of weaker channels.....DTV signal levels are much lower than old Analog, so less should be required. The FM Trap should also be switched IN and OUT to see if the second harmonics are causing problems for Ch7-13 reception and 3rd Order IMD problems on Ch5-6. Although TV Tuner specs are hard to come by, the input level to a Tuner should probably be kept between a Max of about -15 dBm (+34 dBmV) and a Min of about -80 dBm (-31 dBmV)....a 65 dB dynamic range of signals....which is ideally an 80 dB SNR range.....if the IMD levels are sufficiently low.....
The MATV system is supposed to be engineered such that all of the wall taps have roughly the same signal level. Very few multiple dwelling unit master antenna systems were "engineered" for UHF distribution. They were mostly designed for VHF, with the distribution level calculations made at channel 13, and then, as more UHF stations came into the marketplace, VHF/UHF combo amps were sometimes installed, and the residents got whatever benefit from them they could. Bigger budget multiple dwelling units used heterodyne UHF to VHF converters for their most important UHF stations.
MATV wallplates typically would output a level of about 10 to 15dBmV in an ordinary, adequate system, so the same amplifier, fully loaded with digital signals, would get you wallplate levels of a little over 0dBmV, but again, that is at channel 13. The UHF values would be crapshoots, but fortunately, the early unshielded taps were rated to 890 MHz, so if you have those, you may be better off than if you had shielded taps installed in the 1970s and 1980s, because those had roll off frequencies starting anywhere from 300 MHz to 600 MHz, which would choke the UHF at higher channel numbers.
I would want to measure the signal levels for all desired channels at the output of the Preamp
That point is not accessible on any TA series amplifiers.
(the -20 dB Monitor Output may Overload the meter so you can't properly measure weak signals, so you may also need an attenuator on the Monitor Output)
If the max output is 60dBmV analog, I know of no meter that would overload at 40dBmV measured at the test port.Edited by AntAltMike - 2/25/13 at 4:58am