Hello all, I am wondering whether I could use two TinySAs, one as a signal generator and the other as a spectrum analyzer, to verify the amount of signal loss across various lengths of 75 ohm RG-6QS cable.? The frequencies of interest would be 200, 500, 600 and 700 MHz.? The system I am working on would be used for OTA television distribution.? I have tested the cables for return loss with a 75 ohm terminator at the far end, and the return losses are all between 36.8 and 40 dB, which to my understanding is pretty good.? The cables vary in length from 15 feet to 60 feet.
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For each frequency, this would be done first by generating a known signal level with the TinySA that will be the signal generator, with the signal generator directly connected to the other TinySA (which will measure the signal) with an interconnect adapter (for the minimum loss possible).? I would then compare the directly connected signal level to the signal level shown on the SA when the cable under test is inserted between the signal generator and the SA.? I would also like to perform a similar process to verify losses through some high quality splitters that are rated to 1GHz (return loss at the input on these splitters are all between 35 and 40 dB when all output ports are terminated to 75 ohms).
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The 75 ohm cable(s) that I am testing have the following loss specifications per 100 ft from the manufacturer:
200 MHz? 2.0db
400 MHz? 3.0dB
700 MHz? 5.9dB
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My questions are:
- will the performance of the TinySA, both as a signal generator at these frequencies and as a SA, be sufficient to provide me with useful data?? I am concerned whether the readings I obtain at the SA will be stable and accurate enough for the data to be of any value in accurately assessing cable losses on each leg of the system.
- Will the impedance mismatch of the 50 ohm TinySA to the 75 ohm cable be a serious concern to me here, either as a signal generator or a SA?? I am considering using 50 ohm to 75 ohm resistive minimum loss pads (5.7dB loss).? If that is recommended, should I use a pad on both the signal generator as well as the SA?
- Is there a better way to accomplish what I am trying to do above that won't be prohibitively expensive?? I have access to some other test gear, including analog and digital oscilloscopes, as well as an analog Instek RF signal generator (can reach 450 MHz via harmonics) and a freq counter.? I tried to do this using OTA over-the-air signals directly and measuring them with an ATSC analyzer, however, the OTA signal levels constantly change and are not steady enough for me to discern how much of the variation is due to cable losses.
I appreciate any input or advice anyone might be willing to offer.? Thanks in advance, Tony.
