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Old 25-Nov-2020, 5:25 PM   #77
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,676
Quote:
Originally Posted by tripelo View Post
Having the raw data to analyze, when looking for relatively small performance differences (say between two different antenna preamp combinations), could help to ascertain differences of less than one dB.
It would be necessary to compare then two systems at the same instant because OTA signals constantly vary in strength. I have seen OTA signals vary as much as 10 dB in 30 minutes.

I have more confidence in the results when using a constant strength transmitted test signal for a comparison.
Quote:
But more difficult to evaluate the performance of a particular preamplifier and antenna combination. The degree of impedance match or mismatch between amplifier and antenna can affect both noise figure and effective antenna gain.
Very true. Keeping the preamp close to the antenna will minimize the mismatch loss. When you compare the two systems, that will tell you which has the superior performance.

Low noise preamps can make a difference on UHF if the ambient noise is below -100 dBm, but they don't seem to make much difference as compared to average NF preamps on VHF because of the higher ambient noise level on VHF, especially VHF-Low.

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Last edited by rabbit73; 25-Nov-2020 at 5:35 PM.
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