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Old 19th Oct 2018, 1:15 pm   #17
G0HZU_JMR
Dekatron
 
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
Default Re: MuTek Pre-amps for the FT290R

Yes, there are a few potential gotchas with the noise source method. My Agilent noise source ENR is typically 5.7dB and the Noisecom ENR is 13.6dB and I check with both.

I do also make sure there is no compression by running the AF at a suitable level with plenty of headroom. The other issue is noise pickup and I always check across several channels to make sure the radio isn't picking up any local noise or mush. The shape of the noise and any internal birdies can be seen easily on the analyser so this helps reduce the risk of a false result. Ideally, it should be done in a screened room. I've got lots of experience at work (getting strange results!) using the old HP8970B noise meter unless it gets used in a screened room. But here at home I rarely see any noise or interference pickup.

I also use the conventional method with a sig gen but the result depends on the tone frequency on SSB as the passband usually isn't flat. So even with a tiny change in test frequency the results can vary a lot. I've also experimented with a small amount of FM with the sig gen to spread the energy across the passband to get a more realistic result when using this method.
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Regards, Jeremy G0HZU
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