[Collins] Collins 62S-1 Transverter Downconversion Gain??

[Dr. Gerald N. Johnson]

On 9/21/2010 8:03 PM, Carl wrote:
>
> ----- Original Message ----- From: "Dr. Gerald N. Johnson"
> <geraldj at weather.net>
> To: "Carl" <km1h at jeremy.mv.com>
> Cc: <collins at mailman.qth.net>
> Sent: Tuesday, September 21, 2010 8:39 PM
> Subject: Re: [Collins] Collins 62S-1 Transverter Downconversion Gain??
>
>
>>
>>
>> On 9/21/2010 7:22 PM, Carl wrote:
>>>
>>> <SNIP>
>>>
>>> The 8970 doesnt have to work that way to my knowledge but I'd have to
>>> drag the manual out of the file cabinet to be sure. In the case of the
>>> A4 I wanted the true system NF and that included taking measurements
>>> thru the mechanical filters. It was calibrated at the bandwidth of the
>>> image reject filter following the external mixer which should be
>>> sufficient. At HF I wont loose sleep over a dB anyway.
>>
>> My preamp lost 4 dB gain and a couple dB NF. There is no calibration
>> that works correctly for the 8970 with narrower devices under test
>> than its 4 MHz IFs. Yes it will calibrate, but it gives wrong answers
>> because of its assumption of the bandwidth of the noise contributions.
>> There is no other way to get correct NF other than the oldest
>> fashioned 3 dB rise or y factor with everything narrow band. And noise
>> in a 2 kHz filter has to be averaged a long time to get a steady
>> value, plus any common meter that is peak reading calibrated in RMS is
>> driven batty by narrow band noise. The next time I do that I plan to
>> use a true RMS meter that works by heating a resistor with the input
>> and reading the temperature rise. Truly true RMS, not affected by
>> crest factor unless the input amplifier gets over driven on noise
>> peaks. But I'll have to watch the meter for a minute at a time
>> eyeballing an average value, unless I hook a much larger capacitor in
>> parallel with the meter to do that averaging. Then I'll just have to
>> watch for the meter to stop moving as it oozes to the reading in a
>> slow exponential curve with an ever declining slope.
>
>
> Interesting indeed and thanks.
>
> How about feeding an audio SA on peak hold?
>
>
Peak detection, average reading is the worst way to read noise because 
truly random noise will occasionally have tall peaks but the average 
power is much less than the peak reading. Just like a peak to peak AC 
meter calibrated in RMS reads the occasional wild flings and computes a 
too strong average off those. I think the heating meter will work best.

Last year I looked at pseudo pink noise made by a PIC chip circuit with 
a GR audio analyzer, the meter never sat still.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association