[Hammarlund] SP600 - Reduced gain on 13kHz bandwidth

[rrkrr]

Is the AGC (AVC for vintage gear) active when you are making this gain
measurement?

What is the noise bandwidth at your signal generator output?

White noise power is proportional to bandwidth, so the 13 kHz BW would
have roughly four times the 3 kHz noise power and not quite twice the
8kHz power.  Total noise voltage is proportional to the square root of
the noise power, so you would get about twice the noise voltage out of
13 kHz bandwidth as from 3 kHz bandwidth. 

Could it be that the AVC detector is detecting noise voltage and
reducing the IF gain at the wide bandwidth setting?

Try running this measurement for the various bandwidths with a fixed DC
voltage on the AVC line.

Bob K4ERR


David Wise wrote:
> I'm taking a second look for problems in my daily runner.
> One thing I noticed is that the gain on 13kHz bandwidth is
> about 1/3 that of 3kHz and 8kHz.  3 and 8 are equal.
> The manual shows a response curve where all bandwidths
> peak at the same gain.  It's too good, makes me suspect
> someone just drew it reflecting expectations.
> I'd like to compare notes with other SP600 owners.
> Does your signal strength reading stay the same from 3 to 8 to 13?
>
> Thanks,
> Dave Wise
> SWL in Hillsboro Oregon
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