Posted by
Cady, Fred on
Dec 21, 2011; 7:01pm
URL: http://elecraft.85.s1.nabble.com/K3-RF-Gain-control-reduced-range-after-RF-gain-calibration-tp7113809p7116239.html
Thanks Al.
Well, the Figure 1 shows what I expected. Below the AGC gain threshold the output audio is the same with AGC on and off. Figure 2 is not expected, at least for me. Reducing the RF gain ought to reduce the audio levels, which you point out, and which it does. But, it reduces the AGC off signals more than the AGC on as shown in Figure 2. I made these measurements in the context of wondering why I find it necessary and and an improvement to turn AGC off when there is a pileup of signals all of about the same signal strength, something that has happened frequently for me when operating from C6. During our last operation, it was a real pain to switch AGC off and then have to turn up audio gain to compensate. It just seems strange to me that when AGC is on and we are below the AGC threshold, that the RF-audio level audio transfer characteristic is different than when AGC is off.
73 and happy holidays all,
Fred
KE7X
-----Original Message-----
From:
[hidden email] on behalf of Al Lorona
Sent: Wed 12/21/2011 10:46 AM
To:
[hidden email]
Subject: Re: [Elecraft] K3 RF Gain control reduced range after RFgaincalibration
Fred, are you expecting the AGC OFF curves to always produce higher output than
the ON curves? I'm not sure that's a correct assumption. I think the purpose of
OFF is that you have control over the curve, that is, where you place the linear
part of the dynamic range. It's like a variable attenuator in a spectrum
analyzer.
There are two truths regarding AGC OFF:
As you reduce the RF Gain you should see a drop in audio output.
AGC ON is always going to give you a more compressed input-output
characteristic, compared to AGC OFF. That's what AGC does; it wants to make
signals equal to a greater or lesser extent depending on your AGC parameters.
It looks like your measurements have proven these two truths.
A sudden 10 dB jump at the 9 o'clock or any position is an issue. This brings
up a good point... all those who have been experiencing 'pileup mush' should
make sure that their RF calibration is correct. I bet you that's half of the
problem.
Al W6LX
________________________________
There does seem to be something strange in the way the RF gain works.
I also see the 10 dB change in audio level at the 9 o'clock position.
In addition, the RF gain position seems to affect the way the AGC on and
off works as shown on
http://www.ke7x.com/home/miscellaneous-k3-information/unexpected-agc-behavior
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