Posted by
Mike K2MK on
Dec 17, 2009; 8:16pm
URL: http://elecraft.85.s1.nabble.com/Why-K3-appears-noisy-tp4181768p4183243.html
Hi Wes:
I took a look at the RF Gain Calibration on the K3 Utility and they offer
two ways of doing it. One requires a signal generator and one uses factory
default values. Is the factory default method satisfactory or is it
necessary for us to purchase the XG2 to do the calibration properly.
Thanks,
Mike K2MK
Wes Stewart
Thu, 17 Dec 2009 09:34:56 -0800
I believe I've written about this before, at least to a few, but perhaps it
bears repeating. I have done a side-by-side comparison of my K3 with another
K3
when "RF" (actually IF) gain was reduced with the AGC on.
With my radio, tuned to a S9+50 dB BC station, even a slight decrease in
gain
was met by a large *decrease* in SNR. On the other this wasn't the case.
IMHO, this results from the wide differences in the volts v. dB
characteristic
of the gain-controlled hardware, i.e. the FET/diode post crystal filter
amplifier, from radio to radio. This is why one guy can write, "SNR is
improved when I reduce RF Gain" and another can say, "SNR goes to pot when I
reduce RF Gain." Both can be correct, depending on their hardware.
It's not new knowledge that we want to delay the application of AGC to early
stages in the radio so as to maintain SNR. But in this radio, one size of
delay
doesn't fit all.
The RF gain "calibration" is an attempt to fix in firmware what is
essentially
a hardware problem and Lyle has done an excellent job doing this. If I
understand correctly, (always a dubious proposition) he measures the gain v.
volts of the FET amplifier and applies this new found correction to the gain
control partitioning.
This has made a remarkable difference in my radio, which must be a real
outlier. Still, and this is conjecture, I have this nagging concern that
there
might be some latency in the process and under highly dynamic conditions, it
"doesn't keep up."
Wes N7WS
______________________________________________________________
Elecraft mailing list
Home:
http://mailman.qth.net/mailman/listinfo/elecraftHelp:
http://mailman.qth.net/mmfaq.htmPost: mailto:
[hidden email]
This list hosted by:
http://www.qsl.netPlease help support this email list:
http://www.qsl.net/donate.html