Posted by
wc1m on
Feb 06, 2010; 6:23pm
URL: http://elecraft.85.s1.nabble.com/K3-in-a-cw-pileup-needs-work-tp4523884p4526340.html
Dave indicates that the problem occurred when the pileup consisted of four
or five loud stations. This leads me to wonder if the cause is the K3
hardware AGC threshold being too low, even after the mod introduced two
years ago. That mod was supposed to raise the threshold from S9+5 dB to
S9+25-30 dB.
I got into this issue after repeatedly being botherd by thumping from loud
CW stations above my passband during big contests. When I first noticed it,
I was using the 5-pole 500 Hz filters and the DSP set to about 300 Hz. I'd
hear the thumping from stations more than 150 Hz or even 250 Hz above my
frequency. Testing revealed that I could hear thumping from loud CW signals
as far as 700Hz away. The testing also showed that the filters were
effective against a loud continuous carrier, but CW signals were slipping
under the skirts. This suggested that the problem is caused by the hardware
AGC being tripped by the loud signals. I switched to 8-pole 400 Hz filters,
and that improved the situation considerably.
My testing probably wasn't lab-quality, but it showed that the hardware AGC
really kicks in much lower than S9+25-30dB. I think it's more like S9, or
just above. Perhaps if two or more signals in Dave's pileup were that lour
or louder, the hardware AGC kicked in and mushed them together?
73, Dick WC1M
> -----Original Message-----
> From: Dave Hachadorian [mailto:
[hidden email]]
> Sent: Friday, February 05, 2010 10:45 PM
> To: Elecraft Reflector
> Subject: [Elecraft] K3 in a cw pileup - needs work
>
> Tonight I used a pair of K3's in the Sprint practice. Several
> times I had a pileup of four or five loud stations calling me.
> With AGC turned on, they were all mushed together, and I couldn't
> copy any of them.
>
> AGC settings:
> dcy soft
> hld 0.2
> pls nor
> slp 000
> thr 008
> f 200
> s 020
>
> I tried both fast and slow agc. No joy.
>
> So I turned the AGC OFF. Now this introduces another problem -
> the very low threshold of the AF Limiter. The AF limiter, even at
> its highest setting of 030 introduces gross distortion on loud
> signals. This is even worse than the mushy AGC.
>
> So I transfer the headphones to the speaker output, so I can
> reduce the AF gain setting in an attempt to get away from the
> raucous AF limiter. This works for a while, until finally one
> loud signal blows out the K3's audio amplifier. This is the
> second time that has happened to me. I guess I'm a slow learner
> on that issue.
>
> Something really needs to be done here. My suggestions would to
> raise the agc threshold further, and increase the slope of the
> agc line (that would mean a slp setting of less than zero). The
> AF limiter threshold also needs to be raised, and the AF speaker
> output needs better protection.
>
> Dave Hachadorian, K6LL
> Yuma, AZ
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