[LCC] Texas thoughts on K3# operation

[Randy Prewitt]

I sent a couple of my ham buddies some of the recent LCC email postings and thought I'd share their thoughts with you.  They're okay with the idea of sharing this.
Randy K4LJA
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FROM TOM WEBB; W4YOK:

 
> >Charles Harpole, K4VUD, brought his K3 over to my shack a while 
>>back.  Now maybe we were doing something wrong, but we connected the 
>>K3 in parallel with a coax tee with my Drake R-4C and tuned in a 
>>very weak signal on 40 CW which we could copy on the R-4C, but which 
>>was inaudible on the K3.  No amount of knob twisting could bring the 
>>signal up out of the noise on the K3.

REPLY FROM RANDY FARMER, W8FN:
> 
> Charlie's (very early) K3 must have had something wrong with it. I 
> know he had lots of issues with the AGC settings when he first got 
> the radio. It may seem counterintuitive, but running up the gain and 
> turning on the preamp is NOT the way to hear signals near the noise 
> floor, especially on the low bands. High gain together with an overly 
> aggressive AGC just lets the noise control the AGC action and greatly 
> reduces the signal to noise ratio of weak signals. Low sensitivity is 
> certainly not a problem with the K3, especially on 40 meters where 
> the band noise is usually around 20-30 dB above the receiver noise 
> floor with any kind of an antenna at all.
> 
> I normally run the RF gain (which is really an IF gain control) down 
> to where the band noise just barely doesn't cause the signal strength 
> indicator to fluctuate. Most of the time this is anywhere from 
> indicated S3 to S7 on 40 meters here. I've set my AGC Threshold to 
> 008, which puts the onset of AGC action at around -100 dBm. I've set 
> my AGC Slope to 001, which allows an audio output change of around 4 
> dB for every 10 dB of signal input increase once the AGC kicks in. 
> These settings keep the output level nearly proportional to the input 
> level up to around -50 dBm, where the hardware AGC kicks in to 
> protect the A/D in the DSP section. This setup maximizes dynamic 
> range in the audio and provides the best readability of weak signals 
> in the presence of big QRM or noise. In big contests I usually end up 
> switching in the attenuator (the RF gain control) on 40 to keep the 
> huge signals under control, and I have yet to have any problem 
> pulling very weak signals out of the QRM. Of course once a weak 
> signal is truly buried in the noise no kind of receiver is ever going 
> to be able to improve the S/N ratio so you can hear it. Once the S/N 
> is 0 dB the signal is by definition covered by noise.
> 
> The K3 has lots of adjustments you can twiddle to make it do what you 
> want, and taking the time to adjust things like the AGC behavior and 
> the overall gain can make the difference between hearing and not 
> hearing weak signals in difficult conditions. The K3 runs circles 
> around my modified R-4C, and that's really saying something.
> 
> 73...
> Randy, W8FN 
>
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