On Mon, 23 Feb 2009 19:57:09 -0000, Doug Turnbull wrote:
>should see the complaints and problems which people are reporting daily
>including problems with desense when listening to pileups.
The people complaining don't know how to use a radio on CW, they don't know
how to set RF gain on a radio, and they don't know the difference between
AGC pumping and desense. Desense occurs when a gain stage is so badly
overloaded that the rectified signal shifts that bias point and drives it
into cutoff. I've never heard my K3s desense, except on my own 1kW signal
or on my neighbor 0.25 miles away running 1kW. I hear lots of phase noise
and clicks from strong local signals, and if I overdrive the radio with too
much RF gain I can have a very strong station inside the 400Hz roofing
filter pump the AGC.
The K3 has an RF gain control, a preamp, and an attenuator. On the lower
bands, you are a fool if the preamp is on and the attenuator is off. On the
higher bands you need a preamp. The AGC in the K3 is highly adjustable --
variable threshold, slope, etc. Recommended settings work quite well for
me. On 40, 80, and 160, I run with preamp off, attenuator on, and the RF
gain about 30% below full on.
I'm near San Francisco. I ran SOHP in the ARRL CW DX contest this weekend
and made just under 1,200 Qs running only one radio (one of my ICE filters
came from the factory out of alignment and blew up with 100 watts, so I
couldn't run SO2R). I worked a bunch of QRP JAs, including several on 80M,
and one JA on 80M who was running 1 watt. JA is 5,000 miles from me. TI5N,
also QRP, made it into my log on 80, 40, 20, and 15. He's about 3,000
miles. I was also able to work a fair number of 100W EU stations through
the wall of kW stations (and the east coast wall). That's 6,000 miles for
me, and most of the time, I was able to copy EU stations better than they
could copy me.
73,
Jim Brown K9YC
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