[TenTec] Grass not always greener

Jim Brown K9YC k9yc at audiosystemsgroup.com
Mon Feb 23 15:32:39 PST 2009

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. 


Jim Brown K9YC

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