[Elecraft] How much rejection should I expect?

[Jim Brown]

On 2/20/2012 10:01 AM, Allen Brier N5XZ wrote:
> My question is, how much receiver rejection and/or overload should I expect? He pretty much tears up the entire band on my K3 if my antenna is pointed his way, but not quite so bad on the side. On my P3, the entire noise floor is raised many S units (I'll have to switch to dB and see what it looks like.

It will depend a LOT on what rig and amp he is using, and how he tunes 
(or mis-tunes) his amp. A K3 is REALLY good at rejecting off-frequency 
signals, but there are a lot of rigs and amps that fill up the band(s) 
with trash AWAY from their frequency.

In contests, I run two K3s, each feeding a Titan 425 amp at about 1.2kW, 
into mono-band antennas that are about 150 ft apart.  On 20M and above, 
they are 3 and 4-element Yagis. Depending on how those antennas are 
pointed, I can have them as close as 60 kHz ON THE SAME BAND and one K3 
does not know the other one is there! On the other hand, if I point 
either of those antennas at the other, I'll hear a lot of my own phase 
noise, and the K3 will automatically turn off the preamp and kick in the 
attenuator. Now, the smallest coax in my station is very good RG8/213 
and RG11, some of it is CATV hard line and Heliax, all the connections 
are carefully hand soldered to Amphenol connectors, I'm careful about 
how I tune the amp, and I don't use AGC between the amp and the K3.

We also use three K3s for our county-expedition during the California 
QSO Party, and on 20, 15, and10, have two tri-banders set up about 150 
ft apart, carefully located so that when pointed east, they are at 90 
degrees to each other.  We run 500W amps, and this past year one of them 
was a KPA500.  We also used an ACOM and a Yaesu amp.  With that setup, 
we could have both CW and SSB stations on the same band and one would 
hear phase noise from the other at about S6-S7.  Coax is typically a 
grab bag of what's everyone's spares, and a lot of it is crimped from a 
popular ham vendor.

I've got an 80-year old neighbor about two miles south of me who works 
SSB contests by calling CQ non-stop as long as he's awake. I have no 
idea what he's using for a rig or amp, but he wipes out all of whatever 
band he's on with phase noise and intermod.  My neighbor, K6XX, is 3 
miles away, and runs K3s to several different f ancient amps. We can 
work 500 Hz from each other on any band.  Another neighbor 10 miles away 
runs an Icom 7600 into a big amp and sometimes wipes out 20 kHz with his 
phase noise and clicks.

73, Jim K9YC