This is interesting. I had a TS-870 (great rig, btw!) that had a harmonic
of local AM 610 on 1830. In the day (5k watt stn) it was around S9. If I
put in 6db of attenutation, the signal fell to S1. I don't think that meter
miscalibration could be responsible for 50db drop! I've no doubt the
station probably had a weak harmonic there, but always thought the rig was
compounding it somehow.
73 John K4IQ
----- Original Message -----
From: "Lee K7tjr" <k7tjr@comcast.net>
To: <Topband@contesting.com>
Sent: Monday, June 30, 2003 11:46 PM
Subject: Topband: A/B testing K6se etc.
> I would like to add a couple cents worth on testing receivers for quality
> based on using the third harmonic of a broadcast station on the 160 meter
> band. It would be very important to know exactly where this third harmonic
> is being generated. There is one scenario I can think of that would simply
> invert Earls tests and make the last one on the list become the first one
on
> the list. Consider the fact that a third harmonic is often generated from
a
> clipping action resulting from nonlinearities or overload. For strong
> broadcast stations a third harmonic could actually be generated right in
the
> receiver being tested and I have seen this happen. This signal could come
> right in to the antenna input or be a large current on the outside of the
> antenna coax resulting in a large signal. The resultant level of the
> offending signal then would be stronger in each radio tested depending on
> how weak the receiver actually was. Bingo, the poorer the receiver the
> greater the signal to noise ratio on the third harmonic where the rig is
> tuned. Or good radio bad SNR, bad radio good SNR. I for one certainly
would
> not base any rig purchasing decisions based on tests using a signal of
> completely unknown origin or precise signal strength. I spent a lot of
years
> setting behind bench test equiptment as an RF engineer chasing just these
> kind of signals and so I believe we will see a lot more about actual
> performance of these different rigs as time goes by. Then we will see
where
> all the chips will fall. My Omni 6 beats anything I have ever used or
owned
> on SNR and I look forward to the day I can own or at least try an Orion
> under my own test conditions and maybe a few others too.
> Regards: Lee K7TJR Oregon
>
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