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Telamon · October 1st 06, 06:47 AM posted to rec.radio.shortwave

In article . com,
wrote:

You mentioned that in your location the smaller Wellbrook ALA 1530
gave a lower S-meter reading, but was clearer then your Wellbrook
K9AY loop. Is it posible the K9AY produces enough RF to cause your
receiver to, so to speak, "fold".

I have found that too much RF, even well removed from the tuned
frequency, can cause many receivers to act "weird". By wierd I am
referring to non obvious distortion that degrades intelligibility.
Me experiments over the last ~14 months showed me that ANYTHING
that degrades the signal to noise will impair intelligibility.

I found that every receiver I tested, the boring list at the end,
experienced degraded intelligibility with a long enough wire antenna.
Long enough might be 50' with the DX398, to 1000' with the R390/R392.

Receivers used: R2000, R1000, PRC1000,DX398, R390, R392, AOR7030+,
R8B and several ham transceivers with general coverage receivers.

If you have a RF attentuator, in a pinch a the Rat Shack TV
adjustable pad can be used, could you try an experiment? The next
time you encounter a situation where the ALA 1530 gives better, as in
increased intelligibility, place the attenuator/pad inline and see if
reducing the incoming RF voltage helps.

Several things I read got me to thinking about the effect of broad
band "noise" and the effect it could have on cross
modulation/IMD/IP2/IP3 at the first mixer, before great selectivity
is present. IF, please note the IF, the first mixer adds unwanted
RF crap from unwanted, overly strong, RF "noise", then
intelligibility will almost certainly suffer.

"Noise" in this context means every RF signal other then the one you
want.

Longer, as in the length of an antenna, is not always better.

You are on a good line of thought alluding to IP2 and IP3 being worse at
higher signal levels since in a power series equation the terms that
dictate the power of IMD products are higher order terms and so they
increase at a faster rate than the signals that generate them.

Generally you lower power levels so that the IMD products are just above
the noise floor of the spectrum analyzer for best results. All signals
must be in the DUTs linear range for an IMD measurement to be valid.

--
Telamon
Ventura, California