Rich, why should the receiver only be tuned to a 3.7khz offset? What about
the rest of the band? Also, what is generally accepted as an adequate signal
to splatter ratio?
The reason I'm asking this is because I recently have gained access to a
160' tall tower that sits on a mesa top with a steep drop off. This combined
with QRO results in a very high profile signal at this installation. I
received a complaint of splatter and think I've got it isolated to the
transceiver, not the 89A. I suppose that having an exceptionally strong
signal really accentuates any nonlinear behavior in the exciter or amp.
Nonlinearities that are normally not noticed seem to become a problem in
this situation. That's why I'm trying to perform the test. I want to know if
my exciter is out of spec. or not.
If John Fielding's comment about the 2 tone levels not changing fast enough
to adequately exercise the amp are correct then John how about if I
amplitude modulate the 2 tones (on and off rapidly)? I guess I can run a
test with voice but it just seems so subjective and would be hard to show
the results to anyone at the Icom factory in case I decide to send the
exciter in for a tune up.
Thanks,
Dave
----------
From: measures [SMTP:measures@vcnet.com]
Sent: Tuesday, November 23, 1999 11:39 AM
To: Dave D'Epagnier; 'amps@contesting.com'
Subject: Re: [AMPS] 2 tone intermod test
>
>Hello, I want to run a 2 tone intermodulation distortion test on my
hf
>transceiver to check for splatter vs. compression level, microphone
gain
>settings etc. I know this is not an amplifier question, but this
list is
>probably where I can get the best answer. I'm running an Icom-756
(and Alpha
>89A). Running this test on an amp would be pretty straight forward,
but how
>about on a transceiver? Does anyone know how the test is done on
>transceivers?
>
The 2-tone test does not simulate genuine rotten splatter. For this
you
need a complex waveshape. A human or an African gray parrot is such
a
source. The splatter test is done by tuning a double-filter Rx
(such as
a TS-830) about 3.7KHz above and below the test signal to isolate
imd
products from the fundamental) and then comparing the signal
strength to
the fundamental. Since S-meters tend to be inaccurate, a 1db step
attenuator.should be used to measure relative signal strength.
>
cheers, Dave
- BTW -- the only splatter that matters to the FCC is what goes
beyond
the Amateur Radio Service band.
..
- Rich..., 805.386.3734, www.vcnet.com/measures.
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