Some proding from N4NT led to further investigation of the 17m spur
problems in the Omni-C. An undesired signal has been found and here is all
the information I have on it.
When operating on 17 meters, you will transmit on frequencies other that
what your dial is set for. This occurrs ONLY ON TRANSMIT and in any mode.
The undesired signal will be somewhere between 1 to 3 watts in strength.
It is produced by the second harmonic of the VFO MIXER. To listen to this
signal, you need another receiver. Multiply the numbers past 18 by 2 to
determine it. For instance, your dial is set for 18.070. Listen on
18.140mhz. The signal strength of this undesired signal will not vary by
adjusting the drive control because the drive control only affects the
output of the ssb board.
Now if you run an amplifier, that little signal will be even stronger.
TenTec seems to have installed a series trap in the vfo but I haven tried
adjusting this yet. I really doubt if it is capable of reducing the signal
enough.
TenTec probably changed the IF frequency to 6.3mhz in the Delta 580 for
this reason and continued using the 6.3mhz IF in the Corsair, Omni-5,
Paragon etc. The Omni-C probably would not meet the FCC specs for spectral
purity on 17 meters. When the band is opened and you call CQ, you can
expect to be answered on 2 frequencies.
I'll be looking for a cure for this but don't hold your breath.
Steve Ellington N4LQ
N4LQ@IGLOU.COM
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