[TenTec] 219 Filter in Omni V

[Mark Erbaugh]

I just installed a brand new 219 filter (250 Hz @ 6 MHz) in the NAR position
of my Omni V. According to the TT website, the center frequency of this
filter is 750 Hz.

To check out my installation, I hooked up the audio output of my Omni V to
my computer soundcard, supplied broadband RF input noise to the radio and
monitored the frequency response.

I placed the Omni V in CW mode and selected the 2.4 filter at 9 MHz, set the
PBT to 12 O'Clock and set the fade control to full CCW. Thus, I believe that
the audio bandpass should pretty much be controlled by the 219.

What I noticed was that the bandpass seemed to be centered on 500 Hz, not
750 Hz. The top of one of the filter cans did say 219, but there was no
other marking on the circuit board or on the packaging. I contacted TT
service and they gave me another number to look for on the filter 48055,
which is there as well as the 219. They also said that the bandpass
difference could be caused by the BFO being out of alingment and then gave
me instructions for adjusting that. However, the instructions, which are the
same as those in the Omni V manual are for the 9 MHz oscillator.

So my question to the group is will adjusting the 9 MHz oscillator affect
the bandpass of the 219 filter or should I be looking for something else?

An additional piece of information is that the Omni V seems to read about
200 Hz low for a desired signal. This is based on observations, not a
critical measurement with a known frequency source. The radio was factory
aligned in July 2000 for a previous owner (I have the paperwork).  I hear
talk about 'crystal aging.' Is it possible that the crystals are so 'old'
that they fall out of alignment in 16 months?

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And I have a related question:  If the bandpass of the 219 filter is 750 +/-
125, that means that with the fixed 600 Hz CW offset of the Omni V, you are
working with a signal that is in the skirt of the filter bandpass. Is this
the way that it should be?  I guess I don't really understand how to use the
narrow filter on the Omni V. On other rigs, the the center of the filters at
each IF could be shifted via front panel controls. On the Omni V, it
appears, that only the 9 MHz filter bandpass can be adjusted.

73,
Mark