It would not be silly to test and with a receiver with a working S-meter
and a calibrator signal or any other local steady signal you just tune
across the signal and plot the S-meter readings vs. frequency. If you do
it in USB and LSB you will see the response (probably have a sharp null
at zero audio frequency due to audio response not going to DC and audio
derived AGC) and the carrier frequency, e.g. zero audio frequency in
receive should be around 20 dB down the skirt. You could use noise into
the receiver and a computer based audio spectrum analysis but it won't
show that zero frequency notch but it will show the HF side not going to
3.1 KHz where it would with the carrier 300 Hz from the lower edge.
In my opinion transmitting with 2.8 is not using spectrum or transmitter
power efficiently. The added 400 Hz bandwidth over the factory 2.4 or
the 2.1 I've been used to contains mostly noise from speech harmonics,
syllabents and background noise that do nothing at all when received
with a 2.4 or 2.1 filter because the receiver filter rejects them and
they aren't heard, but they are heard on adjacent frequencies. Heck, to
improve received S to N, I generally use an audio DSP filter set to roll
off at 1.9 or 2.1 kHz so I'd ignore a full kHz of the 2.8. Even if
received with a wider filter the stuff in that part of the audio
spectrum out of the receiver will be QRM and stuff that may slightly
enhance the real sound but doesn't improve copy.
Then making the BFO crystal move out further can contribute to the
infamous CW "click" of the Omnis that some hear, and some don't that I
think comes from the frequency shift not being quite complete when the
carrier comes up on CW and its moving through a portion of the filter
resonse that has a rapid phase shift with frequency. The corner always
does have that rapid phase shift with frequency in an analog filter. The
click is nearly always heard only with matching receivers and filters.
73, Jerry, K0CQ
On 10/29/2010 6:05 AM, Richards wrote:
Is it possible the filter is wider than expected? Would one be silly to
test the filter to see if it is in spec? Could the filter skirts be
wider than they should be? Is this easy to measure or test?
Not being critical... just trying to learn from all this along with
the rest of you.
Thanks.
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