Ken Brown wrote:
>>> I found a very narrow heterodyne
>>>
> What do you mean by "very narrow heterodyne?" Is it a single CW carrier?
> Why do you say it is very narrow? Is is so super pure that you can tell
> it has less noise around the center carrier than typical, so it is
> narrower than other CW carriers?
>
> Or does the audio note it produces change more quickly than "normal"
> signals as you adjust your local oscillator (tuning) control?
Ken, on UCW the CW note (tuning up the band) is first heard as a
high-pitched tone at 28,027,618 Hz, falling in pitch until it disappears
at ...627 Hz (not audible at 628). On LCW, tunig up the band again, it
is first heard as a low-pitched tone at 619 Hz and the last frequency at
which it is audible as a high-pitched tone is 627 Hz. My "very narrow"
adjective is relative to CW signals I've been copying for 50 years: I've
never heard a signal only 9 Hz (per sideband) wide. I do not know the
difference between judging that the signal is "very narrow" and that
"the audio note... changes more quickly than 'normal'"; the latter is
how I judge the former.
> If the
> audio note changes more quickly than normal, then it is a birdie.
> Birdies are products generated by undesired mixes of components,
> harmonics for instance, of the various local oscillators in your
> receiver. If one of the components mixing together to generate the
> birdie is a harmonic of the local oscillator controlled by the main
> tuning, then the audio tone it produces will change 2X, 3X, 4X, or
> whatever harmonic number it is, as fast as a normal signal. When local
> oscillators in receivers were not locked to stable reference
> oscillators, these spurious responses would warble, tweet or chirp as
> the LO frequency changed due to mechanical, thermal or power supply
> instabilities. ( I have not found a historical reference to back this
> up, but I think this is why they came to be called "birdies". With local
> oscillators nowadays locked to super stable reference oscillators,
> birdies no longer chirp, they just whistle.)
>
>>> just one sideband
>>>
> Any real signal should be heard with the receiver operating in either
> sideband mode. If a birdie or other spurious response is detected only
> in one sideband, then it would most likely have something to do with a
> spur or harmonic of the BFO in an analog product detector type of
> receiver. Use a different BFO frequency and the birdie moves. The Orion
> is a DSP radio, so it may have to do with aliasing that occurs in one
> sideband detection mode and not the other.
>
>>>
>>> from 28,027,618 to 28,027,627 Hz. (With my step set normally at 10 Hz,
>>> it was audible only at 28,027,620 Hz.) Anyone know its source?
>>>
>>>
> The first thing I would do is try to determine whether it is an
> internally generated product of the receiver, involving no outside
> sources. Disconnect the antenna and see if it goes away.
It does not go away; same signal strength (I'd give it about a 7 on our
RST scale).
> Since others
> have said their identical mode receiver does not hear it, then it could
> be a spurious response of some real signal that is strong in your area
> and not where the other guy tried to hear it. If it does involve a
> signal coming from outside on the antenna port, then a lot can be
> learned by determining how the strength of the spurious response varies
> as known amounts of antenna input attenuation are added. Does adding a
> 10 dB pad to the antenna input make the spurious response drop 10 dB, 20
> dB or 30 dB?
>
I don't know how to add attenuation at the antenna; are these the step
attenuators I've seen that some QRP operators use to reduce their output
power?
> DE N6KB
>
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>
I am going to try turning off other electrical gear near the transceiver
(computer, principally) and see if that makes a difference.
--
John, K3GHH
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