>... the 15M receiver has very poor reception and a very loud,
> steady tone on one frequency. The tone's bandwith is very narrow...
>
>...has anyone any idea what may be the cause of the steady tone?
>...initial hunch is that it is a symptom of a short, possibly in the
>crystal.
It would help if you state at what indicated frequency you hear the tone.
Anyway, **ignore** your hunch in this case.
No doubt you are hearing the seventh harmonic ("birdie") of the K1's VFO on
15m. This frequency varies from unit to unit. On my K1 it occurs near 21072
kHz, where my K1's VFO is just above 3010 kHz. The tuning seems very sharp
because as one tunes upward, the VFO frequency goes downward, which makes the
reception of the VFO's seventh harmonic appear vary narrow as one tunes across
it. The receiver frequency is changing in one direction, while the received
VFO signal frequency is changing in the opposite direction. Thus, very "sharp"
birdies are a dead give-away of reception of an internal VFO harmonic on the K1.
This harmonic near 21072 kHz is the worst case of a birdie that will be be
found on any of the K1's official bands (80m to 15m). Its actual frequency
will vary a little from one K1 to another due to variations in the frequencies
of the product detector and filter board heterodyne crystals. The birdie will
seem very strong if your receiver is working but you have no antenna connected,
or the antenna signal isn't making it to the receiver front end. Since it
seems so loud on your set, that could indicate that the receiver is working
fine (and picking up this harmonic), but you've lost connection to the external
world (antenna) which normally provides noise and signals to compete with the
harmonic. Beware...sometimes, a very dead 15m band will almost duplicate the
effect of an antenna disconnection.
What can be done about the birdie? Not much. Fortunately, most 15m activity
is below the birdie, the birdie is narrow, and an open band with signals will
diminish its perceived effect.
Mike / KK5F
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