Since the same BFO crystal is used for receive and for transmit and with
full QSK, that crystal frequency has to be shifted 700 or 800 Hz, part
of the unique to the radio characteristic may be from the Q of the
crystal. That a high Q crystal won't shift as fast and so its still
moving when the RF is turned on and the crystal is moving over the
corner of the filter where the amplitude and phase changes are greatest
to cause some extra modulation of the signal. Then it may depend on the
exact alignment of the BFO crystal including the shift adjustment with
respect to the corner of the filter. And it surely depends on the band
because CW is always on LSB, while that's the "normal" mode on some
bands and the opposite mode on higher bands. Meaning a different crystal
is shifted on the different bands.
Then maybe its more a receiver characteristic with the punch and
tolerably rapid rise being faster than the receiver AGC can cope with,
cured by turning AGC off or to the slow mode, so it doesn't try to
follow the keyed envelope. Vintage Tentec audio derived AGC suffered
from adding key close clicks to receive signal just because the AGC
voltage rise time is slower than the IF detected rise time and with some
of the controlled stages before the crystal filters that introduce time
delay, some of the strong signal gets into the IF before AGC can cut the
gain. An inherent characteristic of audio derived AGC. Solved usually by
running slow AGC or reducing the RF gain to minimize the need for AGC.
73, Jerry, K0CQ
On 5/17/2010 10:59 AM, Andrew Moore wrote:
Those reports that I mentioned were on this forum a couple years back. I
suspect they came from the most fastidious users of the Omni VI and they
appeared to only come from Omni VI hearing Omni VI.
I could sometimes pick out Omni VI's while listening on a non-Omni VI. I
think it's just a characteristic of the radio - maybe not all of them, but
certainly some. Some ears hear it, others don't. I wouldn't describe it as
particularly bothersome. Just a subtle characteristic of the Omni VI (VI+).
..
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