> I'm not familiar with the Omni V, but in the Omni 6 and 6+,
> there were some reports of chirp on the CW signals. I think it was
> either N4LQ or W9AC that investigated and found out that the CW carrier
> was set very close to the skirt of the 2.4kc filter. The cure for the
> chirp was to replace the 2.4kc filter with a 2.8kc filter. Not only did
> that eliminate the chirp, it gave you a little more bandwidth for SSB
> operation as well.
Actually, the filter helps to diminish the effect of the chirp in the Omni
Six/+. You're absolutely correct in that the Omni
Six's CW carrier is placed dangerously close to the 2.4K filter skirt. This is
not the case in the Paragon, Paragon II, or Omni V
which uses a fixed 600 Hz, rather than 400 Hz TX offset. In fact, on my Omni
the TX BFO frequency ended up below the knee of the
filter on the skirt itself. This exacerbates the effect of what is a really a
root problem in the 9 MHz TX BFO circuitry as first
discovered by Steve, N4LQ. Myself and others have found that by replacing the
9 MHz crystal with something of a better quality
(e.g., JAN, ICM, etc), the problem goes away.
In the 6+ (the real deal), Ten Tec decided to use the opposite SSB BFO crystal
to generate the CW carrier since it results in less
carrier shift between receive and transmit. It's a step in the right
direction, but plenty of 6+ rigs still sound a bit, well...
I ended up ordering a new Omni 6+ BFO board and Control Board from TT and
placed it in my older vintage Omni and it works well.
Both boards require change-out if you do not have an authentic Omni 6+....even
the Option 3 upgrade to an Omni 6+ still requires the
retro-fit.
I ended up ordering about 10 different crystals from JAN in Fort Meyers, FL.
Each was made with different crystal loading
parameters. I then installed a crystal socket, and tried each one until I
found one that sounded best. No, in my haste, I
neglected to document which one it was. Nevertheless, each of the ten sounded
significantly better than the stock 9 MHz crystal. I
believe it was either Dick Green or Dave Hammond who did the same thing to
better temperature-stabilize the BFO and he achieved
excellent results. I know he documented the exact crystal type and it's on the
Ten Tec Reflector archives.
-Paul, W9AC
|