[TenTec] Fwd: OmniVI logic board work

[Barry N1EU]

On Thu, Sep 29, 2011 at 12:59 PM, Glenn <wa4aos at aol.com> wrote:

> Case and point.  I can take two of my calibrated HP 8640B signal generators and set them both for .15 microvolts and separate the carriers by 75Hz.
> Then switching the output of one of the 8640B's OFF and ON rapidly using a shielded keying fixture, (see note below ) I built, I can clearly here both signals
> as defined dits and dahs.  Using the same arrangement on the K3 or Omni 7, the signals are poorly defined with digital artifacts making neither decent enough to
> make understand the dits and dahs. Leading and trailing edges of both signals are distorted and copy would be nearly impossible at those levels. The analog
> front ends in the O6 and Corsair  are difficult copy but you can make out what the keyer is sending.


Glenn, if you could make audio recordings of the test you described
showing good resolution by O6/Corsair and poor resolution by K3, you
would be making a huge contribution toward the 2-year old debate about
poor pileup readability on the K3.  I've often though that the O6
might make a better run radio (i.e. to handle pileups) than the K3.

Appreciate your comments on variability of O6 sensitivity because this
has also been my experience.  I've had 3 Omni 6/6+'s in the shack in
the past couple of months with vintages spanning 1992-2001 and the
oldest unit had the quietest/most sensitive front end.  If someone
could document the front end diode replacement (i.e., how to remove
the board, what diodes to use), they would be doing a real service to
the user community.  I understand it's a tough job and the pin diodes
commonly recommended for the O6 job are no longer available.

Just an aside, but I'm not a big fan of the O6 dsp circuit and my
initial efforts at bypassing it have yielded MUCH more pleasing audio,
although it remains a work in progress needing more of my time.

73,
Barry N1EU