[TenTec] INRAD Audio mod for Omni VI+

[Paul Christensen]

> Haven't asked until now but have thought about it some.  Since the stock
> Tentec filter is stated as being 2.4 khz and going to a INRAD 2.8 khz filter
> "opens" things up a bit and thus is reported to sound better, I am wondering
> if a 3.4 khz filter or 3.8 khz filter wouldn't be even better?

Yes, but be aware that the LSB and USB BFO carrier set point will require readjustment and this will no longer track with your
narrow filters.  I would order a custom INRAD filter with an offset center frequency which could better track with your existing
filters.  Otherwise, you're going to run into alternate sideband rejection issues.

Also, the internal DSP circuit may mask the benefit derived from opening up the IF.  As I recall, the receive audio DSP circuit is
always in line, regardless of whether it's engaged from the front panel.  After such a mod, I would look at the white noise response
on an FFT program like SpectraPlus.  Or, manually sweep the receiver across a fixed CW carrier and plot the receiver response curve.
Other receiver components in the A.F stage may require changing in order to flatten the audio passband.

Recall that the 2.4 kHz at 9 MHz filter is used for transmit as well as receive.  If you opt to go to a 3.4 or 3.8 kHz filter, be
prepared to answer the many hate messages you will get concerning your new wide transmit bandwidth.  An alternative to this for
extended receive-only bandwidth, is to install the new wideband filter in one of the other 9MHz filter positions and leave the
2.4kHz filter alone.

-Paul, W9AC