[TenTec] Paragon Improvements

[Stan Korzep]

Hi again

In response to Mark's comment, the Tx / Rx offset on USB information is
attached.   

The offset was measured at approximately 130 Hz after several stations
commented that they had to retune to make me sound normal.

The problem was isolated to the 9 MHz USB oscillator which was changing to
8.999870 MHz when going to Tx mode.  At the same time the CW / Tune line on
the Transmit Audio / BFO board was rising a couple volts above ground when
going to Tx.  The CW / Tune voltage was forward biasing Q4 (on my
schematic) resulting in an added capacitance being paralleled with the USB
crystal trimmer capacitor.

The problem components were located on the control board: Q4 (again this
nomenclature is as shown in my copy of the manual) on the control board was
going into partial conduction when in the Tx mode.  My control board,
obviously a very early version, did not have a base to ground resistor.  In
newer versions this is apparently R36, 10K ohm.  Base drive resistor R2 was
47K ohm value, and was changed in production to 10K ohm.  Measured change
in Rx / Tx frequency after the change is approximately 2 Hz.

As an interesting aside, my audio reports improved dramatically.  When the
USB oscillator dropped in frequency, the lower part of the audio passband
was eliminated by the SSB filter, moving the audio passband from the
expected 300 - 2700 Hz  up to 430 - 2830 Hz.  



If more information is available on the audio hiss modification on the PBT
board, I would be very greatful to receive it.  My old Paragon has an
almost irritating hiss...also on my agenda.

Stan  W8NNX