[TenTec] Receive 17m on Omni ,Tritons, etc.

[Dr. Gerald N. Johnson]

On Thu, 2007-05-24 at 12:46 -0700, Kevin Purcell wrote:
> Of course. The mixing will invert the sideband even though the tuning  
> direction isn't changed. Better than lots of RF in the IF strip.
> 
> At least they wised up on the next design. Ah, the perils of putting  
> new bands on old hardware :-)

The 5 MHz VFO and 9 MHz IF was chosen long ago in the late 40s or early
50s for phasing rigs. The 5.3-7 MHz command set tuned down and using it
for a VFO worked well because it was very stable. With capacitors made
of invar and coils shrunk to the sturdy ceramic forms it had to be good.

At first 9 MHz IF and 5 MHz VFO added to 20 meters and subtracted to 75
meters. The quality of the audio phasing networks proved that the theory
of inverting one audio signal to change sidebands didn't work unless one
accepted 10 db sideband suppression in that condition after taking hours
to match up RF and audio phase shift to achieve barely 40 db on the
preferred sideband. That is why we still use USB on 20m (the first band
for ham SSB) and LSB on 75. Then it was possible to use harmonics of the
VFO (and a more rapid tuning rate) for other bands, but 40 and 160 ended
up on LSB (3rd and 2nd VFO harmonic), 20, 15, and 10 ended up USB with
appropriate harmonics. Central Electronics made a kit to add the
multiplier band switching and a new dial for the front of the command
set and it was useful with their 10A/B and 20A/B exciters.

WARC bands came along nearly a generation later and didn't fit into the
scheme, especially 17 meters. But by changing the VFO multiplication to
offset crystal mixing, that's how Tentecs worked at least the ham band
only versions and all using a 9MHz IF. The VFO was replaced with a 400
MHz synthesizer and a divider it was still mixed with crystals to get to
the appropriated injection frequency. That makes for an injection with
low phase noise, not characteristic of frequency synthesis at the
desired frequency which sets the Omni V and VI to work better in strong
and weak signal (where the weak signal is the desired signal) situations
than the Paragon.
> 
> So they didn't move to all high side injection on the higher bands? I  
> suspect not if this is the only "inverted" band.
> 

-- 
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer