Interesting tip.
In the Omni series C (TT 546 Series C) I not that design was rather
cobbled together to add the WARC bands.
They had decided on low side LO so they used that for 17m too. So
4MHz crystal osc mixing with the 5.0 to 5.5 Mhz so the LO tunes from
9.0 to 9.5MHz.
Brilliant!
With a 9MHz IF you have leakage through the discrete PN diode ring
mixer at the bottom of the band of perhaps -30dBm or worse 68kHz away
from IF. It gets better as you tune up the band.
With a commercial ring mixer this isolation (assuming no other
leakage (that's a big if)) you should be able to push this to better
than 60dB so the leakage would be around -40dBm.
One possibility to fix this is to mix with a 27068 to 27168kHz from
the 5000 to 5500kHz VFO and 22000kHz crystal osc to get high side LO
injection. The tuning direction is the same (if I got the math right).
I suspect the counter will still work fine (just counting the LO)
though it might show gibberish for the MHz digits (preload will be
wrong) though it might be limited on top the counting speed (was that
why they didn't do it this way?).
Not tried it yet. Not sure if the stock xtal osc will actually do
this. The top crystal is 15.49Mhz so it may or may not work at 22MHz
(fundamental versus overtone). Or an extra separate xtal oscillator.
OH, well it works on the other bands :-)
Or perhaps later drive it with a DDS/tracking PLL to replace the LO
generator.
On May 23, 2007, at 10:31 AM, duane eaton wrote:
I receive 17m on my Omni D ser.B Thusly.
Set band to 20m.
Use SB-R, Tune from 14414 to 14434.
Tune resonator near 21m until noise increases and tune for signals.
I estimate the mixer is using the 5th harmonic of the PTO
which for the 17m band is at 27.068 minus 9 Mhz is 18.068.
On 20m the PTO tunes from 5.0 to 5.5 Mhz.
This worked on my 315 Rx and suppose it will work on any of the
similar
9 Mhz rigs, Triton, Argos.
Best regards, el Rob
KI6FZF
rabbueche@dslextreme.com
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Kevin Purcell
kevinpurcell@pobox.com
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