Hi Gerry,
<SNIP>
Actually the synthesizer is up in the 450 to 500 MHz region for better
phase noise and then divided down to 5 to 5.5 MHz where its used alone
for 80 and 20 and mixed with a crystal for the other bands.
Actually the synthesizer generates 4.97 to 5.53 MHz as I said. The way
it does this is to use a PLL operating at 200 - 220 MHz. The VCO in this
PLL is actually a VCXO using a 39.940 MHz crystal. The 200 - 220 MHz
output (a harmonic from the 39.9 MHz VCXO) is divided by by 40 to get
the 5.0 - 5.5 synthesizer output. It is done this way for the reason you
stated, to minimize phase noise.
Maybe it is the Omni V that does not use a crystal oscillator on 80 and
20 meters. The Omni VI uses a 18.0030 MHz crystal oscillator.
Loss of either oscillator will cause a dead receiver.
The 160m crystal is 5.8 MHz.
The crystal used for 160 meters in my Omni VI XTAL OSC board schematic
is 16.3030 MHz. With the 5.0 - 5.5 MHz synthesizer working 16.303 -
5.503 = 10.800 and 10.800 mixed with 1.800 will give a product at the 9
MHz IF.
Add 1550 that's 7350, quite a ways from the
9 MHz IF, but twice 5.8 is 11.6 subtract 1550, that's 10.050, still
outside the filter. 5.8 + twice 1550 is 8.900 MHz. Still a supersonic
beat note. Twice a 1600 MHz BC station would mix with the 5.8 MHz
crystal to pass through the IF at 9 MHz.
I guess that would be the case in an Omni that uses a 5.8 MHz crystal on
160 meters.
In an Omni VI like mine that use a 16.303 MHz crystal, and the 5.0 - 5.5
MHz synthesizer not working, the most straightforward mixes to 9 MHz
would be from 25.303 MHz and 7.303 MHz. Since Joe identified the MWBC
station that he hears at 1550 kHz, I would say there is some other
component involved in some IMD product he is hearing.
It is also possible that there is another station with the same program
on 7.303/5 = 1.460 and he is hearing the 5th harmonic of that. That is
not too hard to believe if you tune around the MWBC dial and hear how
much duplication of programming there is on multiple stations. I expect
Joe would have heard that one too if it were th
I'd concentrate on the synthesizer.
Yep. First determine whether the synthesizer has any output at all. If
it does, then try to determine whether it is making it to the XTAL OSC
LO MIXER BOARD. The simplest explanation is a failure of the cable and
connectors between boards. I hope it is that simple.
DE N6KB
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