Getting a rough measurement on the frequency difference can be accomplished
by zero-beating WWV with each receiver on the same VFO, or by using a
program like DigiPan and reading the "time tone" (alternating between 500
and 600 Hz). I have found that there is approximately 6 Hz difference in
the VFO's no matter what frequency you are measuring it at.
I wonder if this should be addressed through the software with some sort of
"correction line". That won't phase lock the receivers, but it should get
them to within +- .5 Hz if calculated properly.
Ron N6IE
www.N6IE.com
----- Original Message -----
From: "pfizenmayer" <pfizenmayer@qwest.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>;
<ken.d.brown@hawaiiantel.net>; <shristov@ptt.rs>
Sent: Sunday, December 21, 2008 8:33 AM
Subject: Re: [TenTec] Orion Sub-Main synthesizer offsets
> DE K7HP
>
>>> I have never encontered a condition with both rx on same
>>> freq, not to say it could not happen if both were general coverage . But
>>> I
>>> think it has to do with mathematical resolution limits in the two
>>> synthesizers . They are "phase locked" in that both start from the same
>>> TCXO
>>> but the schemes are different.
>>
> DE VE3EA/YN1NT
>>
>> It's worse than that.
>> There are TWO independent frequency references.
>>
>> The obvious one is the TCXO, and the other one is the codec clock.
>> The ways they are combined in the main RX and in the sub RX are quite
>> different,
>> which causes the observed frequency differences.
>>
>> There is no practical way to calibrate this out permanently.
>>
>
> DE K7HP
>
> It looks to me like the A7-81917-6 MAIN and A7-81971-7 SUB codec use the
> same oscillator at 14.36 mhz with the MAIN codec being the active
> oscillator
> and that feeds a clock signal to the SUB.
>
> Then the DSP clock CLKINA and CLKINB are both driven from a 32 mhz
> oscillator in the CPU/DSP logic board A7-81917-1.
>
> The only other clock oscillator I see is the CPU clock on A7-81917-1 and I
> would think that would not play into this.
>
> The only thing I have found written on how the sub rx 1st LO is derived
> says
> "The sub receiver employs a standard PLL synthesizer, moving in 2.5-kHz
> steps. Fine-tuning to 1 Hz is achieved in DSP software through complex
> mixing, described further below"
>
> This was in Doug Smith's writeup on the Orion but in his document I do not
> find where he gets back to the "as described below" .
>
> Is anyone aware of a document that I can get to study this some more ????
>
> I have toyed with making an external third LO for the sub rx at approx
> 464.0625 khz that I could warp a bit to get the two receivers so they
> don't
> beat against each other - at least for a while. But maybe there is another
> approach.
>
> I have not set up a way to measure the fractional hz offset , but roughly
> on
> my Orion it seems the offset is the same on all ham bands.
>
> All the above discussion is referenced to the O565 - The OI 566 LO/mixing
> scheme has been changed in the MAIN - and that is what I have now but I
> think the princples are the same. Of course even after all this , the
> delays
> thru the two receivers are also different so this complicates things
> except
> on a continuous signal.
>
> Thanks -- Hank K7HP
>
>
>
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