John, I don't know much about TT rigs, but modern rigs using PLL
arrangements, DDS, etc. etc. rely upon a single frequency standard from
which everything else is either derived or slaved to. There are no
independent crystal oscillators involved in determining dial calibration,
accuracy and stability.
I read the various postings on this topic as saying that like many of the
older designs, the Omni VI relies both upon a "master" crystal oscillator as
well as individual crystal oscillators for various BFO functions, etc. That
architecture pretty well dooms any direct and close frequency control by the
"master oscillator" as is done in the newer designs.
Amateur Radio W5YR - the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
"In the 57th year and it just keeps getting better!"
----- Original Message -----
From: "John Clifford" <firstname.lastname@example.org>
Sent: Friday, August 15, 2003 2:24 AM
Subject: RE: [TenTec] GPS and Ten Tec Rigs
> Several people have replied that the overall frequency stability of the
> VI/VI+ depends upon the crystals on the Local Oscillator board. However,
> according to the circuit description of that board, part of the derived
> crystal oscillator signal is used to provide feedback via the Logic board
> the signal is adjusted to be at the 'right' frequency based upon a
> frequency back at the Logic board. Looking at the Logic board circuit
> description and schematic, it appears that the 10 Mhz signal provided by
> xtal oven/TXCO is used by Q1 and Q2 to provide the 20 Mhz signal which is
> divided back down to 10 Mhz and used as the reference frequency. So...
> doesn't this 10 Mhz signal essentially control the generated band-specific
> frequency on the L.O. board, and as long as the frequency emitted by the
> particular L.O. crystal is close enough to be pushed or pulled to the
> correct frequency via feedback from the Logic board, then the 10 Mhz
> reference frequency does in fact control the rig?
> This excepts the BFO crystals, which I have found to be a source of
> frequency drift during transmit (within Ten-Tec specs, but still excessive
> for the various HF digital modes), hence the substitution of
> better-tolerance crystals.
> I'm sure you guys know more about electronics than I do... heck the clerk
> Radio Shack probably knows more about electronics than I do... so more
> education would be appreciated. Is my assertion in the first paragraph
> - jgc
> John Clifford KD7KGX
> Heathkit HW-9 WARC/HFT-9/HM-9
> Elecraft K2 #1678 /KSB2/KIO2/KBT2/KAT2/KNB2/KAF2/KPA100
> Ten-Tec Omni VI/Opt1
> Alinco DR-605TQ
> Icom T90A
> email: email@example.com
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