[TenTec] Omni VI instability, TCXO worth it?

Wed Jul 6 17:53:23 EDT 2016

Gary- thanks for the info. Not doubting, just want to understand better.... are you saying the Omni VI won't just throw a PLL unlock msg on screen whenever that PLL unlock condition would exist? I happen to have FINALLY purchased an Omni VI Plus that is REALLY close to being on frequency using the readout, and I hope to keep it going. It needs a couple relays replaced, as TX on 15 and 40M is DOA, but I already have them frorm TenTec. (Not aLL parts were thrown out, as someone previously said.)  I also have the Inrad audio improvement mod, and roofing filter to install in it. Now all I have to do is get the time to fix/install it all. Because I am a "budding" technician, I plan to do one of those things at a time, with a good test run after each, in case I "fix" something I shouldn't. This group has been pretty quiet, I do hope some more chime in here. I have owned MANY rigs over the years, but the Tennessee Technology always finds a spot in my shack. Never owned an Orion yet, but have had most others at one time. 
Thanks again,
Greg Schippers, KC8HXO
--------------------------------------------
On Tue, 7/5/16, Gary J FollettDukes HiFi <dukeshifi at comcast.net> wrote:

 Subject: Re: [TenTec] Omni VI instability, TCXO worth it?
 To: "Greg S" <oldlongbeard at yahoo.com>, "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
 Date: Tuesday, July 5, 2016, 10:19 PM

 I agree, that the
 “Master” should affect all bands, in most cases (I’ll
 get to the exception later).

 Remember what it is doing. It is “soft
 steering” the crystal oscillators to keep them operating
 at the frequency the the dial says it is operating.

 It does this just lake any
 other PLL does it, by comparing a division of the master
 against a division of the crystal to produce an error
 signal. That error signal tunes the crystal oscillator to
 lock it up in phase with the reference master.

 If one (or more) of the
 crystals is operating so far off frequency that the error
 signal reaches the maximum (or minimum) that it can reach,
 then the crystal oscillator cannot lock up. 

 If things are operating this
 way, it is quite easy to understand why the suspect bands
 can wander in and out of lock, in what seems like a
 whimsical way.

 This state
 of operation could even induce something that sounds like
 chirp on CW because the voltage on the line supplying the
 crystal oscillators may pull just a bit with a CW note and
 thus cause the out of-lock oscillator to chirp.

 Since the recurring problem
 seems to be only 20, 30 and 40 meters, and presumably all
 have been previously ‘tweaked” to make them work, I
 believe this adds credibility to this conjecture. If they
 are tweaked to the limit of the ability of the loop, this is
 exactly what will happen.

 I
 really do not think a new reference master oscillator will
 cure this problem, I think your repair should be a lot less
 costly than that. 

 I may
 still have a crystal board from a defunct Omni 6 and could
 perhaps offer replacement crystals for those bands.

 There is ONE way in which the
 master could cause this problem one some bands and not on
 others. If the crystal oscillators for the three offending
 bands had been adjusted to limits, and then the master were
 to drift off in the right direction, the same problem would
 occur. You would run out of correction range in the PLL. 

 Bands whose crystals were
 closer to their centerlines in operating frequency would
 likely not suffer this fate since the PLL cold still lock,
 albeit at an error voltage not at the normal centerline
 voltage.

 Put a counter on
 the output of the master and see what it is. See if it
 changes as the set warms up (these early ones always did, to
 some extent). If it does NOT drift, likely its oven is
 burned out (as often occurred).

 If you know how, unlock the loop and read the
 frequencies of the respective band crystals to see how close
 they are to their marked frequencies.

 In reality, with proper recalibration of the
 trimmers, you COULD operate this radio without the master
 and you would essentially have the same frequency scheme as
 was used in the Omni 5. You’d always have some readout
 error. That was what the reference master oscillator and PLL
 were added to correct. If you don’t care about being a few
 KHz off from the dial reading, and stay away from band
 edges, you’ll be happy like all Omni 5 owners are.

 Gary

 W0DVN

 > On Jul 5, 2016, at 6:39 PM, Greg S via
 TenTec <tentec at contesting.com>
 wrote:
 > 
 >
 Soooooo...... maybe I am totally off BASE, but if the
 "master"  oscillator is the issue, wouldn't
 he be noticing the problem on all bands, with going higher
 in frequency getting worse?? 
 > 
 > 73-
 > Greg, KC8HXO
 >
 --------------------------------------------
 > On Mon, 7/4/16, Peter Klein <pklein at threshinc.com>
 wrote:
 > 
 > Subject:
 [TenTec] Omni VI instability, TCXO worth it?
 > To: tentec at contesting.com
 > Date: Monday, July 4, 2016, 8:14 PM
 > 
 > I queried service at tentec.com
 > by email about the following issue last

 > Tuesday. I have heard nothing so far,
 so I thought I'd get
 > some advice
 here.
 > 
 >
 Background:  I live in the Seattle area. I have modest
 > wire and vertical 
 >
 antennas. I'm not a contester or hard-core competitive
 DXer.
 > I do try to 
 >
 work DX when I can, and I might jump into a contest to
 snag
 > a new 
 >
 country. But mostly I do HF digital (PSK, Olivia, MFSK),
 > casual CW, or 
 >
 occasionally SSB.
 > 
 >
 I've owned my Omni VI for 20 years. It has the Option 1
 DSP
 > upgrade. 
 > Over
 the years, the radio has several times developed a
 > frequency 
 >
 instability issue. Over a time ranging between less than
 a
 > second to a 
 > few
 seconds, the transceiver moves a few 10s of Hz off
 > frequency, then 
 >
 "snaps" back. It's mostly done this on 30m,
 occasionally on
 > 20m, and now 
 > on 40m. Lately, it happens on 40m, with a
 short "period," so
 > if I am

 > listening to a good, pure CW signal,
 it sounds like it has
 > old-fashioned 
 > "chirp."
 >

 > The frequency shift occurs on both
 transmit and
 > receive.  When it 
 > happens, if I switch to another band, it
 does not happen
 > there. It is 
 > intermittent. Sometimes it appears random,
 and sometimes
 > appears 
 > temperature-related (for example after
 transmitting for a
 > while, or if 
 > the radio has been just turned on in the
 last half-hour or
 > so).
 > 
 > When it first
 happened (1997), Ten Tec Service advised me to
 > tweak the 
 > trimmer
 coil to the 30m mixer crystal 1/8 to 1/4 turn in
 > either 
 > direction
 until the "drift and snap" stopped, and just
 live
 > with the 
 >
 slight display error. I did, and later did the same thing
 to
 > the 40m 
 > coil
 when that band acted up. It worked in both cases.
 > 
 > When it started to
 do the frequency dance on 20m, I sent
 >
 back to the 
 > factory for a tune-up.
 This was in October 2013. Now, it's
 >
 doing it 
 > again on 40m.
 > 
 > I spoke to
 TenTec's service manager a few months ago. He
 > said that the 
 >
 problem might be solved by installing a temperature
 > compensated crystal 
 >
 oscillator (the TCXO was never suggested before).  He
 > said that I could 
 >
 install this myself if I could solder a couple of wires.
 He
 > quoted me a 
 >
 price of $200 to send me the necessary circuit board and
 > instructions. 
 > He
 said it was up to me whether I wanted to spend $200 on
 > "an older 
 >
 radio."  He was also dead-set against my tweaking
 the
 > trimmer coils to 
 > the individual band crystals.
 > 
 > I decided to wait
 and see if leaving the power supply on
 >
 24/7 would 
 > solve the issue. Nope. And
 while I was waiting, Ten-Tec was
 > sold
 and has 
 > new service policies.
 > 
 > I would like to
 install the TCXO, *IF* it is very likely
 > that it will 
 > solve
 the problem, and I can get at least another couple of
 > years of 
 > good
 service out of the radio.  On the other hand, the
 > radio is 20 years 
 >
 old. So if it's just as likely that I will continue to
 have
 > the problem, 
 >
 then maybe the TCXO isn't worth it, and I should think
 about
 > a new radio.
 >

 > So, what would you do if you were
 me?
 > 
 > Thanks and
 73,
 > --Peter, KD7MW
 >

 >
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