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@comcast.net> wrote:
Subject: Re: [TenTec] Omni VI instability, TCXO worth it?
To: "Greg S" <oldlongbeard@yahoo.com>, "Discussion of Ten-Tec Equipment"
<tentec@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@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@threshinc.com>
wrote:
>
> Subject:
[TenTec] Omni VI instability, TCXO worth it?
> To: tentec@contesting.com
> Date: Monday, July 4, 2016, 8:14 PM
>
> I queried service@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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