I have an Omni VI/Opt 1, and the frequency stability has benefited GREATLY
from two modifications.
The first mod is to replace the crystal oven with the TXCO. This is not a
big deal to install, although the instructions could be a little clearer. I
don't know if there is, and didn't see, a difference in stability once the
rig has been running for a half-hour between the two setups, but the TXCO
doesn't drift nearly as much during warm-up. This is one of those changes
that can't hurt, but probably doesn't help much if at all. If anything, it
keeps the rig so that the display matches the actual frequency better but
doesn't seem to affect staying on a particular frequency once the rig is
warmed up.
The second mod, and it really makes a difference, is to replace the two
crystals on the BFO board with higher tolerance parts. I found that when I
did this, I was able to hold to within 10 hz... the factory crystals would
allow the rig to drift during transmit as much as 40 hz (within Ten-Tec's
spec of 50 hz, which works for CW and SSB but isn't suitable for some of the
newer HF digital modes). Ten-Tec will tell you that the rig is working
within spec (which it is) but I wanted better.
This doesn't seem like a lot, but if you're running a mode where tuning is
critical (like MFSK), the difference is in a rig that is hard to keep tuned
and one that stays tuned. In PSK31, the difference here is that you don't
walk down the band. Even when you have transmit locked in your software,
you will start seeing the transmit and receive indicators on your waterfall
'walk', and if the other op isn't similarly locked HE will walk down the
band in order to stay with you.
The crystal change will run you about $50 for the two crystals including
shipping, and take about 20 minutes, most of that time being taking the top
cover off, unplugging the various cables, and reversing this when you
re-install the board. You will need a frequency counter to re-align this
board once you have completed the modification.
Note that the 9.003300 Mhz crystal is not an off-the-shelf product. I tried
the crystal #s recommended in the list archive and they don't work... the
crystal can't be 'pulled' far enough. I spent $60 and waited for over a
month to get a custom crystal made, but now I have a source for these and
they know what to do. The custom crystal is designed specifically to be
frequency stable even though it is being pulled a way. (I think this is why
the BFO board was redesigned for the VI+.) These crystals are much cheaper
if we can put together a bulk order, so if there is any interest in a 'BFO
kit' for the VI please contact me.
I can't recommend this mod highly enough. It really makes the Omni VI a
great rig for HF digital modes, and VERY frequency stable (much better than
the original specs).
- 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
email: kd7kgx@arrl.net
> -----Original Message-----
> From: tentec-bounces@contesting.com
> [mailto:tentec-bounces@contesting.com]On Behalf Of John L Merrill
> Sent: Saturday, March 15, 2003 10:45 AM
> To: Pete Juliano
> Cc: Tentec
> Subject: RE: [TenTec] OmniVI Opt3 question
>
>
> Pete:
> Thanks for the info. I just a beautiful used one with Opt3. I'll give Ten
> Tec a call on Monday.
>
> 73,
> John
> -----Original Message-----
> From: Pete Juliano [mailto:jessystems@cablespeed.com]
> Sent: Saturday, March 15, 2003 1:37 PM
> To: John L Merrill
> Subject: Re: [TenTec] OmniVI Opt3 question
>
>
> Hi John,
>
> About six months ago I bought from Ten Tec a used Omni 6+
> Factory Option 3
> upgrade and asked about the TCXO --they said I had two options either
> purchase and install it myself or have them do it. I had them do
> it as there
> is some tweaking and adjusting required although I suspect it is not
> difficult or detailed. But since the unit I was buying was covered by a
> warranty why not have that piece covered as well. At that time I think the
> TCXO was under $60.
>
> So the short answer is that six months ago they were carrying
> the TCXO and
> it can be user installed.
>
> The TCXO I think is a very worthwhile accessory and really adds to the
> value. I leave the power supply on at all times and find that the
> Omni 6+ is
> always right on frequency. I frequently participate in a net where the net
> controller starts chewing on you if you are more than 20 hertz off
> frequency. Guess he likes to tout that he is never off frequency.
> I set the
> net frequency in VFO B and never had him tell me I was off frequency or
> drifting!
>
> Call Stan at Ten Tec and I am sure he will give you the latest
> info. Oh, I
> believe that Ten Tec must outsource the TCXO as my Omni 6+ was held up in
> their shop for about a week until they received a new shipment of
> boards. So
> that is another possibility as their source might have boards too.
>
> 73's
> Pete W6JFR
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