[TenTec] Fwd: OmniVI logic board work
CSM(r) Gary Huber
glhuber at msn.com
Thu Sep 29 18:13:32 PDT 2011
Hi Glenn,
Thank you for your explanation and continued efforts to keep a couple of my
favorite radios in operation. While I'm now operating the OMNI-VII (with
FLEX-1500 as the sub-rx) with DXLab Suite station automation and my old
CORSAIR-II / model 253 VFO, having sold my OMNI-VI+, I'm still the license
trustee (N1SF) of a station with a OMNI-VI+ which I continue to maintain and
operate on occasion.
When I had my OMNI-VI+, I had it configured (keying loop open to prevent
TX) to use the aux receiver port of my CORSAIR-II so that they shared the
same antenna and I could listen to both or or either. If there was any
difference in the audio recovery of S-0 to S-2 DX signals on a quiet band, I
could not differentiate it with my calibrated ears (before the significant
hearing loss and nerve damage).
What I do recall was the overload mixing problem during contests and huge DX
pile-ups where the in passband signal was less than S-2 with multiple 40
over 9 signals from 1 KHz to 10 KHz from the desired frequency. In those
conditions the minimal RF gain necessary to hear the desired signal in the
passband is more than enough for all those huge close-in signals to cause
overloading in the first mixer with sum and difference products producing
phantom signals on and near the desired signal.... I know that’s not your
focus at this point but when you get time, I'm sure a number of us would be
interested in seeing a comparison of the OMN-VI+ and the CORSAIR-II; I'm
thinking the CORSAIR-II is a bit better - more resistant to overload.
My practical experience with commercial communications products from 1981 to
2002 led me to believe that analog circuits and in particular crystal or PTO
type VFO circuits were as sensitive but more resistant to overload than the
DDS, PLL, and DSP circuits. The CORSAIR-II is NOT for sale and never will
be.... if it gets to the point it cannot be repaired and is non operational,
it will be a reminder to me of more than two hundred DXCC entities worked
with it, the last of the true analog (except for the frequency display)
radios from TenTec.
73 es DX,
Gary - AB9M
-----Original Message-----
From: Glenn
Sent: Thursday, September 29, 2011 2:55 PM
To: tentec at contesting.com
Subject: Re: [TenTec] Fwd: OmniVI logic board work
Hi Gary,
Yes but the scope of my testing and interest thus far has been more about
weak signals in a typical QRP sprint or simple weak signal work in the
absence of contest conditions.
The K3 or an Orion or any number of transceivers that have excellent close
in dynamic range specs
will be best for contest conditions where signals are mixed from QRP to
above legal limit signals being transmitted;
November Sweepstakes comes to mind Hi..
Many times when the bands, 30, 40 and 20 meters as examples, may be active
but not wall to wall with big signals. This is when I like to work CW QRP.
Often times there are 10 or more QRP stations within a KHz or two of the
calling freqs. This is when I want my rig to be able to separate and CLEANLY
DEFINE weak signals close together.
It is a given, that good close in dynamic range is important as well as
decent sensitivity. This is where I find DSP derived IF rigs to be deficient
in cleanly defining
signal detail when the signals are close together.
This is also where I find the Omni 6 and Corsair 1 or 2 to be superior. As
mentioned, I have not yet tested the same scenario where
I have two very weak signals in the same passband and an S9 or stronger
signal 2 KHz up or down. There will be a trade offs and at some point.
Once the signals are strong enough a K3 or Orion will be better but again
when the signals are very weak, the analog IF, In my controlled test, proved
to be superior,
Personally, I think many Hams are too focused on Sherwood's specs. Although
Robert is a very talented man who has provided a great deal of well though
out testing and Data, many operators will not realize those slight
variations in performance for the most part.
I enjoy weak signal QRP and casual, cheery picking, contest. Another guy may
be content operating SSB nets and SSB rag chew.
Others are enamored with rig size and fancy knobs or how heavily weighted
the tuning knob is..
My point is, if you are after a sexy looking radio with a heavy tuning knob
and lots of pretty illuminated knobs and buttons, perhaps neither Elecraft
or Ten Tec is the right company for you.
If you are a contester, CW op, or QRP op, they certainly are companies to
consider very strongly.
Not saying that the off shore made radios are not good, they are indeed very
good and some very expensive but for my interest in the hobby,
Ten Tec has had the most to offer.
This my interest in gearing up to support the Logic board in the Omni 6. So
far I have found sources for all of the 22) O6 IC's, some are getting very
hard to find. I have spent over $1500 stocking up on these parts
and building special test fixtures. I have dedicated 2) Omni 6 as test beds
and that was expensive. One is to QC my inventory of incoming IC's or to
test IC's when a board is not running well enough that I can troubleshoot it
with my logic analyzer, scopes, logic probes and DVM's. The other test bed
is to test client boards and to burn them in after repairs are effected
without disturbing the bed with the the special ZIF sockets.
ZIF, means Zero Insertion Force. It has a lever that allows socket pins to
open and close so an IC can be installed tested and removed quickly.. I will
assume any logic board with more than 2 IC's defective to possibly have
experienced a nasty surge or a TIP... TECHNICIAN INDUCED PROBLEM.. Hi Hi As
such, those boards are subject to additional failuers and need to be burned
in for at aleast 48 hours or longer.
I recently repaired a board with 18 out of 22 IC's defective; obviously, I
lightning hit. In that case, My test equipment was of no help in this case.
The micro-controllers were not working, the front panel was dead, no clock
signals; that was the worse case scenario. Keep in mind, most of the IC's on
the Omni 6 logic board are soldered in. I prefer to install high quality
machined sockets when changing IC's. This will save time replacing that part
if it fails again.
I started by replacing U1 the main micro-controller to see if I could get
the primary buss up, No go, Next was the ROM, still no go,
then The RAM, no go. Next, I replaced the Codec and finally had a bus
working well enough that I could use my logic analyzer and scope to start
looking at signals. In that case, I had to take one IC off at a time and
test it in my test board unit that has ZIF sockets. If the processor is
running there are many things that can be observed such as all 3 of the
encoders communicating with the logic board, the Serial interlace signals
and logic stat signals when front panel functions are invoked.
Regards,
Glenn WA4AOS
DSM Labs (dot com)
-----Original Message-----
From: CSM(r) Gary Huber <glhuber at msn.com>
To: tentec <tentec at contesting.com>
Sent: Thu, Sep 29, 2011 10:53 am
Subject: Re: [TenTec] Fwd: OmniVI logic board work
Glenn,
Wouldn't a true weak DX and pile-up simulation have the two strong signals
at 2KHz and 2KHz plus away from the passband so that the mixing product(s)
fall inside the passband?
I've kept my Corsair II and 253 remote VFO for DXing.... it may not have the
numbers, but you can't drive specifications.
73 es DX,
Gary - AB9M
-----Original Message-----
From: Glenn
Sent: Thursday, September 29, 2011 1:22 PM
To: tentec at contesting.com
Subject: Re: [TenTec] Fwd: OmniVI logic board work
Hi Barry,
Good idea.. I will try to set up soon and make a recording, however, the
limiting factor, is still
how well our ears/brains can decipher/separate two weak signals in the same
passband, choosing one or the other signal.
My observations, SO FAR, were under lab conditions where the only RF getting
to the front end of the transceivers was coming from two
signal generators. I actually have 4) 8640B's in the lab all with recent cal
stickers.
The test I would like to perform is with two weak signals, less than S1 in
the passband and an S 9 signal 2 KHz above then 2KHz below the passband.
My guess is the K3 may get the nod here due it's close in dynamic range.
However, I know how bad the K3 resolves multiple signals close together
at .1uv. I'll need to increase the output of the generators enough so that
the K3 does clearly resolve/process the two signals. Whatever that turns out
to be
is where I'll test the K3, Omni 6 and Corsair II.. BTW, i should have
mentioned earlier, the Omni 6 I was testing with had the INRAD front end
roofing filter and
all other filters were also INRAD. At some point, I would like to do the
same test with all things being equal but with Ten Tec filters vs INRAD
filters.
To many plans and not enough time... Hi
73,
Glenn WA4AOS
DSM Labs (dot com)
-----Original Message-----
From: Barry N1EU <barry.n1eu at gmail.com>
To: Discussion of Ten-Tec Equipment <tentec at contesting.com>
Sent: Thu, Sep 29, 2011 9:30 am
Subject: Re: [TenTec] Fwd: OmniVI logic board work
On Thu, Sep 29, 2011 at 12:59 PM, Glenn <wa4aos at aol.com> wrote:
> Case and point. I can take two of my calibrated HP 8640B signal
> generators
and set them both for .15 microvolts and separate the carriers by 75Hz.
> Then switching the output of one of the 8640B's OFF and ON rapidly using a
shielded keying fixture, (see note below ) I built, I can clearly here both
signals
> as defined dits and dahs. Using the same arrangement on the K3 or Omni 7,
> the
signals are poorly defined with digital artifacts making neither decent
enough
to
> make understand the dits and dahs. Leading and trailing edges of both
> signals
are distorted and copy would be nearly impossible at those levels. The
analog
> front ends in the O6 and Corsair are difficult copy but you can make out
> what
the keyer is sending.
Glenn, if you could make audio recordings of the test you described
showing good resolution by O6/Corsair and poor resolution by K3, you
would be making a huge contribution toward the 2-year old debate about
poor pileup readability on the K3. I've often though that the O6
might make a better run radio (i.e. to handle pileups) than the K3.
Appreciate your comments on variability of O6 sensitivity because this
has also been my experience. I've had 3 Omni 6/6+'s in the shack in
the past couple of months with vintages spanning 1992-2001 and the
oldest unit had the quietest/most sensitive front end. If someone
could document the front end diode replacement (i.e., how to remove
the board, what diodes to use), they would be doing a real service to
the user community. I understand it's a tough job and the pin diodes
commonly recommended for the O6 job are no longer available.
Just an aside, but I'm not a big fan of the O6 dsp circuit and my
initial efforts at bypassing it have yielded MUCH more pleasing audio,
although it remains a work in progress needing more of my time.
73,
Barry N1EU
_______________________________________________
TenTec mailing list
TenTec at contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec at contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec at contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec at contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
More information about the TenTec
mailing list