[TenTec] Fwd: OmniVI logic board work

Thu Sep 29 12:55:03 PDT 2011

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
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