[TenTec] Fwd: OmniVI logic board work

[Glenn]

Hi Allen,


I would be interested in your pin diode work on the Omni VI.
I have seen Omni 6 + here that had sensitivity down to .10uv and others that were close to
.6 or .7.. Even that, .6,  is decent but I suspect the diodes in the TR section are to blame, however, I have not
tried to change them out yet. I used pin diodes to mod some Yaesu, FT 101E's, I think they were101E's, don't remember, back in the 80's and had decent results.


Most of my Omni 6 work thus far has been in the logic, PA, and AF/IF sections. These are robust and 
complex transceivers and though, I have repaired many of them, there is always more to learn.


With regard to the K3, it performs exceptionally well on the bench and has an incredible front end.
What I have found though, on the air or on the bench, is once two weak signals are in the passband an Omni 6 or Corsair
do a better job resolving the signals. The K3 shines when you are trying to copy a weak sig and a much stronger is just outside the passband
the K3 does well, UNLESS, the signal in the passband is very weak.
My thoughts are that the DSP circuitry is simply is not good, yet, at accurately decoding very weak signals close together.


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.  


NOTE* My fixture uses N connectors on the IN and OUT of my test box with a isolated, transistor keying line that is exercised with an external AEA Morse Machine keyer with a shielded key line.
The test box is hand fabricated from a material called TI shield which has isolation characteristics  from DC to almost day light.. In other words, it's a very shielded fixture box. TI Shield can be purchased from
Michael Percy Audio dot com. It comes it sheets of different sizes and can be cut up with a cheap hand shear and looks like Copper foil. 
This way I can set the keyer to make clean dits or dahs with whatever speed or spacing I want. 


Like many of us, I enjoy QRP as often as band conditions will permit and very weak signals is part of the game. In all of my testing with this arrangement,
the only other receivers/transceivers that did as well as a Corsair or O6 was my modded Drake R 4C with Sherwood mods and INRAD filters, A properly working R 390A and 
an Atlas 350XL. Of the DSP derived IF rigs, the Orion is the only one I have tested that came close but under my test conditions, the O6 and Corsair II out performed the 
Orion in terms of weak signal resolution where the signals were very close together. 


My interest in this test is simple. When you think about it, if you are a CW, weak signal operator and have operated enough to get decent at deciphering weak signals, then
you have also fine tuned the filter in your head. I call this the, "GRAY FILTER." Hi  Often you will have two weak signals in the passband and you simply concentrate on the one of interest,
usually, the one that's slightly stronger and your brain filters out the rest as much as possible. Kind of like being in a loud cafeteria and you only listen to your buddy across he table talking to you.
Again, your brain ignores or filters out the rest. Sometimes in the scenario I described, the signal of interest may be the weaker of the two and with a little more concentration and a lot of experience,
we focus on the slight difference in frequency and decipher the weaker signal, albeit, not perfect copy but passable.


In my opinion, this needs to be the next thing that Manufactures look at. I think close in dynamic range is probably as close as it's going to get with K3's, Orion's and others but being able to
clean up the DSP chain by increasing sample time of better DSP components is the next step. DSP offers much promise, in my opinion, it can and needs to get better; in time I believe it will.


I have had several K3's and simply don't care for the weird audio they make. The Orion 1 or !! have superior audio of all of the DSP unit's I have tested. 
The Omni 7, is a very decent transceiver and if Ten Tec ever gets the real band scope working, I'll buy another one but again with my weak signal test.
it is about as band as a K3. I do like the audio on the O7 better than the K3 though and believe for most operators the O7 is a superior transceiver, second to the Orion.


73,
Glenn WA4AOS
DSM Labs ( dot com)



-----Original Message-----
From: Allan Taylor <k7gt.cw at gmail.com>
To: wa4aos <wa4aos at aol.com>
Sent: Thu, Sep 29, 2011 7:33 am
Subject: OmniVI logic board work


Glenn,

I want to thank you in advance for beginning work on the logic board
of the OmniVI rigs. I love mine
(have two option 3s).  The logic boards on both are working fine but I
want to be in the loop
for future developments, etc. I also followed the emails regarding the
Corsair II. I had one at one
point but sold it. It had a great receiver but initial drift was a nuisance.

When I get caught up, I will be implementing a change to the bandpass
board on my OmniVIs. I will
be doctoring up the PIN diode T/R switches to use in a poor-man's SO2R
arrangement to protect
the front end from the 'other' transmitter.  Tom, N5EG, has worked
out, at my instigation,  the simple
logic so that the 'T' signal from the 'other' rig will cause the T/R
switch to activate in the 'listening' rig.
I will also be putting in an open collector transistor switch to the
'T' line to switch an Alpha 87A amp.

As far as the K3 (I have S/N 740), I find the QSK is smoother than the
OmniVI but the NR doesn't
work nearly as well. The 'primitive' audio DSP of the OmniVI works
great, especially on the
higher bands. But you already knew this. I also miss the analog
metering. I hadn't noticed
harshness in the K3's audio. Maybe it is my 64-year-old ears?

I am not a E.E., but a retired physics guy who worked in scientific
programming. I can follow
a schematic most of the time.

73     Allan    K7GT






-----Original Message-----
From: Glenn <wa4aos at aol.com>
To: k7gt.cw <k7gt.cw at gmail.com>
Sent: Thu, Sep 29, 2011 8:38 am
Subject: Re: OmniVI logic board work


Hi Allen,


I would be interested in your pin diode work on the Omni VI.
I have seen Omni 6 + here that had sensitivity down to .10uv and others that were close to
.6 or .7.. Even that, .6,  is decent but I suspect the diodes in the TR section are to blame, however, I have not
tried to change them out yet. I used pin diodes to mod some Yaesu, FT 101E's, I think they were101E's, don't remember, back in the 80's and had decent results.


Most of my Omni 6 work thus far has been in the logic, PA, and AF/IF sections. These are robust and 
complex transceivers and though, I have repaired many of them, there is always more to learn.


With regard to the K3, it performs exceptionally well on the bench and has an incredible front end.
What I have found though, on the air or on the bench, is once two weak signals are in the passband an Omni 6 or Corsair
do a better job resolving the signals. The K3 shines when you are trying to copy a weak sig and a much stronger is just outside the passband
the K3 does well, UNLESS, the signal in the passband is very weak.
My thoughts are that the DSP circuitry is simply is not good, yet, at accurately decoding very weak signals close together.


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.  


NOTE* My fixture uses N connectors on the IN and OUT of my test box with a isolated, transistor keying line that is exercised with an external AEA Morse Machine keyer with a shielded key line.
The test box is hand fabricated from a material called TI shield which has isolation characteristics  from DC to almost day light.. In other words, it's a very shielded fixture box. TI Shield can be purchased from
Michael Percy Audio dot com. It comes it sheets of different sizes and can be cut up with a cheap hand shear and looks like Copper foil. 
This way I can set the keyer to make clean dits or dahs with whatever speed or spacing I want. 


Like many of us, I enjoy QRP as often as band conditions will permit and very weak signals is part of the game. In all of my testing with this arrangement,
the only other receivers/transceivers that did as well as a Corsair or O6 was my modded Drake R 4C with Sherwood mods and INRAD filters, A properly working R 390A and 
an Atlas 350XL. Of the DSP derived IF rigs, the Orion is the only one I have tested that came close but under my test conditions, the O6 and Corsair II out performed the 
Orion in terms of weak signal resolution where the signals were very close together. 


My interest in this test is simple. When you think about it, if you are a CW, weak signal operator and have operated enough to get decent at deciphering weak signals, then
you have also fine tuned the filter in your head. I call this the, "GRAY FILTER." Hi  Often you will have two weak signals in the passband and you simply concentrate on the one of interest,
usually, the one that's slightly stronger and your brain filters out the rest as much as possible. Kind of like being in a loud cafeteria and you only listen to your buddy across he table talking to you.
Again, your brain ignores or filters out the rest. Sometimes in the scenario I described, the signal of interest may be the weaker of the two and with a little more concentration and a lot of experience,
we focus on the slight difference in frequency and decipher the weaker signal, albeit, not perfect copy but passable.


In my opinion, this needs to be the next thing that Manufactures look at. I think close in dynamic range is probably as close as it's going to get with K3's, Orion's and others but being able to
clean up the DSP chain by increasing sample time of better DSP components is the next step. DSP offers much promise, in my opinion, it can and needs to get better; in time I believe it will.


I have had several K3's and simply don't care for the weird audio they make. The Orion 1 or !! have superior audio of all of the DSP unit's I have tested. 
The Omni 7, is a very decent transceiver and if Ten Tec ever gets the real band scope working, I'll buy another one but again with my weak signal test.
it is about as band as a K3. I do like the audio on the O7 better than the K3 though and believe for most operators the O7 is a superior transceiver, second to the Orion.


73,
Glenn WA4AOS
DSM Labs ( dot com)



-----Original Message-----
From: Allan Taylor <k7gt.cw at gmail.com>
To: wa4aos <wa4aos at aol.com>
Sent: Thu, Sep 29, 2011 7:33 am
Subject: OmniVI logic board work


Glenn,

I want to thank you in advance for beginning work on the logic board
of the OmniVI rigs. I love mine
(have two option 3s).  The logic boards on both are working fine but I
want to be in the loop
for future developments, etc. I also followed the emails regarding the
Corsair II. I had one at one
point but sold it. It had a great receiver but initial drift was a nuisance.

When I get caught up, I will be implementing a change to the bandpass
board on my OmniVIs. I will
be doctoring up the PIN diode T/R switches to use in a poor-man's SO2R
arrangement to protect
the front end from the 'other' transmitter.  Tom, N5EG, has worked
out, at my instigation,  the simple
logic so that the 'T' signal from the 'other' rig will cause the T/R
switch to activate in the 'listening' rig.
I will also be putting in an open collector transistor switch to the
'T' line to switch an Alpha 87A amp.

As far as the K3 (I have S/N 740), I find the QSK is smoother than the
OmniVI but the NR doesn't
work nearly as well. The 'primitive' audio DSP of the OmniVI works
great, especially on the
higher bands. But you already knew this. I also miss the analog
metering. I hadn't noticed
harshness in the K3's audio. Maybe it is my 64-year-old ears?

I am not a E.E., but a retired physics guy who worked in scientific
programming. I can follow
a schematic most of the time.

73     Allan    K7GT