Even with that approach, any noise coming out of the computer sound
card output stage will be sent to the input of the Omni VI. This will
occur even when the audio gain of the computer is reduced or muted as
the gain control is before the output stage of the sound card. Just the
fact, any noise coming out of the computer will be introduced into the
MIC audio due to the design of the circuit.
One can add some 20 dB of attenuation in the form of an L Pad between
the output of the computer and the input to the radio. This will reduce
the amount of noise to perhaps a satisfactory level. But still, there
will be some noise coming from the computer sound care, reduced 20 dB.
And one will then need to raise the gain of the data signal in the
computer application to off-set this 20 dB attenuation. While I find
this works and I operated this way for years, the digital artifacts from
the computer may still exist to some lesser extent, although may be
found to be satisfactory.
The best solution is to disconnect the cable to the rear input when not
used. But when used, you will still likely need the 20 dB attenuation
to clean up the digital noise out of the computer. A Transformer is
an OK idea as long as it is configured to have voltage loss and not
matched loss. The idea of the transformer is to eliminate a "ground
loop" what ever that might be. {The only ground loop I'm familiar with
is upon less than a careful landing of a Piper Tripacer in a cross wind.}
73
Bob, K4TAX
On 9/18/2018 4:50 AM, Barry N1EU wrote:
Stan, to get rid of the residual hash do one of the following:
1. assure you have the computer chassis and Omni 6 chassis properly bonded
to common station ground.
2. put an audio isolation transformer in the line between PC soundcard and
Omni 6 audio in
73, Barry N1EU
On Tue, Sep 18, 2018 at 2:41 AM, Stan Gammons <s_gammons@charter.net> wrote:
Hi Bob,
I removed the split core I had on the audio cable and put a solid core
with several turns of the the audio cable wrapped around the core at the
sound card output. That drastically reduced the hash picked up from the
PC. So, it should have a MUCH cleaner digital signal now. Now when I
remove the mic and short pin 3 to ground and turn the mic gain fully
clockwise, the rig is putting out maybe 1 watt. Much better than the 100
watts it was putting out when I tried the same thing before! Yeah, it is a
bummer that both are hot all the time. I'll have to remember to
disconnect the cable from the PC when operating phone. Would have been
nice if one were able to select the audio source.
Thanks for your help. Hopefully I'll sound better when I check into the
net now :)
73
Stan
KM4HQE
On 9/17/2018 9:25 PM, Bob McGraw K4TAX wrote:
Stan
Unfortunately that input on the rear is "hot" all of the time and the
signal (noise) is mixed with mike audio. It is isolated by a 10k ohm
resistor. The MIC gain and SP level controls both inputs.
You must physically connect one or the other, but never both. There is no
provision in the radio to select between the two inputs.
I wouldn't bother with chokes as any noise from the computer or interface
will appear in mike audio. Just the way it works. Bummer.
Bob, K4TAX
Sent from my iPhone
On Sep 17, 2018, at 9:16 PM, Stan Gammons <s_gammons@charter.net> wrote:
Hi Bob,
One thing I forgot to check before and I pretty sure I found out what
the problem is. I have the PC soundcard out connected to the audio in on
the back of the radio so I can use it for digital modes. Seems as though
it's picking up hash from the PC and it's getting mixed with the audio from
the mic. When I disconnect the cable from the PC, things are normal. Dang
it! Guess I need to put another or more ferrite cores on the audio cable.
I hear the computer hash when I test PTT with WSJT-X too. So it's
transmitting a cruddy digital signal too. That's unacceptable. I have to
fix that.
73
Stan
KM4HQE
On 9/17/2018 8:51 PM, Bob McGraw K4TAX wrote:
Stan:
First I suggest turning the speech processor OFF and forever leave it
OFF. If you want to use it, just remember, more is worse.
Even though the mikes worked on the TR7, I view this is no indication
the wiring is correct for the Omni VI. I suggest checking the manual for
the correct mike wiring and physically confirm the mike of choice is wired
correctly. I find mike wiring standards to be as varied as dust
particles in a Texas sandstorm.
Pin #1 is mike high or mike audio
Pin #2 is ground and shield. Be sure the shield of the mike cable also
folds back into the Amphenol cable connector to make contact with the shell.
Pin #3 is PTT
Pin #4 is +4 DCV for use with an Electrect mike.
Check the plug in filters on the bottom to see they are seated
correctly and correct location. Again, contact cleaning of their pins
might be in order.
One other test, disconnect the mike, turn the MIC gain fully
counterclockwise {off}, transmit and listen to the radio. With the 2nd
receiver, tune across the frequency and listen for carrier. In general all
should be quiet. If you hear significant carrier, there is a procedure to
null the carrier. Probably need an oscilloscope and dummy load to do that.
Next would be to check the frequency of the BFO crystals. Again there
is an alignment procedure. This must be adjusted in the exact steps
outlined in the manual as there is interaction between the adjustments.
Repeat the procedure a couple of times. A frequency counter is required
for this adjustment. Don't skip one step just because you don't intend to
use that mode. There is interaction between the adjustments.
And of course my last suggestion, which normally is my first
suggestion..........take time to pull each cable, using a Q-Tip moistened
with contact cleaner, scrub the male pins of each and every connector.
Then plug and unplug the connector a couple of times so as to wipe the
female contacts. Do this one at a time and double check to see each
connector is inserted fully and correctly.
NEVER NEVER NEVER spray anything into the radio. {One fellow I know
[not me] removed the plugin IC's, sprayed into their sockets, and now he
has a radio full of issues and weirdness. Remember contact cleaner is
used to promote the flow of current. Imagine what takes place in a logic
IC socket that is wet with cleaner. ugh!!!! }
With a radio of that age, it not at all unusual for the electrolytic
caps in the audio stage to deteriorate. One issue which can exist is the
output of a stage can drift negative a few millivolts. In effect it will
reverse polarize the coupling capacitor. The result is after time the 1
MFD cap will migrate to about 0.01 MFD. Not a good path for audio in these
circuits. Makes the radio sound funny too. I always replace the audio
coupling capacitors with nonpolar electrolytics of the same voltage and C
value. There is no need to change parameters. Problem solved. I had a
lengthy discussion with Tentec management and engineering on the subject
some years ago. It almost caused me to not buy a new Omni VI Plus.
Finally, I did and loved it.
Hope this helps.
73
Bob, K4TAX
On 9/17/2018 8:00 PM, Stan Gammons wrote:
Hi All,
I was tinkering with an old D-104 T-UG8 that I had put a Heil
conversion kit in since the original element bit the dust. I ask for an
audio report from some of the locals that know what I sound like and they
said I sounded terrible. So, I switched to the Ten-Tec 707 mic, same
report. So, I tried my trusty old EV-638. Same story. I didn't try it with
the converted D-104 to see what it sounds like. They initially told me it
sounded like the mic was picking up something like a fan maybe, so turning
the gain down helped a little but not a lot. SO, today I decided to put the
Omni VI on a dummy load and listen to it with my Drake TR7. Yuck! The Omni
VI sounds terrible! It's almost like there is a little bit of a carrier
and it has what sounds like digital hash on it. It gets worse the higher
the mic gain is cranked. When I modulate, the audio sounds all distorted.
Even without modulation, if I turn the processor on and crank it up, the
digital hash in the audio seems to get even wo
rse. SO, just to make sure it wasn't something weird going on, I did
the same thing with the TR7. I put it on a dummy load and listened to it
with the Omni VI. I tried it with the same mics and the audio is clean. No
hash or anything. Anyone heard of a problem like this with an Omni VI?
73
Stan
KM4HQE
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