Yes, 9 o'clock on the mic gain seems to be about right for the EV-638.
Think I'll put the 707 on shelf next to that Vibroplex bug... :) I may
tinker with the converted D-104 some more. I think the Heil conversion
uses the HC5.1 element. Not sure how that element will work with the
amplified D-104's.
I'll try the L pad and bonding the computer chassis to station ground.
Thanks Bob.
73
Stan
KM4HQE
On 9/18/2018 9:55 PM, Bob McGraw K4TAX wrote:
I've found typically the mike gain runs 9 o'clock to 10 o'clock on
these radios. Yes the 707 has much lower output and will require one
to raise the gain a considerable amount. My 707 sits on the shelf
with my original D-104. They "look good" sitting there, which is
where I prefer they remain.
I fought the computer interface issues to my Paragon and my Omni VI
series. Both have the same type of input on the rear where the mike
audio and the rear connector audio are summed together through a pair
of 47K resistors on the TX audio board.
The better solution I found was to build a resistive L pad with about
20 dB loss. The 1/8 watt resistors were mounted in the shell of the
RCA connector which plugged into the rear connector. This required
I raise the level out of the computer sound card but in doing so, I
improved my transmit S/N ratio about 20 dB. This is worth doing
regardless of your final decision. Makes for cleaner digital signals
and allows easier adjustment of the audio out of the computer for
transmit level control. This allowed me to keep the mike gain at
the 9 o'clock position. Just be sure the mike connected to the front
is off so that any room noise being picked up is not transmitted.
73
Bob, K4TAX
On 9/18/2018 9:43 PM, Stan Gammons wrote:
For now I'm just going to disconnect the sound card output from the
PC when operating phone. I did try another core at the sound card
output and for some strange reason that made matters worse. One core
on each end of the cable reduces the hash/noise a lot. Only when I
have the mic gain around 1 o'clock do I notice the increase in output
when I have the rig keyed without a mic attached. Normally, I run the
mic gain around the 9 o'clock position. I don't believe Ten-Tec 707
has as high an output as the Electro-Voice EV-638, but 9 o'clock on
the mic gain seems to be Ok with either mic. The 707 is pretty, but
I like the EV-638 as much or more.
I don't have the PC chassis bonded to station ground. I'll mess with
that this coming weekend.
Thanks for all the replies.
73
Stan
KM4HQE
On 9/18/2018 9:25 PM, Greg S via TenTec wrote:
Run both audio sources in the back. Switch between them with a
conveniently mounted DPDT switch. These rigs ain’t worth much any
more. I little hole, or a bracket added somewhere isn’t gonna kill
what little value they have left. I like mine, but have a few
tinkerers mods slated for the upcoming winter months.
Kind regards,
Greg, KC8HXO
Sent from my Linux device
On Sep 18, 2018, at 09:29, Bob McGraw K4TAX <rmcgraw@blomand.net>
wrote:
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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