[TenTec] No SSB from Omni D

Wed, 08 Oct 2003 07:54:14 -0500

Don't forget you stated that the Omni D works satisfactorily in CW.  Use 
this fact as you attempt to isolate the problem!!

73, Jim

>From: "Jay Eimer" <[email protected]>
>Reply-To: [email protected]
>To: <[email protected]>
>Subject: Re: [TenTec] No SSB from Omni D
>Date: Tue, 7 Oct 2003 22:33:59 -0500
>
>The scope has a 60Mhz bandwidth.  I have the manual and several copies of
>the page with the SSB board schematic in hard-copy.  I'll have to see if I
>can get one "electronic".
>
>I'll get back with you tomorrow evening.
>
>Jay
>AD5PE
>----- Original Message -----
>From: "Kenneth Stringham" <[email protected]>
>To: <[email protected]>
>Sent: Tuesday, October 07, 2003 9:37 PM
>Subject: Re: [TenTec] No SSB from Omni D
>
>
> > Hi Jay,
> >
> > Well, I don't know what the bandwidth is of your
> > 'scope. If is in excess of 10Mhz. (Mine is 5Mhz.) you
> > should be able to chect the output of the balanced
> > modulator at 9Mhz. You should see the classic pattern
> > shown in the ARRL hand book when you speak into the
> > microphone. You should see a similar pattern on the
> > output of the 9Mhz. Xtal filter.
> >
> > I have not been able to locate my book, since I last
> > sent you e-mail. I have a number of people here using
> > this PC and a 16 month old who touches everything.
> >
> > I performed my tests on 160Meters and viewed the
> > output after the MC1496 Mixer, but I would perform the
> > test I just noted about. You need to look at the 9Mhz.
> > output of the balance modulator and then at the output
> > of the Xtal filter. My belief is that you will find
> > the signal is significantly attenuated at the output
> > of the filter.
> >
> > Do you have a frequency counter? This instrument
> > should be used to check the output of the carrier
> > oscillator. This Xtal oscillator is used for LSB, USB,
> > and CW. The difference is the amount of loading
> > capacitance that is placed in the circuit for each
> > mode. It does not take much of a frequency error with
> > the sharp Xtal filter to attenuate the signal
> > significantly. There is significant room for an error
> > in the 200A1 carrier frequency and still get
> > sufficient output from this circuit.
> >
> > Let me know what the bandwidth is of your 'scope and
> > if you have access to a frequency counter.
> >
> > Regards...
> >
> > Ken
> >
> > P.S. If you can scan the SSB generator board and send
> > me the image file. I can view it here and make an even
> > better diagnosis for you.
> >
> > AE1X:kes
> >
> > --- Jay Eimer <[email protected]> wrote:
> > > Okay, I borrowed a scope and checked some things.
> > > One thing I confirmed is
> > > that my mic is getting to the SSB Gen board.  Turns
> > > out, out of 4 mics that
> > > I tried only one was working with one other
> > > marginal.  Once I tried with the
> > > good mic I got output enough that a friend was able
> > > to hear me on 28.330.
> > > Unfortunately, he was on his HTX-10 (radio shack)
> > > mobile sitting in my
> > > driveway.
> > >
> > > He heard me up to about 2 miles away, then my signal
> > > faded.  I could hear
> > > him about twice that distance.  Note that he was on
> > > a base loaded vertical,
> > > and I was using an 132 ft. dipole and a tuner so the
> > > polarization was
> > > mismatched.
> > >
> > > I tried making some contacts last night with the
> > > good mic, no go.  It seems
> > > that I'm getting out, but very, very weak (5W or
> > > less).
> > >
> > > So I did some other checking with the 'scope.
> > > Here's some of the anomalies
> > > I found.
> > >
> > > I have modulation at the MIC test pin on the SSB Gen
> > > board.
> > >
> > > I have modulation at pin 7 of the dual op amp IC1.
> > > This is the output of
> > > the first stage amp IC1b.
> > >
> > > I have an unmodulated 4V dc at pin 3 of IC1.  This
> > > doesn't make sense,
> > > especially since the manual lists a test voltage
> > > (SB-N receive with no
> > > drive) of 0V dc.
> > >
> > > I have no output (unmodulated ~4V) out of pin 1
> > > (final output of the second
> > > stage op amp, IC1a) that feeds into IC2.
> > >
> > > I'd suspect the IC, except for a further anomaly.  I
> > > appears that there is a
> > > voltage divider/step down circuit.  Out of pin 7 on
> > > IC1, it goes through R25
> > > and feeds pin 6 (feedback) and divides to R26.  This
> > > feeds one side, while
> > > Reg+ feeds the other side of voltage divider through
> > > R19 and R23.  R23 feeds
> > > R24 and then pin 3 (+ Wiper?) and R19 feeds R18 and
> > > then Pin 1 to Pin 1 of
> > > IC2.  Where this is wierd is that every resistor
> > > shows 4V (no drop) on both
> > > sides.  This doesn't seem right, but I'm no expert.
> > >
> > > So, is this the same IC that you had a problem with?
> > >  Or do I have a bad
> > > component somewhere else on the board?  I suspected
> > > a bad cap was blocking
> > > modulation, but I can't see which one that would be,
> > > since the problem
> > > appears to be between output of pin 7 to input of
> > > pin 2 and or 3 of IC1.
> > >
> > > What I think I need most is a test plan to isolate
> > > which of these might be
> > > the problem.
> > >
> > > Thanks,
> > >
> > > Jay
> > > AD5PE (just got my new call last Thursday!!!)
> > >
> > > -----Original Message-----
> > > From: [email protected]
> > > [mailto:[email protected]]On Behalf Of
> > > Kenneth Stringham
> > > Sent: Tuesday, September 30, 2003 11:02 AM
> > > To: [email protected]
> > > Subject: Re: [TenTec] No SSB TX from Omni D
> > >
> > >
> > > Hi Jay,
> > >
> > > My first question is: do you have the Operator's
> > > Manual. This includes a detailed description of the
> > > circuitry and the schematic. If you do not, I have
> > > one
> > > here that you can purchase, I sold my 546C recently
> > > because of my need for cash.
> > >
> > > You problem will be located by looking at the SSB
> > > generator board. This radio generates the CW signal
> > > by
> > > moving the Carrier Oscillator 750Hz so it is inside
> > > the filter pass band and then it unbalances the IC
> > > balanced modulator. My guess is that you have
> > > problem
> > > with the circuitry that moves the oscillator
> > > frequency
> > > for LSB/USB. The frequency is offset to far down the
> > > filter pass band. One of mine had a defective
> > > balanced
> > > modulator IC which I replaced and all was well.
> > >
> > > rest of original snipped....
> > >
> > >
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