[TenTec] No SSB from Omni D

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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>
>
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