[DSP-10] Lurker now needs help

Wed, 19 Feb 2003 22:16:24 -0800

Hi Don (and Roger) - Looks good to me.  The output of U9 is limited by the
diodes in the mixer to something like what you show. In fact, if you look at
the output of U106, measured over right at U3, it is also clipped. This does
take a fast scope to see it, though.

Like Roger, I think it looks good to be on the air soon!

Congratulations on the construction award!!  Sounds like a good contest.

73,
Bob  W7PUA

Thanks for the comments on the book!  It has been a fun project and the big
reward is seeing it put to use!

At 07:44 PM 2/19/03 -0800, you wrote:
>Don:
>
>Good to have you onboard.  Congratulations on the blue ribbon as well.  Glad
>the judges didn't ask you to put it on the air, huh?  Great to see so many
>people experimenting and constructing.
>
>I looked over your email and I believe, from a DC perspective, you are
>probably fine.  I had a few measurements that were off a little bit.  I'd
>question whether the measurements around the MAR amplifiers were loading the
>circuit (capacitively).  I had great luck by removing C78, then soldering a
>piece of coax & a BNC connector at that point.  Measure the power by
>terminating into 50 Ohms.  For 19 MHz, you could take a p-p reading with the
>oscilloscope, or use one of many other circuits.
>
>I think you are good-to-go at this point.  Have you tried to talk to the
>unit via computer yet?  Any 2m appliance can be used as a nearby signal
>source for a first smoke-test.
>
>Happy operating.
>
>Regards,
>	Roger Hayward
>
>
>
>
>
>
>-----Original Message-----
>From: [email protected] [mailto:[email protected]]On
>Behalf Of Don Jackson (AE5K)
>Sent: Wednesday, February 19, 2003 5:20 PM
>To: [email protected]
>Subject: [DSP-10] Lurker now needs help
>
>Hi everyone...
>
>I've been lurking on this list for a very long time, trying to gain
>some tips and information.  I finally "got a round tuit" and put my
>DSP-10 together.  The incentive was our "Four States QRP" group had a
>builder's contest this past Saturday.  Finished up (construction at
>least) the DSP-10 and applied power to it early Friday evening.  Out
>of 74 entries, it won 1st place in the homebrew transceiver category
>and also the "best of show" ribbon.  Pictures on pages 1 and 3 of:
>http://w0ch.com/fsqrp/feb03/feb03a.htm  (Beb, I'll send you some
>better pictures soon.)
>
>Now, I'd really like to get my DSP-10 working good and am in the
>midst of the tune up and check out.  That's where I'd like some
>advice and help from some of you who have already done this.  I'm
>trying to make this a learning experience for myself and others.
>
>First off, most of the voltages check out OK, but a couple do differ
>by what I am concerned is enough to indicate possibly a problem.
>>From the QST article voltage checks, the following are different:
>R110 - should be 0.23, reads 1.7 vdc.
>U105 pin 3 - should be 3.5, reads 2.5 vdc.
>U106 pin 3 - should be 4.6, reads 3.8 vdc.
>In addition, the following two read a little low:
>U8 pin 3 - should be 2.8, reads 2.46 vdc.
>U9 pin 3 - should be 3.6, reads 3.41 vdc.
>
>My instrumentation consists of a Fluke 87 digital multimeter and a
>Tektronix TDS220 100 MHz scope.
>
>I've checked out the two PLL oscillators, first by breaking the loop
>as suggested by KA7EXM, and then adjusting frequencies.  Doesn't seem
>to be a problem.  The 10 MHz. xtal osc. was padded down on frequency.
>
>Besides the voltages being some off as mentioned above, I used my
>scope to check waveforms.  Maybe I'm worrying about something that is
>normal, but I'd like to get it right (and learn from the experience).
>The 126 MHz. waveforms on my 100 MHz scope look reasonable at U105
>and U106.  I didn't try to measure voltages due to scope limitation.
>
>However, the 19 MHz waveform is another story...looks fine (close to
>sine wave) at the junction of C70/C71/C72.  Measures about 4.5 v p-p
>on scope.  On the other side of C72 at U8 pin 1 (input to MAR-6) it
>becomes distorted and is about 1.5 v p-p.  U8 pin 3 is about 5 v p-p
>and of course remains distorted.  U9 pin 1 reads 3.5 v p-p and U9 pin
>3 is about 1.4 v p-p, the same on the other side of the blocking cap
>C78 where the coax is connected.
>
>My +10vdc supply is at 9.99vdc, while the 5vdc supply to the Q4 VCO
>shows 4.91 vdc and 3.64 vdc on either side of the R45 series
>resistor. (measurements all to ground)
>
>For the other oscillator, Q101, R111 shows 4.94 vdc and 4.56 vdc at
>each end.  This tallies with the R110 voltage (which is high)
>indicating about 17 mA. of current flowing -- more than it should be
>by a factor of 7.
>
>If you've followed this so far, I ask: are these measurements still
>in the ball park for proper operation, and should I be concerned with
>the distorted waveform of the 19 MHz signal as it goes to the TUF-1
>mixer?
>
>Thanks for any help anyone might give.
>
>73,
>Don AE5K
>(North Arkansas Ozarks)
>
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