[DSP-10] DSP-10 15kHz off frequency

Fri, 2 May 2003 12:00:15 -0500

I got it figured out.  For my original testing I was using a spectrum
analyzer and a scope to determine the frequency of the 10mhz osc and the two
PLLs.  Unfortunately, neither instrument was accurate enough for me to
realize how little the reference was off.  I borrowed a high accuracy
frequency counter and determined that the lowest I can tune the internal
reference is 10,000,221Hz.  This 221Hz difference makes about 13.2kHz
difference in the total output frequency.  By using a freq generator at
10,000,000Hz the PLLs lock up at 19.68MHz and 126.000MHz with the PLL test
program and the radio is almost dead on now.  Go figure...

Were using the DSP-10 as a base for a senior project in Electronics
Engineering Technology at Texas A&M and we wrote a front end in LabVIEW and
AM demodulation software (the radio is being eyed up for MRI research
~200MHz AM) and we thought our software was bad.  It amazes me how much
221Hz can make a difference.

Thanks for the advice,

Tyson - W5TJB

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Roger Hayward
Sent: April 30, 2003 11:15 PM
To: [email protected]
Subject: RE: [DSP-10] DSP-10 15kHz off frequency

Tyson:

I was expecting one of the real experts to chime in today at some point.  In
lieu of that.....

Have you done any checking on any of the sub-systems themselves?  For
example, is the 19.68 MHz PLL actually running at 19.68 MHz?  Is the 124 -
128 MHz oscillator giving you the frequency you expect?  If the 10 MHz
oscillator is off by a little bit, this can in essence amplify to perhaps
the 15 KHz offset you are seeing at 2m.

My first hunch / guess would be to examine the 10 MHz oscillator and make
sure it is on, either with a frequency counter or an oscilloscope (it will
be easier with a counter).  Measure on or around R150, and adjust C110 until
you see 10.000 MHz (the closer the better).

For the 19.68 MHz PLL, you should be able to see this frequency at U8 pin3,
or U9 pin 3.  The tuneable PLL should show 124 MHz at U105 pin 3.

See Bob's web page for discussions on how to download code into the EZKIT to
set the PLL's to a given frequency for tuning purposes.  I have a couple of
programs of this sort as well at
http://users.easystreet.com/rhayward/dsp10/index.html that might be of some
use.

Hope this helps you out.

72.
	Roger Hayward
	ARS KA7EXM

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Tyson Baker
Sent: Wednesday, April 30, 2003 1:14 PM
To: [email protected]
Subject: [DSP-10] DSP-10 15kHz off frequency

I have the dsp-10 assembled and working, but it is 15kHz off frequency  (too
low).  Initially, I substituted the less expensive epson crystal and it was
slightly off so I purchased the international crystal one.  That hasn't
fixed the problem.  Anyone have a suggestion as to why it would be 15kHz off
frequency in all modes tx&rx?  I think I have the pll's tuned to spec and
the radio seems to work fine (USB has amazing sound).

Thanks,

Tyson - W5TJB

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