[DSP-10] On the air.

Sat, 29 Jun 2002 02:50:57 GMT

Thanks to N7HPR, W7CQ, KO7N, WB6HKA, PA0OCD and WB9OWN another DSP-10 is completed and working.

Assembly went smoothly as I followed the expanded testing notes from W7CQ and KO7N.  Those notes saved me a lot of time because I did have the DAC Left and DAC Right lines reversed.

I only have a couple of comments of my own to add regarding the assembly process.  Concerning the 10 MHz oscillator, I warped this onto frequency by adding a 27 pF mono ceramic cap to pins 2 and 3 of J106.  I did this by simply crimping the cap into Molex terminals, along with the jumper that goes between pins 1 and 2.  I did this because I was working at home during the final assembly, and I could not "borrow" any chip caps from my employer.  This seems to be a satisfactory solution until I can build an accurate 10 MHz reference.  The measured drift using this method was about 24 Hz in 6 hours.

I think that the alignment of L8 through L13 is easier to do by tuning for maximum power out during transmit.  It seemed easier to me to peak  my rf probe than to dip for a quiet signal.

I checked my DSP-10 at work on a Motorola service monitor, and it seems to work as advertised.  Signals that are -152 dBm are easily seen 10 dB above the noise.  20 dB quieting is at better than .3 uV.  And power out was 29 mW measured with an HP 8481H Power Sensor on an HP 435B Power Meter. Adjacent channel selectivity for FM (30 kHz spacing) was so good that it was off the scale.

I am still plagued by the 5 kHz birdies, though.

Thanks to W7PUA and TAPR.

73,

Jim Albers N9CYL    

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