Posted by
Howard W. Ashcraft on
Jun 17, 2007; 4:14pm
URL: http://elecraft.85.s1.nabble.com/K2-Filters-Will-Not-Align-Properly-tp449275.html
After several years of faithful service, my K2/100 (with KDSP2 and KSB2) has developed a perplexing malady. The crystal filter passband will not adjust to center on a 600hz sidetone. As you adjust the filters towards 600 hz using Spectrogram (say OP1), the filter shape degrades and then severely attenuates the signal until NO audio signal is visible on the Spectrogram display. I have repeated the key realignment procedures three times, with identical results.
The long story. The K2/100 generated an Info 080 message that I started diagnosing. The problem "self-corrected" which lead me to believe it was probably a loose connection to the KPA100. Despite lots of opening and closing the case, the problem has not reappeared.
I now have better test equipment than I had when I built the K2 (serial 4357) and it seemed like a good time to realign the transceiver. I did a complete realignment, with minimal changes except a slight kick to the 4Mhz oscillator and a reasonable amount of repeaking of the bandpass filters. So far so good. All of the key tests/parameters were within range.
When I started to set the filters, however, I could not get them within range. As noted above, I can not shift the passband to cover a 600hz sidetone. The filters appear to center around 900-1000 hz. I have attempted to set the filters back to my prior CAL FIL BFO settings, but to no avail.
The following are the test results from this realignment.
PLL Reference Oscillator Range Test
High = 12101.55
Low = 12088.14
Dif = 13.44 (Acceptable 9.8 - 15)
VCO Voltage all greater than 1.5 v, less than 7.5 v.
BFO Test
BFO High = 4917.42 (Acceptable >= 4916.3)
BFO Low = 4912.34 (Acceptable <= 4912.7)
Range = 5.08 (Acceptable >= 3.6)
Transmit frequency is +- 10 hz. However, zero beating a 600hz sidetone against the 7.00 Mhz birdie **appears** to be around 7000.35 Khz. (I never fully trust zero beating as I am tonally challenged...)
Any ideas??
Howard W. Ashcraft, Jr.
Hanson, Bridgett, Marcus, Vlahos & Rudy
425 Market Street, 26th Fl.
San Francisco, CA 94105
ph: 415.995.5073
fax: 415.541.9366
e:
[hidden email]
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