[Elecraft] Getting KX3 ready for Digital modes

[Kenneth A Christiansen]

Hi to the group

I hope to take part in the NDQP next week end using RTTY and PSK31.

I have an IMD METER by KK7UQ and the first thing I found was the K3 had an IMD of 29 to 30 at all power levels when set up properly. The KX3-KPA100 had an IMD of 34 at all power levels when set up properly.

I tried a PSK31 QSO and I am a rag chewer so my transmissions were a bit long. I was using 25 watts and both the KPA100 and the KX3 OSC got quite warm. I felt I was having to chase the other station with my DIGIPAN software but of course it could have been the other guy drifting. I decided to do the KX3 custom VFO TC procedure. I had the best in test equipment 14 years ago but since I retired I have to use what I can find. My K3 has the KTCX03-1 TCXO option. I calibrated the KX3 against the 15 meter WWV station. I tuned the K3 to 50.0 mhz and turned the power down to minimum. I then put a brick on the key and noticed both temperatures stayed constant and low. I did not start using the K3 to do the procedure for an hour so it should have been stable on the dummy load.

I then followed the KX3 custom VFO TC rev A9 procedure with the refrigerator and the hair dryer using the K3 for the reference signal. I again calibrated it against the 15 mhz WWV. The KX3 is now stable as far as I can tell when changing the temperature of the KX3 and checking zero beat against the 15 mhz WWV.

I tried another digipan QSO at 30 watts and it went OK but I was concerned about the temperature of the OSC and PA. I turned the power all the way down to 11 watts but the temperatures still kept increasing. I found two 12 volt 4 inch muffin fans in my junk pile and wired them in series to the 12 volt supply to run quieter. One blows on the heat sink of the KPA100 and the other on the back of the KX3. Now I will describe the tests I ran not because I operate this way but to learn if I had a good cure. I ran 100 watts CW key down for 5 minutes and at the very end I got a PA fault on the KX3 but not on the KXPA100 utility. I let it cool down again and ran it 6 minutes at 95 watts with the PA peaking at 42C and the OSC peaking at 42C. Next I ran a PSK31 signal at 50 watts for 7 minutes and again the PA peaked at 42C and the OSC peaked at 42C. Now I feel PSK31 at my normal 30 watts should not be a problem for either drift or heat.

By the way I could not cause any problem at 100 watts of CW no matter how long I ran my test before I made the above changes so the digital modes even at low power are much more stressful to the KX3 and KPA100 than CW.

I hope my experiences are helpful to some one else. It would have been fun to have the good equipment I had at AT&T so I could have documented my results better but I still know that I made an easily observable improvement.

I hope to work some of you on the NDQP using the digital modes the 4-19-14 18:00 to 4-20-14 18:00. I won't be on a lot but I do hope to work it for several hours.

73 and hope this information can be of help

Ken W0CZ   w0cz at i29 dot net

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