[Lowfer] 74.324.5 WG2XLP

[pbunn]

I see that I have a much better signal this morning on Dex's grabber. I am running 300 watts to the antenna with no sign of corona or arcing. I moved to 74325.5 to move a little further away from Bob's strong signal. Hopefully, I can ease the power up to 500 watts without sparks. I don't have a perfect 50 ohm match so I may improve the signal a bit with modifications to my matching transformer. Not noticing any heat in the transformers , the transmitter output network, or the filter.

Yesterday afternoon I put the filter on the SA and found the cutoff frequency was at 110 KHZ rather than the designed 80 KHz. Adding turns to the inductors was not possible as they had all the turns that they could hold. The filter capacitors were .047 uF  and adding .01uF in parallel on each moved the cutoff to 85 KHz and the third harmonic down 36 dB .  The second harmonic was down about 16 dB but being  a push pull circuit knocks that down 15 dB or better anyway. I ended up getting a nice clean sine wave. Didn't look at it on the SA, but the scope's FFT function showed it to be clean enough.

The Class D 74 KHZ transmitter was unstable into a dummy load as it was on the antenna during my first testing. Probably damaged the FETs with the arcing on the old set of coils. I am using my 137 KHz Class D transmitter on 74KHz and it is working well.

The matching network need to be cleaned up and the clip leads removed and replaced with high voltage wires and ceramic standoffs installed.

I'll leave it running all day today. All reports would be greatly appreciated.

Pat Bunn
WG2XLP