Re: 7000 intermittent?


david vanhorn
 

Ok.. Intermittent oscillation may explain it all


On Tue, Jun 1, 2021, 5:02 PM Leroy Higgins <leroy.higgins@...> wrote:
Bill, does your radio have a parasitic oscillation on 6M?

Using a 100 MHz oscilloscope, tape the 10:1 probe to your RF output coax and look at the waveform with the transmitter keyed.  Should be a nice clean sine wave of your transmit frequency.  If a parasitic is present the waveform won't be a clean sine wave.   Try this method using your antenna and the dummy load.  

The last time I used this method was on a 2 kW, CW, vacuum tube test transmitter with low RF output power at 15 MHz.   The oscilloscope on the coax method indicated the RF had 60 Hz modulation caused by a power supply filter failure, in the exciter.   When the 60 Hz modulation was eliminated the Bird watt meter read the correct power.

Most coax with stranded wire braid has enough RF leakage to monitor your transmit frequency and modulation.  You can't measure transmit power level accurately, with this method, but you can easily observe modulation and frequencies without an RF power tap, or wiping out your oscilloscope input channel from overvoltage.

Leroy  AD6LH

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