RE: LF: Antenna or transmitter tuning

["Laurence KL1X" <hellozerohellozero@hotmail.com>]

Just statiing one of things I found was the I had probs with high local fields from my own transmiiter aerial affecting the oscilloscope readings. I had a load of v/m as my loop running N amps was only meters from the shack - nothing was wrong per say but I had to take care with the screen test leads and add an RF filter on the AC power lead - all became clear. Ao as I ramped up the power, save for a small change in the waveform everything looked fine -without the filters it looked worse and worse. Prob not your prob though.
 
Laurence in rainy Singapore

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> From: vy1ja@northwestel.net
> To: rsgb_lf_group@blacksheep.org
> Date: Mon, 31 Jul 2006 06:57:27 +0000
> Subject: LF: Antenna or transmitter tuning
> 
> Hello again Friends,
> 
> The single FET amp which Steve lent me has been working fine, but if you 
> remember, during tuning the antenna system would come up with some weird 
> wave shapes.  The amp uses an air core output coil.  The antenna loading 
> coil , its matching coil and both coils in the transmitter's Low Pass Filter 
> are air core as well.  So there is no iron in the working system.
> 
> Remember that when the antenna was tuned, one suggestion was to place a 
> matching transformer with TV Horizontal Ferrite core in the circuit.  When 
> that was done, the waveform on the scope turned to garbage.  (high in odd 
> order harmonics)
> 
> Today, the two FET amp which Scott lent me was put on the air.  It has a 
> ferrite TV output core which I wound and even though it was placed at the 
> exact length of coax from the antenna which Steve's amp had been, it 's 
> output waveform is badly distorted.
> 
> It is important that I run the station at the maximum allowed IERP for the 
> sake of proving non-interference.
> 
> On Scott's amp, the current and voltage waveforms are identical and in 
> phase, the amp runs very stable at over 300 Watts input, but the waveforms 
> look awful.  I have decided to switch back to Steve's transmitter and 
> revisit both the output of Scott's amp and the antenna system.  I am 
> considering winding a air core transformer for it, but am unconvinced doing 
> so will solve the real problem.
> 
> I have a scopematch, and scope, an rf source capable of 18 kHz  and up.
> 
> Any ideas on how to approach this waveform problem?
> 
> J.
> 
> 
>

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