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Ham Radio

More on First Transmitter and LPF

[Today’s run: nothing.  Yesterday 1 mile]

I looked up my calculations for that low pass filter (LPF) that I am using with my “first transmitter”  (see previous blog posting.)

I have been measuring the transmitter output with my O-scope. When I run into a dummy load the waveform looks really nice.  When I run into my antenna tuner/antenna, it doesn’t look so nice.

I reviewed my notes on the LPF.  Then I sent an email to the author of the article in QEX last December from which I derived my LPF design.  He was very gracious and confirmed my design.  Also, he suggested that maybe I am seeing some other signals on the antenna when I measure things that way.

That prompted me to have a couple of ideas. 1) I would do the same measurements with another signal source other than the transmitter.  and 2) I could make a specific antenna (dipole) so that I could make a measurement without the antenna tuner in the circuit.

So, I got a bit of a start on number 1.  I used my TenTec Century 21 transmitter and the same frequencies as the “first transmitter” and measured into the dummy load and into the antenna.  I see the same effect!  So it is not the fault of the transmitter at all, or most likely not.

My antenna tuner is an open breadboard construction.  I think maybe the RF is getting back into my measurement connection somehow and messing things up.  I tried measuring with a regular o-scope lead and I tried using a coupler and a bnc cable.  Both show the same effect.

So I am not yet sure what the problem is, but I am now more confident that my LPF is working ok and I can use my little transmitter without splattering my signal all over the place.

I still think it would be useful to build a 40-meter dipole antenna so that I can test without the tuner in line. Stay tuned for that.

As I typed this entry, I’m wondering if my antenna tuner is set up as a low-pass configuration or high pass.  I think it is low-pass.  I will have to check.  (didn’t I post about that awhile ago?  found it)