[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)