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I have been working on a simple antenna analyzer and am posting the current state of the project.? I will update the files if I make any changes.
Because of the way this group works, I could not put the bridge circuit photo in the same place as the program,? So the circuit is in the photo section ( /g/QRPLabs/album?id=14984 )?? and the program is in the files area
.? ( /g/QRPLabs/files/Arduino%20Shield%20Antenna%20Analyzer%20-%20%20K1URC )

Hope those links work ok, I am having a bit of trouble pasting them in.

Ron? K1URC

Hi Ron, links work fine, thanks for an interesting project.? I just layed out a Si 5351 board for fun and hope to follow you.

Greg

I conducted some experiments with using a lowpass filter between the BS170 and the bridge circuit.??? I had been using a jumper wire in place of a lowpass filter up until now.? When testing with a pure resistor as a load, the jumper works fine as the fundamental frequency and all the harmonics will have the same SWR and the readings are not effected.?? When testing a real antenna ( or feeding an antenna tuner ), the harmonics cause the SWR to read high.?

The results of my experiment are:

?*??? The experiment consisted of feeding a T type antenna tuner.? The antenna was a 120 ohm resistor
?*??? as the rf load.? The tuner was adjusted for best SWR on a number of bands and using a number of low
?*??? pass filters.
?*?????
?*????? Band??? No Filter??? 30 lowpass??? 20 lowpass??? 10 lowpass
?*?????????????? Jumper
?*????? 80?? ?? ?? 2.0??? ?? ????? 1.3?????? ? ? ? ?? 1.3????? ? ? ? ???? 1.7
?*????? 40??? ? ? 1.8????? ? ? ??? 1.0?????? ? ? ? ?? 1.0???? ? ? ? ????? 1.7
?*????? 30???? ?? 1.4??????? ? ? ? 1.0??????? ? ? ? ? 1.0?????? ? ? ? ??? 1.0
?*????? 20????? ? 1.0????????????? xxx??????? ? ? ?? ? 1.0?????? ? ?? ??? 1.0
?*????? 15??????? 1.0????????? ? ? xxx???????? ? ? ? ? xxx??????? ? ? ? ?? 1.0

?*??? To me, the 20 meter lowpass looks like a good compromise for low band work.
( I am not sure how that table will look with the proportional font.? The program listing has the same table. )

The program in the files area has been updated.

Ron? K1URC

I changed the circuit and program to support switched lowpass filters.? The program is written to support 3 filters.? I uploaded another circuit diagram.? The new circuit could also be used without relay switched filters if one wished, so I think this is the better way to go.

I don't expect to be making many more changes

Ron? K1URC