Friday, November 20, 2020

RF antenna current meter

For future experiments and the one done recently I really need a antenna current meter. Best is something that shows the balance as well since that is one of the features a S-match offers. Another thing you can measure of course is the RF current which should be as high as possible. That way it's possibible to compare antennatuners on open line.

PA0FRI  has a good design on his site. Components are not really critical as long as they are the same for both lines. 



As a real amateur experimenter I first look around in my scrap box for parts. It took a while but I found everything except the plastic boxes to build everything in. Some soldering and fitting....this is the result:



Frits does use T80-2 torroids with 25 windings. I found two pre winded ones in my scrapbox, 23 windings on a unknown torroid. The big 2W resistors should be 50 Ohm, other designs show 100 Ohm. I found two indentical 82 Ohm resistors that will do the task. For meters I found a nice AKAI VU meter combo I salvaged from a AKAI cassette player. It took me some research to find out these are microA meters, just what I needed.

Because I didn't know if it would work well I decided I would not build the meters in a box yet. 


Basically this is bare system. It actually works better as expected so I'll continue to make it look nice in some time.


Now, I was very curious about my antenna system (2x 20m inverted-V "doublet") balance...first test on 10m behind the S-match tuner shows a reasonable balance. It's not perfect but close, nothing is perfect in the real world.



On 20m, the system behind the S-match is almost perfect in balance.

However.....



Left is 50W on 60m with the Palstar AT1KM (with 1:4 ruthroff balun inside).
Right is 50W on 60m with the S-match.

It clearly shows a unbalance with the Palstar, the S-match does a fine job in balancing.

I can show more pictures but it is not necessary I think. Other bands all showed the current in balance. I also tested with the Palstar, except 60m all other bands had a balanced current on the open line.

Well, I finally managed to get the meters in a box...


The tiny lightbulb lighting in this combo was still intact. Wow, it looks pretty nice...
Scrap parts remember! It looks very professional after all...

2 comments:

Thanks for your comment. Bedankt voor je reactie. 73, Bas