[VHFcontesting] VHFcontesting Digest, Vol 140, Issue 15

[James Duffey]

Ben - You asked:

> Trying to decide on which T-match to use for a 144 MHz Yagi. K1FO is
> using a 4:1 balun for a 200 ohm T-match setting while KK1CW is using a
> 1:1 balun for a 50 ohm T-match setting. Pros and cons? Is one easier to
> adjust than the other? And has anyone info regarding dimensions for a
> 144 MHz hairpin stub for a split dipole to be fed with a 1:1 50 ohm
> balun?

To answer your last question first, YagiCad will give you the dimensions for a hairpin stub for a given driven element and Yagi design. It will also tell you how much to lengthen or shorten the driven element to get a 1:1 SWR match with the hairpin. YagiCad is free and very useful, just google YagiCad. It will also design Tee matches for a given design. There are excel spreadsheets and a PDF file that will help you understand matches of all sorts. 

The driven element length and diameter is pretty much noncritical for a Yagi. It just serves to launch the wave to the rest of the Yagi. Adjust the length for the best match given your matching scheme and be done with it. 

I am not sure of the 50 Ohm vs. 200 Ohm tee match issue, but I suspect that the 200 Ohm match is more forgiving with respect to length errors in fabricating the match. Also, before VHF ferrites were commonly available, the 4:1 balun may have been easier to implement with respect to efficiency. - Duffey KK6MC