this post was submitted on 13 Mar 2024
7 points (88.9% liked)
Amateur Radio
1056 readers
5 users here now
A Lemmy Community to share links about and for amateur (ham) radio to advance the technology, and promote communication and international goodwill. This community IS NOT for CB, GMRS, MURS, FRS, etc topics unless they are related to ham radio in some way.
We won't tolerate personal insults, illegal activity, or anything contrary to good amateur practice.
If asking questions about regulations, please include your country because we recognize that, while the hobby is international, regulations often aren't.
founded 1 year ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
If you only need these two bands, then maybe you have an additional option. Consider 3:1 OCFD with 40m as fundamental: at 40m it would have something like 100-120ish ohms and closer to 50 on 20m. If you feed this with 75 ohm cable 1/4wl long on 40m, you'll get 50 ohms, and on 20m this section of cable is 1/2wl so impedance is matched there too. No balun needed, common mode choke at feedpoint could be useful tho. Maybe it would even work at 15m
I haven't built a feedline match before. That may be worthwhile just for the experience in building such.
Modelling this OCFD would be in order because these impedances will vary depending on exact placement of feedpoint and height above ground. When you have some impedances then you can match it by hand on smith chart or if you're lazy like me you can use interactive one like this https://www.will-kelsey.com/smith_chart/