Sup hamfagsI wanna make an end-fed halfwave antenna (single band, no tuner), and I don't know if I should use an L network with a variable cap, or a 9:1 unun. I'd like to be able to switch between 20m and 30m by switching out the 33ft wire with a 50ft

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Anonymous 12/08/14 (Mon) 22:54:22 No.139

Sup hamfags

I wanna make an end-fed halfwave antenna (single band, no tuner), and I don't know if I should use an L network with a variable cap, or a 9:1 unun. I'd like to be able to switch between 20m and 30m by switching out the 33ft wire with a 50ft one. I'm only running QRP on both bands (3w on 30, 1w on 20).

Suggestions?

(Pic unrelated)

Anonymous 12/09/14 (Tue) 03:36:28 No.140

What are you currently using?

Anonymous 12/09/14 (Tue) 04:28:08 No.141

>>140
Nothing, this is going to be my first HF antenna. I'm a full-time RVer, so I can't mount a center-fed antenna easily enough to warrant the extra simplicity of it.

Anonymous 12/09/14 (Tue) 20:30:00 No.142

File: 1418156999955.jpg (70.56 KB, 750x688, 375:344, 1418064312183.jpg)

I think with the portable nature of your antenna, the difference in location will de-tune it. plus a 9:1 balun will not transform a half-wave straight to 50ohms. You're better off with making a simple tuner with a coil of wire and a variable cap. As you are QRP a simple coil and capacitor will do, there are many plans for "QRP longwire tuners" on the internet, i suggest you look them up

Good luck OP, i started out as a HAM with QRP and half wave wires

Anonymous 12/09/14 (Tue) 20:58:42 No.143

File: 1418158722437.jpg (15.78 KB, 320x174, 160:87, handk-thumb-320x174.jpg)

>>142
The idea behind using a 9:1 unun was that the impedance transformation varies with the square of the turns ratio (I think?), and 9:1^2 is 81:1, which would transform 5kohms to about 60ohms. Good point about the location problem, though.

The 'coil of wire and variable cap' was what I meant by the L network idea, although I could still explore other arrangements for it. I've ordered a copy of RF Circuit Design by Chris somethingsomething, once that gets here I should be able to look at some other matching circuits. I'll also go ahead and Google it like you said, too.

Thanks for the help!