There’s a concern that the 14MHz trap might affect the 21MHz resonance but I’ll experiment and investigate.
Barry, I’ve been following this with interest since I would normally not use traps but links. However, the availability of tiny traps intrigues me to try them. Your question of should you use 2 traps for 20/15 or just one trap for 20 and have the antenna has a 3/2 on 15 is one I cannot answer. But maybe, just maybe you can dry run it by building a link dipole with 2 links. You can then try it in situ to see the effect on 3/2 or a 1/2 with a link. I do realise you want a trapped not link and I’m suggesting trying the link version to help answer on how well a 3/2 works so you can decide how many traps to put in the that version.
It will be a bit off resonance on 15m due to end effect.
Brian
1 Like
Thanks for picking that up, I originally thought that tuning would be a little bit out, but tired brain told me I was kidding. I believe it becomes more pronounced with inverted-V dipoles; well, it has in my case.
I guess that depends on whether the trap for 20 metres (which will, of course, be blocking 14MHz) passes or blocks 21MHz. Time to stick one in an analyser and plot its respone, perhaps?
Yes, hopefully the pico trap kits will arrive shortly from SotaBeams and I can get to work and report back here on the results.
73, Barry N1EU
Another thought - assuming you can deal with a full-sized 40m dipole, why not try a (2) fan dipole with ends of the 20m dipole attached with ~2ft of mason line to (midpoint of) the upper (40m) radiators. This would save you from supporting 4 ends instead of 2. The 20m dipole would end up a little more ‘vee’ than the 40, but will probably work fine (and probably a little more omni). Then you just have to live with what the 40m does on 15m. Just a thought.
1 Like
I built a 40/20M dipole with one trap per side, with the trap resonant at 13.95MHz. The antenna tuned up well on 40 and 20M but SWR on 21060KHz is 3.8:1. My KX3 ATU can easily handle the mismatch, so the antenna is still usable, if not optimum, on 15M. The antenna seems to perform well on all three bands based on RBN spots.
73, Barry N1EU
I just did a comparison of the trapped 40/20M dipole fed thru a 1:1 balun with RG174 versus 44ft doublet fed with 300-ohm twinlead to a 4:1balun into KX3 ATU. Both antennas were supported by a 30ft sotabeam pole. Trap and 1:1 balun were from sotabeam kits. 4:1 balun was Elecraft.
Based on my 40/20/15M RBN spots, I’d call it even performance between the two - they both performed well.
73, Barry N1EU
4 Likes