Posted: 1/23/2017 1:42:01 PM EDT
| I was thinking of building a small 40 meter beam using the MFJ -2240 ham stick dipole mount , its a mount that holds two 40 meter hamsticks opposite of each other to mount on a pole as a dipole. My question is if i mount this on a small boom as the driver will i have to use 2 more mounts with the hamsticks for the reflector and director because of the loading coils for the electrical length or could i use a solid rod cut 10% longer and shorter than the hamsticks drivers for the reflector and director. Of course the spacing will be another problem to figure out. thanks |
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Not quite sure what you're asking, but what's needed is a reflector a bit electrically long, and a director electrically shorter. So, the loading coil turns and/or rod length would need to be adjusted.
How much longer/shorter is more complicated than just saying 10% - the best way to figure out where the R and D should resonate is using a modeling program and trading off gain vs. bandwidth. It's going to be a quite narrow band yagi, and there are probably no "rules of thumb" for shortened versions. |
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I say don't waste your money. Ham sticks work ok for a quick, cheap mobile or portable situation, but they are very in-efficient especially on the lower bands.
Yes, you would need a Hamstick for each half of each element, then a way to "tune" them, then figure out spacing etc.. |
| It would probably work with 10 meters ok and spacing on them wouldnt be a problem . Using 40 meter ham sticks would be nothing but a guess at the spacing. Thanks again looks like something i could do on 10 meters and would only need 2 hamsticks the reflector and director could be solid rod with no coils for the length i need. |
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Quoted:
I say don't waste your money. Ham sticks work ok for a quick, cheap mobile or portable situation, but they are very in-efficient especially on the lower bands. Yes, you would need a Hamstick for each half of each element, then a way to "tune" them, then figure out spacing etc.. ^^This, plus you will only get about 10 KHz bandwidth. It's not worth wasting time and money for this. I would look at building several 2 element quads, with fixed direction, made out of wire, hung of trees ad spaced accordingly. You can rig a remote switch to switch the frames for directional performance. A vertical rhombic antenna with switched wire loops is another great choice that's somewhat compact and easy to build. Full size loops are always a lot quieter that verticals or dipoles. This may be important if you live in a high RF noise environment. |