New tower/beam project going on soon. Could you post a link on what ferrites to get? I've been on the fence about this subject some say air wound some say ferrite chokes. I'll probably go with lmr 400 flex
Mix31. Don't go for unmarked ones. Fair-rite ones are good.
There is no discussion to be had with whether to go for air wound or ferrite chokes. Its as simple as this:
Air wound. You're building LC circuit. Where that circuit ends up providing the most choking depends on the diameter of the coil, the spacing of the turns, even the velocity factor of the coax. And it only does that over a very narrow bandwidth. The maximum choking will be over a couple of MHz, it'll do almost no choking 7MHz off centre. Making one from RG213 on a 4.25" core, changing the number of windings from 5 to 7 results in a drop of the frequency for choking of over 7MHz. You cannot trust suggestions for building them from anyone online unless it is from someone like Steve G3TXQ who has built them and measured them with a vector network analyser and even then the chart he produces only works if you build the air wound chokes exactly as stated. A turn more or less or substituting a different coax means there's no guarantees. The only way you can ensure the one you're building is working the most where you want is to build it then measure it with test equipment.
Ferrite chokes. The manufacturers of the ferrites produce data sheets with charts on which show the impedance for a single turn or number of turns of wire at different frequencies.
Looking at the following chart for a Mix31 Fair-Rite one taken directly from their website data for a 2631102002 ferrite....
We can see from the bottom graph that three turns gives approximately 1600 Ohms choking on the 11m band. It does not matter what coax you're using or what size the loops are through the ferrite, the result will be the same. We can wind that choke with certainty that it will do what it states with any testing done only really verifying the manufacturer spec.
