[TowerTalk] Antenna relay switching. Bias Tees de K0FF

[K0FF]

Subject: Antenna relay switching. Bias Tees de K0FF


 Alan, if you want to make a high power "bias tee" for your application, you
 can use a pair of .01 at 3kV Z5U disc capacitors in series, with about 40
uH
 of choke. One can be made with about 30 T of 26GA (or so)enamel wire on a
 T-106-3 core. This will stand up to anything a ham will put out. It will
 work from 160 thru  LO VHF with no problem.
 Of course if you run only low power, you can scale back on the capacitors,
 and go with a light duty choke. The values are somewhat uncritical for the
 capacitors as far as the series reactance is concerned, it's more the
 current handling that is an issue there. For HF thru VHF values of .01,
 .015, .02 are fine. For VHF thru UHF it can be as low as 500 - 1000 pF.
  On the choke, anything from 27 thru 100 uH will work with little
 interaction, with values in the of 27 and 47 commonly used in broadband
 applications. Just make sure the wires are sized properly for the current
 required  by the relays  .

 Happy Homebrewing, Geo>KØFF
 http://homepages.dstream.net/K0FF

 ----- Original Message -----

 > I want to control an antenna relay at the base of my tower by feeding
 > control voltage down the coax instead of running a separate control
cable.
 > I know this is usually done by putting blocking caps at each end of the
 coax
 > cable and using chokes to isolate the power supply and relay coil from
the
 > RF.  Anyone know what value choke I should use?  Is the value of the caps
 at
 > all critical?  I was planning on using 1000 pf.  I know I've seen a
 project
 > like this in print but can't recall where.
 >
 > Thanks
 >
 > Allen Jones, W9DZ
 > w9dz@arrl.net
 >




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