[TowerTalk] Antenna relay switching. Bias Tees de K0FF

[alsopb]

Ameritron uses 3 0.01 1KV ceramics in parallel in both the control
head and switch box.  At lower freq's, this effectively gives you the
series value of 0.015 ufd. That translates into 3 ohms.  I don't
consider this to be low enough on that band.  IMHO 1 kV disks are
pushing it.  Something closer to 2 or 3 kV would seem to be more
appropriate to handle oddball conditions -- like unexpected ice on the
antenna.

73 de Brian/K3KO

K0FF wrote:
> 
> 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
>  >
> 
> --
> FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
> Submissions:              towertalk@contesting.com
> Administrative requests:  towertalk-REQUEST@contesting.com
> Problems:                 owner-towertalk@contesting.com

--
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com