[TowerTalk] Antenna relay switching. Bias Tees de K0FF

[Tom Rauch]

Hi George and Alan,

>  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

I'm not sure you mean to put the caps in series. That would be 
.005 uF. On 160 meters, it would be almost 18 ohms Xc, and give 
an SWR of 1.42:1

If two .01's are in parallel, the Xc is about 9 ohms and SWR is 1.09.

Voltage across two parallel .01uF capacitors with 1500 watts into 
50 ohms is 50 volts. I'd stay away from really high voltage disc 
capacitors because they generally have more current handling 
problems.

RF current would be 5.5 amperes, a multilayer capacitor would be 
better but some disks will work.  

>  about 40
> uH
>  of choke. One can be made with about 30 T of 26GA (or so)enamel wire on a

40 uH might be a bit small for 1.8 MHz at 1500 watts, since it is 
only 432 ohms. It's right on the edge of being a problem.

RF current through the choke would be .63 amperes RMS at 1500 
watts into a 1:1 SWR. 

Of course all of these rating assume a 1:1 load SWR. Things can 
get bad in a hurry as SWR goes up.

It would be very wise, if you are unsure of the current rating of the 
capacitors, to use a whole bunch of them in parallel. I'd stay at 
least with 100 uH and make sure the choke has a fairly high Q.



73, Tom W8JI
w8ji@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