[TowerTalk] Antenna relay switching. Bias Tees de K0FF

[Tom Rauch]

Hi Brian,

Sometimes it helps to put numbers on our thoughts.

> 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

When the inductance of the choke is included, that gives an SWR 
of 1.05 : 1 at 50 ohms.

What amount do you think would be acceptable, considering the 
fact virtually all 50 ohm cables we use range someplace between 
48 and 55 ohms? 

Remember, you have to keep AC current into the radio through the 
capacitor to a low value.

(BTW, I searched sample cables for weeks looking for a "real" 50 
ohm cable for a critical application, and I wound up going to 
hardline. Do you think the typical 54 ohms or so many small foam 
cables have is a major problem?)

> 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

With 5.5 amperes (1500w 50 ohms) of current through the caps, 
peak voltage across those capacitors is something like 50 volts or 
less. Rather than only a 200:1 safety factor, what would be safe 
and why would we need that much margin?

Is the current rating and dissipation factor of a 3kV capacitor 
generally higher or lower than a lower voltage part?





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