You mean DC transparent UNUNs, as in the kind with a capacitor from the bottom
of the UNUN winding to ground to keep from shorting out the DC, and the control
relay current passes through the UNUN windings?
In this case the only the difference between the input and output RF currents
pass through the capacitor to ground, and since the impedances are so close
this is rather small.
For a well matched load at 1500 watts, this would be 5.48 minus 4.47, one amp
for government purposes, not really a lot. You should be able to use the same
value/ratings that is used for the blocking capacitor in the tower end switch
box since it will be *less* stressed at the bottom of the UNUN winding.
>
> From: Pete Smith <n4zr@contesting.com>
To: <towertalk@contesting.com>
> Date: 2001/05/14 Mon PM 01:43:14 EDT
> To: towertalk@contesting.com
> Subject: [TowerTalk] DC isolated UNUN
>
> If I wanted to build a pair of UNUNs for my 75-ohm CATV feedline, and need
> to have them isolated from ground except for RF, what value of capacitance
> would be appropriate for 1.8-30 MHz service? Reason for this is to
> continue to use my current antenna switch, which sends +DC, -DC and AC down
> the coax to control the relays at the tower base. What rating factors need
> to be considered for legal limit power (I assume one needs to figure on as
> much as 1KV being present, but don't know how to anticipate what RF current
> might be involved).
>
> 73, Pete N4ZR
> Contesting is!
>
>
>
>
>
> List Sponsor: Champion Radio Products - We'll be at the Dayton Hamvention
> with all of our safety equipment and other products. Stop by booth #559 and
> say hi.
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>
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>
>
List Sponsor: Champion Radio Products - We'll be at the Dayton Hamvention
with all of our safety equipment and other products. Stop by booth #559 and
say hi.
<A HREF="http://www.championradio.com";>www.ChampionRadio.com</A>
-----
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