Date: Fri, 24 Jun 2016 08:16:29 -0700
From: jimlux <jimlux@earthlink.net>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] To get a truly balanced antenna feed
Balanced lines are probably of limited use these days:
1) amateur radio
2) fixed broadcast HF stations with high power (feeding a multi bay
dipole array with open wire line is a natural, and low loss, too)
3) high power RF/pulse work over short distances
>
> Paul, W9AC
## Check out the open wire 300 ohm lines used by 100-500 kw SW AM broadcast.
They are typ supported by 21 /26 foot tall AL supports. Alumoweld wire used
for the
300 ohm line. From TX to this massive box, like a pair of double wide
fridges, but taller,
typ whats used is 50 ohm coax.... in either 6-9-12 inch diam. Inside the
box is some
form of a tuner, plus a balun, then the open wire output side. They did not
depict how the
balun is configured, nor the tuner.
## On some of the smaller setups, up to abt 45 kw, ferrite baluns are used,
but in huge multiple
20 lb blocks. I saw some more 1:1 CM chokes on a UK site. Damned things
weighed 100 KG,
and were inside an aluminum, ribbed box. Pumped full of silicone varnish, like
used on dahl plate xfmrs,
and done in a vac chamber, then baked in a kiln. These were used on 50 ohm
systems, like lpda arrays.
## Interesting to see how the big boys do things. Too bad they didn’t provide
more details.
Jim VE7RF
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|