On Sep 2, 7:51*am, Cecil Moore wrote:
wrote:
On Sep 1, 3:25 pm, Cecil Moore wrote:
Actually, 1000 ohms is pretty liberal. For instance, on
15m, the G5RV coax sees 36+j230 ohms or about 233 ohms.
The balun needs to be 10x that value or 2330 ohms.

Why not 500 ohms, assuming a 50 ohm source and transmission line?

Be the current making a choice of paths at a junction.
How much of you would flow through 500 ohms and how much
would flow through 233 ohms? (If 500 ohms is the total
impedance seen by the shield current looking back toward
the source, about 1/3 of the current would flow back
through the 500 ohms down the coax.)

http://eznec.com/Amateur/Articles/Baluns.pdf
--
73, Cecil *http://www.w5dxp.com

I got confused as to whether we were talking "choke" or "balun". For
the balun, you want to be as close to 50 ohms as possible. Actually
233 ohms is not that bad. 1K would be really bad and illustrate that
the balun is not working well. It 233 ohms, it is sort of OK,
especially with a tuner, which you use with a G5RV anyway, along with
the ugly balun. In priciople, the frequency works OK for my G5RV/ugly
balun system.

By the way, I have seen so many articles about baluns written by other
hams and they tend to repeat the same mistakes and assumptions. Most
hams do not understand how a balun works. Some even think you do not
need a balun if the antenna is at resonance which is totally untrue.
Anytime you feed a dipole directly with an unbalanced coax, the
balanced dipole "load" forces current down your ground shield and into
your radio and makes your radio part of your transmitting antenna.
Inserting a balun does not "choke" the current in the shield, it
merely shifts the output phases so that the current (voltage) is
directed towards the dipole at all times (see my other post in this
thread).