[SOC] G5RV

[JMcAulay]

At 07:18 PM 06/12/2003 +0100, Chris G4PDJ wrote, in part:

>Paul,
>Things seem to be running away a bit here. What you need is not=20
>a 'choke' (which is a device for 'choking-off') unwanted currents,
>but a 1:1 balun transformer.=20

Chris, maybe you think I've gone nuts.  It's only partly true.  I had moved
some text around in my previous email, and it didn't quite come out the way
it should have.  So if I may (in real SOC fashion), I'd like to straighten
out what I wrote:=20

1.  "In most applications, I'd rather see a real balun transformer."  True.
 A balun transformer is the best fix.  "But for this case [G5RV] the
impedance transformation provided by joining the two lines is an integral
part of the design."  Prior to that sentence, a deleted comment mentioned
the common 4:1 ratio balun transformer.  In the G5RV antenna system, you
must use a 1:1 balun transformer, not 4:1. =20

2.  Re balun transformer cost:  "the last time I looked, about twenty
dollars for one that'll handle a kilowatt!"  Chris says it's now about
=A330.95 (delivered) for a good one, somewhat more than I expected. =20

3.  "Hence, with the G5RV, the choke is the preferred device."  It's
preferred by most users because a few feet of coax line is much cheaper
than a balun transformer.  That, of course, means users who bother to do
anything at all about the radiating line problem.  I'd bet most G5RV
installations just let it rip.=20

Note also that Paul M3CRQ wrote, "...most G5RV manufacturers recommend a
choke balun comprising about 10 turns of the co-ax feed close wound with a
diameter of four to six inches fitted, as Chris suggested,mright at the
point the phasing line connects to the feed."

The manufacturers aren't crazy.  A coax choke will *probably* cure any
problems, or at least reduce them to a very low level.  But I agree with
Chris:  I would still rather see a real balun transformer there.  Reason?
If the antenna is otherwise built with reasonable care, you should
definitely, not just probably, fix the line radiation problem by using one.

I have had two fairly close acquaintances who built G5RV antennas.  One
swore by it, the other swore *at* it.  I would suspect, but do not know for
sure, that the one who hated it had not bothered at all to consider the
line radiation situation.

73
John WA6QPL  SOC 263