In Varney's original r.s.g.b. article in July 1958 he showed it both
ways, 100% open wire feeder to a tuner, or 34' of open wire feeder to
any length of 72 ohm coax or twin lead to a tuner or the transmitter.

bob
k5qwg

On Thu, 11 Jun 2009 10:43:38 +0100, Ian Jackson
wrote:

In message
,
writes
On Jun 10, 3:360 Is it advisable to use a combination of Coax and a ladder line to feed a
simple horizontal multiband dipole antenna?

In my new QTH it would be very easy for me to get a short run of coax out of
my shack window but I would like to use a low loss ladder line for the main
run up to the antenna feed point. Is it OK to place a 4:1 balun just outside
of the window 0
Kash, AG4EL

The G5RV antenna uses a combination of coax and ladder line, so this
type of antenna is in use by 1000's of Hams.

The 4:1 balun is a bad idea for a multiband antenna, due to the
impedances involved at the various operating frequencies. Just
transistion from the ladder line to the coax and use a 1:1 choke balun
at the antenna input of your tuner. You did not mention an antenna
tuner, but you will need one for multiband operation.

In general keep the coax length as short as possible.

If I remember correctly, the original design of the G5RV does NOT use
coax. [If interested, check it out on Google.]

I agree with Gary N4AST: the direct answer to your question is:

* Use the shortest length of good quality coax you can get away with.
* Use a good quality 1:1 current (choke) balun at the ladderline/coax
junction.
* If you find the tuner can't reach a match on some bands, only then
consider a 4:1 balun; even so choose a 4:1 **current** balun.

On the topic of G5RVs, some (unscrupulous) antenna suppliers provide a
nice long length of RG58 as part of the package to "tame" the VSWRs.
Take a look at some of the losses that introduces:
http://www.karinya.net/g3txq/g5rv/

73,
Steve G3TXQ