[Elecraft] Balun with a G5RV?

[kc4kgu@ENTERZONE.NET]

On Sun, 21 Apr 2002, Tom Crites wrote:

> I am using a G5RV antenna with my K2 (with KAT2 tuner) fed with 60 feet of 50
> ohm coax.  I've been trying to figure out if I need a balun between the 450
> ohm ladder line and the coax.  Will a balun improve the antenna performance
> or just help keep RF out of the shack?  My existing setup with no balun is
> marginal on 10 meters.  With the G5RV I've seen suggestions just needing just
> a tuner, to a 1:1 air-core choke balun, a 4:1 balun, 75 ohm coax,...., etc.
> 
> 73,
> Tom, KC8SES
> 
> p.s. I did put a Solarcon A99 this weekend!

Your marginal performance on 10m is probably a result of high SWR on the
coax.  Remember: a tuner provides a 50ohm match to the RADIO.  It does
NOTHING to improve any mismatch you may be seeing between your antenna and
the tuner on the feedline.

Last week, I converted the feed to my 80m doublet antenna from 50ohm coax
to TWO 50ohm coax (100ohm unbalanced-balanced).

Antenna--|
         v
----------------+    +----------------
                |    |
               | |--| |
Twin coax ->   | |  | |
with shield    | |  | |
tied together  | |  | |
at antenna end | |  | |
"floating".    | |  | |
Do NOT connect | |--| |----+
the shield on   |    |     |  <- Shields at shack end are tied
the antenna     |    |    ---    together and grounded.
end of the feed |    |     -
to anything!    +    +     =              
               --------
               |TUNER | <-- Center wire two coax feeds connects
               --------     to balanced output of antenna tuner.
                |
                |
               RIG

On 75m, signal reports from the guys I ragchew with went from 20-30over to
40-60over and that is with the terrible band conditions we've been having
this week.  On 10m, I listened to p49mr (Aruba) give 5/7 - 5/9 to folks
tons and tons of people.  I got 59+30 on 28.445. That was enough
validation for me.  My feedline is 150ft long from shack to antenna so, I
was seeing a LOT of loss using an unbalanced feed.  Your milage may vary.  
Another PLUS of using twin coax vs open-wire or ladderline: You can bury
it, run it right against metal objects, moisture on the feedline doesn't
effect SWR, no RF in the shack on ANY band, even running 1kw, etc, 
etc.  It's like a dream come true!

Next project, remotely switchable N/S/E/W phased arrays.  I just have to
find (or build) a remote balanced feedline switch.

73 de John - KC4KGU
K2 #2490