Tuning Twinlead Fed G5RV
 

I'm considering making a G5RV like antenna and tuning it by changing
the length of twinlead by scraping off some of the insulation at
various locations and attaching it to the radio with alligator clips.
I'm wondering if the excess twinlead hanging off the connection point
would be a problem?

Brock

Brock wrote:
I'm considering making a G5RV like antenna and tuning it by changing
the length of twinlead by scraping off some of the insulation at
various locations and attaching it to the radio with alligator clips.
I'm wondering if the excess twinlead hanging off the connection point
would be a problem?

The "excess twinlead hanging off the connection point" will act like
a stub and if you don't understand stubs, it will definitely be
a problem.
--
73, Cecil http://www.qsl.net/w5dxp



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"Brock" wrote in message
om...
I'm considering making a G5RV like antenna and tuning it by changing
the length of twinlead by scraping off some of the insulation at
various locations and attaching it to the radio with alligator clips.
I'm wondering if the excess twinlead hanging off the connection point
would be a problem?


Hi,

I use a multiband G5RV from WIMO.de with 10m or so of twinlead copper ended
with a balun 4:1 and coax.
My mother cut 1m of twinlead with the lawnmower... sorry Thierry... !
At first sight I though there could be a problem due to the velocity factor
of 0.92 now a bit changed...
This was not a problem. I resoldered the cut part to the balun, make a new
adjustement with with antenna tuner (built-in in my Kenwood TS-570D), VSWR=
1:1. My AT Tuner did a perfect job !
If you don't have a built-in AT tuner, the cheap and external manual Yaesu
antenna tuner do the same job.
All is perfect again !

Info G5RV :http://www.astrosurf.com/lombry/qsl-g5rv.htm

Thierry
ON4SKY, LX3SKY


Brock

I use a multiband G5RV from WIMO.de with 10m or so of twinlead copper ended
with a balun 4:1 and coax.

If I were you, I would remove this 4:1 balun and solder the coax
direct to the twinlead. I would then use good coax right to the
radio.

The reason is: the impedance at the solder point is not 300 ohms and
with your balun, you're inserting more losses .

73, de Stef

Stef wrote:
If I were you, I would remove this 4:1 balun and solder the coax
direct to the twinlead. I would then use good coax right to the
radio.

The reason is: the impedance at the solder point is not 300 ohms and
with your balun, you're inserting more losses .

True, but without a balun, one is introducing common mode effects.
I, personally, would use a 1:1 choke at the balanced to unbalanced
connection point.
--
73, Cecil http://www.qsl.net/w5dxp



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The reason is: the impedance at the solder point is not 300 ohms and
with your balun, you're inserting more losses .

True, but without a balun, one is introducing common mode effects.
I, personally, would use a 1:1 choke at the balanced to unbalanced
connection point.

There sure is RFI coming from the coax . I should try it. I'll
disconnect my coax and try 10 turns of coax as a balun. I'll know for
sure. Or would the "bead baluns" be better ?

Stef wrote:
There sure is RFI coming from the coax . I should try it. I'll
disconnect my coax and try 10 turns of coax as a balun. I'll know for
sure. Or would the "bead baluns" be better ?

Bead baluns would be better but cost more. One could virtually
eliminate common-mode currents with $1000 of bead baluns. :-)

A good engineering rule of thumb is to install a balun whenever
the transmission line changes from unbalanced to balanced.
--
73, Cecil http://www.qsl.net/w5dxp



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Cec, do you own shares in Fairite or Amidon? ;o)

All the enquirer needs to do is buy an HF-grade ferrite ring, about 1.5" or
2" in diameter at a car-boot sale, and wind on about 8 distributed turns of
18 or 20 gauge twin, clear-plastic, stranded, speaker wire.

Insert this choke balun at the junction of the coax and the balanced
feedline. If it is outdoors dunk it in some water-repelling goo.

For multi-band working make the coax as short as possible and make the
balanced feedline long enough for the whole to extend from the antenna to
the tuner, with perhaps a little extra.
----
Reg.