Hi Barry -
If I had another hand I would give you three thumbs up for that. Since I
don't I'll just give you two. I agree that too many people get too worked up
over too little things. Just try to use relatively low loss line and a tuner
if you need it. I realize that if you throw away a db here and an half a db
there it can become significant. But, for a given piece of equipment, you
will meet a point of diminishing returns when you try to get ever last
fraction of a db out of it.
Gene / W2LU
----- Original Message -----
From: "Barry Kirkwood" <barry.kirkwood@gmail.com>
To: <towertalk@contesting.com>
Sent: Wednesday, February 02, 2011 9:59 PM
Subject: [TowerTalk] Musing on G5RVs, baluns et al......
> Greetings from Chiangmai
> where every prospect pleases.
>
> Been following the thread started by the gentleman asking about feeding
> his
> G5RV (or variant thereof).
>
> The humble G5RV antenna was invented not long after WWII by the
> multitalented Louis Varney (SK), intended as a cheap and cheerful compact
> all hf band antenna. In those days the hf bands were 10, 20, 40 and 80m.
> The
> 15m band had not yet been opened to the amateur service and the WARC bands
> were not even a gleam in the radio amateur's eye.
>
> Basically a dipole (or inverted V) of some 100 ft length (the UK had yet
> to
> be metricated) centre fed with a balanced feeder of around 33 ft and
> thence
> by 75 ohm coax of length sufficient to reach the transmitter.
>
> If the thing was unravelled it approximated a dipole of 80ft per side. The
> magic 80 ft length gave an impedance at the coax junction that was not 75
> ohms with zero reactance, but a value of R +jx which was not too horrible
> on
> most of bands.
>
> So with a bit of luck and the wind in the right direction the coax could
> be
> connected to the transmitter of the day which like as not was home built
> and
> had the final tank coil link coupled to the antenna, or if one of the new
> fangled pi couplers was intended to cope with a range of R+jx that a
> modern
> all singing all dancing solid state transceiver would refuse to deal with
> except via an ATU.
>
> Once a generation of amateurs who had happily used open wire feeders and
> who
> gave not a damn about SWR had gone to the great ham shack in the sky, or
> converted to txs in tin boxes that had coax connectors on the output,
> things
> changed.
>
> Low SWR became all the rage. Gentlemen even wrote learned articles
> reporting
> studies where G5RV like dipoles had their dimensions tweaked in an
> endeavour
> to get something like 50 ohms non reactive at the feedpoint. 15m was
> always
> a problem but, hey, the thing had never been meant to work on 15.
>
> Bit like the search for the Philosopher's Stone or the Lost Ark.
>
> Seems like this tradition is alive and well today right here on Tower
> Talk.
>
> My advice:
>
> Relax!
>
> Build the G5RV to a reasonable approximation of the original design. If
> you
> want a balun wind say 10 turns of the coax around a 100mm/ 4 inch plastic
> pipe before hooking it on to the bottom of the balanced line. Back in the
> shack , see what you get. If necessary use an ATU to get the antenna to
> suck
> power.
>
> Then enjoy amateur radio. Chances are you will be pleasantly surprised by
> the performance of this modest antenna.
>
> 73 es gl
>
> Barry ZL1DD
>
>
> --
> Barry Kirkwood PhD ZL1DD
> barry.kirkwood@gmail.com
> NZ: 021 160 8999
> Thailand 081 235 1556
> _______________________________________________
>
>
>
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