I agree with Barry's observations as well. I have worked some decent DX
with less than perfect matches. Worked my first C5 on 80 meters with a 3.5:1
SWR. My only question about the balun was to minimize the radiation from
the coax portion of the feedline. I have gotten some good ideas from this
discussion as to the balun to use.
73s John AA5JG
----- Original Message -----
From: "Gene Fuller" <w2lu@rochester.rr.com>
To: "Barry Kirkwood" <barry.kirkwood@gmail.com>; <towertalk@contesting.com>
Sent: Thursday, February 03, 2011 3:25 AM
Subject: Re: [TowerTalk] Musing on G5RVs, baluns et al......
> 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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>
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