[Antennas] G5RV

[Buck - N4PGW]

The length of the coax should not matter UNLESS it is part of the matching
network.  For example, some antennas require a given length of 75 ohm coax
connected to a random length of 50 ohm coax to make the proper match.  I
don't remember that being part of the G5RV antenna.  

IIRC, in the G5RV, the matching is the twin lead.  The length of the antenna
wire (dipole portion) is designed to resonate on the various ham bands.
However, the impedance varies greatly depending on the frequency.  The
twin-lead helps match the impedance more closely to 50 ohms and, may become
an extension to the radiating elements of the antenna.  The coax should use
a choke balun such as several turns of coax, ferrite beads or a 1:1 balun to
prevent RF from following down the braid of the coax. 

Varying the length of the dipole elements will change the resonant
frequencies of the antenna and may result in a mono-band G5RV or dipole.  

I have been reading a lot about the G5RV antenna.  It was originally
developed as a mono-band 20 meter antenna, but has evolved into various
multi-band antennas with various lengths of dipole and ladder-line or
twin-feed.  There is a variety of theories as to why it matches the various
bands and how much radiates on each frequency, but the length of the dipole
portion and the twin-lead or ladder-line are important to whichever
frequencies of operation any particular version is designed to operate.


Buck
N4PGW



> -----Original Message-----
> From: antennas-bounces at mailman.qth.net [mailto:antennas-
> bounces at mailman.qth.net] On Behalf Of Gene Mason
> Sent: Friday, March 11, 2005 3:48 PM
> To: antennas at mailman.qth.net
> Subject: FW: Re: [Antennas] G5RV
> 
> 
>    Larry   et al,
> 
>        Don't  be  naive, the coax length does matter !  Just think length
>    matters !!!!    and you will never go wrong.
> 
>        In  a perfect antenna in free space, maybe length is not an issue,
>    but I have not seen one of them yet.
> 
>    KZ5V
> 
>    PS I am not an antenna expert just feel better to tell the truth.
>    From: PaulKB8N at aol.com
>    To: laflamme at ncia.net, antennas at mailman.qth.net
>    Subject: Re: [Antennas] G5RV
>    Date: Fri, 11 Mar 2005 11:10:37 EST
>    Larry,
>    The  length  of  the  coax  should  make  no  difference.  The G5RV is
>    nothing  more
>    than  a  shortened  80M  antenna  with  a  twinlead matching stub.  If
>    the  length of
>    coax  affects  the  tuning,  then  it  means  that  you  don't  have a
>    good  match to
>    the  antenna  and  need  to  adjust  either  the  ends or the matching
>    section  to
>    bring down the SWR.
>    Paul, K5AF
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