Glenn....
Great write up!! I think what you did with the antenna is part of
what this hobby is all about...getting your hands dirty trying to improve
something or to build something...that is why it continues to be fun to me
after some 52 active years. Congrats on trying different things until you
got an improvement that you wanted.
One of the 'unknown' things about wire antennas and finding 'great'
antennas from experimentation is the surrounding area where you do the
experimenting. In other words, what works great at one QTH will not
necessarily work great at the next location! Due to many factors. The
so-called big time DX'ers refer it as "Location, Location, and Location" !
I urge you to at least read the first nine pages of this paper by
Walter Maxwell, that Cliff just brought to our attention. The URL is:
http://www.arrl.org/members-only/tis/info/pdf/Reflect.pdf
Just print the first nine pages and read it carefully (I've read it seven
times now and at least some of it is beginning to sink in!!). Almost all
arguments about antenna/transmission lines are eventually solved by reading
Mr. Maxwell's paper "Another Look At Reflections".
Good luck with your modified G5RV and keep playing...!
73,
Tom/W4BQF
-----Original Message-----
From: Wa4aos@aol.com [mailto:Wa4aos@aol.com]
Sent: Tuesday, October 22, 2002 1:34 PM
To: kc8aon@juno.com; qrp-l@Lehigh.EDU; tentec@contesting.com
Subject: [TenTec] Re: G5RV
Hi,
If you search around the Internet, you will see much has been written about
the G5RV and much of what has been written is in strict contrast to what
others have written. For what it's worth, I will explain an observation that
I have made based on someone else's G5RV after his exaustive
experimentation.
Most G5RV's that I have listened to have only fair performance. They often
seem to be several S units below an appropriate dipole cut for a given band.
I have used them for Field Day and as a Non-DX antenna, they work fine but I
hardly ever seem to be top gun when trying to work an AL, HI, NE, SD, ND or
WY from SC. Many others seem to snag those contacts before I finally get to
them and it's even worse on SSB.
I was not very impressed with the antenna until A friend who does lots of
antenna testing did the following changes to the G5RV and now the antenna
works MUCH BETTER ! ! !
1) Pull the center up to around 40 feet. A tree branch or 4, 10 foot
sections
of TV Mast works great.
2) Fan out the two 51' segments and 34' ft feedline in such a way that all 3
legs are 120 degrees apart. This happens to also be a great way to guy a 40
foot mast. Just run a length of nylon rope on the feedline side to act as a
messanger ans to take the stress off of the 300 ohm feed line and coax. Use
tape or tiewraps to secure the feed line to the nylon rope. The 120 degree
spacing seems to be part of the antennas improvement in performance.
3) Get the 3 ends as high as possible with the ends at least 20' or higher
above ground.
4) Use 300 ohm ladder line for the 34' run and attach it to a 50 or 75 ohm
good quality coax. The 300 Ohm Line should be a better impedance match than
450 ohm line. We found 75 ohm Coax to have slightly more bandwidth on 80
meters. Although the entire 80 meter band was below the 2.5 to 1 points
either way.
5) Where the Coax and 300 ohm line come together, seal the coax and install
a
series of clamp on toriods or torriod beads around the coax; use a minimum
of
4. This will keep RF off of the coax and will help minimize RF burns in the
shack. Do not use any other kind of Balun except the Choke type which is
what
the beads do.
7) Check with an ARRL antenna book or Old Handbook and find a Non Resonant
length of coax on all of the bands that you plan to use the G5RV on. As I
recall, 70 foot was one on the lengths that is non resonant. However there
are others. This will improve the efficiency of the antenna.
This arrangement requires no transmatch on 80, 40, 20, 15 or 10 meters in
that the SWR is no greater than 2.5 to one on any of these bands. I know
this
is in contrast to what others have said but try it this way and see for
yourself.
I am not an Antenna Designer nor do I claim to be an expert with the G5RV
but I can say that the above configuration has made a huge improvement in
the
G5RV's performance and before anyone Flames me for any of my comments,
Please
try it this way and see for yourself. I see performance that rivals an 80
meter dipole on 80, On 40 meters the other station will be as much as an S
unit higher close in and DX , over a 40 meter dipole. On 20 meters, WOW !!!
2
S units over a 20 meter dipole anywhere I have used it. 15 and 10 meters
are
also an S unit to 2 S units above comparable Dipoles.
In my opinion, this is the perfect antenna for someone who just wants one
antenna. Apparently the combination of non resonant coax length, 300 ohm
feed
line, toriod beads, height, and spacing of the 3 segments of the G5RV makes
a
significant improvement in this antennas efficiency,
I would be very interested if someone who is a GURU with modeling antennas
could set this arrangement up on the computer and report what if any
improvements this configuration has over a standard G5RV or Dipole. I can
say
that from an imperial approach to antenna configuration this arrangement
works very well and to the point that I was VERY IMPRESSED ! ! !
73,
Glenn WA4AOS
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