In message K3X2k.2824$lE3.246@trnddc05, Dale Parfitt
writes

"Andy" wrote in message
...
I have just put up an 80 Meter End Fed Flexweave wire. Its about 63 feet
long and fed direct with 50 Ohm coax at the far end of the garden. The
shield is connected straight down to a ground earth stake at this point and
it is tuned for 3.700 MHz. It receives better than any thing I have used so
far, but it is very death on 40 meters. Almost unusable.

Is there a reason for this?

The antenna is only up at 20 feet and my old G5RV is only 6 feet off the
ground at the moment and receives far better on 40 meters than the End Fed
wire.

73 Andy
Yes there is- it's a half wave long on 40M which implies voltage feed and a
VSWR in the 60--80:1 range.

Dale W4OP


The question is, what are the consequences of having such a high SWR? It
all depends on how much attenuation the coax has. If the coax was
lossless, there would be no signal loss, regardless of the SWR.

For many years, I have been an advocate of this 'far-end feed' type of
antenna. Its great advantage is that it greatly reduces the amount of
local interference it receives (and creates). Also, all the essential RF
grounding is at the far end. You don't need an RF ground in the shack.
The shack is RF-dead.

Ideally, you would use a tuning/matching unit at the antenna feedpoint
but, provided your coax has adequately low loss, you can get away with
having the tuning unit at the shack end of the coax. It's surprising how
well this works - especially on the lower frequency amateur bands.

For reception only, it might be worth while considering fitting a
matching transformer at the antenna feedpoint. These typically have an
impedance ratio of 9:1. The essential purpose is to prevent extremes of
impedance mismatch between the antenna and the coax. Below, I have
appended some information from 'RHF', one of the contributors to the
rec.radio.shortwave newsgroup. Note that these devices are NOT baluns!

My present antenna is about twice the size of that described. It's about
120 foot inverted-L, at around 25 feet. The coax length is about 90
foot. I can tune it up from 160 to 10m. It certainly seems lively enough
up to 20m.

As I said, you do need really good low-loss coax. CATV trunk cable is
pretty good, if you can lay your hands on some. Don't worry about it
being 75 ohms.

Depending on frequency, you are going to get quite a variety of weird
impedances at the shack end of the coax. What you get will be whatever
the feed impedance of the antenna is, but transformed by the length of
the coax, and influenced by its attenuation. In the example of the
Flexweave wire, the antenna is around a halfwave long, so the impedance
is very high. However, the coax will be (guessing) 40 foot long, which,
allowing for a velocity factor of 0.6, will also be a halfwave at 40m.
The impedance at the shack end will therefore be very high, which may
not suit the receiver. You will certainly need a matching unit to
transmit.

Finally, having used the 'tuner-in-the-shack' method for around 30
years, in my old age I am considering investing in one of the automatic
remote tuning units (such as the SG-230). However, one slight
disadvantage is that, in order to work, they need to be fed with RF, so
are not suitable for SWL-use only.

-------------------------------------------------------------------------
------------
From 'RHF' in rec.radio.shortwave (29 March 2008)

Some people as a result of the coining of the Word "Balun"
[Bal-Un] for Balanced-to-Unbalance Matching Transformer :
Also like to use the Word "Unun" [Un-Un] for the Unbalance-
to-Unbalanced Matching Transformer.

"Balun" a specific Contraction becoming an inclusive Buzz Word
relegated to commonly misused technical Jargon.
http://en.wikipedia.org/wiki/Balun

Most of these Matching Transformers used between Single Wire
Antenna Elements and Coax Cable are 'not' Baluns but Ununs
since the Match-up an Unbalanced Antenna Element with an
Unbalanced Coax Calbe feed-in-line.

Many Manufactures have come-up with Trade Marked Names
for these Products like :

* Magnetic Longwire Balun (MLB)
-by- RF Systems
http://www.rf-systems.nl/pdf/mlbm.pdf

* Magnetic Longwire Balun(MLB-1)
-by- Palomar Enginers
http://www.palomar-engineers.com/MLB-1/mlb-1.html

* Long Wire Antenna Adapter (LWA) LWA-0130
-by- WinRadio
http://www.winradio.com/home/lwa.htm

* Longwire Balun 9:1 Transformer
-by- LowBander
http://cgi.ebay.com/_W0QQitemZ180227972387

* Universal Magnetic Balun (UMB)
-by- Wellbrook
http://www.wellbrook.uk.com/longwire.html
+ UMB and Antenna Feed-in-Line Isolation
http://www.wellbrook.uk.com/UMB.html

* Longwire Impedance Matcher (LIM)
http://www.angelfire.com/mb/amandx/lim.html
http://www.shortwavestore.com/pdf/lo...ce-matcher.pdf

READ - Magnetic Longwire Balun - Not Really a Balun
http://www.hard-core-dx.com/nordicdx...d/magbal2.html
From : John Doty )
Date : August 24, 1995
Original Source : UseNet's Rec.Radio.Shortwave

READ - Magnetic Longwire Balun - A Con or Not ?
http://www.hard-core-dx.com/nordicdx...d/magbal1.html
-hosted by- Hard Core DX .Com

READ - The Verdict {One Man's Opinion} :
The Magnetic Longwire Balun Is Too Expensive
http://www.hard-core-dx.com/nordicdx.../magbalun.html
-by- Alan Johnson

READ - About the MLB "Magnetic Longwire Balun" - How To !
http://users.belgacom.net/hamradio/s...ire%20Balun_ML
B.htm
-by- Guy Roels [ON6MU]