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

"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

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]

Hi Dale,

Does this only apply to 1/2 wave long end feds only?

Does this apply to any frequency?

The maximum space here is only 66 feet at best.

What options am I left with that would work for 80-40 meters?

I have a question about traps. I read yesterday that traps should not be
tuned to resonance of the wanted frequency. If I constructed a homebrew trap
for say 7.1 MHz.
How far away from this frequency should I tune the trap?

Should it be tuned higher or lower?

I did search the internet, but I could not find any info on whether its best
to setup the trap higher or lower than the wanted frequency and by how much.

Andy




"Dale Parfitt" wrote in message
news:K3X2k.2824$lE3.246@trnddc05...

"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

Ian Jackson wrote:
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.

True, but the value of Z0 of the transmission line has a
large effect. Let's say we are feeding one of those 5000
ohm antennas. The SWR on 50 ohm coax would be 100:1. The
SWR on 450 ohm ladder-line would be 11:1. Even if the coax
had the same matched-line loss as the ladder-line, it would
still be much lossier than the ladder-line - and much more
expensive.
--
73, Cecil http://www.w5dxp.com

Andy wrote:
I have a question about traps. I read yesterday that traps should not be
tuned to resonance of the wanted frequency. If I constructed a homebrew trap
for say 7.1 MHz. How far away from this frequency should I tune the trap?

Should it be tuned higher or lower?

Tune it for lower than the operating frequency to
minimize trap losses. The point to shoot for is
the maximum inductive reactance point which is
at a lower frequency than the parallel resonant
resistance point. How much lower depends upon
the Q of the trap.
--
73, Cecil http://www.w5dxp.com

I have nothing here to measure the Q of the trap.

Is there another way of working out the correct frequency needed for the
trap?

The traps are made from RG58 C/U. I think these are a low Q but I'm not
sure.

Andy


"Cecil Moore" wrote in message
...
Andy wrote:
I have a question about traps. I read yesterday that traps should not be
tuned to resonance of the wanted frequency. If I constructed a homebrew
trap for say 7.1 MHz. How far away from this frequency should I tune the
trap?

Should it be tuned higher or lower?

Tune it for lower than the operating frequency to
minimize trap losses. The point to shoot for is
the maximum inductive reactance point which is
at a lower frequency than the parallel resonant
resistance point. How much lower depends upon
the Q of the trap.
--
73, Cecil http://www.w5dxp.com

In message , Cecil Moore
writes
Ian Jackson wrote:
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.

True, but the value of Z0 of the transmission line has a
large effect. Let's say we are feeding one of those 5000
ohm antennas. The SWR on 50 ohm coax would be 100:1. The
SWR on 450 ohm ladder-line would be 11:1. Even if the coax
had the same matched-line loss as the ladder-line, it would
still be much lossier than the ladder-line - and much more
expensive.

I think that the secret is to make sure that antenna is not exact
multiples of a halfwave. This prevents the SWR being absolutely sky-high
- say, 'only' 20:1, worst case. The proviso is certainly that the coax
should be as lossless as possible. I'm happy to lose 3 or 4dB in the
interests of simplicity and good EMC. It's mainly 160/80/40 which I'm
interested in. There's just a load of foreigners on the higher bands!

Some time ago, I did some (more) Smith Chart guestimation with the
object of trying to find which 'magic' inverted-L antenna lengths would
present 'reasonable' impedances on all (or most) of the amateur bands up
to 30Mhz. [Many years ago, I reckoned that around 185 feet was a good
length.] However, my recent efforts ended in dismal failure. In the
meantime, I will continue in complete ignorance, and use my antenna as
it is, accidentally having the occasional QSO and causing no obvious
interference problems. But, after all these years, I might treat myself
to an automatic tuner for the far end of the coax.
--
Ian

Andy wrote:
I have nothing here to measure the Q of the trap.
Is there another way of working out the correct frequency needed for the
trap?

Sorry, I would just be guessing. I made my 40m traps
resonant on 7.4 MHz and they worked well over the
40m band. But I never made any measurements or A/B
comparisons.

The traps are made from RG58 C/U. I think these are a low Q but I'm not
sure.

The following web page might be of interest:

http://www.seed-solutions.com/gregor...n/CoaxTrap.htm
--
73, Cecil http://www.w5dxp.com

I've given up on this idea for now. I just can't get any ground wires above
or below ground here at present and the couple of earth rods that I have
sunk in just doesn't do the job.

73 Andy


"Cecil Moore" wrote in message
...
Andy wrote:
I have nothing here to measure the Q of the trap.
Is there another way of working out the correct frequency needed for the
trap?

Sorry, I would just be guessing. I made my 40m traps
resonant on 7.4 MHz and they worked well over the
40m band. But I never made any measurements or A/B
comparisons.

The traps are made from RG58 C/U. I think these are a low Q but I'm not
sure.

The following web page might be of interest:

http://www.seed-solutions.com/gregor...n/CoaxTrap.htm
--
73, Cecil http://www.w5dxp.com