Magnetic
Longwire Balun
-- a con or not?
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Gives marvalous
reception in a noisy environment.
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An expensive solution. (Ian Smith)
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Mixed results. (Andrew Clegg)
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Just a con? (Dave Kenny)
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No, it's not a con. (Brian Underdown)
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Works great on lower frequencies.(Wian Sianstian)
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Misleading ads - and a very expensive solution. (Don
Moore)
Question:
Has anyone tried the Magnetic Longwire Balun by RF Systems. Does
it work? Does it work as good as the manufacturer claims?
I have two Longwire antennas both terminated by an RF systems Balun.
One antenna is 75 foot long the other 35 foot long and running in
different directions. The shielded cables from both antennas are
lead to a antenna switch and from there again a shielded cable to
a YAESU FRT7700 antenna tuner. From there a little shielded cable
is running into my Sony SW7600. Yes a SW7600!!
The reception is marvalous in a noisy environment. Only when my
wife switches on the television I have a little noise on some frequencies.
But most of the day and at night everything is quite.
Subject:
Magnetic Longwire Balun - an expensive solution
From: Ian Smith (ian@isis.demon.co.uk)
Date: February 4, 1995
Original source: Usenet's rec.radio.shortwave
Here's another
view.
A matching transformer (and the MLB) mounted outside on the end
of a wire provide, I believe, three features:
1. A ratio dividing the impedance mismatch. (Of course, where
there was a match the ratio will make things worse, but the worst
case will be reduced.)
2. A DC path to earth which reduces (at least) local static noise.
3. A shielded signal feed through the dwelling's noise field.
Since it's difficult to separate these gains, I can't tell you
which gives the biggest benefit. The sum total *is* a distinct
reduction in noise and some signal strength gain compared to the
same wire, sans matcher/co-ax.
I've used a home-brewed matcher based on the suggestion in the
Lowe booklet and the RF Systems MLB. The MLB is just as good as
the home made one and it's weather proof. It's also expensive,
not a balun and I find it hard to believe that it adjusts it's
matching ratio with frequency. I can't say that it doesn't, but
let's say that I'm a sceptic.
I don't know what sort of receiver you use, but if you can hear
signals/RFI without any antenna you could get a better one. I
know boatanchors are a sod to silence because of the ventilation
requirements, but modern solid-state receivers can and should
be totally silent. Even if your receiver is shielded, the power
lead may need attention. If you can't hear signals, but can hear
RFI without any antenna, I'd suggest that the receiver is generating
it's own RFI.
Subject:
Magnetic Longwire Balun - mixed results
From: Andrew Clegg (clegg@funafuti.nrl.navy.mil)
Date: February 3, 1995
Original source: Usenet's rec.radio.shortwave
I have a
little experience with the magnetic balun. I bought a magnetic
longwire balun (I think from Palomar, I'm not sure) that's designed
for coupling a long wire to 50 ohm coax. It claims to cut down
on noise pick up. I have a 40 ft wire connected to the balun,
and then 50 ft of RG-8 coax (I went first class... see below)
leading to my rig (a Yaesu FRG-100). The wire is up about 20 feet
from the ground. I also have a wire about 15' off the ground right
below (parallel to the first wire), and that one is connected
directly to RG-58 coax (no balun), and the shield of the RG-58
is connected to a 4' radio shack ground rod. My observations are:
(1) The antenna with the magnetic balun picks up more noise
from my computer than the one without the balun. The computer
is just a few feet from my radio, so it's the coax that's picking
up the noise. I thought this was exactly the problem the balun
is supposed to cure!
(2) On the other hand, the signal strengths received with the
balun antenna are substantially higher than the non-balun
antenna. E.g., a signal that is 20 dB over S9 on the non-balun
antenna is 40 dB or so over S9 with the balun antenna. Is this
due to the balun or the fact that the balun antenna is 5 feet
higher than the non-balun antenna? I don't know.
(3) I tried grounding the shield of the RG-8 coax to the ground
rod, jus like for the non-balun antenna. It did not seem to affect
noise pick-up one way or the other.
So, the results are mixed! I'd be interested in hearing anybody
else's experiences.
About the coax... RG-8 vs RG-58. I bought the MFJ antenna analyzer
(handy thing to have!). I used the analyzer to measure the attenuation
of the two types of coax, both 50' long. I found that neither
coax had significant attenuation of 30 MHz signals across the
entire 50'. Attenuation at lower frequencies will be even less.
So, if you need coax in reasonable lengths, may I suggest not
wasting your money like I did on RG-8? Another benefit of RG-58
is that it's softer and more flexible. When I hook my RG-8 up
to a small antenna matcher unit, I can't get the unit to sit straight
because the darn stiff coax likes to torque it into a particular
position.
Subject:
Magnetic Longwire Balun - just a con?
From: Dave Kenny, UK
Date: February 4, 1995
Original source: Usenet's rec.radio.shortwave
I have come
to the conclusion that magnetic long wire baluns may be just a
con, at least the one I bought from Barton Communications here
in the UK (19.95 pounds as advertised in Shortwave Magazine etc)
did not appear to work and I ended up returning it for a refund.
I tested it on several diffrerent receivers and aerials, but inserting
the balun always resulted in a LOSS of signal of between 6 and
20dB...
Subject:
Magnetic Longwire Balun - it's not a con
From: Brian Underdown, Lowe Electronics (brian@g7lij.demon.co.uk)
Date: February 5, 1995
Original source: Usenet's rec.radio.shortwave
One point
I always make about RF Systems MLB is that it shows good performance
across VLF/LF/SW range for recieving. Prior to using a MLB our
antenna system for recievers was a dipole fed into a a.t.u(global
at1000). That particular system was poor below 3 MHz; of interest
to us was the ability to recieve 132.5 kHz fax station in Europe,
and very rarely was it able to recieve reliably.
Some may say, why not use a wire design for the vlf/lf? No point
when this product produces good results without the need of extra
add ons. Using the MLB, this proved to be more effective and still
able to produce acceptable performance across range up to 30 MHz.
It's not a con, otherwise I would have something like a 100 returned
used MLB's if this was the case.
Subject:
Magnetic Longwire Balun works great
From: Wian Sianstian (sti11368@stud.hg.hanze.nl)
Date: February 5, 1995
Original source: Usenet's rec.radio.shortwave
Dave Kenny
wrote: I have come to the conclusion that magnetic long wire baluns
may be just a con.
Hmm, that surprises me. I have been using the (original) RF-Systems
MLB for quite a while now, and I am quite pleased with it. The
coaxial inlead does help to conquer a lot of the locally generated
computer hash.
More important, however, is that it shows a consistent improvement
in reception on the lower frequencies, when compared to connecting
the same aerial to the high impedance antenna connector on my
Lowe HF-225.
On frequencies above 6 MHz or so, the improvement is not so obvious,
but the advantage of having a coaxial inlead remains there.
BTW, I should point out again that I use the original RF-Systems
MLB (a Dutch product :), and that I don't trust the other MLB's.
I just don't think they are able to make goods of the same quality
RF-Systems' products have, also because the expertise RF-Systems
has built up over the years.
Subject:
Magnetic Longwire Balun - very unfairly priced
From: Don Moore (MOORE@ACC.MCREST.EDU)
Date: February 18, 1995
Original source: Usenet's rec.radio.shortwave
Following
is a direct quote from the article in the 1994-95 edition of Fine
Tuning's PROCEEDINGS. The article is "Impedance Matching Devices
for Simple Wire Antennas" and it is by John Bryant and Bill Bowers.
I do not have the technical background to explain this anymore
myself, however the authors are well-respected for their knowledge
of the technical aspects of the hobby, and I certainly have no
reason to doubt their conclusions. The CAPS are those of the authors,
not me. I have sustituted *asteriks* in place of their underlining.
"...the manufacturer makes the claim (in several places) that
the 'transformation ratio changes with frequency.' At the end
of the tests, the authors cut the Magnetic Balun apart. The housing
is rather cleverly asssembled from a short section of plastic
plumbing pipe and two end caps. Inside the case we found what
appears to be a normal ferrite-based transformer further encapsulated
in plastic 'potting' material. Rather than cutting further, Bill
put the device on his sophisticated test bench. Sure enough, DX
Systems' claim that the 'transformation ratios change with frequency'
is simply NOT TRUE and is, at best, very misleading advertising
and a clear misrepresentation. The manufacturer also states that
this 'balun' provides 'static protection'. This is also not true
in the accepted technical sense of the term since there is no
external grounding stud on the unit. The only path for static
charges to take to ground is down the coaxial shield to the receiver
chasis. You should also note that the parts and material costs
of this device, if purchased RETAIL on the open market, cannot
exceed $6.00, less than 1/10th of the purchase price. Finally
this devise is NOT a balun. The normally accepted definition of
'balun' is a transformer which converts from *bal*anced to *un*balanced
configuration. This unit is an impedance matching device designed
to attach an *un*balanced feed line to an *un*balanced antenna.
Although the foregoing description is harsh, the 'Magnetic Longwire
Balun' is misrepresented by the manufacturer and is VERY unfairly
priced."
PROCEEDINGS is an excellant read if you want to get into some
really intelligent and deep material for serious radio hobbyists.
This is absolutely NOT a beginners' book, however! The 1994-95
edition is $20.50 plus $4.00 shipping to North American addresses
from
Fine Tuning Special Publications
Rt. 5, Box 14
Stillwater, OK 74074
USA
Overseas prices are available upon request.
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