Magnetic Balun or is that magic balun..?

[Copy the Pacman]

A few guys at the radio club swear by these things..

http://cgi.ebay.co.uk/TRANSMITTING-MAGN ... 2558a030d7

I can't see it, 66' of wire, no RF ground, attach your RG58 and see a flat 1.1:1 SWR across HF and 6m...with no atu.

A wire will be resonant somewhere, yes and with an atu perhaps elsewhere as well.

I suggested to one of them that a dummy load presents a nice low swr across the bands, but the dummy load does naff all for an rf o/p signal, to which I was told by the M6 that he's worked all over inc Japan.

I asked him if he had any rf in the shack isues/TVI, answered no.

Am I missing something here, or perhaps I'm smelling a little BS ?

[YB135]

You still need a tuner mate, its just a 9:1 un un at a guess....

[BK]

You can make one yourself
http://www.m0ukd.com/Magnetic_Long_Wire_UnUn/index.php

[Copy the Pacman]

I've already got one connected to 66' of kevlar wire with 1/4 wave counterpoises for 80/40/20, still need the atu.

Maybe I should disconnect the counterpoises..?

[crusty]

A randomwire with an un-un gets progressively more 'end-fire' as the length of wire proportional to the operating frequency gets greater than one wavelength. Worth thinking about before erecting if anyone wants to exploit this behaviour. Some un-un's have ground lugs, but the ground feeder should ideally be kept under 1/4 wavelength at the highest operating frequency. They work well for people who need a low profile antenna.

[EI2KC]

If I might join this discussion I could add to it somewhat. I purchased one of these magnetic baluns earlier this year and put it on a 55-metre W-shaped random wire antenna. It is W-shaped because I have a fairly small garden. I would say that while it does work well in terms of getting me out (Got HS0 on 40m CW in the first week I had it and also recently worked VK6 again on 40m CW) it is noisier on receive than my Butternut vertical. Also, there are RF in the shack issues, no doubt. Sometimes when I transmit on it I get computer errors - my laptop begins to behave erratically. Also it causes the voltage on my W-25AM power supply to fluctuate. This seems to happen more on the lower frequencies (80m and 40m) and sometimes it doesn't happen at all.

[crusty]

Is your UNUN grounded at the feedpoint to a suitable earth?

[EI2KC]

Is your UNUN grounded at the feedpoint to a suitable earth?

No. There is no lug or attachment on it from which to run an earth.

[G0TVJ]

'Magnetic Longwire Balun' is a strange name for these things as they're not magnetic, they're usually used with fairly short wires and they're not really baluns

I bought one of the German Wimo MTFT ones a few years ago and I must admit I'd be lost without it. Decent HF aerials are a no-no for me as my garden is 15 feet long and 11 feet wide. I can stretch to about 23 feet from the rear upstairs wall to the end of the garden over the ground floor extension but the garden rises upwards and the average height above ground of all the wire antennas I've used is probably no more than about 10 feet.

I have tried all sorts of wire antennas over the years, from w- and z-shaped end-feds and doublets to precarious contraptions made from mobile whips. The aerial I keep coming back to is a 9 foot whip on a bracket on the rear upstairs wall with the MLB at the bottom and a 23 foot counterpoise. The counterpoise is a truly random length inasmuch as it just happens to be the distance from the antenna to the shed at the end of the garden.

I can match this antenna on 160m - 6m using both my SGC MAC-200 and LDG AT-897 tuners. Let's not get carried away here - I said I can match it on 160m, not that it was a good antenna on 160m! I made about s3 to a friend around 12 miles away on it, compared to s7 on an antenna designed with 160m in mind - I know I won't be winning any dx awards any time soon but it'll do for local stuff on the lower bands. It works well from 20m upwards, can get contacts on 40m sometimes and is pretty hopeless on 80m.

BUT - it's just a 9ft whip, and that's where the magic of the MLB comes in. In the end a crappy aerial is a crappy aerial and it's not going to fix that but it does at least allow me to easily listen on all bands, and work plenty of stuff on the higher bands, using a very simple, low-profile and low-visibilty antenna. I have tried it with longer lengths of wire and, as you would expect, this greatly improves things on the lower bands but I enjoy seeing what I can do with just the whip.

The MLB is not a magical device and - I can't stress this enough - it will not make a good antenna out of a bad one but if you're really, seriously stuck for space it can make all the difference between getting on the air and enjoying some radio and not getting on the air at all.

Neil

[crusty]

Well put Neil and congrats on experimenting with the unun and making do with what you've got. It's easy to fall into the trap of despondency with limited space for HF antennas, creativity wins the day.

EI2KC, sink an earth rod (or several) below your antenna and use a couple of large crocodile clips to connect an earth wire to the outer of the pl259 plug on the unun, you should find your RF problems go away. Ideally the earth wire should be as short as possible, but I appreciate you may have restrictions on placement. If you're unable to sink an earth rod you may have to get creative, avoid earthing to the mains earth or internal plumbing, however you may find even a bad earth is better than none.

[JOHN,YORK]

The minimum they recommend for earth is a 1 metre rod.Some also say that they prefer to have the 9:1 in the shack and feed the aerial wire through the window,less coax to be used.Another suggestion,earth the ATU in the shack as well as the 9:1 in the garden.

SNOWDONIA RADIO do them for a fair price.
160m-10m 150 watts £16+£3pp.........750 watt version £24+£3pp

NOTE....they must be used with an ATU.

Regards,John.

[EI2KC]

EI2KC, sink an earth rod (or several) below your antenna and use a couple of large crocodile clips to connect an earth wire to the outer of the pl259 plug on the unun, you should find your RF problems go away. Ideally the earth wire should be as short as possible, but I appreciate you may have restrictions on placement. If you're unable to sink an earth rod you may have to get creative, avoid earthing to the mains earth or internal plumbing, however you may find even a bad earth is better than none.

Thanks indeed for the suggestion. As it happens I should be able to put a ground rod directly beneath the balun, which is in the corner of the garden at the wall, and the earth wire will be perhaps three feet but probably less. I will try to do this during the coming week - I am on holidays from work for two weeks.

By the way, I am fairly happy with some of the DX contacts I have made on 40m as well as 15m on the wire. I can't use it on 20m because it blanks out my neighbour's TV. It works okay on 80m too but it tends to be noisy on that band. I don't seem to be able to get much further than the UK on top band, but let's be honest that's a bit of a stretch for most short antennas!