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Old 13th May 2017, 2:37 pm   #1
bill knox
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Default Shortwave aerial

Hi

I have posted several threads on this site and enjoy the site immensely.
This next enquiry is slightly different in that I want to purchase an aerial suitable for shortwave, at the moment I have a piece of wire slung around the garage (my workshop) but I get so much interference from the fluorescent lights that most times I have to turn them off.

I am also under threat of DEATH (from my wife) if I put anything like a long wire aerial up, so what I need is something compact.

What I have seen on several web sites is an "Spectrum Compact Active Antenna" this covers up to 30Mhz which is as high as I want to go.

Has anyone had dealings with this or similar aerials at all
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Old 13th May 2017, 2:54 pm   #2
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Default Re: Shortwave aerial

Lots of info on active antennas on this web site.
http://www.g8jnj.net/activeantennas.htm

I have used an AA and found it ok but you need to get the antenna part as far from the interference as possible.

No experience of the Spectrum Compact but the web site should give you an idea of what to look for in one.
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Old 13th May 2017, 2:55 pm   #3
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Default Re: Shortwave aerial

What do you want to listen to on SW? What frequencies are you interested in?

Anything indoor is going to pick up RFI from mains wiring, lighting, digiboxes etc. You can run a longwire along a garden fence or up a tree if you need to hide it.
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Old 13th May 2017, 3:42 pm   #4
bill knox
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Default Re: Shortwave aerial

We do not have any trees in our garden or in our next door neighbours gardens.

My garage is my workshop in the front of our house.

I did look at a long wire aerial but I got an impression that type of aerial is approx. 60ft long, and that is longer that the width of our house, plus it would have had to be mounted very close to the house and while I would not be transmitting (I am not a radio amateur) I thought that the adjacent wall would take a lot of signal away

Bill
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Old 13th May 2017, 3:47 pm   #5
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Default Re: Shortwave aerial

There is no fixed length. Attaching it to the side of the house is far from ideal but much better than using an amplified indoor aerial.

If you have access to the loft you can run the wire around the roof joists and rafters.
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Old 13th May 2017, 4:05 pm   #6
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Default Re: Shortwave aerial

Another idea is run the wire under the gutter, if the gutter is plastic. There is no ideal solution, you may have to try a few different installations.

You may also find that using some type of matching system from the aerial to the receiver can help.
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Old 13th May 2017, 4:19 pm   #7
bill knox
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Default Re: Shortwave aerial

Hi Paul

Excuse my questions, aerials were not my strong point

I have been looking at a long wire aerial that could possibly go in my loft
(Windom Off Centre Fed Dipole ocf Dipole 4-1 Balun )

The aerial impedance is 2000 Ohms and the balun brings that down to 50 Ohms so that coax can be connected, would that balun match the aerials 2000 Ohms to 50 Ohms across 3 Mhz to 30 Mhz and if not would I need an ATU.

Regards

Bill
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Old 13th May 2017, 4:47 pm   #8
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Default Re: Shortwave aerial

This question comes up from time to time, after many aerials (some good some bad) I have plumped on a Wellbrook loop such as the http://www.wellbrook.uk.com/ALA1530LN-1 for my receive antenna. Their performance is superb and as it capable of being located away from the house (a bit of co-ax is all you need) local noise is much reduced. To placate SHMBO I painted mine with Halfords camouflage paint.

I have been more than pleased with my loop for many years, they are a bit pricey but that is a one off cost. They are also 50 ohms which makes matching very easy!

If you want it a bit cheaper Wellbook sell the amplifiers as spares, make your own loop and power "injector".

Usual disclaimer, I am merrily a (very happy) customer of Wellbook.
 
Old 13th May 2017, 5:10 pm   #9
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Default Re: Shortwave aerial

Are you looking to buy something complete off the shelf or do you want to construct something?

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Old 13th May 2017, 5:49 pm   #10
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Default Re: Shortwave aerial

In general, balanced antennae such as centre-fed dipoles and loops offer the best immunity from nearby interference.

You haven't said what you want to receive. If it's just anything and everything, you hit the problem that most antennae exhibit resonances and their impedance changes wildly with frequency. A simple transformer might match one impedance to 50 Ohms. Usually for reception, accurate matching isn't needed. Active antennae are one way out of the quandary for reception only. There are designs for active antenna boxes with an amplifier inside and two elements sticking out opposite sides like a short dipole. The Wellbrook is a loop variant with a reputation for both working well and its high price. There have been numerous designs in magazines.

Even with active antennae, balanced designs and loops help with interference.

Wire antennae can be made virtually invisible with fine wire.

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Old 14th May 2017, 12:21 am   #11
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Default Re: Shortwave aerial

The length of a wire aerial is not critical for short wave listening. However, when you consider that the short wave spectrum stretches from about 2MHz to 30MHz, were you to build a resonant half wave aerial for 2Mhz you would need to run a length of wire of around 264 feet whereas at 30MHz only 16 feet of wire is required for a half wave aerial. Thus in practice most aerials that are used across a spread of shortwave frequencies, even by transmitting amateurs to whom resonance is very important, are a compromise.

Fortunately, for listening purposes at least, a random length of wire (in the bad old days this was often 30-50 feet or so) coupled to the receiver via tuning unit - a relatively easy home construction project - will give adequate results - or at least used to before all the all the electrical noise pollution that has come with the digital age. For those locations where a pole at the end of the garden was not possible a wire running around the loft was next best but these days will pick up mains-borne interference radiated from the house wiring and will be only feet from ceiling mounted low energy light bulbs which are a prime source of electrical noise.

Thus today it is more important to site the aerial from the source of noise and in practice that means as far away from houses as is practical. A discreet loaded and remotely tuned vertical at the bottom of the garden could be one answer or running a length of wire along the garden fence and, again, using a tuner to bring it to resonance. Another possibility is a helical vertical aerial wound around a length of plastic tube such as a length of electrical conduit. The helical provides a means of getting a reasonable electrical length of wire out whilst remaining physically short and offers the possibility of temporary installation only when you want to listen - mounting it on a fence post for example.

The other solution is to use a compact magnetic loop aerial such as the Wellbrook loop. These magnetic loops are physically small and can be installed near ground level and have the added advantage of good noise cancelling properties. The Wellbrook loops have a good reputation though the down-side is that they are not cheap to buy and as they are directional are best controlled with a rotator which adds to the expense.
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Old 14th May 2017, 7:36 am   #12
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Default Re: Shortwave aerial

I've sent you a PM Bill.

Jim
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Old 14th May 2017, 8:17 am   #13
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Default Re: Shortwave aerial

I echo the comments and advice here.

Wellbrook's are great, and "Long" wires can be near invisible, depending on colour and gauge. Insulated copper wire ratted from old transformers can be put to use, but subject to breakage due wind and if it gets snagged by something. Run across the wall of a house it's pretty safe though.

You might google "stealth antennas".

One local (to you in the U.K.) site with good info:

http://www.g4ilo.com/stealth.html
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Old 16th May 2017, 12:09 pm   #14
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Default Re: Shortwave aerial

Anyone with constructional abilities might like to consider building the excellent loop antenna design by Gary Tempest which featured in the BVWS Autumn 2016 edition. Early in 2016 Gary had mentioned to me his intention to research, develop and construct an amplified magnetic loop aerial, and kept me informed of how things were progressing. I was keen to build one as soon as Gary had finalised and tested his design, and was delighted and surprised when – at the 2016 NVCF - he presented me with a completed amplifier to evaluate at my location near Hull, East Yorkshire.

When in my workshop - a 10ft x 8 ft wooden shed - I always have a restored radio from my collection to listen to. So that the radios in my collection get a regular ‘airing’ rather than just gathering dust on shelves, I alternate them each month or so. Most of my radios need an external aerial, though some have a plate aerial – usually foil applied to the rear of the back panel, or a wire threaded through a few holes in the panel. Good enough for strong local stations, but not for much else. For reception, the aerial that I'd relied on was a 20 Metre length of wire attached to a 2 Metre high garden fence, which had produced adequate, though not exceptional results. (wouldn't make much difference if it was 10 Metres up in the air - that's only a twentieth of a wavelength above ground on 200 Metres).

Where the loop aerial scores of course is not only does it not need a large garden, it doesn't even need to be outdoors - it could be in a spare bedroom say, hidden behind curtains. I guess that compactness is a key selling point of commercially made (highly priced!) magnetic loop aerials, but the ‘GNT Loop’ can be built for a fraction of the cost, and from my experience, with a marked improvement over a wire aerial.

A convenient location for the loop for me was on the outside end wall of the workshop, where a 2 Metre square loop of 15mm copper tube would just fit, mounted on plastic stand-off clips. The coax lead from the amplifier to the radio and power supply is about 5 Metres, but if need be, could be much longer with no loss of performance, and I believe that Gary has tested the amplifier with 50 Metres of coax with no discernable loss of signal strength. (Rather like TV masthead amplifiers, the coax is used to provide DC power to the amplifier at the loop, and to send the amplified signal down the coax to the radio).

Prior to having the loop, I'd assumed that my wire aerial gave reasonable reception of such stations as are transmitting these days, and to an extent, I’d fallen for what seems to be a common perception - 'there isn't much to listen to these days on MW and SW' and on L.W. there’s only really Radio 4’. The magnetic loop has been revelation. The first thing I noted when unplugging the wire aerial and plugging in the loop was the almost complete absence of background noise - what's often called 'static'. Secondly, stations that are inaudible or weak on the wire aerial become loud and clear on the loop. One is an Irish station which I’d thought it was Radio Eireann, but that closed down in 2015 on LW. In fact it appears to be RTÉ Radio - a division of the Irish national broadcasting organization Raidió Teilifís Éireann, which broadcasts on 252 KHZ. It was inaudible on my wire aerial, but is loud and clear on the loop. Its ERP is 300kW during daytime and 100kW at night time. BBC Radio 4 on 198KHz is audible on the wire aerial, but signal strength is far greater on the loop.

There are two French stations on LW, but I've yet to hear any station I.D, and on a broadcast radio the dial settings aren't really accurate enough to be sure of the transmitting frequencies. However, I note that 'France Inter' broadcasts on 162 KHz from Allouis with 2 megawatts. The French broadcasting service has called itself RTL for many years and still broadcasts on 234 kHz long wave using the Beidweiler Longwave Transmitter, so I guess that will be the other station. Both are barely audible on my wire aerial but excellent on the loop.

On Medium Wave I logged some 18 UK stations at good signal strength. Scores of UK stations use MW, but of course many are 'local' community broadcasters using low power. On Short Wave, later in the evenings, many stations were received on the magnetic loop on all the short-wave broadcast bands - 49, 31, 25, 19 & 16M. Quite a lot of Asian music, and on 25M, a broadcast in Cantonese, but of course, we've no idea where the stations are broadcasting from – quite possibly relay stations located in Europe. Also, there were lots of Eastern European sounding stations - some Russian maybe? Others were from Europe, including the Netherlands, and Scandinavia.

In contrast, on the wire aerial many of those stations were either very weak, with high background noise, or were inaudible, down in the noise. Most domestic radios are hampered on short waves due to the lack of bandspread, but my Ekco A22 has a rudimentary slow motion drive which helps to separate the stations. I’ve had the opportunity to try several of the domestic radios in my collection to compare and contrast the performance of the magnetic loop with that of my wire aerial. In addition to the Ekco A22, these include an HMV ‘1122’, Pilot ‘754’, and a Murphy A167M.

Using the magnetic loop has made listening much more pleasurable, and will, I’m sure, repay the effort in building one. I’m indebted to Gary for having saved me the trouble, but I was so enthused by the performance that I've set about making another for use indoors. Gary's neat 'Manhattan style' means that no printed circuit board is needed, but I've designed and made one and have built it, though have yet to test it.

For anyone who isn't a BVWS member, I'm sure that the BVWS will be able to supply back issues of the Autumn 2016 magazine. I don't want to infringe copyright, but with Gary's permission I've attached a few pics which might encourage anyone who may wish to consider building the excellent amplified magnetic loop aerial.

The first pic is of Gary's circuit, which uses five 2N5109 transistors. The second is of the neat 'Manhattan style' circuit board, using a sheet of copper clad board, with small 'tiles' of PCB material (the little grey squares) glued on to act as component mounting pads, obviating the need for a PCB. The third pic - the gable end of my workshop photographed from my neighbour's side of the garden fence, shows how unobtrusive the aerial is. The amplifier can be seen mounted in the centre at the top of a 2 metre square 'loop' of 15mm diam copper tube on stand-off brackets. The fourth pic is a sketch of how my workshop and aerials are orientated. The last pic is of a PCB I've designed and built, almost identical to Gary's 'Manhattan style' board. It's ready for testing and if it works anything like as well as Gary's, I'll be highly chuffed.

All in all, an excellent home-brew project which won't break the bank!

Don't know if anyone on here has built one, but if not, I hope a few might be inspired to do so.
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Old 19th May 2017, 6:47 pm   #15
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Default Re: Shortwave aerial

Hello.
I too have one of Gary Tempest' Loop Antennas on the outside wall of my workshop, just like David has. Before this I had a 40 metre length of wire 4 metres high but was never happy with the reception I was getting. Then Gary sent me one of his loop Antenna. Well, from that day on the reception on my radios was out of this world - no more hissing and no more interference on the radio stations. Best of all on my RCA-AR88D-AR88Lf, MW/LW/SW have no background noise and I can receive more stations.
I never realised the aerial I had could be bettered, but boy was I wrong! It just goes to show you are never too old to learn.
A big thank you to Gary for all the work he has done.

Regards Kevin
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Old 21st May 2017, 6:48 pm   #16
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Default Re: Shortwave aerial

Pleased to hear that your experiences accord with mine Kevin.

I should perhaps say that when Gary researched and designed this broadband Amplified Loop Antenna, he already owned a Wellbrook, and can't tell any discernable difference in performance between the two, yet Gary's version costs only a fraction of the cost of a Wellbrook. I don't say that to 'knock' the Wellbrook in any way - it's an off-the-shelf plug & play device for those who aren't into home-brew, as few seem to be these days, and owners speak very highly of them. (In the same vein, radio amateur buy G5RV antennas and other simple wire antennas off the shelf, with which they're delighted, rather than to make their own. For the most part, we live in a time-poor/cash rich-society).

Worth reiterating that though my own loop is sited only 5 Metres from where the radio position is in the workshop, Gary tested it with up to 50 Metres of coax from the loop to the operating position, with no loss of DC voltage from the PSU up the coax to the amp, and no attenuation of the signal from the loop to the set.
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Old 27th May 2017, 2:30 pm   #17
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Default Re: Shortwave aerial

David,

An excellent write up of a clearly succesful project. I assume that there is a deep null along the axis of the loop. This could be used to advantage if the antenna was rotatable (presumably rotating the workshop is not an option!).
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Old 28th May 2017, 12:56 pm   #18
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Hi All, I fully endorse the use of a magnetic loop. I first tried a tuned version using a model servo driving a 2 gang cap. It worked well but the tuning was fiddly so I tried a simple 2 transistor untuned loop using 2 BF199s. I actually built 2 on the basis that they would be quite directional, I was going to set them up at rt angles to each other and switch between them. After tests I found that they didn,t give a sharp peak but gave a very narrow null. The pre amp used was a 2 transistor version of the Gary Tempest design. Later I bought a Wellbrook and mounted it on a rotator in the loft. It confirmed the broad peak/narrow null I found with the 2 transistor design. All the tests I did was with various loops mounted in a loft about 5 Mtrs above ground. The loops used with the 2tx design were about the same diameter as the Wellbrook loop, about 1.1Mtrs, made of 3mm copper wire. I cant find out what Wellbrook use for their loop, It appears to be an alloy tube but one report says it is filled with ferrite type material. My main listening is 7Mhz 40 Mtrs and general HF, 4 to 12 Mhz My final thoughts, I,ve tried voltage probe types and various very high impedance input pre amp with short whips but none have the interference rejecting properties of a loop. My home made loops work very well but none as good as a Wellbrook.


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Old 28th May 2017, 4:50 pm   #19
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Quote:
It appears to be an alloy tube but one report says it is filled with ferrite type material
Not heavy enough (mine isn't) it is just a tube.
 
Old 28th May 2017, 5:07 pm   #20
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Default Re: Shortwave aerial

They could fill a metallic tube with ferrite or any other material and it shouldn't make any effect.

The subject of antennae has been well-infused with all sorts of strange beliefs (and in some cases the very highest purity of snake oil) for over a hundred years. Sorting out what works and what doesn't, what to believe and what not can be quite a challenge.

There are broadband active antennae where a broadband amplifier lives at the centre of a dipole or at a gap in a loop, or at the base of a monopole element. Some of these work well. Then there are tuned versions of the above where variable capacitances or inductances are used to resonate the structure, These can be a bit better, but at the cost of convenience.

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