G1HBE

Better than Nothing.

 

 

 

 

 

 

I use this loop antenna to listen on all HF bands up to 30 MHz, and I reckon it has been one of my best buys so far. MSF on 60KHz absolutely romps in and it has extremely good noise rejection properties. Just as well, because around here the wide-band 'hash' is over S9 all day and night if I use the vertical on receive. On the loop, the daytime noise is around S1 to S2. I've mounted the loop on a Maplin rotator so I can null out troublesome noises, and if I use my QRM eliminator as well things get pretty good. My homebrew topband rig has separate RX and TX sockets, so there's no fancy switching to be done. If you think one of these might be the answer to your problems, it's the Wellbrook ALA1530. It's just over one metre in diameter and comes with its own PSU and interface box.

 

I've gone into full-on mode about this antenna further down the page.

 

 

 

 

 

 

 

 

  

After trying many recievers and scanners over the years, I've finally(?) settled on this, the AOR AR5000. It's a beautifully designed piece of clobber and it does everything I ask of it without fuss. It covers 15KHz to 2600MHz in all modes and any step size from 1Hz to 500KHz. IF bandwidths are 3, 6,15, 30, 110 and 220 KHz  This is one of the few scanners that has genuinely good SW performance. 

 

 

 

 

 

 

 

 


Below is the new version of the QRM eliminator. The signal from the receive loop goes straight to a resistive combiner which feeds the output socket. The signal from the auxilliary antenna (a bit of wire) also goes to the combiner, but first it gets the following treatment: Tuning (green knob) - this peaks up the noise, and also allows a variable amount of phase shift to be applied. The noise signal is then split into 0 degrees and 180 degrees and these two are applied to opposite ends of the 'amplitude/reverse' pot (yellow). When this control is half way, the signals cancel and no noise signal gets through. Turning the knob one way increases the 'phase' signal, and the other way increases the 'antiphase' signal.  Then it's into the combiner to add or subtract from the main signal.  

 

 

 

 

 

 


 

 

 

 You can't have too many scanners. I bought the Icom IC-R5 a few years ago to replace a previous model that was falling apart. It's a great little receiver that is well-built and sturdy. Coverage is 150KHz to 1310MHz in AM/FM/WFM modes and a selection of step sizes. It doesn't have a numerical keyboard, instead dividing its coverage into several bands which are selected with the 'band' button. From there, the rotary tuning control is whizzed until the wanted frequency arrives. Very easy indeed once you get used to it.The Uniden 72 is er...different. Everything about it is cheap - low-quality plastics, fragile build quality etc, and it looks like something Fisher-Price might flog. However, it has a great feature called 'Close Call', which is a kind of combined frequency counter and automatic tuning device. What you do is this: lurk in a furtive and shady manner near the establishment you wish to listen to and press the 'go' button. The 72 then looks at the entire band and as soon as it finds a signal it says 'FOUND!' and a quick press of the hold button reveals the frequency.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(updated June 2009)

This compact, noise-busting antenna may be the answer to our polluted bands.

When I got my Amateur licence in 1984, noise simply wasn't a problem. Although my 'class B' status limited my transmissions to 144 MHz and above, I had been a keen SWL for many years, and one of my favourite bands was 160 metres (1810 to 2000 KHz), often referred to as 'Topband'. Even listening on a random wire, noise levels were rarely enough to lift the s-meter, except for the dreaded TV timebase noise which popped up every 15 KHz across the band.
Today, things are much worse. Almost every home has a PC, a set-top box or two, any number of mobile phone chargers and much else besides. Most of these are powered by switch-mode power units which are meant to conform to rigorous EMC standards but usually don't, and the interference from these can be conducted along the mains wiring and radiated far and wide. Noise from TV sets can be very efficiently radiated from the aerial lead and in tightly-packed modern housing estates there is very little to be done about it. If you get on well with your neighbours you may be able to fit a braid-breaking filter to their TV coax and this can work wonders (it certainly did in my case) but there are now so many sources of interference that our influence is limited.

 

Antennas

The problem is that end-fed wires are by their very nature open to electrostatic noise fields, and the unbalanced currents caused by their reliance on the local earth are guaranteed to cause problems at the receiver. Dipoles are better because they are balanced and - in theory at least - do not include earth currents, but a dipole has to be made for one band only and its balance is only useful within that band. At all other frequencies it can be just as bad as the random wire.
Is there a way around this? Well, loop antennas can be useful. Because they consist of a closed loop, they pick up very little of the electric field associated with local noise sources, instead working on the magnetic component.
Most amateur-constructed loops are of the single-turn, tuned 'magnetic' type which can be used for transmitting, but short wave listeners and MW DX'ers prefer the multi-turn frame aerial. Even when used in the shack, these can drastically reduce the noise levels commonly found on our bands these days. However, these antennas need to be resonant on the frequency of interest and keeping them on-tune as you trawl the bands can be a pain, and almost impossible if you want to site the loop away from the house.

 

Enter the broadband loop

This is where the Wellbrook ALA1530 comes in. It is an aluminium, single-turn loop slightly more than 1m in diameter with a small cylindical junction box at the bottom. In this box is a carefully-designed amplifier with a shaped frequency response, designed to compensate for the falling response at low frequencies which is inherent in small loop design. The amplifier has a wide dynamic range to guard against overload and the input is balanced to ensure the loop can not act as a simple wire aerial.
As with other loops the 1530 is directional, displaying a strong, bi-directional 'figure of eight' pattern with sharp nulls from the axis of the loop. This feature works most effectively at low frequencies, and is very useful for MW DX'ing when one station is being hidden by another from a different direction.

 

 

 

 

 

Installation
 
The loop is untuned, so there are no tuning controls and this means it can be mounted at the far end of the garden or high up a wall, like mine in the photograph. I decided it would be useful to be able to rotate the loop to null out unwanted signals, so I bought a cheap-as-chips rotator from Maplin.  Connection is via a BNC socket, which I carefully wrapped in self-amalgamating tape to keep out the Manchester rain. At the other end of the coax, another BNC connects to the interface unit which injects the 12 volt supply into the coax and takes the signals out to your receiver. Wellbrook supply a mounting flange which attaches to the underside of the loop junction box, but I thought this was a bit fragile for the kind of weather we get here on the side of the Pennines. Instead, I mounted the loop on a piece of 40mm wastepipe which supports the top of the loop and prevents it from putting too much strain on the amplifier box.

 

 

 

 

 

 

 

Performance

The proof of the pudding is in the eating, and even after owning this antenna for years I still find myself amazed by its noise-busting properties. When I first got the Wellbrook, I used it in the shack and was immediately impressed by the way it rejected the hash that I was receiving on my conventional antennas. To null some noise sources, I had to wedge the loop into crazy falling-over angles to point the null at the source, but it certainly worked.  I managed like this for several months before finally deciding to move it to a more remote location.
On the 160m Amateur band, any attempt to receive on my 35ft vertical is greeted with S8 of white noise.  Take a look at the spectrum analyser shot (plot 1) to see what I mean.  There's a big lump of noise all across the band, and it's only by switching over to the Wellbrook that we can see that there is a signal present (plot 2). Note how the noise has been almost completely banished.

 

 

Above: Plot 1

 

Above: Plot 2

 


Wellbrook have a website at
www.wellbrook.uk.com and if you'd like to hear how delighted Topband fan Barry G0BDE is, take a listen to the audio file in which he switches between his wire antenna and the loop during a QSO. It's in the reviews section, but you can go directly to  www.wellbrook.uk.com/G0BDE/ and listen if you wish.

It's a similar story at the VLF end of the spectrum. The standard time and frequency transmission from MSF on 60KHz is nowhere to be seen on a 30 foot random wire, but there's plenty of noise! Switching over to the loop reduces the noise and gives a clean, strong signal.
I don't do a lot of MW DX'ing these days, as once you've heard one 'Magic 1152' you've heard them all! However I sometimes get the urge, especially at dusk when it can be quite interesting to hear the more distant local radio stations coming up, and being able to null out unwanted locals is very useful indeed.
One thing that really amazed me was when I discovered quite by accident that I could transmit on my topband vertical while listening to MW stations on the loop without any problem. This is indeed astonishing, as the two antennas are only a few feet apart!
At higher frequencies the loop tends to lose its directional properties to a certain extent, but it still seems very good at rejecting local hash. I've spent hours tuning the higher bands comparing signal levels versus signal to noise ratios, and although signals tend to be a bit stronger on my wire antennas than on the loop, there is always far less noise and better readabilty from the Wellbrook. At lower frequencies (up to about 7 MHz) the loop is a clear winner every time.

 

 


 

Conclusion

No antenna is perfect, but for those of us who live in properties with little space to spare or who are plagued with noise, the Wellbrook ALA1530 is a Godsend. It is compact and easy to mount on the end of a house, and it will even work well indoors. The noise-busting qualities of this antenna are quite amazing, and if you've been suffering for years with local hash and crackle, I'm sure the Wellbrook will bring a smile back to your face. I'm not sure it would be suitable for the serious HF bands enthusiast, as it becomes more omni-directional and less 'lively' at the top end, but for those of us who like to dig around in the basement it is a marvellous piece of kit. If you are worried about squeezing it through that tiny opening into the loft, Wellbrook has already thought about you - they make a '1530P' which has a flexible polythene loop element.
I paid £120 for my 'original version' ALA1530 several years ago, but the price is now £159 for the latest improved type. Highly recommended.

 

 

 

 

 

 

 

 

 

 

 




A new ferrite antenna!



As a low-band enthusiast, I enjoy listening around MW and the low HF bands. At home, this is easily done with the Wellbrook Loop Antenna, but on holiday it's a bit more awkward. Tuned loop or 'frame' antennas will work well, but to be effective they need to be of a fair size and they have a habit of getting in the way, falling over etc. I have a home-made 9-inch 'holiday loop, but its small size limits its performance.
Ferrite rod aerials work well for their size, but the one in your radio is about as good as it gets....until now.

What I needed was a small, easily portable antenna with pots of gain, and I wanted it to work without any need of mains or battery power.  Step forward  Graham Maynard. His website is full of interesting stuff, but it was his Spin-field ferrite sleeve antenna' that caught my eye. 

Like myself, Graham has for many years been experimenting with standard ferrite rods, but the problem has always been that they are still rather 'deaf' compared to a decent-sized air-loop. Common sense says a bigger, fatter rod would pick up more signal, but it seems that both myself and Graham had found that the improvement was small. 
 I have a fair collection of rods and two of them are pretty hefty, but every time I've tried to press them into service as 'super-rods', the results have been decidedly average.  
No defeatism at Graham's workshop though, for he decided to get to the bottom of the mystery.
The theory proposed on Graham's website is long and involved, but at its most basic it says (I think) that the alternating radio frequency fields set up in the rod are confined mainly to the surface of the ferrite, and that further inside is an 'anti-field' which works against and partially cancels the signal we are trying to receive. A standard rod does not develop much of this destructive field, but a big fat one does, and it is this action which causes the poor performance. What he needed was a large-diameter ferrite rod with a hollow centre, so that there was nowhere for the anti-field to develop.

After reading of his experiments, I decided to have a go myself.
 I ordered 40 rods at just 40 pence each from Rapid Electronics and while I waited for them to come I searched my shack for a suitable former.  I found two sturdy cardboard tubes, one with an outside diameter of 110mm, the other 140mm, and when placed one inside the other the space between them looked just big enough for the rods to sit in. The wall thickness of these tubes was 4mm, so the outside tube would provide the necessary spacing that Graham recommends.
A couple of days later the rods arrived (none of them broken!) and I wasted no time in beginning the construction of my own version of the 40-rod Spin-field antenna.






In the end I managed to fit 39 rods snugly around the inner cardboard tube. The bigger tube was then carefully slid over the rods, and 20 turns of standard hook-up wire were wound around the outside. Again, a standard 300+300pf tuning cap was connected across the ends. The pictures tell the story.

















 
 
 
 




 
 
 
 
 
 To get the analyser plot above I added a single-turn coupling winding to plug into the analyser.  I used our local Gold station as a signal source. These are the results I got:

Wellbrook(outdoor, broadband):  -37dBm
39 rod Ferrite Sleeve (tuned):  -40dBm
9 inch holiday loop(tuned)  -55dBm
Single rod(tuned)  -59dBm

 
 
As expected, the Wellbrook comes out on top. After all, it is one metre across and has an amplifier built in. In a close second place is the 39 rod spin-field antenna. My old holiday loop is in third place and the standard rod brings up the rear.
The spectrum analyser screenshot above shows the comparison of the 39 rod spin-field against a standard rod. You can also see the high 'Q' of the antenna in the shape of the noise floor, which increases sharply within just a few KHz on each side of the station






In August we spent a very pleasant week on the Norfolk coast, and of course this was the ideal opportunity to test the new aerial. Luckily the noise in the rear garden was quite low, and I found that MW stations which were very weak and unreadable on the portable radio without the spin-field antenna came up to entertainment quality as soon as the antenna was brought anywhere near the radio. 
Results on Topband (160m) were equally impressive, and I was able to listen with ease to our Manchester-based evening net on 1963 KHz.
 


 
 
 
 
 
 
 What are we to make of this seemingly amazing aerial? I'm certainly impressed, even though I don't fully understand quite what's going on inside it! It is compact at just 140mm in diameter, but with all that ferrite it is a bit heavy. Graham's theory about destructive fields makes sense, but is it correct? Why not see what you think by taking a look at his website   http://www.zen22142.zen.co.uk/Media/fsi.htm   and if you fancy a go at building a spin-field antenna, you can find Rapid Electronics at 
http://www.rapidonline.com/.
I'd like to thank Graham for his interest in my ferrite-fuelled adventure and for giving me permission to write this article about his work.