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Old 3rd May 2019, 5:53 pm   #1
David G4EBT
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Default Clone of 'Wellgood' Magnetic Loop Receiving Aerial

At the outset, let me stress that I’m indebted to the efforts of Gary Tempest and Dr George Smart G1GEO in the considerable amount of experiementation, research and construction of magnetic loop receiving aerials, for which I claim no credit in this thread. I'm just a guy with practical skills who cobbles stuff together, inspired by other people’s clever ideas!

In June 2017 I started a thread entitled ‘Magnetic Loop Receiving Aerial (Gary Tempest)’ - a 5-transistor design by Gary Tempest, published in Autumn 2016 BVWS Bulletin. I stated that I was the lucky recipient of one of a small batch that Gary had made for evaluation prior to the article being published. I said how impressed I'd been with it in terms of very low background noise, and the level of amplification. (Stations that are down in the noise and inaudible on my 60ft wire aerial come in loud and clear on the loop).

Gary had devised a neat 'Manhattan style' circuit board for the loop amp which obviated the need to etch a PCB. He used double-sided PCB sheet and cut small 'tiles' of PCB (approx 3mm square) which he stuck to the PCB sheet, to which to solder the leads of the components. ‘Manhattan’ technique is widely used for homebrew construction.

I was so impressed with the performance of the aerial, which I’d sited on the gable end of my outdoor workshop, (the 'loop' consisting of a square with 2 Metre sides, with the amplifier unit sited at the centre top), that I decided to build one myself for use indoors, for which I designed a PCB based on Gary's proven 'Manhattan style' layout. I built my PCB version of the amp which worked very well, though admittedly for a one-off loop amp there’s little merit in etching and drilling a PCB over and above Gary's Manhattan style board. However, for say a club project or where several are to be made, a PCB wins, and reduces the prospect of errors.

Here’s the original thread (now closed):

https://www.vintage-radio.net/forum/...t=Loop+Antenna

That thread had 174 posts and more than 17,600 views, so there might be interest in further developments.

Gary continued his experiments, discovering that Dr George Smart, M1GEO, had accidentally transmitted into his WellBrook ALA1530 Loop and killed it. George had been very impressed with the Wellbrook so decided to see if he could repair or replicate the amplifier. A friend of George’s, Dave G7UVW, who works in an X-ray lab, was able to X-ray the amp (encased in potting compound) to assess the feasibility of replicating it. From the X-ray images it was apparent that the amp was made on Veroboard, with several capacitors, ferrite transformers, and two transistors, identified as being ZTX327.

From his‘teardown’ of the Wellbrook, George Smart designed a ‘clone’ amplifier built on a neat compact PCB rather than stripboard. He named it the ‘Wellgood’ and outlined his ‘teardown’ of the Wellbrook in detail and the subsequent design that he developed. The circuit, full constructional details, including winding the two small binocular ferrite transformers, even the bill of parts with RS part numbers is on his website and I believe he is also able to supply PCBs, so for anyone who wished to build a ‘Wellgood’ with the minimum of hassle, head on over to Geoge’s website. Here’s the link:

https://www.george-smart.co.uk/projects/wellgood_loop/

In the Spring 2018 BVWS Bulletin a five-page well-illustrated article by Gary Tempest was published entitled 'Magnetic Loop Aerials Part 2'. In that article, Gary referred to the Wellbrook, and the 'Wellgood' and had designed and produced a two-transistor loop amp along similar lines. As with his Autumn 2016 five-transistor design, Gary devised a Manhattan style PCB. Details of both designs were posted by Gary at this link:

https://golbornevintageradio.co.uk/f...d.php?tid=5944

As with his earlier design, Gary housed his PCB in a 90mm x 90mm plastic box type IP55, EN82322, which is excellent and costs just £1.57 inc VAT from CPC:

https://cpc.farnell.com/eterna/220-l...p55/dp/EN82322

The design of ‘power feed box’ for the amp was covered in the first article and is housed in a plastic box type EN83938 which presently costs £2.05 inc VAT:

https://cpc.farnell.com/spelsberg/31...p55/dp/EN83938

The plug-top power supply used to provide a regulated 12V dc output at up to 500mA with no minimum load and carries full safety approval. Short circuit and over current protection are integral: It is available from CPC/Farnell and is described as: ‘12V 500mA 6W UK Plug Top Power Supply, 2.5mm, Level 6 - SW4381-C’. At the time of writing, this PSU costs £5.34 inc VAT:

https://cpc.farnell.com/powerpax/sw4...wer%20supplies

As with his five-transistor design, Gary used 2N5109 transistors rather than the ZTX237s used in the Wellbrook/Wellgood. As I’d been so impressed with Gary’s original design, I decided to build the two-transistor version to see how it compares. As before, I designed a PCB for it, based on Gary’s 'Manhattan' layout. David – ‘Radio Wrangler’ - had kindly gifted me several premium grade Motorola 2N3866 devices. All with gold legs, all marked with "4-247" which is the shortened version of the HP part number 1854-0247 so I decided to use those. (On George Smart’s site there is debate and discussion about the merits of various alternative transistors).

I’ve now built my PCB version of what might be termed a ‘Wellgood’ clone, which itself is a clone of the Wellbrook, and I’m pleased to say that it works very well, with no discernible difference in performance from the 5-transistor version. This comparison is subjective as I have neither the knowledge nor the equipment to do any objective testing. I guess the real test of how such homebrew designs perform would be alongside a Wellbrook at the same location and time.

There are four units which comprise the complete project, namely:

1) An off the-shelf regulated short circuit/over voltage protected plug-top 12V 500mA power supply.
2) The ‘power box’ which sends DC to the remote loop amp and carries the amplified signal back to the radio.
3) The amplifier box which is mounted on the loop.
4) The ‘loop’ element.

In this-post I’ll give details of the magnetic loop amp itself, and in another post, details of the 15mm copper tube loop that I constructed and how I fitted the amp and mounted the loop. In the next post, Ill cover the construction of the Power Feed box and the loop element.

Pics:
1: Circuit of the ‘Wellgood Loop’ revised to use 2N3866 transistors. (Gary didn’t fit C9 & C13, neither did I).
2: Gary Tempest’s ‘Manhattan’ style PCB layout and my PCB component layout on similar lines.
3:PCB UV masks – two positive, two negative.
4: Etched PCB.
5: Completed board.

More to follow in another post.
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Old 3rd May 2019, 6:09 pm   #2
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Default Re: Clone of 'Wellgood' Magnetic Loop Receiving Aerial

Part 2.

Construction of the loop amplifier:

I etched drilled and tinned the PCB, spacing the holes to suit the components I used. I wound the two ‘binocular’ ferrite cores (‘T1’ & ‘T2’) using 28SWG solderable copper wire as shown in the diagrams at the links to Gary’s article and George Smart’s website. I secured the cores to the PCB with a blob of UHU adhesive. When fitting the 2N3866 transistors I made sure that the legs were long enough to accommodate a ferrite bead on the base connection. I fitted heatsinks to the two 2N3866 transistors.

Construction of the power feed box:

This functions in a similar manner to a mast-head TV amplifier, in that the coax feed from the power supply to the amplifier carries DC to power the amp and conveys the amplified RF signal from the aerial to the receiver. The 1mH RF choke is mounted on the underside of the lid with two solder tags. The heads of the mounting screws can be used to monitor the approximate current being drawn by the amplifier. The resistance of the choke is 1 Ohm, so if a voltmeter is placed across the screw-head test points and the Voltage drop across the choke in say 0.1V, we know from Ohm’s law that 0.1Amp (100 mA) is flowing, which is about what we’d expect.

Construction of the 1 Metre diameter copper tube loop and mounting of the amplifier:

The ‘loop’ of my five-transistor amp consists of 15mm copper tube in a square with 2 Metre sides, fitted to the gable end of my wooden workshop. As the Wellbrook uses an aluminium loop 1 Metre in diameter using 20mm diameter tube, I considered making a loop from 22mm copper tube as I have a 22mm bending spring, but I didn’t fancy forking out £15.00 for a 3M length of 22mm copper tube as I had two pieces of 15mm two metres long to hand. The only advantage of 22mm tube would be that it would be more robust, but 15mm copper tube is quite robust enough.

I made a simple bending jig from scrap chipboard and T&G offcuts then annealed the copper tube by heating it to cherry red with a propane blowlamp then allowing it to cool down. (The tube would have bent without annealing, but during bending it ‘work hardens’ making any slight adjustments to the shape a bit tricky). I bent two halves of the loop, pulling the bending spring through the tube with an attached steel wire a stage at a time to ensure that it was supported by the spring along its length as the bending progressed.

I joined the two halves of the loop at the top with an end-feed soldered coupling and at the bottom end, with an acetal rod insulator that I turned to shape on my lathe. I used a piece of scrap 12mm thick white plastic chopping board on which to mount the amp and the loop, along with ‘U’ bolts to attach the loop to a 28mm diam mast. The loop is secured with two 15mm plastic pipe clips at the top and bottom as shown in the picture below. Low density polyethylene chopping boards can be cheaply bought from catering equipment suppliers. For example, 12mm thick x 300mm (12”) x 450mm (18”) £5.99 +VAT at the time of writing:

https://www.nisbets.co.uk/hygiplas-s...ing-board/j252

The connections to the copper loop were via soldered tags secured with self-tapping screws into the copper tube and acetal insulator. Once assembled, set up and tested, the connections can be waterproofed with self-amalgamating tape. (Anyone who feels disinclined to bend a loop of copper tube could of course use eight 45 degree end-feed ‘elbows’ to make an octagonal copper tube loop).

Setting up and testing:

This is best done before fitting the completed PCB in the plastic box. Set RV1 on the PCB to midway and check the supply current. If it’s around 100mA, that’s a good sign, but if it’s low - say 25mA - the circuit is in oscillation and Gary advises that the secondary wires of T1 will need to be reversed. With the circuit stable, RV1 is adjusted so that both transistors pass roughly the same current. With a current meter in the power lead, when balanced by adjusting RV1, the least current will be drawn. (In my case, 95mA).

My own amp worked right away with no complications.

Pics:

1: Power box circuit and layout.
2: Measuring the current drawn at the power box.
3: Copper tube bending jig with the bending spring removed.
4: Acetal insulator on the lathe.
5: Amp box mounted to the loop.

In a further post I'll add some notes about the performance of the loop amp.
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Old 3rd May 2019, 6:34 pm   #3
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Default Re: Clone of 'Wellgood' Magnetic Loop Receiving Aerial

Performance of the loop amp:

I don’t have a communications receiver, so I used a restored Ferranti 045 domestic radio for reception tests. It has long, medium and short wave-bands, and a magic eye tuning indicator. As a benchmark for comparison, I used my 60ft horizontal end fed wire aerial. As with the earlier 5-transistor loop amp, the 2-transistor loop amp (which I guess could be termed a ‘Wellgood clone’) is far superior to my wire aerial, both in terms of very low background noise and higher signal strength.

As an example, the first magic eye display below shows RTE Radio 1 from Ireland on 252 kHz Long Wave weakly received on the wire aerial, and the second pic in on the 2-transistor amplified loop at excellent listening volume.

On MW, lots of ‘local’ radio stations (not ‘local’ to me) could be heard at good strength. For example, BBC Radio Wales, which broadcast throughout Wales on 657kHz (north east Wales), 1125kHz (Llandrindod Wells area) and 882kHz for the rest of Wales. The station wasn't audible on my wire aerial. Likewise, Radio Caroline on 648 kHz (463 metres) MW serving Suffolk and North Essex with just 1 kW, comes in loud and clear here near Hull on the loop amp but is barely audible and down in the noise on my wire aerial. (For comparison with Radio Caroline, Radio Five Live from Droitwich on 693 kHz is 150 kW with a much more impressive aerial).

On the short-wave broadcast bands, little could be heard on my 60 ft wire, but on the loop, several foreign language stations could be heard, and Radio China in English, but I don’t know where the transmitter is located or what power is used. The loop has a null and can be rotated for best signal strength. At my location, broadside on, SW/NE is a good compromise.

The loop can be positioned at a considerable distance from the radio and the power box. Gary Tempest has tested his with 50 Metres of coax with no discernible loss of signal strength. The loop can be used indoors or outdoors, would fit on the balcony of an apartment, or even in a loft space, where insulated wire could be used as the ‘loop’ element rather than tubing.

From my own experiences in evaluating the performance of magnetic loop aerials compared to a 60 ft end fed wire aerial, the loop is incomparably superior and I’m now even more ‘sold’ on magnetic loop amps.

More pics:

1: upper mounting support for loop.
2 Completed loop.
3: Sketch of the complete loop layout
4: RTE Radio 1 (252 kHz) magic eye display on 60 ft wire aerial.
5: RTE Radio 1 magic eye display on Loop amp.

Due to time constraints I’m unable to etch PCBs for others, but anyone who doesn’t have PCB facilities and would like to build the amp might wish to consider Gary Tempest’s ‘Manhattan' style board, or for greater simplicity, get in touch with Dr George Smart M1GEO to see if he is able to supply his own ‘Wellgood’ PCB.


I hope this thread is of interest.
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Old 3rd May 2019, 7:07 pm   #4
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Default Re: Clone of 'Wellgood' Magnetic Loop Receiving Aerial

Thanks for that info David. I started construction of a pucker "Wellgood" a while ago (using one of George's PCB's and the Motorola transistors kindly supplied by Graham) but got sidetracked with problems on my VCM.

George's board provides a 'fairly compact' layout and originally was intended for use with the physically smaller 2N2222 transistors, so the larger transistors are a slight squeeze. The transformers are wound and mounted and there are just a few components to add to the main board and the DC/RF filter to assemble.

I'll ask my Production Manager if this can be pushed up the priorities list .

B
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Old 3rd May 2019, 8:36 pm   #5
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Default Re: Clone of 'Wellgood' Magnetic Loop Receiving Aerial

Thanks for reading the thread Bazz.

Yes, the 2N3866s are quite a bit larger physically compared to 2N2222 where compactness is called for, and 2N2222s at typically 18p apiece from UK suppliers have price in their favour. (or a penny each on a slow boat from China. Hmmmm!). Thanks to the kindness of David, 'Radio Wrangler' my top spec 2N3866s were even cheaper than that!

Every good wish with the 'Wellgood'!
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Old 3rd May 2019, 9:26 pm   #6
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Default Re: Clone of 'Wellgood' Magnetic Loop Receiving Aerial

I think that somewhere on George's Wellgood site someone compares the performance of the 2N2222 and the 3866 in that circuit and found the latter to be the better transistor.

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Old 3rd May 2019, 10:20 pm   #7
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Default Re: Clone of 'Wellgood' Magnetic Loop Receiving Aerial

The 2N2222 was designed as a switching transistor. Nonlinearity wasn't too important, but saturation voltage was. So some things in the processing are slewed this way.

2N3866 was aimed at the CATV market where low intermod between many simultaneously present signals is the name of the game. This is a closer fit to what comes from a broadband antenna.

2N5109 may also be a good possibility.

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Old 3rd May 2019, 11:32 pm   #8
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Default Re: Clone of 'Wellgood' Magnetic Loop Receiving Aerial

If you recall a thread on Loop antennas a couple of years ago David, it became apparent that a few people had bought (online) some "RCA 5109's" which proved to have gains of about 40, and were very suspect. So, at that time, the Motorola 3866 became the favoured device.

David (EBT), I want to use mine on 5MHz. If you've got a local friend who could lend you an Rx that would cover that, I'd love to know what results you get .

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Old 4th May 2019, 2:29 am   #9
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Default Re: Clone of 'Wellgood' Magnetic Loop Receiving Aerial

I've got part way through this thread, will get back to it later, but very interesting, thankyou David.

Just one query - what is the function of the 1N4007 after R2 (2k)?
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Old 4th May 2019, 5:14 am   #10
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Default Re: Clone of 'Wellgood' Magnetic Loop Receiving Aerial

Dunno. It's reverse-biassed but it won't work as reverse polarity protection because of the path to the collectors via the output transformer comes off before R2.

1N4007 and the other higher voltage ones of the 1N400x family are terribly slow and make great sources of RFI if used as rectifiers. OK as DC bias diodes, but then there's no need for high voltage ratings, so they are parts best avoided as there are better choices for all other applications. Internally, they are PIN diodes. and can be useful as cheap RF PIN switches!

The effort to keep the DC supply current out of the output transformer secondary is curious. It really only transfers any saturation issues to that choke which carries the DC and bridges the RF output anyway. There's room for a bit of simplification, I think.

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Old 4th May 2019, 10:18 am   #11
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Default Re: Clone of 'Wellgood' Magnetic Loop Receiving Aerial

A few comments on the responses.

Re the 1N4007, it wasn't on George Smart's circuit, Gary added it stating in his Spring 2018 BVWS Bulletin article: 'I added my customary diode to protect against reverse voltage - unlikely but it has happened, usually when bench testing'. (Though it is on Gary's circuit, it wasn't in fact on his Manhattan layout and has no bearing on the performance of the amp). Gary's circuit is below.

As to the choice of transistor, though the Wellbrook featured ZTX237s and they're shown on the circuit at George Smart's website, for Q1 & Q2 George states: "ZTX327 (original, obsolescent). PN2222 my preferred replacement. Others have used 2N3866, ZTX653 & MPSH10".

https://www.george-smart.co.uk/projects/wellgood_loop/

Gary used 2N5109s, and I used the 2N3866s kindly donated by David, Radio Wrangler. I tested them on a Peak Atlas DCA55. (A Maplin bargain basement £22.00 impulse buy). The Hfe ranged from 165 - 190, and I chose two with similar gain. Gary felt that C8 & C10 provided adequate decoupling so didn't fit C9 & C13, and nor did I, though they're on the circuit.

Incidentally, with heat sinks fitted the transistor temperatures stabilised at 45 degrees C (113 F) , so I guess they'd get considerably hotter without heat sinks.

In both Gary's BVWS Bulletin article and on George Smart's website, there is discussion and debate about the attributes of various transistors. For the technically minded (which excludes me!), there's a link on Georges' site to an IEEE paper explaining the original design and theory of operation for the loop entitled 'Distortion Improvement of Lossless Feedback Amplifiers Using Augmentation':

https://www.george-smart.co.uk/wordp...2/MWSCAS99.pdf

Well worth reading George's write-up, and Gary's 5-page article from Spring 2018 BVWS Bulletin at post #11 at this link:

https://golbornevintageradio.co.uk/f...id=5944&page=2

As I said at the outset, my skills - such as they are - are largely practical, not theoretical.

A lot of thought must have gone into the design by Wellgood, and by George in developing the transformers T1 & T2. Having successfully built a Wellgood clone based on Gary's experiences and been very pleased with the results, I added the thread to maybe help anyone who might wish to build a 'Wellgood' clone and to make a loop to go with the amplifier, to give a few pointers as to the practicalities.

I know how much better it performs compared to a 60ft end-fed wire aerial. It would be interesting to know how the Wellgood performs compared to a Wellbrook (built on a piece of stripboard encased in potting compound after all).
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Old 4th May 2019, 10:33 am   #12
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Default Re: Clone of 'Wellgood' Magnetic Loop Receiving Aerial

Quote:
Originally Posted by Bazz4CQJ View Post

David (EBT), I want to use mine on 5MHz. If you've got a local friend who could lend you an Rx that would cover that, I'd love to know what results you get .

B
I'm not in touch with any radio amateurs or SWLs these days - I lost interest 15 years ago.

Gary used an HMV650 radio with a magic eye and likewise, the Ferranti '045' domestic radio I used had a magic eye. Better than nothing, but not as good as an S Meter or being able to check the S/N ratio. All I can say is that very little on the short-wave band was audible on the 60ft end fed wire, but on the loop, the background noise was far lower, and quite a lot of stations were listenable. (5 MHz is towards the lower end of the HF spectrum. The Wellbrook on which the Wellgood is based, was designed to work well up to 30MHz. ).

Also, of course, a loop is far easier to accommodate, is portable and rotatable so wins on those scores too.

You'll have to crack on and build yours Baz!
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Old 4th May 2019, 11:26 am   #13
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Default Re: Clone of 'Wellgood' Magnetic Loop Receiving Aerial

Regarding the 1N4001 diode, and other aspects, Gary have been in touch with me and has stated that the diode is drawn the wrong side of the 2K2 resistor R2. In his actual layout it was mounted where it might be useful! I've circled the diode on Gary's 'Manhattan' board below.

He also states that there is a significant gain reduction when running with long lengths of coax.

In his Part 2 article there are 'eye' tube pictures indicating the drop.

Used with short lengths of coax, as I'm doing, Gary makes the point that some receivers may not have good enough AVC to cope. He adds that if the Loop & Amp mounted in the loft, or somewhere in the house, most likely will still pick up interference, certainly my indoor loop does using the basic 2 transistor version, with a 3m length of coax. But performance is good enough if he turns off the PC and Wi-Fi in the room. The least interference is likely to be experienced with the Loop & Amp remote from powered buildings using modern electronic devices, which makes sense.

Much depends on individual circumstances - not everyone has the luxury of a garden!

In the Part 2 BVWS Spring 2018 Bulletin article Gary was surprised that his 4 transistor version of the Amp had better performance at 15 to 17mHz to the WellG. Whether this is true at the 5mHz that Bazz is interested he doesn't know, but he'll see what he can receive there one evening and compare it to the WellBrook (He doesn't have a WellG at the moment). The 4 transistor Amp was just Gary's earlier 5 transistor design with the current tail removed and replaced with resistors, and the transistor base stabilising resistors removed.

Hope that clarifies a few points.
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