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Old 18th Jun 2017, 4:22 pm   #81
David G4EBT
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

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Originally Posted by Radio Wrangler View Post
A fair amount of luck, I think, David. If you've been buying mostly jellybean parts then there is less profit in faking those so your chances are better.
David
Given that the transistors in question aren't exotic devices - they're just 2N5109s NPNs, as best as I can tell, there are currently three UK ebay listings. The sellers all have 100% good feedback ratings, and to date have had the following trades on ebay: 185,000, 48,700, 37,000. Id be happy with any of those, but for those whod rather steer clear of e-bay, there are other sellers such Mouser, which have them at 2.12 each (1.90 each for ten), plus VAT plus P&P (free shipping on orders above 33.00)

http://www.mouser.co.uk/ProductDetai...XHBK9WNBb9CQ==

From China on e-bay, there are several listings. EG:

Ten for $7.40 post free (146,000 trades 100% feedback), another at $7.40 USD (284 sold, 62,000 trades, 100% feedback), and $0.99 each (40,000 trades, 100% positive feedback). I can't help but think that with such high levels of activity, if these suppliers were passing off any dud devices, they'd soon be exposed. Hopefully, those who you say have passed on fake devices get found out, and though customers may be inconvenienced, will seek and obtain redress through the disputes procedure.

True, if I were putting rockets into space I want absolute assurance that whatever I bought had 100% traceability, but since I'm just an old buffer hobbyist whiling away his twilight years in a garden shed, tinkering away whilst listening to R4 on my loop, I'm content with cheap and cheerful off e-bay. And these days, most stuff seems to arrive via China post within 2 - 3 weeks. (The words 'Gift - value $1.00' readily come to mind!).

Happy days.
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Old 18th Jun 2017, 4:40 pm   #82
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

I'm just a little bit fascinated that classic devices whose primary makers were in the US and stopped making them many years ago are still available in quantities, mostly from China.

If they are real devices, who is actually making them and why? I thought the large turnover markets died off some time ago.

All those 2N3866 came from a lifebuy bought nearly 2 decades ago. If a major manufacturer could find no continuing and acceptable source and they would have tried hard before blowing 100s of kilobucks on a big buy, then what is going on now?

The parts you bought may be perfectly fine, but they do raise some questions.

David
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Old 18th Jun 2017, 6:08 pm   #83
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Hi.

I am about half way through the assembly of the amplifier, it's been too warm today to be in the workshop so I set up a small table in the garden and did the work there whilst enjoying the garden and watching the birds, a sort of alfresco workshop. I have had many years experience assembling projects of one form or another but the Manhattan style is quite fiddly to achieve a neat result. It's important to carefully bend the component lead outs as close as possible to fit the layout of the tiles. I trimmed the leads before soldering. It can be tricky supporting the component during soldering as it's preferable it doesn't move spoiling the appearance/clearances. Again, with practice good results can be achieved. Some of the tiles have quite a few connection points and if I was to make another Manhattan style board then I'd increase the size of these tiles so it's not too cramped.
The Manhattan style construction is a very time consuming process. Cutting and filing the tiles takes some time and if anyone enterprising could supply these ready made then it would save a lot of work. I think the next loop aerial I build will be using David's PCB layout.

Although I have a fair stock of 15mm copper pipe to make the loop, I was considering using say mains 10mm stranded copper wire fitted around a large garden trellis screen. It could be the brown or blue from twin and earth. I think it would need an additional covering over the PVC insulation so that UV doesn't affect it. The bottom of the loop would be around 12 to 15 inches above the ground. Does that sound reasonable or is it preferable to use the copper pipes instead?

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Old 18th Jun 2017, 6:13 pm   #84
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

http://www.qrpme.com/?p=product&id=STX

http://www.qrpme.com/?p=product&id=MES

In use:

https://aa7ee.wordpress.com/2011/07/...-40m-by-n1byt/

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Old 18th Jun 2017, 6:16 pm   #85
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Thanks Lawrence, very interesting.

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Old 18th Jun 2017, 6:41 pm   #86
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Hi Symon.

If you were going to build a loop to transmit with and you were going to resonate it to get the maximum current in it and hence the best radiated signal, copper pipe would matter.
The radiation resistance of a small loop is very low indeed, and the resistance of a few soldered pipe couplings can halve your efficiency.

Receiving MF and HF is different, you don't need that much care to get signals above your amplifier noise floor. terrestrial noise is more significant. Thickish wire will be more than adequate. The source impedance from the loop will be very low and it would be quite a special amplifier to get its front end noise-optimised for that sort of impedance. You don't need to go to that trouble to get satisfactory results. I'd expect amplifiers with grounded-base type input stages to have a bit of advantage.

I've built 'dead bug' prototypes for years without using lilypads much at all. Things were built flying in the air. Power rails mounted on a row of decoupling capacitors. ICs glued upside-down, legs in the air (dead bug!) I keep a stock of 1 meg ohm resistors as standoffs BNC and SMA connectors get soldered facing off board edges. You can get very creative and three-dimensional. It's also not so bad to tear a bit up and start again.

David
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Old 18th Jun 2017, 8:16 pm   #87
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

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If they are real devices, who is actually making them and why? I thought the large turnover markets died off some time ago.
I seem to recall reading somewhere a few years ago that a fab in India(?) was making batches of older semiconductors. They seem to have a knack for making modern copies of old designs using what is now mature technology. For some time parts of their car industry worked in this way.
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Old 18th Jun 2017, 8:18 pm   #88
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

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I'm just a little bit fascinated that classic devices whose primary makers were in the US and stopped making them many years ago are still available in quantities, mostly from China.
Central Semiconductor (USA) based a lot of their business (over the last 35 years or so) on making clones of the classic Motorola RF transistors and selling them to various companies to provide support for legacy products. eg 2N5109, 2N3866 etc etc.

https://www.centralsemi.com/search/s...rchtext=2N3866

So some of these parts will be new parts from Central Semi as they are still making these parts today. However, I'm not sure how much of the process they do themselves. I suspect they buy in the raw materials from fabs around the world and then make the transistors from these materials. But I could be wrong.

As we all know, there will also be copies/fakes available from various companies in Shenzen, China that could turn out to be anything from a hopeless/rebadged fake to something that might work OK.
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Old 19th Jun 2017, 12:43 pm   #89
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

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Radio Wrangler was good enough to send me several of these transistors awhile back.

If anyone wants any for this project I'd be happy to supply them for the cost of the postage.
Hi Graham.

Transistors arrived in Today's post and I'm very pleased with them. They have a decent HFE of around 200 as well. I have more confidence with these than the 2N5109s that I have. I'll put in a donation to the Cornwall Air Ambulance charity as per our PM.

Thanks again, much appreciated.

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Old 22nd Jun 2017, 1:40 pm   #90
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

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Regarding orientation, if I where using a loop for local reception i.e. nonnulled rare stuff I would build two of these and put them at 90 degrees. It would work out much cheaper than my Welbrook and rotator and it (the array) could be rotated electrically, two pots and a bit of ingenuity.

Hindsight, a wonderful thing. Another thought, pot rotation would be instantaneous rather than the lag caused by the rotator (mine takes a second or so for 180, even then it is hard to get a null easily).
I've been experimenting with crossed loops on and off (mainly off) for quite a while. My main aerial is a Wellbrook loop which is excellent at getting rid of 80-90% of the local noise, but there are a few annoying ones that it cannot reduce or null.
A while ago I built a 'phaser-outer' and fed it with noise from a simple active whip which was roughly co-sited with the loop. Again, this worked on some noises, but with others it seemed to be receiving a completely different noise than that from the loop, so obviously no cancellation was possible no matter how I threw reversal switches and twirled knobs. There is one noise (a sharp buzzing sound that I suspect is a plasma TV) that is particularly stubborn.

So I've made a loop to the simple 2-transistor design that crops up in the magazines (very similar the PA1M one) and mounted it on the same stub mast as the Wellbrook, of course at right angles. This feeds the same phasing unit as before.
At last I can cancel the wretched plasma noise! I've also modified the phaser for a selectable second noise input from a basic 'bit of wire' antenna, and this works well on some interferences that the noise loop can't hear!
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Old 22nd Jun 2017, 2:08 pm   #91
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

That's a few bobs worth of aerial, what price good reception though!

Having my loop some 80' from any other houses at the end of the garden has reduced noise considerably. I suppose it's a long way from any mains cables that can re-radiate such things as plasma TVs etc.. It is funny that people are willing to put up a TV aerial or satellite dish but not one for radio. I quite like the process and results.
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Old 22nd Jun 2017, 2:58 pm   #92
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Although the Wellbrook is a bit on the steep side, the noise loop cost almost nothing. There's a 1 plastic hula-hoop and a counduit junction box, but everything else (2x2N2222, a few passives and a select-on-test ferrite toroid) is pennies from the junk box.
The phasing box in the shack is likewise made up of parts in stock or picked up from rallies.
It's all good fun!
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Old 22nd Jun 2017, 10:49 pm   #93
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Andy, we're interesfed in how you've implemented the phasing unit, can you share please?

T
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Old 22nd Jun 2017, 11:19 pm   #94
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Hi T. No circuit I'm afraid, as it was one of those projects that 'took shape' as it went along.
Basically the main signal from the Wellbrook loop goes via a level control to the resistive combiner at the output.
The 'noise' signal goes to a set of switchable tuned ccts covering 300KHz to 3.8MHz and into a low-gain dual-gate preamp. This section of the circuit enables the phase of the noise signal to be swung relative to the main signal.

Then there comes a simple transistor phase splitter (output switchable from collector and emitter) to 'flip' the phase 180 degrees should it be necessary.
I think the 'noise level' pot is at this point.

Finally an emitter follower shoves the noise signal into the resistive combiner to add/subtract from the main signal.
The input tuned ccts limit this circuit to a max freq of 3.8 MHz, and probably the audio style of design of the phase splitter etc would not work well at HF either.
It certainly works well across the designed range.
Hope this helps!
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Old 23rd Jun 2017, 8:09 am   #95
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

PS I can do a quick block diagram if it would help.
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Old 23rd Jun 2017, 9:18 am   #96
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

I think we are all very curious so a circuit, even if a bit rough, would be good.
Thanks
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Old 23rd Jun 2017, 10:23 am   #97
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

I cannot remember the exact details, and as it's all boxed up I don't really fancy stripping it down to trace the circuit!
I'll do a block diagram and include all the details I can recall. I'm sure it will be at least a guide.
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Old 23rd Jun 2017, 12:53 pm   #98
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Back again.

Here's the block diagram of the phaser. A few notes might help:

The two DC injectors will only be required if you are using active (powered) aerials. Wire aerials can go straight to the next stage.

The level pot for the main path should be low value, say 100 to 500 ohms.

The resistive combiner is simply two resistors commoned at the OUT socket. Low values such as 50 or 100 ohms should be OK. This will lose a little signal but I don't find it to be a problem.

In the noise path, L1, L2, and L3 are chosen to resonate with the variable capacitor on the required bands. Iused small axial inductors from the junk box. Values in the range 20 to 150uH rings a bell, and bigger if you want to go down to LW. I *think* I had to add a couple of hundred pf across the noise antenna input when using a wire aerial to make the tuning behave.

The dual gate fet in mine is the old-but-good 40673. G2 is fixed biased to a couple of volts and I think the source r is a couple of hundred ohms with the drain r at 1k or so. Worth a fiddle with.

Phase splitter is standard stuff with 1k in emitter and collector. Set base bias to get a couple of volts across each.

As the level pot feeds the emitter follower, a value of a few k is OK.

Emitter follower load is a few hundred ohms.

Apart from the 12v for the active antennas, the whole thing runs from an 8v regulator.

**Just remembered I added on/off switches to enable the quick selection of one or both channels. A good place for them is after each level pot.**


If you haven't used a phaser-outer before, be prepared for some frustration as the null can be shallow and difficult to find at first.
First of all, check that both channels are working. The main channel is broadband so your receiver should work as normal via this channel.
The noise channel is tuned, so it should be possible to hit a peak on any chosen frequency in the design range. Bear in mind I have never tried this cct above 4 MHz - I suspect the noise channel will have a falling response as the frequency rises.

Once you know it's all working, tune your radio to a moderately strong MW broadcast and using only the noise channel, make sure you can peak it. If your receiver has a signal level indicator, note the strength at peak.

Switch over to the main channel only and adjust the main level pot for the same strength. Level-matching to within a few dB is important for the best null.

With both channels on, flip the reversal switch and use the setting that gives *minimum* signal. The null may be only small at this stage.

Carefully adjust the tuning cap for a dip in strength. Re-adjust the noise level pot for a better null. Repeat these two adjustments until the null is sharp and deep.

It's the same procedure when nulling noise, but it's worth checking that both antennas are hearing the same kind of noise, because if they aren't the noise won't cancel.

I've also found a few photos of the phaser during construction.
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Old 24th Jun 2017, 2:27 am   #99
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

A similar system is described by Lloyd Butler VK5BR on these two pages:-

http://users.tpg.com.au/users/ldbutl...Cancelling.htm

http://users.tpg.com.au/users/ldbutl...oiseCancel.htm

and the magazine articles he references are available from here:-

http://www.armag.vk6uu.id.au/index.html

There is also a construction article based on the late 80's design (also used by SEM around the same time) coming out in the next issue of Sprat (GQRP club magazine).

Terry
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Old 24th Jun 2017, 8:04 am   #100
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Thanks for that, Terry. Interesting reading. His phase shift/aux tuning is the same as the one I used in my prototype and it provides more 'swing' than the simple L type in the one I've described. If ever I do a re-build I'll probably go back to the two gang cct.
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