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Old 14th Jun 2017, 11:31 pm   #41
Al (astral highway)
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

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Originally Posted by Radio Wrangler View Post

If that's not enough, these antennae are untuned and wide open to all signals in the environment, every last one. You want a transistor with high linearity at these frequencies otherwise intermodulation products of strong signals (even ones outside the tuning range of your radio can create sproggies all over the place ...
That qualifies as a fair bit of convincing, David!
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Old 15th Jun 2017, 7:31 am   #42
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Several years ago,a firm was shutting down all manufacturing in the UK, and there was a stock of lifetime-boought 2N3866 transistors to support an older product. The new manufacturer out East didn't want them. They were destined for scrap, but I was asked if I knew people who would actually use them. You don't turn offers like that down. They were passed on to the QRP fraternity for free distribution. Strictly free, no exceptions. Some rally traders offered to buy them, but I'd agreed to free. So there are over 10,000 premium quality 2N3866 kicking around in drawers in radio shacks in the UK. I wonder what proportion made it into radios? These devices would be just as good as 2N5109 in these sorts of active antennae.

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Old 15th Jun 2017, 9:29 am   #43
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Re Post #38, it looks as if it's going to be a case of trial and error in answer to my request for help on this project.

Symon
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Old 15th Jun 2017, 12:38 pm   #44
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

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Hi.

I'd like to ask members' views on the following points:

1. The 'tiles' used in the Manhattan style of construction are secured with cyanoacrylate adhesive (superglue). I was wondering if quick set Araldite would be suitable as it gives you a chance to position the tiles before setting? I've not used Araldite for copper to copper bonding before so that's the reason I ask this question.

2. With the bifilar wound transformer, are the two lengths of ECW twisted together prior to winding or are they just kept reasonably separate?

3. In Gary's article, he encapsulated the amplifier in a potting compound. I thought about using a good quality circuit board lacquer, any thoughts on this?

4. In the article, an earth rod is used in an early prototype. I'm not sure if it's required in the final set up, maybe not as it could be a source of noise?

5. My bungalow is located closely to the four main compass points, What wall should the loop be mounted to give the best performance?

Thanks in advance.

Regards
Symon.
1) I'd have thought that Araldite would be fine.

2) The two lengths of wire are twisted together before putting the turns on the ferrite core.
I've attached a pic showing mine. (bottom RH corner of the PCB with four bits of red sleeving). Just need to make sure that you connect the four ends to the right points, as per the circuit.

3) If the amp is to be used outdoors, (as yours is Symon), at some point, moisture ingress is inevitable.The potting compound that Gary used is readily availableand isn't expensive (£6.10 plus £1.45 P&P). It isn't messy to use and has a long cure time. Personally, I'd be inclined to test the amp to make sure it works, then fully encapsulate it as Gary did. That does mean that future repairs aren't possible, but then that's the same as a Wellbrook, but if the 'GNT' amp should ever fail, it's only a tenth or less than the cost of a Wellbook.

Gary used Robnor Twin Pack Two Part PX700K 100g Potting Epoxy Resin. Spiratronics state Thus: "These twin packs of black flame retardant epoxy resin are suitable for potting electrical and electronic components and assemblies. Supplied in a twin pack enabling the resin and hardener to be mixed in the bag, preventing air entrapment and direct contact".

Curing: time
at 25°C: 24 hours
at 60°C: 2 hours
at 100°C: 30 minutes
Useable life: (at 25°C 1 hour)
Max. operating temperature: 115°C
Mix ratio by weight: 8.7:1
Mix ratio by volume: 5.6:1
Supplied in: 100g

The full Data Sheet is here:

http://www.spiratronics.com/data/9616.pdf

Spiratronics online shop is here:

http://www.ebay.co.uk/itm/Robnor-Pot...-/121656556022

4) I just connect mine to the aerial and earth sockets of the radio and rely on the mains earth, which hasn't proved a problem. I made an adaptor to couple the BNC coax lead to the radio, using a small pill container, a BNC socket at one end, and twin flex at the other end, terminated in a pair of re/black wander plugs. Might be worth re-stating that the loop amp can't be used on 'live-chassis' sets such as DAC90A etc. All of the sets I use mine with have the chassis earthed via 3-core flex.

5) I don't know how directional the loop is as I didn't swivel it round when testing, because I intended to fix it to the outside gable end of my wooden workshop. For what it's worth, I've attached a sketch of its orientation, which in my case, (broad-side on), is NW/SE.

Hope that helps a bit Symon.
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Old 15th Jun 2017, 12:57 pm   #45
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

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There was a very large number of 2N3866 transistors (many thousands) distributed for free amongst the QRP groups of the world. They are similar enough to the 2N5109. TO-5, they carry the Motorola 'Batwing' markings and '4-247' in case anyone comes across some. They were going to go for scrap metal otherwise.

David
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.
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Old 15th Jun 2017, 1:00 pm   #46
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Hi David.

Thank you for your comprehensive reply and your usual good advice.
I hope I didn't come over being too abrupt in post #43 as lately things have not been going to plan with one thing and another. I must be more positive!

Early stages, but attached is the 'Manhattan' style circuit board prior to assembly.

Thanks again.
Regards
Symon.
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Old 15th Jun 2017, 3:23 pm   #47
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

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Originally Posted by Station X View Post
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.

I'd be very pleased to accept your offer for five these transistors. PM on its way. Thanks.

Regards
Symon
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Old 15th Jun 2017, 4:04 pm   #48
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

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I don't know how directional the loop is
My Welbrook loop is on a rotator I only find the null usefull, anything over a few degrees from the null is at good strength.

Handy hint, when potting spray some conformal coating on first, this gives a slightly elastic layer twixt components and the (rigid) potting. I also reduces the chances of water migration as no small gaps can generate. Mind you with properly applied conformal coating potting may not be needed.
 
Old 15th Jun 2017, 4:04 pm   #49
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

I've replied to your PM.
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Old 15th Jun 2017, 4:19 pm   #50
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Hi Philips 210,

I'm out and about so it is tricky to format the quotes function on my phone, but in answer to your query 1 on the Manhattan style of construction, you aren't bonding copper to copper, you're bonding the (insulating, unclad) back of the tile to copper. Superglue goes off with an exothermic reaction but takes a good few seconds , allowing you to move the tile around as you wish. If you make a mistake, you can pull the tile off with long-nosed pliers and start over again.
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Old 15th Jun 2017, 4:36 pm   #51
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Hi Al.

I am actually using double sided copper clad board, which is what I had available. The tiles were cut from the same board so it will be a copper to copper bond. In Gary's article he mentions that he had better success bonding the d/s copper tiles to the main board rather than the insulated back of say a single sided copper tile to the main board. Thanks though for your input.

Regards
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Old 15th Jun 2017, 5:26 pm   #52
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Quote:
Originally Posted by Philips210 View Post
Hi.

I'd like to ask members' views on the following points:

1. The 'tiles' used in the Manhattan style of construction are secured with cyanoacrylate adhesive (superglue). I was wondering if quick set Araldite would be suitable as it gives you a chance to position the tiles before setting? I've not used Araldite for copper to copper bonding before so that's the reason I ask this question.

2. With the bifilar wound transformer, are the two lengths of ECW twisted together prior to winding or are they just kept reasonably separate?

3. In Gary's article, he encapsulated the amplifier in a potting compound. I thought about using a good quality circuit board lacquer, any thoughts on this?

4. In the article, an earth rod is used in an early prototype. I'm not sure if it's required in the final set up, maybe not as it could be a source of noise?

5. My bungalow is located closely to the four main compass points, What wall should the loop be mounted to give the best performance?

Thanks in advance.

Regards
Symon.
Epoxy ought to be fine if you make sure the board is grease-free. I've used superglue for decades and never felt the need for anything else.

Bifilar normally means twisted together, I have used glued pair for very specialist transformers. About 8 twists/inch and about 32SWG is a starting point. For funny transformers I've used hexafilar (6 separate strands twisted) and used coloured 'verowire' to make identification easier.

I'd go for a VERY well sealed box with sealed lead-throughs and a sealed coax connector like type N, and add a light spray of varnish to the board.

There is a sort of earth via the coax outer from the power supply. Adding an outside rod would create a loop... it sounds like a bad idea.

Loops have a null in their plane, therefore pick a wall with no wanted transmitters in the directions of its plane.

David
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Old 15th Jun 2017, 6:16 pm   #53
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Quote:
Originally Posted by Philips210 View Post
Hi David.

I hope I didn't come over being too abrupt in post #43 as lately things have not been going to plan with one thing and another. I must be more positive!

Early stages, but attached is the 'Manhattan' style circuit board prior to assembly.

Symon.
Didn't sound abrupt to me Symon - I'm northern - we don't go all flaky with kindred spirits!

The circuit board and 'tiles' looks neat.

Re the orientation, Gary saw your post re orientation and dropped me an e-mail to say:

"Best way for me is flat side facing dead north (gives best R4 reception). All depends where you are and what particular station you want it optimised for".

If you have a choice of positioning, I guess you might wish to try it in different orientations.

Good luck with it - you've made a start, which is the main thing!
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Old 15th Jun 2017, 6:57 pm   #54
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

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).
 
Old 15th Jun 2017, 9:25 pm   #55
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

You could build a...... Goniometer!

I've wanted to use that word in anger for ages. It'll be yonks before another opportunity comes around.

David
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Old 15th Jun 2017, 10:17 pm   #56
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Slight aside and word of warning: When using superglue, be sparing and try to keep it off the component leads- I was asked to solder up some jewellery recently but wasn't told that previous attempts at mending with superglue had been made and just a tiny wisp of the resultant vapour getting in the eye was surprisingly painful and took some time to get back to normal.
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Old 15th Jun 2017, 10:58 pm   #57
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Hi.

It's been most interesting reading all the posts in this thread and some very good technical explanations regarding the characteristics of the transistors used in the amplifier.

turretslug raises a good point about superglue. I experienced something similar a few years back. It's like something acidic being directly sprayed in your eyes, not a good situation.

Regarding the special properties of the 2N5109 transistors, it's no doubt obvious this is an ideal candidate to be faked. It's a case of trying to find a dependable supplier who doesn't deal in junk components, easier said than done these days when trying to source special/obscure parts.
I have just bought some from a reputable source (not cheap), they're made by RCA and have a 1976 date code so are getting on a bit but should hopefully be fully up to spec.
What I'd like to do is build a second loop aerial using suspect fake 2N5109s so that a comparison can be made with the real thing. It would also be useful for trying out possible alternative transistors as well.

Regards
Symon
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Old 16th Jun 2017, 1:10 am   #58
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

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What I'd like to do is build a second loop aerial using suspect fake 2N5109s so that a comparison can be made with the real thing. It would also be useful for trying out possible alternative transistors as well.
For use below 30MHz, I'd guess that you'd probably get away with transistor holders to allow swopping in and out? Alternatively, perhaps use the simple W7IUV design I mentioned above as a "transistor tester".

B
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Old 16th Jun 2017, 2:02 am   #59
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

Just on various transistors for antenna amp use, Chris Trask did some studies and published them in this paper:-

http://home.earthlink.net/~christras...Evaluation.pdf

Terry
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Old 16th Jun 2017, 9:39 am   #60
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Default Re: Magnetic Loop Receiving Aerial (Gary Tempest)

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For use below 30MHz, I'd guess that you'd probably get away with transistor holders to allow swopping in and out?
A very good point Bazz and when I build the second amp I'll uses some TO-5 holders.
I purchased the 2N5109 transistors from here : http://www.ebay.co.uk/itm/2N5109-JAN...cAAOxyLN9SpbJ2 As I say, not cheap but feel these should be genuine so have more confidence the amplifier will perform as expected.

Something occurred to me for mounting the loop aerial set up on a shed, the amplifier could be housed inside the shed with the loop mounted on the outside. A small hole drilled through the shed allowing the relatively short loop cables to connect to the amp inside. I appreciate that the wires from the loop to the amplifier need to be kept short to avoid picking up noise. It's the same with TV aerial amplifiers, the best place for the amp is close to the aerial otherwise the S/N ratio will suffer. What if the slightly longer wires to the amp in my suggestion are screened using RF coax to help matters? This would keep the amplifier in the dry and save encapsulating it, just a suggestion.

Thanks to all that have so far replied to my questions.

Regards
Symon
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