20th Nov 2017, 9:56 pm | #161 |
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
Hi Bazz.
Thanks for your kind comments. So far, I've only conducted the tests with my Hacker Helmsman but will see how it performs on many valve sets including my 1937 Pilot U385 and the Pye P93 W/U. I don't have any specific interest in the HF bands so I'm just an occasional SW surfer I guess. I found that there was some MW breakthrough on the SW bands, perhaps a HP filter fitted to the SW aerial socket on the Hacker might improve this. I'm also interested in seeing the results if the loop is rotatable. That will I'm sure give improved results. I like your suggestion of using the blue alkathene water pipe for the aerial. I'm having thoughts of rigging up such a setup on my garage roof which will be conveniently close to my workshop. Regards Symon |
20th Nov 2017, 11:41 pm | #162 | |
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
Quote:
I've been spending some time searching Google; lots of interesting stuff about using loops as transmitting antennas on the HF bands, but it looks very much as though tuning is best done with a vacuum variable capacitor and my junk box is sadly devoid in that department . B
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21st Nov 2017, 1:36 pm | #163 | |
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
Quote:
Symon. |
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24th Nov 2017, 11:34 pm | #164 |
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
Hi.
I'd be keen to see if other members have successfully built the loop aerial amplifier. It's quite a considerable effort building the amplifier and loop aerial but the results are worthwhile. During this thread, I have learnt a considerable amount and asked a number of questions but unfortunately didn't seem to get many answers in more recent posts. I hope that discussing the possibilities of using various transistor types hasn't offended the designer in any way. It certainly wasn't my intention it's just that I like to experiment. To date, I think that I'm the only person to successfully build the PCB version of the amplifier by David G4EBT. This thread has gone very quiet and I wonder if the OP has lost interest in this thread as he's normally keen to acknowledge members' efforts. I can't help feeling I've done something wrong. Regards Symon. |
25th Nov 2017, 8:00 am | #165 |
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
It looks to me like you've done quite a lot of things just right.
For any constructional article, a lot of people take great interest in reading about it. Many start collecting the bits, a few actually get as far as building the thing and a smaller number persevere as far as getting it going. There was approaching 40,000 of those 4-247 transistors distributed free to the amateur radio world. They're all salted away in people's component boxes! I'd expected them to pop up all over the place and to at least be seen in the pages of Sprat, but I was wrong. Hoards have swallowed them up like a bottomless swamp. Not even a burp has surfaced. If ever offered another lot, I probably won't bother. David
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25th Nov 2017, 10:00 am | #166 |
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
A very nicely-finished job, Symon. The noise-ignoring qualities of loops have virtually saved my hobby, as the noise around here when using long-wires and verticals is a constant s9. As I'm a 160m user and an LF fan in general, the loop has worked wonders for me. Mine's a Wellbrook 1530 on a budget rotator, but I've also built a few of the simple two-transistor designs as well, all based on plastic hula-hoops and electrical conduit boxes. All work well, especially if time is taken to minimise intermodulation effects by adjusting the balance and collector currents of the transistors.
We have a number of very strong signals around here (909 KHz and 1215 KHz from Moorside Edge are the worst, with 1458 KHz and 1152 KHz from Ashton Moss bringing up the rear) so optimisation is important.
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25th Nov 2017, 12:35 pm | #167 | ||
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
Quote:
In Post #104, 9 July, I stated: That's a considerable effort Symon, but built for a tenth of the cost of a Wellbrook, it's worth that effort - leastways, I think so. I'm sure that when Gary spots your post he'll be well impressed. I do hope it passes its 'MOT' - 'Moment Of Truth' and that you're as impressed with its performance as I and several others have been. Every good wish with it. End quote. But you are right in feeling that I've largely lost interest in this thread. Back in June I said that for me, the thread had run its distance as it had drifted off into discussions which had no relevance to the original topic, often from those who hadn't read the 10-page BVWS Bulletin article by Gary Tempest and had no intention of building it. Topics such as Loop antennas in general, their orientation, possible rotation, performance on short waves, other designs, possible fake transistors and other types than those that Gary used. I don't mind that a bit and certainly wouldn't wish to inhibit debate, but such discussions hold no interest for me. That said, I have written 19 comprehensive posts to answer queries that others have raised. The project was conceived as a compact loop amplifier which would reduce background noise, increase signal strength, could be unobtrusively sited indoors or outdoors, and built at a fraction of the cost of a commercial alternative. I was able to compare it with the 60ft horizontal wire aerial I was using up till then and the results were far superior, so for me, that was mission accomplished. But homebrew is about experimentation and if others wish to develop things further, that's fine by me. At the outset, I thought it might attract maybe a dozen responses relevant to the PCB design. This thread has now had 164 posts and almost 12,800 views so has clearly stimulated interest, even though much of it has little relevance to the original post. (Gary posted the full BVWS article on another forum on 24 October 2016, since when it's had 820 views and just two responses - one the same day saying 'well done', another nine months later on 27 June 2017 from someone who had a Wellbrook that had failed, and wasn't incline to fork out £100 to replace the amp, so made one along similar lines, using a couple of transistors, as does the Welbrook I believe). In post #43 on 14 June I wrote: Quote:
(As far as I can tell, only Symon and Bazz have given feedback on their experiences in actually building Gary's design).
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25th Nov 2017, 12:57 pm | #168 |
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
Hi.
Thanks David for your usual comprehensive reply and positive comments it's much appreciated. My main concern was if I had stepped out of line in any way. I didn't want to offend the original designer, Gary and yourself by apparently questioning the virtues of different transistor types. I feel relieved that all's well. It would be good to see a few more of Gary Tempest's Loop Aerial setups. As I say It's been an enjoyable project and I've gained considerable knowledge as a result. Regards Symon. |
25th Nov 2017, 1:05 pm | #169 |
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
Hi
Thanks also to Andrew2 and Radio Wrangler for your positive comments. The 4-247 transistors originally from Radio Wrangler gave better performance than the Motorola 2N5109s, the 4-247s seem to have more gain at the higher frequencies. Perhaps my 2N5109s were slightly low spec. One small point about the 1mH RFC in the power distribution box, Yesterday, I went to order a couple more from CPC (order code FT00799) but now they're no longer available so an alternative needs to be found. The fixed copper tube loop aerial on my fence works well and I'm next going to try a rotatable loop along the lines that Bazz and Radio Wrangler described. Regards Symon. |
25th Nov 2017, 1:28 pm | #170 |
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
Hi
Yes, just to summarise my own position, I think I mentioned in a previous post that when I got the loop working I only had my Realistic DX-160 to test it out on, my HRO being in it's "on-going rebuild" . I have 2 HF band transcievers, but let's leave them on the side. On long wave and medium wave, the loop was pulling in signals on the DX-160 that were so strong that I literally had to ping my finger against the S-meter to bring it back off the end stop but background noise was extremely low. This was using the 3866's (4-274) from Graham. Consequently, I want to get the HRO complete in the expectation that it would really show off the loop even better. Additionally, I'm now going up a learning curve regarding the loops for use on the amateur bands for both receiving and transmitting, and there's lot's of material to be found via Google. The points that authors make about loops is that;
The bottom line is that I'm very pleased that this thread about Gary Tempest's loop design came along because it was an area I had no knowledge of, and it has opened up a new area of ham radio which I intend to explore. And certainly, I'm interested in hearing about anything that anyone else of the forum is doing with loops . B
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25th Nov 2017, 3:11 pm | #171 |
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
And to make them even better to the eye, 45 degree plumbing elbows are available.
https://www.screwfix.com/p/flomasta-...Fca1UQod4pQN4Q An octagonal loop would be very art deco. And along with a cross tee https://www.ebay.co.uk/itm/15mm-22mm...-/282125022751 at the top a double loop could be made. I fancy doing this rather than rotating my Wellbrook, all I need is some electronic way of rotating it. I do have power and data (three core cable currently supplying a heavy duty radio control servo which swings the loop in less than a second, great for nulling interference) and only one co-ax to the aerial so it needs to be done at the antenna. |
9th Mar 2018, 4:59 pm | #172 |
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
The Spring BVWS Bulletin arrived today, which has an interesting five-page well illustrated article by Gary Tempest entitled 'Magnetic Loop Aerials Part 2'. In the article, Gary refers to the Wellbrook, and the 'Wellgood' - a copy of the Wellbrook by a George Smart based on an X-Ray of a defective Wellbrook and 'reverse engineered' by him as a replacement. Gary has designed and produced a two-transistor amp along similar lines, and in the article gives full constructional details, using a Manhattan style PCB.
Gary has had a Wellbrook for some years, and the article compares and contrasts the performance of the Wellbrook, the earlier five transistor amp that Gary designed, (which featured in the Autumn 2016 Bulletin and prompted me to start this thread), and his latest 2-transistor design, along similar lines to the Wellbrook. Hope that might be of interest.
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9th Mar 2018, 7:05 pm | #173 |
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
Very interested, David. As a loop-user and builder myself I'd love to see that article if it is humanly (and legally) possible.
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9th Mar 2018, 7:14 pm | #174 |
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
I wanted the article on Emor globe radios, simply emailed the BVWS and it was in the return. I am a subscriber, worth a punt I guess.
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10th Mar 2018, 9:30 am | #175 |
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Re: Magnetic Loop Receiving Aerial (Gary Tempest)
I could add some remarks about loops.
Firstly there are loops for receiving and loops for transmitting and there are two types of loops, large air cored loops and small loops on ferrite rods. Then of course there is the frequency range over which the loop is operating. For air cored loops for > 20 to 30MHz, single turn loops of a good size like 1m diameter or larger can suffice, but for MW loops need at least 5 to 7 turns with a tap at one turn for receiving, or injecting a signal if transmitting. In any case this is what I have learned over many years of making loops for transmitting and receiving: Receiving loops respond to the magnetic component of the transmitted EM wave. Far off from the station (greater than a few wavelengths) the ratio of the electric to magnetic field is about 377 volts per amp. An air cored or ferrite cored loop antenna are about equally effective in receiving. Because they respond to the magnetic (H field)component of the EM wave, they tend to ignore noise voltages of the E field. This is why pocket transistor radios appear to work so well with a small ferrite rod.But the rod is very directional. The noise immunity effect is improved for an air cored loop if it has an electrostatic shield to shield the E field (hence the value of the coax as suggested by RadioWrangler) But for this, for MW band, the 5 to 7 turns need to be close together to apply the electrostatic shield. This effect can be exploited for any radio including valve radios (see below) For transmitting on the MW band, it is another story. With a loop transmitting antenna, the 377 doesn't apply in the near field. The electric component of the EM wave (H field) is very weak, the H field strong and the E:H ratio reversed . In the near field, for pantry transmitters, say less than 100 meters from the transmitter , when the wavelength at one MHz is 300m, the air cored loop antenna is great if you are transmitting to a radio with a magnetic response, ie a radio with a ferrite rod or a frame aerial or loop antenna. If it is a wire antenna on a valve radio, forget it, the result is poor. The reason is, in the near field, the electric component (E field), from a loop antenna is very very low and the magnetic component (H field)high. The above means that if you are transmitting from a loop antenna from a pantry transmitter, and you want a good result with a transistor radio with a ferrite antenna you are fine. But if you have a valve radio receiver you are in fact better to rig up a tuned ferrite antenna (on the frequency of interest) with a Tap at about 20% of the earthy end to feed the radio's antenna input. This also gives excellent noise immunity in conjunction with the loop transmitting antenna. If you don't do that you are better to couple the output of the pantry transmitter to a long wire and receive the electric component of the field, with a wire antenna on the valve radio, but there will be a lot of extra background noise / interference this way. Finally, although ferrite cored loops make excellent receiving loops in the far field, as good as a medium sized (say 1m diameter) air cored 5 turn loop, compared to the 1m dia air cored loop they make hopeless transmitting antennas. The primary reason for this is the small cross sectional area of the ferrite cored loop (compared to a large air cored loop)making the radiation resistance very low. But for receiving the ferrite rod antenna is excellent for either a near field signal from a loop transmitting antenna or a far field radio station, and you get the benefits of noise immunity. This is why even your average valve radio will benefit from a tuned ferrite rod (on the station of interest) with a tap feeding the radio's antenna input, in terms of the signal to noise ratio. |