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Old 24th Nov 2020, 3:54 pm   #21
stevehertz
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Default Re: How effective is an earth for reducing noise on AM?

How's about this one? I mean, the price of 'pro' level loop aerials is high, this comes in at under £30 all in.

https://www.ebay.co.uk/itm/TECSUN-AN...UAAOSw0vdd-vQF
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Old 24th Nov 2020, 4:10 pm   #22
Bazz4CQJ
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Default Re: How effective is an earth for reducing noise on AM?

Quote:
Originally Posted by stevehertz View Post
Quote:
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Well, if a passive loop seems interesting, you have to wonder what an active loop might be like, which brings us back to posts 2&3.

B
Indeed, I think I'm going that way. They are expensive though.
Not if you build one. I think the Wellbrook clone is do-able for ~£20; the main components are two transistors and two ferrite beads. The construction of a Wellbrook clone has been described in detail in a BVWS bulletin by a member of this forum who decided not to use the tiny PCB which can be bought. The one challenge about the Wellbroke clone is making the multi-winding transformer using a binocular ferrite core, but that's a question of time/effort rather than expense.

There are other designs. David (EBT) is using a design by Paul Tempest (also in BVWS). There's an amateur in Bulgaria who started building magloops as a hobby but now runs a business doing it. His older designs are around.

I suspect that the big difference between the various designs is how they perform at higher frequencies, but as you seem to be mainly interested in MW/LW, they might all do a good job. My Wellbrook clone does a reasonable job on the 80m amateur band and stands a good comparison against my inverted V.

Cannot comment on the Tecsun; have not previously encountered them.

B
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Old 25th Nov 2020, 12:28 pm   #23
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Default Re: How effective is an earth for reducing noise on AM?

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.......The one challenge about the Wellbroke clone is making the multi-winding transformer....
Honestly, that is a typo....unless it was Freudian

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Old 25th Nov 2020, 3:48 pm   #24
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Default Re: How effective is an earth for reducing noise on AM?

This thread has drifted from the original question, of 'How effective is an earth in reducing noise on AM?' To which my answer would be 'not very'.

Furthermore, in my experience, whilst putting up longer wire aerials if space permits may marginally increase the signal strength, it has the undesirable effect of increasing the background noise level too. What are often termed 'long wire antennas' are in reality 'short wire' antennas. My understanding of a long wire antenna is that it is at least 1.5 wavelengths long, so on 200 Metres, it would need to be 300 Metres long.

About the best that most of us with suburban gardens could manage is 20 Metres (in my case exactly that). Height wise, most of us would struggle to get a wire antenna up more than 5 Metres, that's 1/40th of a wavelength long. 'Back in the day', that's what most householders managed with, but of course, they were not beset with the proliferation of noise levels that exists today.

In my view - and I'm not alone - for low noise and good signal strength, magnetic loop antennas are far superior to wire antennas of any length. I guess that's why Wellbrook are still in business selling their own magnetic loop version at eye watering prices.

All lot of experimentation and construction of 'home-brew' amplified loop receiving antennas has been undertaken since 2016 by Gary Tempest, who will be well known to BVWS members. The three versions of Gary's designs that I've built worked first time and I'd commend them to anyone who wishes to receive MW stations at good strength with minimum background noise. (It should be said at the outset that they're they connected to the aerial and earth sockets of AC only radios and not designed for live chassis sets such as the ubiquitous Bush DAC90A).

Gary Tempest originally bought a Wellbrook Loop and in 2016 but the Amp failed while under guarantee, so Wellbrook replaced it. It had lasted until a few weeks ago then that too went low gain with gritty noise, so rather than pay out for a replacement Gary built a new Amp. He reported that performance of his latest version into an HMV 650 was 'back to stunning again - crystal clear R4 and RTE better than before. MW is excellent on many stations and SW better than he can remember it, not that there is anything of much interest on the bands'.

BVWS members will know that Gary wrote two articles on building Mag Loops in the BVWS Bulletin. For his most recent amp he went for the simplest design with least components that he could string together using the 'Manhattan' construction technique to replace the second failed Wellbrook one, using the same power and signal feed (12V at 100mA). The power is spread over 4 transistors (Hfe: Tr1/2 >130, Tr3/4 >80 and matched) rather than just two in the WellBrook.

He was originally inspired to investigate and experiment with magnetic loop antennas by the home-brew design by a Dutch radio amateur, PA1M:

https://www.pa1m.nl/simple-active-receive-loop/

Details of Gary's recent 4 Transistor version can be found at this link:

https://golbornevintageradio.co.uk/f...d.php?tid=8065

His 2016 five transistor version, one of which he gifted to me is 2016 (which is still performing excellently in my garden workshop) is here:

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

I constructed one myself for indoor use and wrote it up in this thread:

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

Gary’s 2 transistor version based on the Dr George Smart ‘Wellgood’ 'Welbrook clone' article can be found here:

https://golbornevintageradio.co.uk/f....php?aid=18052

In Spring 2019 I built that 2-transistor version and posted details in a now closed thread entitled 'Clone of 'Wellgood' Magnetic Loop Receiving Aerial'. at this link:

https://www.vintage-radio.net/forum/...d.php?t=156263

I installed that loop in my brick garage loft. I spend a lot of time in the garage where my metalworking lathe is sited and where I make larger woodworking projects, so the loop is in use most days, connected to one or another restored valve, which I change every few weeks to give them an airing.

At Dr George Smart's website there are very clear instructions and diagrams on how to wind the little binocular transformer, and I had no problem in doing that (or with the little transformers in the other designs):

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

(It will be evident from George Smart's investigations that the Wellbrook Amp is built not on a PCB, but on a piece of stripboard, which only became apparent when he X-Rayed the Wellbrook).

In each of Gary's designs he used the 'Manhattan' construction technique with little 'tiles' of PCB material stuck to a piece of PCB laminate to obviate the need for a PCB, but for repeatability, I designed a PCB using Gary's layout. In each case, the diagrams and photos make it clear how to construct the amplifier. Minimal expense and effort for maximum enjoyment - Id rather be indoors soldering, than up a ladder outdoors faffing about with wire antennas to no good effect!

A nice winter project.
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Old 25th Nov 2020, 4:33 pm   #25
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Default Re: How effective is an earth for reducing noise on AM?

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At Dr George Smart's website there are very clear instructions and diagrams on how to wind the little binocular transformer, and I had no problem in doing that (or with the little transformers in the other designs):.
Well, considering that you end up with a transformer wound on small binocular ferrite core, which has no less than ten leads coming out of it, I suspect that a few people may take more than one attempt to be sure they've got that right. My QA manager rejected the first one I produced. If you are not experienced in making such things, with bifilar windings, there is a learning curve. I wonder if a larger ferrite could be used to make things easier?

B
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Old 25th Nov 2020, 4:52 pm   #26
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Default Re: How effective is an earth for reducing noise on AM?

I guess 'how effective is an earth at removing noise' depends on _how_ the noise is getting into the receiver; if it's mains-borne then just adding another earth [your DNO's grounding-schema also being relative for safety reasons] won't necessarily make much difference.

With my Eddystone 840A bedside radio the thing I did find made ab improvement was fitting a common-mode choke to the [2-core] mains cable _and_ using an earth. The common-mode choke stops noise coming via the mains; if you just add an earth without 'choking' the supply then noise on the mains may actually flow through the earth-impedance of your new earth and possibly make noise worse!

[My common-mode choke is a small ferrite item scavenged from a switched-mode computer power-supply, mounted in a diecast box and installed about 10 feet from the radio]
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Old 25th Nov 2020, 5:07 pm   #27
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Default Re: How effective is an earth for reducing noise on AM?

@G6Tanuki - what is the best way of fitting such a choke to the mains lead? I've often wondered.

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Old 25th Nov 2020, 5:16 pm   #28
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Default Re: How effective is an earth for reducing noise on AM?

In my case, like I said, I took the choke from a scrap computer-PSU and fitted it inside an [earthed] diecast box.

My 840A has a 2-core mains lead (it's an AC/DC 'live chassis' radio) so I just ran a 2-core cable from the output of the filter to the radio's input.

(The 840A has an earth-terminal on the back which connects to the inner circuitry through a high-voltage ceramic capacitor to allow the passage of RF to earth but blocking any significant supply-frequency currents from getting out)
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Old 25th Nov 2020, 5:27 pm   #29
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Default Re: How effective is an earth for reducing noise on AM?

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In my case, like I said, I took the choke from a scrap computer-PSU and fitted it inside an [earthed] diecast box.

My 840A has a 2-core mains lead (it's an AC/DC 'live chassis' radio) so I just ran a 2-core cable from the output of the filter to the radio's input.

(The 840A has an earth-terminal on the back which connects to the inner circuitry through a high-voltage ceramic capacitor to allow the passage of RF to earth but blocking any significant supply-frequency currents from getting out)
So did you connect the 840A's earth terminal to the diecast box, or to an independent earth?

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Old 25th Nov 2020, 5:35 pm   #30
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Default Re: How effective is an earth for reducing noise on AM?

I have my loop at the end of the garden, about as far away from other houses as possible. This works very well and having a rotator helps too. I would try a proper earth spike at least you will have common mode noise reduction and it will be cheap.
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Old 25th Nov 2020, 5:53 pm   #31
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Default Re: How effective is an earth for reducing noise on AM?

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So did you connect the 840A's earth terminal to the diecast box, or to an independent earth?

Mike
The diecast box is connected to the mains-earth (via its 3-core supply-cable) a 2-core cable then runs from the filter-box to the 840A. The external earth [details in this thread: https://www.vintage-radio.net/forum/....php?p=1092363 ] is connected to the 840A's earth terminal via a length of 2.5mm 'singles' conduit-wiring cable.

There is no connection between my radio-earth and the mains-earth.
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Old 25th Nov 2020, 6:24 pm   #32
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Default Re: How effective is an earth for reducing noise on AM?

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I have my loop at the end of the garden, about as far away from other houses as possible. This works very well and having a rotator helps too.
Who was it, in some previous thread, who promised faithfully to post some pictures of their loop rotator, which uses inexpensive RC servos?

B
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Old 25th Nov 2020, 9:52 pm   #33
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Default Re: How effective is an earth for reducing noise on AM?

Yes the thread has deviated, but as the OP I have become very interested in the mag loop aerials, so all such input is appreciated.
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Old 30th Nov 2020, 10:56 am   #34
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Default Re: How effective is an earth for reducing noise on AM?

Many moons ago when I was about 14 for a time we lived on an old MOD estate in Helston Cornwall.

I had an old HMV 1124 valved radio which I used as my main radio as well as for short wave listening. I used a 60' long wire aerial across the garden with a mains earth. Reception was ok but the noise levels especially across the Long, Medium and lower frequency HF bands could be rather high at times especially during the evenings when everyone was using their televisions.

Access to a separate earth became available and what a difference that made. The noise levels across the lower frequency bands dropped significantly and the performance of the long wire aerial seemed to improve especially across the higher frequency short wave bands.
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Old 1st Dec 2020, 3:06 am   #35
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Default Re: How effective is an earth for reducing noise on AM?

G'day everyone.
I have played with random wire antennas and various earth arrangements and all with differing achievements.
Without doubt in my eyes there is no one solution for the noise problem. As other posters have made mention it is becoming quite prevalent in our modern times.
I think you have to just try different approaches to find a solution.
Now if I may deviate just a little.
I have found and played with a novel approach to the noise problem.
So easy to try and I guarantee you will already have the bits to make it.
A "low on ground loop antenna".

https://kk5jy.net/LoG/

Well worth a read.

I have made and played with a few of these and all perform a treat. The only difference I have is I make the loop round rather than square and I make it larger for the lower frequencies.
These really drop the QRM noise level a lot. Where I live I have 3 neighbours with very noisy solar power supplies and all manner of electronic devices. With conventional wire antennas I can not listen to AM broadcast stations or very much short wave radio.
I use the log loop for receive and a vertical for transmit.
Anyway, I won't rave on. I have offered my bit and I hope it helps.

Cheers all.
Robert.
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Old 1st Dec 2020, 3:27 am   #36
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Default Re: How effective is an earth for reducing noise on AM?

Well, that's technically very interesting, but I'm worried about about the way my lawn mower will react to it . I notice that in the original article provided by the link the comment "A year in the yard had caused the box to be completely buried in dirt and covered by sprigs of grass". The British psyche and climate generally means that we tend to desire lush green lawns; sprigs of grass don't do it for many of us .

B
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Old 1st Dec 2020, 9:46 am   #37
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Default Re: How effective is an earth for reducing noise on AM?

For reception of stronger local stations, I have frequently used a simple wire loop around the window, room or outside. One end in the aerial socket and one (via a 1kV 0.01 uF cap - to be on the safe side) to the earth socket.

It doesn't need to be huge. Five or ten feet per side might be good enough, but if you can string it about outside for a much bigger loop, give it a try.

It probably hopelessly mismatches the aerial input circuits, but it can greatly reduce noise, at the expense of also reducing the wanted signals. But the point being the noise is reduced MUCH more than than stations - in my experience at many locations anyway

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Old 2nd Dec 2020, 8:15 am   #38
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Default Re: How effective is an earth for reducing noise on AM?

G'day everyone.

To go to the effort of building something and then running a lawn mower over it Yehhh ------- well??
The idea is to just make one and lay it on top of the lawn to try it.
Work out that it does drop the noise level down more than the sky wave signal you are trying to listen to.
Yes you have to increase the RF gain a little to compensate but you will work it out.
If you like the results then you bury the wire just under the grass. No more than 2 inches. Easy to do with a garden spade. Don't dig a big trench. Just insert the spade and wiggle it back and forth then push the wire into the slot.
I have refined it a little more by running the wire inside small grey electrical conduit to reduce the capacitance between the wire and general earth around it. Seems to work just a tad better than having the insulated wire buried direct in the earth.
I made my loop round as I don't want directivity as I talk to people all over the place.
Also made it larger in diameter as I can then use it for 160 metres.

Anyway. I have said enough about it.

Cheers all.
Robert.
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