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Old 23rd Nov 2020, 4:11 pm   #1
stevehertz
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Default How effective is an earth for reducing noise on AM?

Some forum member may recall how a couple of years ago I installed a long line AM aerial from next door's house to mine. It's as high as the chimney pots and impressively long. Anyway, although I kinda tried it out back then, it's only now that I've been trying to use it in earnest. Hmm, the darned grinding AM interference just seems to get everywhere. Yes, due to the nice big aerial the actual signal level is high, but the dreaded, grinding background noise is a major problem. I've tried switching stuff off and using a portable trannie to home in on the source but it just seems to be everywhere.

Just a thought and a question. I have a nice copper earth just outside the house that is connected to my mains board. I haven't tried it yet, but would/should connecting the earth connection part of the 'AE' socket on my receiver (a Tandberg Huldra 12) to the mains plug earth pin via a separate wire help with noise reduction? Yes, I will try it in due course, I just wondered what our experts thought. The mains is presently two wire.
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Old 23rd Nov 2020, 4:22 pm   #2
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Default Re: How effective is an earth for reducing noise on AM?

Hi Steve,

I'm by no means an expert but in your case my instinct would be to run a screened feeder lead to an aerial wire well away from the source of the interference; ie. houses and their wiring... say up the garden.

You may find an aerial that responds to the magnetic aspect of the signal rather than the electric, such as a Welbrook Loop, beneficial too.

Steve O
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Old 23rd Nov 2020, 4:23 pm   #3
Bazz4CQJ
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Default Re: How effective is an earth for reducing noise on AM?

Not sure about earthing, but have you read any of the threads about how well magloop aerials work in these circumstances?

B

overlapping posts on magloops - great mind think alike!
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Old 23rd Nov 2020, 10:35 pm   #4
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Default Re: How effective is an earth for reducing noise on AM?

When you say AM, are you talking about the Broadcast Bands, MW and SW ?

Power Line Transmitters which so many people are using these Days in the
Home virtually wipe out the MW Band with noise and a large portions of the
SW Band as well.

Add to that, Broadband sent down Copper Telephone Cables are notorious for
doing the Same if the Lines aren't balanced properly which is often the case.

Unfortunately, if you live in a built up area, the chances are you won't be able
to escape this Noise.
Yes, I know, it's very frustrating.

Ofcom seem to have no interest these Days in protecting the Radio Spectrum.
How those PLT devices are legally allowed to be sold or used is a mystery.

Ian
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Old 24th Nov 2020, 9:07 am   #5
stevehertz
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Default Re: How effective is an earth for reducing noise on AM?

I think you've hit the nail on the head there Ian. For many of us the bottom line is, clean, interference free AM reception is a thing of the past.
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Old 24th Nov 2020, 9:16 am   #6
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Default Re: How effective is an earth for reducing noise on AM?

Well, for some years now, the Wellbrook company has been demanding a painful 350 for its magloop aerials and many people have spent that money and have been delighted with the results. More tight-fisted individuals (like me) have built clones of the Wellbrook for next to nothing, and we have been even more delighted with the results.

I speak as someone who sees S8 noise levels on long wires, being surrounded by overhead power cables and overhead telephone lines.

For broadcast stations, the best solution is to use an internet radio; I have three of those - couldn't live without them.

B
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Old 24th Nov 2020, 9:36 am   #7
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Default Re: How effective is an earth for reducing noise on AM?

I did a quick test about half an hour ago with my car radio. It is an Audi built in radio. AM / DAB / FM. No earth of course, a small DAB stub on the roof : I imagine the rear screen heater is used for AM/FM. I am in a built up area, car parked in the driveway. I have a number of SMPS, WiFi and smart meters operating. On AM I did a station update and it found a little over 20 stations and it displayed their frequencies. Selecting a random 6 or so, the stations were all clear with no obvious interference.

I realise the electronics will be pretty complex in a modern radio but thought it interesting. Also, of course a car radio eliminates interference from the domestic AC mains.
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Old 24th Nov 2020, 9:54 am   #8
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Default Re: How effective is an earth for reducing noise on AM?

Adding an earth may help, but most of the noise is probably being picked up on the wire antenna. A screened lead may also help, but unless you try some sort of matching(*) where the wire connects to the centre of the coax you are in effect just shunting much of the signal to earth via the capacitance between the coax centre and the outer braid. (This doesn't happen with matched systems like TV antennas and active antennas like the Wellbrook loop.)

There are a few active antenna designs out there much cheaper than the Welbrook loop to build yourself. Wasn't there an article in the Bulletin a year or two ago?

The Mini Whip by pa0rdt has a good reputation. Only about 40 (14 if you supply your own waterproof housing) although you can build one yourself. It might be successful if you can locate it in the least-worst area for noise. It's not directional like a loop or active dipole so you can't null out the worst interference.

Unfortunately active antennas can be very expensive because it's essential that they are well designed so they don't overload and cause more problems than they solve.

(*)On the other hand there are baluns which attempt to match the long wire to the coax. Again you can buy or make.

https://m0ukd.com/homebrew/baluns-an...re-balun-unun/

https://www.iw5edi.com/ham-radio/317...ongwire-baluns

https://www.google.co.uk/search?sxsr...dZCOZbizRhEEVM

etc.

All of these antennas use coax which is designed for a 50 ohm receiver input. Our vintage sets usually just have an antenna wire input, the impedance of which will vary greatly across the LW/MW/SW, but in practice won't matter too much.

Last edited by Ian - G4JQT; 24th Nov 2020 at 10:12 am.
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Old 24th Nov 2020, 9:56 am   #9
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Default Re: How effective is an earth for reducing noise on AM?

Quote:
Originally Posted by rontech View Post

I realise the electronics will be pretty complex in a modern radio but thought it interesting. Also, of course a car radio eliminates interference from the domestic AC mains.
Actually I have some clip on ferrite slab beads that are for use on the mains input of sound reproducing equipment. I'll try one. That could be a source of interference.
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Old 24th Nov 2020, 10:02 am   #10
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Default Re: How effective is an earth for reducing noise on AM?

Quote:
Originally Posted by Ian - G4JQT View Post
Our vintage sets usually just have an antenna wire input, the impedance of which will vary greatly across the LW/MW/SW, but in practice won't matter too much.
The input to vintage radios is normally fed into a high impedance node in an input tuned circuit, in order to reduce the attenuation experienced by signals from a high-Z antenna (Long wires are inevitably not long enough, and are below resonance, so they look like a small value capacitor to the set.... hence what Ian said about the effect of screened cable capacitance)

Connecting in a 50 Ohm antenna source is poor match on the power transfer front, but it also will excessively damp the radios input tuned circuit, widening it appreciably and letting more signals in and more interference power.

That said, a resonated loop would normally give far better selectivity.

David
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Old 24th Nov 2020, 10:15 am   #11
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Default Re: How effective is an earth for reducing noise on AM?

Round here my level of QRM on my RA17 was vastly reduced by moving to a vertical longwire.

Since most house wiring, networks, burglar alarms have the majority of their wiring horizontal I figured a vertical mast might give me a better result. I bought a 10m telescopic mast and my RA17 has never been so happy!!
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Old 24th Nov 2020, 11:23 am   #12
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Default Re: How effective is an earth for reducing noise on AM?

What about if I replaced the inside the house portion of the aerial lead with a length of 75 ohm modern low loss coax? Where would I then connect the screen? - to the earth connection of the 'AE' socket on the solid state Tandberg receiver that I'm using and experiencing the problem with?
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Old 24th Nov 2020, 11:40 am   #13
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Default Re: How effective is an earth for reducing noise on AM?

Antenna coupling etc, might be worth a read.

Mag. page 442 and page 463:

https://worldradiohistory.com/UK/Wir...ld-1937-11.pdf

Mag. page 218:

https://worldradiohistory.com/UK/Wir...ld-1939-03.pdf

Mag. page 389:

https://worldradiohistory.com/UK/Wir...ld-1975-08.pdf

Lawrence.
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Old 24th Nov 2020, 11:59 am   #14
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Default Re: How effective is an earth for reducing noise on AM?

Quote:
Originally Posted by stevehertz View Post
What about if I replaced the inside the house portion of the aerial lead with a length of 75 ohm modern low loss coax? Where would I then connect the screen? - to the earth connection of the 'AE' socket on the solid state Tandberg receiver that I'm using and experiencing the problem with?
As we've said, without matching at least at the antenna end, the capacitance between the coax inner conductor and the braid/screen will act as a capacitor and just short most of the signal to ground. (Whether it's branded 'low loss' or not doesn't matter in this application.)

Have a look at the Google images link I posted for baluns/un-uns to consider fitting one where the antenna wire joins the coax. These will to some extent try to match the random wire to the coax and help reduce loss. The screen is then connected to the ground connection on your radio.
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Old 24th Nov 2020, 12:01 pm   #15
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Default Re: How effective is an earth for reducing noise on AM?

Quote:
Originally Posted by ms660 View Post
Antenna coupling etc, might be worth a read.

Mag. page 442 and page 463:

https://worldradiohistory.com/UK/Wir...ld-1937-11.pdf

Mag. page 218:

https://worldradiohistory.com/UK/Wir...ld-1939-03.pdf

Mag. page 389:

https://worldradiohistory.com/UK/Wir...ld-1975-08.pdf

Lawrence.
Thanks Lawrence but I'm looking for practical solutions, reading heavy academic theory mostly goes over my head I'm afraid. TBH I'm past studying theory (much). Plus I'm not sure the first two articles from the 30s are relevant to today's situation and the design of a solid state Tandberg receiver. Thanks though.
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Old 24th Nov 2020, 12:02 pm   #16
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Default Re: How effective is an earth for reducing noise on AM?

Quote:
Originally Posted by Superscope View Post
Power Line Transmitters which so many people are using these Days in the
Home virtually wipe out the MW Band with noise and a large portions of the
SW Band as well.

Add to that, Broadband sent down Copper Telephone Cables are notorious for
doing the Same if the Lines aren't balanced properly which is often the case.

Unfortunately, if you live in a built up area, the chances are you won't be able
to escape this Noise.
Agreed. I feel sorry for people who depend on AM radio for their listening pleasure. I live in a built-up area and there is no reception whatever on LW.

A Hacker Herald in the window is my go-to for MW listening. It is selective and sensitive enough to pull in Radio 4 loud and clear. Obviously, this has a magnetic (ferrite rod) aerial and so it's all about the H-field, rather than the E-field.

This indicates a possible direction for you and your listening dilemma, and points away from a long-wire.

I see that post #10 by David covers off all the bases.
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Old 24th Nov 2020, 1:27 pm   #17
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Default Re: How effective is an earth for reducing noise on AM?

Quote:
Originally Posted by stevehertz View Post
Thanks Lawrence but I'm looking for practical solutions, reading heavy academic theory mostly goes over my head I'm afraid. TBH I'm past studying theory (much). Plus I'm not sure the first two articles from the 30s are relevant to today's situation and the design of a solid state Tandberg receiver. Thanks though.
No problem, though it's not heavy academic theory, if it was I wouldn't have posted those links, I wouldn't have thought that your receiver being solid state would have much to do with what's happening, the antenna in effect has to be coupled by some means to a high impedance circuit, eg: a parallel tuned circuit at resonance.

Back in the day an antenna for broadcast reception that was sometimes used to combat interference was a vertical rod antenna coupled to the receiver via balanced transformers and a twin screened lead.

Lawrence.
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Old 24th Nov 2020, 1:35 pm   #18
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Default Re: How effective is an earth for reducing noise on AM?

Thanks so far guys.

I've go a Tecsun passive loop aerial that I've just tried. Here's the results:

1) The general level of interference between stations and on stations is greatly reduced.
2) The actual signal level is reduced compared to the long wire.
3) Positioning of the loop seems quite critical from an interference POV, although rotating it does not seem to affect the signal level too much.
4) It is affected by magnetic devices like transformers and speakers - as you'd expect. There's a fair amount of 'hummy' interference.
5) I have to adjust the tuning knob on the Tecsun for each station on MW.

Any tips?
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Old 24th Nov 2020, 3:01 pm   #19
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Default Re: How effective is an earth for reducing noise on AM?

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
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Old 24th Nov 2020, 3:36 pm   #20
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Default Re: How effective is an earth for reducing noise on AM?

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.
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