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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 6th Jun 2006, 10:56 pm   #21
Phil G4SPZ
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Default Re: Radio earths

Quote:
Originally Posted by G4ILN
All the other radios have their signal earth connected to chassis earth, so you're using mains earth as a signal earth whether you like it or not.
It was common for receivers not to be earthed, i.e. the mains cable was two-core, hence the receiver chassis (whether 'universal' or AC-only) would be 'floating' with respect to earth. In such cases, a reasonably low impedance connection to earth helped to reduce interference and also made sure that all the incoming signal potential was applied where it mattered, across the aerial coil.

As a transmitting 'ham' myself I agree with most of what's been said about the importance of good earthing for transmission purposes, having been burned by metalwork 'hot' at RF in the shack! However, for receiving on the MW and SW broadcast bands, every vintage receiver I've ever had has possessed sufficient gain to pull in hoards of stations on a simple untuned aerial wire of under 10 metres in length. This is all that many sets were designed to expect!

Phil
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Old 6th Jun 2006, 10:59 pm   #22
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Default Re: Radio earths

Quote:
Originally Posted by JHGibson
Most of this disscussion is really about how to make a perfect earth for a transmitter. Receivers are much less fussy. A heavy wire to a plate or rod in damp soil, or to a cold water tap is usually sufficient.
Quote:
Originally Posted by Biggles
I would agree with you JH. The theory is probably the same for transmission and reception, but unless you are after that last picovolt of DX, for receivers it probably isn't that critical.
After having chewed on your relies for a better part of the evening, I'm sorry to say that my reaction is as follows: You guys have got to be kidding me, right?

This has nothing to do with transmitters but everything to do with impedance matching and maximum RF power transfer between a generator and a load.

If your arguments had been that if one was to add tuning components to an antenna system, then it might be more worthwhile to build an all out transmatch / 'antenna tuner' instead of messing with tuning out the reactive component of the ground connection, then I might readily have agreed. That would have made a fair bit of sense.

If all you want to receive is one of the local AM stations on MW, then yes, forget the ground connection. Just plug a random piece of wire into the antenna connection.

But if you do care enough about signal strength that you might consider using a quarter wave radial or have erected a long, outside wire up high, then things are a bit different IMHO. About a quarter of a century's worth of experience listening on shortwave on many different wavelengths have at least taught your's truly that proper care in construction of an antenna system can make a huge difference for reception. We are not talking picoVolts here, gentlemen.

For reception when using a random antenna I frequently use a good transmatch, an old Yeasu FC-901. This unit has a 'Pass Through' setting, so it is easy to switch the unit in and out of the circuit for doing comparisons.

The bottom is that I wouldn't make an antenna system for anything but very casual reception without going to some effort to optimize the impedance matching and minimize ground losses when possible.

In my previous postings in this thread I made the implicit assumption, perhaps incorrectly, that we were discussing MW and lower SW frequencies, below 10MHz or so. On those frequencies the random end fed wire alone will often have an impedance suitable for a direct connection to a receiver. This is assuming that the ground connection isn't completely off the wall.

Best regards

Frank N.

Last edited by YC-156; 6th Jun 2006 at 11:13 pm.
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Old 7th Jun 2006, 12:11 am   #23
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Default Re: Radio earths

No matter how good your earth and aerial I'm afraid the main problem is interference radiated by every bit of electronic equipment in your own and neighbouring houses. Much of this interference finds its way into the electrical mains and is radiated from the wiring, or finds its way into your receiver via the mains lead.

When my neighbourhood used to suffer from frequent power cuts it was wonderful to listen to interference free signals on a battery powered comms receiver with a decent aerial.

With the posible exception of filament light bulbs I'd say that every bit of modern equipment radiates significant interference.

Rant over!
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Old 7th Jun 2006, 10:23 pm   #24
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Default Re: Radio earths

Quote:
Originally Posted by G4ILN
When my neighbourhood used to suffer from frequent power cuts it was wonderful to listen to interference free signals on a battery powered comms receiver with a decent aerial.
I agree with G4ILN. I operate on the HF ham bands from a mobile installation in my car. Parked on a hilltop site, the signals I receive are so noise-free compared with operating from home, it's a real pleasure!

Now... my car is insulated from earth by its rubber tyres. The antenna is tuned against the car metalwork, which acts as 'ground', even though the car is floating with respect to true 'earth' potential. However, that doesn't stop me hearing and contacting amateur radio stations all over Europe, the Middle East and America!

It would probably work even better with a low impedance earth connection, I guess. Some of the strongest ham signals emanate from ships and even narrowboats, where the hull is 'earthed' via contact with water.

Phil
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Old 8th Jun 2006, 10:19 am   #25
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Default Re: Radio earths

Even though your car is insulated from true earth via the tyres, wouldn't there still be some capacitive coupling between the car underside and the ground? Regarding all the theory discussed in this thread, RF is never an exact science in my experience, there being so many influences on its behaviour from other sources. I often find that a little intuition and experimentation produce better results than following text book preachings to the word.

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Old 8th Jun 2006, 1:35 pm   #26
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Default Re: Radio earths

Quote:
Originally Posted by G4SPZ
I agree with G4ILN. I operate on the HF ham bands from a mobile installation in my car. Parked on a hilltop site, the signals I receive are so noise-free compared with operating from home, it's a real pleasure!

Now... my car is insulated from earth by its rubber tyres. The antenna is tuned against the car metalwork, which acts as 'ground', even though the car is floating with respect to true 'earth' potential. However, that doesn't stop me hearing and contacting amateur radio stations all over Europe, the Middle East and America!

It would probably work even better with a low impedance earth connection, I guess. Some of the strongest ham signals emanate from ships and even narrowboats, where the hull is 'earthed' via contact with water.

Phil
Hi,
Your car aerial is probably a quarter wave,and is tuned against the body of the car,this represents the missing half of a dipole,these sort of aerials dont need an earth, I believe most hams use dipoles,qtr wave or some other 2 connection resonant arrays.
The earth we are discussing is the one used with a long wire which has to have a ground to complete the circuit.We can get away with this connection for receiving because of stray capacitance,the earth terminal of the receiver is "earthed" via the mains,or,across the transformer windings,and in so doing will be added all the noise and interference that exists with the public mains today.Any other earth connection is often better,even a long lead to a ground spike,but,again best results when this is a very,very short and thick wire to a good ground spike,even though we have a high impedance circuit,you certainly dont want inductance in this connection.
One other thing,dont connect a ground spike earth to the earth terminal which is also connected to mains earth.(This is one reason why radios do not have 3 core leads)
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Old 8th Jun 2006, 5:45 pm   #27
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Default Re: Radio earths

Quote:
Originally Posted by Biggles
Regarding all the theory discussed in this thread, RF is never an exact science in my experience, there being so many influences on its behaviour from other sources. I often find that a little intuition and experimentation produce better results than following text book preachings to the word.

Biggles.
I fully agree! And I'm going to try a few experiments myself over the next few days. I have a metal ground spike adjacent to my shack, so I'll run a thick earth wire inside and up to the workbench, and try to measure the effect of the earth connection on the performance of some of my vintage valve receivers...

Zak is correct in that most home-based transmitting hams use either a 'balanced' antenna which is isolated from earth, such as a dipole, rather than a long-wire antenna of the 'Marconi' type which is unbalanced and tuned against earth. The reason is that long-wire antennas often cause awful interference to neighbouring TVs when transmitting. My mobile HF antenna is essentially an very short inductively-loaded quarter-wavelength monopole (ie half a dipole) and the vehicle body acts as a ground plane. The ground plane behaves like a mirror, producing a reflection below it of the monopole above it, so you have your dipole again. Whether it causes TVI, I've no idea. I'm usually miles from anywhere or moving along pretty fast when I'm transmitting!

I'm not sure whether capacitive coupling between vehicle body and earth is a significant effect at such low frequencies and with such a large spacing between the 'plates'.

Phil
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Old 8th Jun 2006, 8:36 pm   #28
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Default Re: Radio earths

Quote:
Originally Posted by G4SPZ
I fully agree!

Zak is correct in that most home-based transmitting hams use either a 'balanced' antenna which is isolated from earth, such as a dipole, rather than a long-wire antenna of the 'Marconi' type which is unbalanced and tuned against earth. The reason is that long-wire antennas often cause awful interference to neighbouring TVs when transmitting. My mobile HF antenna is essentially an very short inductively-loaded quarter-wavelength monopole (ie half a dipole) and the vehicle body acts as a ground plane. The ground plane behaves like a mirror, producing a reflection below it of the monopole above it, so you have your dipole again. Whether it causes TVI, I've no idea. I'm usually miles from anywhere or moving along pretty fast when I'm transmitting!

I'm not sure whether capacitive coupling between vehicle body and earth is a significant effect at such low frequencies and with such a large spacing between the 'plates'.

Phil
I agree there will be a reflection from the ground plane,the car body,being close to ground will effectivly lower the feedpoint impedance,since a dipole has an impedance of 75ohm only in free space,however we see 50 ohm used a lot on dipoles that are not mounted high enough,this proves that the proximity of the earth will have some effect even on balanced systems.I remember seeing a lot of TV band 1 dipoles with the lower rod missing,but strangely did not seem to make any difference to reception! I find antenna theory and operation etc much of "suck it and see".
Sorry, topic drifting.
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Old 9th Jun 2006, 11:21 am   #29
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Default Re: Radio earths

Some car aerials that you wouldn't expect to work actually perform quite well. I used this configuration http://www.jag-lovers.org/snaps/snap...?id=1117063708 with an HMV 100 for a while. I only gave up with it because I kept skinning my knuckles when gear changing.

Peter.
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Old 9th Jun 2006, 11:27 am   #30
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Default Re: Radio earths

Sorry, I think you need to sign up to see the previous link. Here are the images..
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Old 9th Jun 2006, 9:48 pm   #31
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Default Re: Radio earths

Back in the 1970's I ran my old HMV1124 on a 60' longwire aerial and mains earth. Results were ok but effected badly every evening by interference from TV sets. I then used a seperate earth provided un wittingly by the GPO (for a part line) the results were amazing. Far better pick up on all frequencies and much lower levels of local electrical interference.
When I get some spare time I will be fitting a seperate radio earth as the results are well worth it.
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Old 12th Jun 2006, 1:33 am   #32
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Default Re: Radio earths

Quote:
Originally Posted by peter_scott
One of my fellow retired work colleages just related his experiences to me about resurrecting an old radio.

This may be obvious to you RF guys but without giving it much thought I had always assumed that a domestic ring main earth would serve as a radio earth but my friend found that the 30 or so feet of earth cable between his radio and the earthing rod was clearly acting as an aerial and thus reducing his effective aerial signal by common mode.

After burying an old stainless steel sink in the garden close to the radio he
was very pleasantly surprised by the substantial increase in signal strength
which brought the weaker signals within range of agc control.

Peter.
I wonder if anyone else remembers the days when the "installation" leaflet for a valve radio used to talk about using a "mains aerial" ?
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Old 12th Jun 2006, 1:44 am   #33
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Default Re: Radio earths

Quote:
Originally Posted by YC-156
After having chewed on your relies for a better part of the evening, I'm sorry to say that my reaction is as follows: You guys have got to be kidding me, right?

This has nothing to do with transmitters but everything to do with impedance matching and maximum RF power transfer between a generator and a load.

If your arguments had been that if one was to add tuning components to an antenna system, then it might be more worthwhile to build an all out transmatch / 'antenna tuner' instead of messing with tuning out the reactive component of the ground connection, then I might readily have agreed. That would have made a fair bit of sense.

If all you want to receive is one of the local AM stations on MW, then yes, forget the ground connection. Just plug a random piece of wire into the antenna connection.

But if you do care enough about signal strength that you might consider using a quarter wave radial or have erected a long, outside wire up high, then things are a bit different IMHO. About a quarter of a century's worth of experience listening on shortwave on many different wavelengths have at least taught your's truly that proper care in construction of an antenna system can make a huge difference for reception. We are not talking picoVolts here, gentlemen.

For reception when using a random antenna I frequently use a good transmatch, an old Yeasu FC-901. This unit has a 'Pass Through' setting, so it is easy to switch the unit in and out of the circuit for doing comparisons.

The bottom is that I wouldn't make an antenna system for anything but very casual reception without going to some effort to optimize the impedance matching and minimize ground losses when possible.

In my previous postings in this thread I made the implicit assumption, perhaps incorrectly, that we were discussing MW and lower SW frequencies, below 10MHz or so. On those frequencies the random end fed wire alone will often have an impedance suitable for a direct connection to a receiver. This is assuming that the ground connection isn't completely off the wall.

Best regards

Frank N.
re: maximum power transfer. Couldn't agree more! Every amateur knows that whatever he's using for an "aerial", if the ratio of the power forward to the power reflected is poor, he ain't putting much up the stack! Ipso facto, the same applies to reception. In this case, the generator is the aerial - which assuming it is matched to its transmission line - "wants to see" a matched termination at the receiver. If there's an imperfect match, some power will be reflected back up to the aerial and will be re-radiated. Hence, the importance of "matching" - often achieved on reception with an ATU. The G5RV is a good study in the importance of matching at various freqs. and ways of doing this. And, therefore, it works well. That's one of the reasons why it's so popular.
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Old 12th Jun 2006, 9:30 am   #34
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Default Re: Radio earths

Please keep this on topic. It's about signal earths for receivers.

If you want to discuss transmitting aerials, SWR etc please start a new topic.
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Old 30th Jul 2006, 8:49 pm   #35
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Default Re: Radio earths

My old Strad had no earth connected and suffered from some hum and was very prone to interference from computers and mobile phones made it go nuts!
So when I replaced the mains lead I installed one with an earth. The results are far better than before. more is picked up than before and there is far less interference that before.
Watch out for radio's with a live chassis if you try this though!
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Old 5th Nov 2006, 8:33 pm   #36
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Default Re: Radio earths

I would urge anyone connecting their radio earth terminal to a water or central heating pipe to make sure the earth terminal is isolated with a class-Y capacitor and not to rely on the old wax Hunts effort..even if your radio has a mains transformer.
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Old 6th Nov 2006, 8:50 pm   #37
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Default Re: Radio earths

Quote:
Originally Posted by Dickie View Post


On a similar topic, has anyone solved the problem of how to get a good earth in a loft room, where my workshop happens to be?

Cheers, Richard
Hello Richard,
This method usually works ok if you keep the pot watered. Its also fully portable.
Regards John.
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Old 6th Nov 2006, 9:06 pm   #38
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Default Re: Radio earths

That's an approach I hadn't considered. I assume that the green/yellow colour coding of the wire is essential for this to work effectively? And presumably a John Innes no.3 will also give the best results?
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Old 6th Nov 2006, 9:34 pm   #39
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Default Re: Radio earths

That trick must have been played on hundreds of apprentices over the years. "Go and get the portable earth from the van" is up there with "Go to the stores for a long stand"
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Old 6th Nov 2006, 11:27 pm   #40
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Default Re: Radio earths

Don't over water it though, Cacti don't like their feet to be too damp!

Regards,
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