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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 13th Sep 2010, 1:57 pm   #21
Skywave
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Question Re: Gutter aerial

Pete - G4MRU

I like the idea of a screened earth - but isn't there a potential problem with this arrangement at frequencies above, say, 10 MHz, if the coax needs to be of any appreciable length - say 20 feet for example? Taking velocity factor of the co-ax into account, a quarter-wavelength at 10 MHz is about 21 feet - producing in a high-impedance at the 'receiver' end of the co-ax.

Afterthought - I do accept that at this freq. & up, earthing of RF aerial currents ceases to become important - for reception purposes, that is; transmitting arrangements are a totally different matter!

Al.
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Old 13th Sep 2010, 3:08 pm   #22
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Default Re: Gutter aerial

Yes, my understanding is that the earth should be conductive, so in effect you need it to be wet and organic rather than sand or rock. I have lots of cunning plans in a 1950s crystal set book that show ways of attracting water to the earth conductor - ranging from digging a pit and filling it with coke, to filling a tin can with salt and burying that.

My 1950s Bush DAC34 and Pye P75A work very well with 2m of wire thrown out the window and no earth, but my Invicta AW75 is from an age when people were expected to have a decent aerial and earth at home if they were going to spend a fortune on a radio
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Old 13th Sep 2010, 6:18 pm   #23
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Default Re: Gutter aerial

Hi.

Another small point on quick antennas. We used to say to make the best of an earth use multiple earths. So to do this we would say if spike one was 2ft deep then put the second one 2ft away, if spike one was 3ft deep then 3ft away then so on in the other direction. Not to favor one direction unless up against a wall. Then water it with your morning tea dregs.

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Old 14th Sep 2010, 12:52 pm   #24
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Default Re: Gutter aerial

There is a potential (pun not intended) risk using an external earth, if, like most homes, the household 'earth' is the incoming neutral split off at the meter (a TNC-S system). If there is a neutral fault further back down the line there can be a large voltage between house earth and radio earth, or if they are connected a large current. Best to put a 0.1 in series with the radio earth.

For a first class radio aerial I use a Welbrook ALA100 (http://www.wellbrook.uk.com/antennas...&product_id=35), this is an amplified loop type that I have at the end of the garden, feeds lots of radios at once and doesn't need an earth.

Being far from the house I get much less interference on LW/MW than in the house.
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Old 14th Sep 2010, 1:42 pm   #25
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Default Re: Gutter aerial

You can of course buy earth spikes from an electrical wholesaler. I think they're galvanised steel. Not as conductive as copper of course, but very rigid so that you can hammer them into the ground.
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Old 14th Sep 2010, 3:07 pm   #26
Dave Moll
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Default Re: Gutter aerial

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Originally Posted by merlinmaxwell View Post
If there is a neutral fault further back down the line there can be a large voltage between house earth and radio earth.
There would also be the same voltage between mains earth and the ground, so the radio earth isn't really substantially increasing the danger.
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Old 14th Sep 2010, 3:16 pm   #27
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Default Re: Gutter aerial

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Originally Posted by Dave Moll View Post
There would also be the same voltage between mains earth and the ground, so the radio earth isn't really substantially increasing the danger.
That is why the equipotential bonding requirements are more stringent for a PME installation.

There is, AFAIK, no requirement to bond guttering and similar extraneous metalwork which is unlikely to become live. (Trying to steer it back on topic!)
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Old 15th Sep 2010, 10:01 am   #28
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Default Re: Gutter aerial

The very reason that most guttering these days is plastic and hence nicely insulated from the house, yet in a straight line and high up, is why I thought it'd make a good support for an aerial wire.

Thinking about it - my house earth is derived at the meter from the neutral wire. It's bonded to the cold water pipe at the main stop tap nearby, so the cold water pipes are earthed obviously. However - my water supply pipe is iron, so the earth circuit in the house wiring is in fact directly connected to a pretty reasonable 'real' earth as well as the neutral derived one.

Or have I got that incorrect? Obviously I don't want to use the earth in the mains socket for a radio signal earth as it's rather closely coupled to a lot of noisy electrical equipment...
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Old 15th Sep 2010, 10:52 am   #29
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Default Re: Gutter aerial

Quote:
Originally Posted by Dave Moll View Post
Quote:
Originally Posted by merlinmaxwell View Post
If there is a neutral fault further back down the line there can be a large voltage between house earth and radio earth.
There would also be the same voltage between mains earth and the ground, so the radio earth isn't really substantially increasing the danger.
In PME the neutral is the mains earth, it can rise up a lot if there is a neutral fault, up to phase if the fault is near. This is safe in the house as everything is the same potential because of the bonding, however the voltage between house earth and a 'radio' earth can be very high, high enough to kill.

Back to the OP, the radiator will be a good radio earth, stick with it.
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Old 15th Sep 2010, 10:57 am   #30
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Default Re: Gutter aerial

This may help, or a least scare you enough to get it done properly!
http://www.rsgb.org/emc/docs/pdf/lea...leaflet-07.pdf
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Old 20th Feb 2011, 3:38 pm   #31
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Default Re: Gutter aerial

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Originally Posted by richrussell View Post
... Ideally I'd like to get round to burying a decent metal earth down where the ground is permanently damp. (or try one of the traditional 'tin can full of something that attracts water' designs). But stupidly we laid a paved patio right round the house last year. So I'll need a very good excuse to get permission to pull up a couple of slabs next to the house! ...
Just spotted this thread by chance ...

If you're still looking for that excuse, here it is:

Laying a paved patio right up to the house can cause problems because falling rain that would previously have been absorbed by the ground will now bounce off the hard surface. The harder the rain, the higher the bounce.

What happens is that the bouncing rain is driven against the brickwork by the wind and the height of the bounce enables it to bridge the damp course.

If the paving is higher than the previous ground level, the problem is even worse because the damp course is effectively lowered.

So, remove a row of paving slabs adjacent to the walls and replace with gravel (and as many earth rods as you like!)
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Old 20th Feb 2011, 11:15 pm   #32
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Default Re: Gutter aerial

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Originally Posted by Station X View Post
You can of course buy earth spikes from an electrical wholesaler. I think they're galvanised steel. Not as conductive as copper of course, but very rigid so that you can hammer them into the ground.
They are steel with a thick copper coating, 1m in length. In very soft ground two can be coupled with a threaded sleeve. I sank one in purely for radio use (mainly crystal set) just outside my workshop. It should be a lot 'cleaner' electrically than the house wiring earth.

Greg
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