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Thread: 'Random' wire

  1. #1

    Default 'Random' wire

    I'm going to have a go with a random wire (31 feet). As I need a good ground, is it acceptable to use the bonded earth in the house - eg. the central heating pipework that is bonded to earth?

    Thanks

    David

  2. #2

    Default dronley lodge

    You can certainly try it although most CH uses plastic piping these days and you will be using the mains earth which will introduce some noise. A good earth is not an easy thing to achieve and you may have to lay ground radials just as you would for a vertical to get best results.

  3. #3

    Default Thanks

    Quote Originally Posted by G6KIZ View Post
    You can certainly try it although most CH uses plastic piping these days and you will be using the mains earth which will introduce some noise. A good earth is not an easy thing to achieve and you may have to lay ground radials just as you would for a vertical to get best results.
    Thanks G6KIZ. Thankfully out CH system was fitted when the Ark was at sea and is copper throughout. I have tested continuity between the mains earth and a radiator feed pipe and it's very low resistance...I do appreciate your comment about mains-born noise...esp as we use some IP over mains - although this is on a different ring-main.

    I'll certainly consider ground radials if the noise is too frightful!

    Thanks again

  4. #4
    Super Moderator pmh's Avatar
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    Default

    I had a random wire, around 14 metres in length, plugged directly into the back of my MFJ intellituner for some time without an earth and it worked okish.

    I did eventually take an earth to a ground spike. However, before connecting, I checked the voltage between the spike and the house earth, which was around 5 volts, so I had no concerns over using it.

    If your house is PME, which is very likely, there are potential hazards in using an external earth, especially if there is a local neutral fault. This is the reason I checked before connecting.

    One of our club members is just under 50 volts on his, for which the local DNO said wasn't a concern.

    Kind regards,



    Phil

  5. #5

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    Without a good earth ground, you run the risk of RF in the shack when running QRO and using a long wire antenna. Great antenna for QRP not so much for QRO without extensive ground and common mode choke.

    Bill W3PNM


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  6. #6

    Default

    Thanks for all the advice...

    The earth on the pipework seems clean enough - I might try a spike in due course but will check potential between radio and domestic ground.

    A couple of further questions if I may - same subject...

    1. I'm using a random wire length as suggested on a US ham site - went for 31 feet just because it was a manageable length. There's only about 1.5 feet inside the house - attached to the MFJ tuner. Are we talking 31 feet EXACTLY or is there leeway? BtW I'm QRP.

    2. I'm using a laptop for CAT, Logs etc. The amount of noise from which drops by at least 80% when the power connector is removed (20v). I've put a ferrite choke around the low voltage cable but it makes virtually no difference. Should add another choke or is there something else I could try!

    Thanks

  7. #7

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    Quote Originally Posted by M3EVF View Post
    I'm going to have a go with a random wire (31 feet). As I need a good ground, is it acceptable to use the bonded earth in the house - eg. the central heating pipework that is bonded to earth?

    Thanks

    David
    Only 31 feet ? What bands will you be operating, sounds kind of short to me unless you will be working 40 meters and up. Don't expect great performance from it, it will get you on the air and you will make some contacts but for the most part your signals will be weak. With only 31', you would probably do well to hang it vertically if you expect to work some DX, but the better your ground is, the better it will work. So try your house ground and see how it works, then add to it if needed.

  8. #8

    Default

    Quote Originally Posted by M3EVF View Post
    Thanks for all the advice...

    The earth on the pipework seems clean enough - I might try a spike in due course but will check potential between radio and domestic ground.

    A couple of further questions if I may - same subject...

    1. I'm using a random wire length as suggested on a US ham site - went for 31 feet just because it was a manageable length. There's only about 1.5 feet inside the house - attached to the MFJ tuner. Are we talking 31 feet EXACTLY or is there leeway? BtW I'm QRP.

    2. I'm using a laptop for CAT, Logs etc. The amount of noise from which drops by at least 80% when the power connector is removed (20v). I've put a ferrite choke around the low voltage cable but it makes virtually no difference. Should add another choke or is there something else I could try!

    Thanks
    There is lots of leeway, depends on what bands you want to operate - lower bands require more wire. You might want to consider something the W3EDP antenna that uses an 84' wire and a 17' counterpoise wire and will cover 10 thru 80 meters via the tuner if you have the room. Just google the W3EDP antenna

  9. #9

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    Quote Originally Posted by KC8AON View Post
    Only 31 feet ? What bands will you be operating, sounds kind of short to me unless you will be working 40 meters and up. Don't expect great performance from it, it will get you on the air and you will make some contacts but for the most part your signals will be weak. With only 31', you would probably do well to hang it vertically if you expect to work some DX, but the better your ground is, the better it will work. So try your house ground and see how it works, then add to it if needed.
    Thanks KC8AON - Bit pushed for space but what would be the next length up from 31...bearing in mind all of the 'shouldn't use' lengths? 40 meters and up is OK for me - possibly 80 meters.

  10. #10

    Default

    Quote Originally Posted by M3EVF View Post
    Thanks KC8AON - Bit pushed for space but what would be the next length up from 31...bearing in mind all of the 'shouldn't use' lengths? 40 meters and up is OK for me - possibly 80 meters.
    Can you squeeze in 54 feet ? It would work 80 and up but somewhat a compromise on 80.

  11. #11

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    Going back a bit - 50V between spike and PME earth? That would concern me greatly. 50V is way outside what would be seen as normal, and depending on where it's originating could be interesting with an accidental double earth path. I'm thinking about perhaps putting an antenna on a mast where the other aerial is connected inside the house via the antenna cable to ground, and then your new radio antenna grounded outside the equipotential zone tries to bring this 50V down to the spike potential. You could have some serious current being sunk here - maybe more than a piece of thin foil can manage, or possibly the grounding in the TV set. 50V would be a nice spark even with minimal current. 50V is quite 'feelable' - and through a pair of headphones, or a boom mic could be interesting.
    Last edited by paulears; Sat 6th May 2017 at 19:13.

  12. #12
    Super Moderator pmh's Avatar
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    I couldn't agree more. 50v is no doubt the maximum permissible safety limit, but a voltage hovering around this level shows that something is wrong somewhere and warrants further investigation.

    Kind regards,



    Phil

  13. #13

    Default

    Sorry - yes would agree with the 50V PD! Needs checking out!

    Does anyone have any comment about shielding noise from my laptop? Two chokes on the low volts side but still quite a bit of noise. If I remove the power supply from the laptop, peace is restored!

    Thanks

    David

  14. #14

    Default

    Quote Originally Posted by M3EVF View Post
    Sorry - yes would agree with the 50V PD! Needs checking out!

    Does anyone have any comment about shielding noise from my laptop? Two chokes on the low volts side but still quite a bit of noise. If I remove the power supply from the laptop, peace is restored!

    Thanks

    David
    It's that switching mode power supply/charger - they are notorious for radiating noise and hash ! You might want to find a DC to DC supply for you laptop that allows you to charge it mobile and then run that off you station power supply which I hope is a linear type supply.

  15. #15

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    The Dell ones are really awful - the worst out of what I have had. Using the magnet from a 15" old loudspeaker as a torrid, did reduce it significantly, wrapping ten or so turns of the DC cable through it.

  16. #16

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    CH, PME, 50V PD; I'm in the USA, so I guess these acronyms are unique to DX. I can't follow..

  17. #17

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    They're not radio related terms, they're to do with electricity supply system - protective multiple earth (PME) 50V Potential difference (PD). The topic is asking about grounds. There is in most homes an electrical ground - designed to shunt fault current out of the way of us humans. The idea that electricity takes the shortest and most direct path to ground, and not through us! A random length of antenna wire needs a proper RF ground - which isn't the same thing really. In most cases, RF is looking for a large physical entity to use as a reflector/balance/antenna component - so ships at sea have the best one - thousands of miles of salty water. Soil, sand and rock are worse as a ground. So if your aerial system needs a ground - your outside surface is the biggest one, so many folk belt a big copper spike into the ground in the hope that it will be the access point to the real 'ground'. It was mentioned about plastic pipe. Years ago when we used lead piping, then copper, a water pipe in the home was also connected to the ground. Now, with plastic, not so certain. In the UK and I believe also in some areas of the US, the house wiring does what appears to be an odd thing. We have two conductors essential for our power - the hot live one, and the return, or neutral. Two conductors to make the circuit (and all we have on equipment with the figure 8 two pin power connection. No grounding at all. At the power station and the local substations, they join the neutral (return) conductor to ground, and then do the same in some homes - bond the ground and neutral near the meter. In your house or business, a volt meter between ground and the neutral should read around 5V or thereabouts, because the ground and neutral drift away from 0V as distance increases. It was mentioned above that somebody had 50V between them. Clearly, something is not right. For the difference to be that much, it's leaking from somewhere else, and is a fault.

    The upshot of all this is that electrical systems are designed to protect your life with grounding. Antenna systems need ground for something totally separate. If your home has a fault that allows the ground to be 50V away from real ground potential, then it's going to be interesting to try to use it as part of your antenna system - RF will be appearing through everything connected - computers, home entertainment, even the oven! Not good.

    In the UK we even have rules about electrics in outside 'shacks'. We don't allow an outbuilding to connect to the house ground system unless some complicated rules are followed, so in most cases, the outside building has Live and Neutral and then an earth rod. Inside the house we then have the question about should the RF ground be the house ground. Ideally no it should be separate. Practically, many people do use it. RF performance then relies on how good your home grounding is TO RF! Perfect electrical grounding does not automatically mean perfect RF grounding - two different needs.

    If you have a cheap multimeter, and a long power extension cable, do an experiment. Measure on the AC range between ground on the wall outlet and ground at the cable outlet fed from a different room. If you get between 0 and 5 Volts or so that is normal. If you get 10V plus at different outlets around the house, replugging your long cable, then your grounding is not as good as it should be. As one of it's uses is saving your life, you might want to investigate further.

  18. #18

    Default

    Very detailed explanation, thanks! I often wish I had followed my keen interest in electronics and all things electrical. I often regret that I choose different careers. As a result, I know some stuff, but in a shallow way.


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