Hi, Could anybody please help me. I am just starting out and am currently in the process of constructing an end feed antenna in my rear garden (Approx 20m with a 9:1 balun) I have driven in an 8 foot copper tube into the ground but am unsure as to what gauge of earth wire i should use, between the ground tube and the antenna. Any advice would be greatly appreciated.
Regards
Chris
Gauge of ground wire ?
- Chris57tx
- Regular
- Posts: 5
- Joined: 08 Jan 2016, 13:34
- Location: Lowestoft, Suffolk. England
- theEarwigger
- Super Member
- Posts: 434
- Joined: 24 Jul 2007, 20:59
- Call Sign: M0RZF
- Location: Portsmouth
- Contact:
Re: Gauge of ground wire ?
The gauge won't make much difference.
There is no such thing as RF "ground". For example at 30MHz 2.5m of wire (less if insulated) is a quarter wave and looks like an open circuit to the signal. In other words the wire running to the copper tube is part of your antenna and radiates.
Earth stakes do have their uses for safety purposes. Use green/yellow stuff like this -
https://www.tlc-direct.co.uk/Products/CA6SGY.html
There is no such thing as RF "ground". For example at 30MHz 2.5m of wire (less if insulated) is a quarter wave and looks like an open circuit to the signal. In other words the wire running to the copper tube is part of your antenna and radiates.
Earth stakes do have their uses for safety purposes. Use green/yellow stuff like this -
https://www.tlc-direct.co.uk/Products/CA6SGY.html
... www.M0RZF.co.uk ...
- kr0ne
- Veteran
- Posts: 4536
- Joined: 25 Sep 2011, 18:33
Re: Gauge of ground wire ?
You want to put your RF ground point as close to the antenna feedpoint (your 9:1 balun) as possible and you want to connect to it with something far more substantial than the wire used for a mains safety earth.
The braid from a bit of RG213 works well but keep the connection as short as possible.
The braid from a bit of RG213 works well but keep the connection as short as possible.
- Tigersaw
- Radio Addict
- Posts: 895
- Joined: 19 Oct 2013, 15:48
- Call Sign: GW6RRL
- Location: Llanwrtyd Wells Powys
- Contact:
Re: Gauge of ground wire ?
Agree on using braid rather than wire. Better still attach the 9:1 directly to the earth stake with a copper bracket
- Chris57tx
- Regular
- Posts: 5
- Joined: 08 Jan 2016, 13:34
- Location: Lowestoft, Suffolk. England
Re: Gauge of ground wire ?
Many thanks for the advice, it much appreciated.
Regards Chris
Regards Chris
- Adriano9966
- Veteran
- Posts: 3526
- Joined: 07 Jul 2008, 22:13
- Location: Banbury Oxfordshire
Re: Gauge of ground wire ?
I agree with the comments above but may I suggest that you also use some ground radials with your vertical and as many as practical . The length is not critical but longer is better if you are using lower HF bands. You can bend these to fit into the available space and if it's mounted on a lawn you can peg the wire down with stiff garden wire or aluminium tent pegs. If this is done well and the radials are pegged tight to the ground you should be able to mow the lawn over the top
HTH kind regards Adrian
HTH kind regards Adrian
-
- Top Poster
- Posts: 1090
- Joined: 10 Jun 2007, 22:41
- Call Sign: G4RMT
- Location: North East Suffolk
- Contact:
Re: Gauge of ground wire ?
I'm a little mystified by the need for a substantial capacity in the ground wire? While there can be fairly high voltages on the cable, I'd always considered the current demand to be modest. A low resistance/impedance path would be the aim, surely?
- kr0ne
- Veteran
- Posts: 4536
- Joined: 25 Sep 2011, 18:33
Re: Gauge of ground wire ?
It's because of something called 'skin effect'. Perhaps 'substantial capacity' is the wrong term, but RF does not behave like DC or low frequency AC when traveling along a conductor - whereas DC uses the entire cross sectional area of a piece of wire, RF only travels along the surface...
OK, actually it is slightly more complex than that, the frequency of the RF determines exactly how deep into a conductor the current will penetrate as it travels (the 'skin depth') but essentially, the higher the frequency the less metal in a given conductor is used to carry the current. At 80m, skin depth is around 35μm and at 2m it is closer to 5μm!
Because of this, maximising the surface area of a conductor is key. It's not necessarily about how thick or heavy it is, but how much surface area it has for the RF current to travel along.
OK, actually it is slightly more complex than that, the frequency of the RF determines exactly how deep into a conductor the current will penetrate as it travels (the 'skin depth') but essentially, the higher the frequency the less metal in a given conductor is used to carry the current. At 80m, skin depth is around 35μm and at 2m it is closer to 5μm!
Because of this, maximising the surface area of a conductor is key. It's not necessarily about how thick or heavy it is, but how much surface area it has for the RF current to travel along.