HF and Earth

Submitted: Friday, May 23, 2008 at 11:41
ThreadID: 57913 Views:1750 Replies:2 FollowUps:3
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I know that the earthing of the auto tune aerial is very important and there is an earth strap at the base of the aerial that has to be fixed to the body of the vehicle.

Is there a problem with running a heavy cable (12v X 150amps the same as used in dual battery set ups) from the earth strap to the - pole on the battery? The same battery that the HF radio unit runs off.

Advantage would be a good earth but would it have interference when using the HF or is there some other thing that might cause a problem?

Wayne
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Reply By: Mike Harding - Friday, May 23, 2008 at 11:48

Friday, May 23, 2008 at 11:48
Yes, there is.

Your cable is only low impedance (resistance) at DC and low frequencies, once the frequency rises to some number of megahertz the inductance and (to a lesser extent) capacitance of that cable will cause issues - in other words at 8MHz that cable is not zero ohms it may be (guessing) 5000 ohms.

The best solution is a short braided strap to a good, clean chassis point.

Mike Harding
AnswerID: 305442

Follow Up By: Wayne (NSW) - Friday, May 23, 2008 at 11:59

Friday, May 23, 2008 at 11:59
Mike,

Thank you for the reply, I will stay with the braided earth strap.

Wayne
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FollowupID: 571445

Reply By: Member -Signman - Friday, May 23, 2008 at 11:51

Friday, May 23, 2008 at 11:51
Hi Wayne,
Just my tuppence worth..
Don't confuse RF earth with electrical (battery) earth..
What your trying to do is make the vehicle a large ground spike- hence the surface area of the earth strap braid to the chassis/body of the vehicle....so long, of course, all the connections are clean and tight.
If someone could organise a base (I found a spring)- I could set you up with a tapped whip..
Cheers

AnswerID: 305443

Follow Up By: Wayne (NSW) - Friday, May 23, 2008 at 12:04

Friday, May 23, 2008 at 12:04
Signman,

Thank you for your reply, it has cleared a few things up about the importance of the vehicle. The bigger the vehicle the bigger the ground spike. I have never thought of the Troopie as a ground spike.

What does this base for the whip look like, can one be made?

Wayne
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FollowupID: 571448

Follow Up By: Member -Signman - Friday, May 23, 2008 at 12:31

Friday, May 23, 2008 at 12:31
The base is just a bigger version of a CB base- except for a 1/2" stud (instead of 5/16)- and a side entry for PL259 co-ax connection..

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FollowupID: 571455

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