Barrett hf radio earthing

Submitted: Sunday, Mar 09, 2014 at 09:55
ThreadID: 106621 Views:2429 Replies:8 FollowUps:16
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i have used heavy round cable to earth the auto tune antennae to the vehicles body,but i am advised that i should use flat braided copper wire for the earthing.
Can anyone confirm or advise if there is any difference between the two.
Is there a supplier for this flat braided wire,i am in the illawarra nsw.
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Reply By: Member - PJR (NSW) - Sunday, Mar 09, 2014 at 10:10

Sunday, Mar 09, 2014 at 10:10
You'l be fine. As long as the terminations both end are secure and clean.

Phil
AnswerID: 527953

Follow Up By: PeteS - Tuesday, Mar 11, 2014 at 17:59

Tuesday, Mar 11, 2014 at 17:59
Congratulations Phil,
You made the first response, it was simple, to the point and answered Peppers question.

I'll 'try' and learn from this............ Can't promise but I will try ;-)

Cheers,
PeteS
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Reply By: Stu & "Bob" - Sunday, Mar 09, 2014 at 10:25

Sunday, Mar 09, 2014 at 10:25
You should be good. Barrett uses a heavy round cable, while Codan uses flat braid.
The antenna earth is an RF earth not an electrical earth. RF travels on the surface of the cable, so therefore more surface area is better.

As long as your connections are clean and tight, you shouldn't have a problem.
AnswerID: 527954

Follow Up By: pepper2 - Sunday, Mar 09, 2014 at 10:44

Sunday, Mar 09, 2014 at 10:44
Thankyou for taking the time to reply ,your advice is appreciated.
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Follow Up By: Member - John (Vic) - Sunday, Mar 09, 2014 at 15:00

Sunday, Mar 09, 2014 at 15:00
Codan now use round also on the new 3040 autotune.

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Reply By: The Bantam - Sunday, Mar 09, 2014 at 10:44

Sunday, Mar 09, 2014 at 10:44
The reason that flat braid is used is that it is most flexible.

If you are using some form of round insulated cable, make sure that it is fine stranded and flexible and you have it arranged so that it does not produce a stress point.

a loop is a means of distributing stress.

Braided earth straps cold be a little difficult to find out there in retail land.

One of the heavy electronic suppliers like eliment 14 or radio spares (RS components) may have something in their catalogue.

cheers
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Follow Up By: Ross M - Sunday, Mar 09, 2014 at 10:59

Sunday, Mar 09, 2014 at 10:59
My thoughts as well. Fatigue resistance is better with flat braid.
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Follow Up By: Stu & "Bob" - Sunday, Mar 09, 2014 at 11:38

Sunday, Mar 09, 2014 at 11:38
Here you go.

Flat braid
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Follow Up By: Member - John and Val - Sunday, Mar 09, 2014 at 12:28

Sunday, Mar 09, 2014 at 12:28
Guys - As already said, the RF properties here are important. Flat woven cable is good for flexibility, but also provides lots of surface area which is desirable for RF. Introducing a loop is good practice for flexibility but very bad practice when handling radio frequencies, even the low rf involved here.

Cheers

John
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Follow Up By: The Bantam - Sunday, Mar 09, 2014 at 12:58

Sunday, Mar 09, 2014 at 12:58
Due to the size of the conductors being used the "skin effect" will have little effect in the earth strap in comparison to a circular.

The major consideration in an earth strap in this situation is mechanical strenght and durability.

If ya going to start arguing skin effect...lets start with the RG58 coax....if the diameter of the earth strap is bigger than the feed line...the skin effect arguement simply fails...remember the central conductor in the coax will be .9mm.....yeh there will be skin effect there and more complicated besides.

As for a loop being bad practice....a 2 inch single or part turn loop will have bugger all effect at HF frequencies..particularly in an earth strap.

In commercial radio it is common, recommended and often required practice to install loops in feeders leading to antennae and other cables.

If the idea of a loop bothers you, a dog leg, a J loop or a carefully laid bend will provide the relief required.


OH...BTW..what are you earthing too...and is that then properly bonded to other parts of the body.

SO..if you are mounting the auto tune on the spare wheel carrier....the auto tune needs to be bonded to the carrier, that in tern needs to be bonded to the chasis and the adjacent body needs to be bonded to that.

quite often the complicated earth path puts paid to any concerns about a loop in the earth wire.

cheers
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Reply By: PeteS - Sunday, Mar 09, 2014 at 11:58

Sunday, Mar 09, 2014 at 11:58
Hi Pepper2,

High Frequencies tend to run on the surface of the copper, they call this the skin effect.
http://en.wikipedia.org/wiki/Skin_effect

The braid has a greater surface area and therefore it is more suitable.
Braid also has the advantage of flexibility.

Cheers,
PeteS
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Follow Up By: The Bantam - Sunday, Mar 09, 2014 at 13:17

Sunday, Mar 09, 2014 at 13:17
I hear this skin effect beeing tossed arround so much.....sorry most of the time it is irrelivent.

If we have an RF feeder of RG58......there will be less skin in that than there is in a piece of 10mm2 plain fine stranded circular cable.

Just to confirm..I went out to the shed and checked...no contest.

That is what I would be using as an earth strap if I was running circular.

That is before you start arguing about if it is the skin of the whole cable or the individual conductors.

Even if you could buy one you would not be wise to use a braided earth strap with less than 10mm2 copper content.

the mechaical constraints will override any notion of skin effect.

cheers
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FollowupID: 810411

Follow Up By: The Bantam - Sunday, Mar 09, 2014 at 13:25

Sunday, Mar 09, 2014 at 13:25
OH just to complicate the matter.

Most of the higher performance coax feeders, do not use braided outer conductors...they use plain foils or tubes.....or they use plain foils with a covering braid.

Braid is used mostly for flexibility.

the argument is that because of skin effect, the braid is inferiour because the electrical path in some sutuations is longer and higher resistance than straight laid strands or a foil or tube.

Start with the skin effect argument and most of the time it is all minutia and irrelivent......there are mostly greater considerations.

cheers
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Follow Up By: The Bantam - Sunday, Mar 09, 2014 at 13:36

Sunday, Mar 09, 2014 at 13:36
Just to bang another nain in the skin effect coffin.

follow the link provided above to the braided earh strap.

It's 25mmm wide.....that would have to be 20 to 25 ish mm2......forget about skin effect there boys.....its pure weight of copper doing the work..and lots of it.

Oh yeh there will be skin effect.....but there will be more skin than the sauna of a weight loss clinic.....plain or braided with that much skin....there is no shortage.

cheers
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Follow Up By: PeteS - Sunday, Mar 09, 2014 at 13:44

Sunday, Mar 09, 2014 at 13:44
Hi ya Bantam,

Did I incorrectly answer Pepper2's question?

Thanks,
PeteS
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FollowupID: 810416

Follow Up By: The Bantam - Sunday, Mar 09, 2014 at 14:08

Sunday, Mar 09, 2014 at 14:08
Braided or plain will make no difference in this case due to skin effect, as long as the conductor is of a practical and sufficiently robust size.

Depending on the situation and the frequencies involved...braided conductors may be inferiour as the braid will have a higher resistance than plain straight conductors.

Its not always a case of right or wrong.

There is so much said about skin effect....mostly incomplete information leeds to less than good conclusions.

So often skin effect is rasied as a major consideration where it is insignificant.

Sorry but the whole skin effect thing is a bit of a hobby horse.


cheers
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FollowupID: 810419

Follow Up By: PeteS - Sunday, Mar 09, 2014 at 14:14

Sunday, Mar 09, 2014 at 14:14
Thanks Bantam,

Hope I didn't get under your 'skin' :-)

Sorry for the head-spin Pepper2...

Cheers mate,
PeteS
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FollowupID: 810420

Follow Up By: Member -Ted (Vic) - Sunday, Mar 09, 2014 at 15:26

Sunday, Mar 09, 2014 at 15:26
Skin effect at HF frequencies is negligible it really only becomes significant at VHF and more so at UHF. I run an auto Barrett and use a piece of 6mm wire and have had no problems. Providing the connections are good and earthed to the body of the vehicle you should not have a problem.

Cheers
Ted
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FollowupID: 810424

Reply By: Ozhumvee - Sunday, Mar 09, 2014 at 13:29

Sunday, Mar 09, 2014 at 13:29
Also make sure the antenna mount is well grounded to both the vehicle body and the chassis whether it is bull bar, towbar, tyre carrier or roof rack. Otherwise you may have weird tuning problems.
When autotune antennas first appeared I used to install HF's in everything from prime mover to cars and it never ceased to amaze me the weird problems caused by the antenna mounting not being being well connected electrically to the vehicle. Just a few ohms makes a big difference.
Peter
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AnswerID: 527973

Reply By: pepper2 - Sunday, Mar 09, 2014 at 14:25

Sunday, Mar 09, 2014 at 14:25
Thankyou for the replies , the mounting point is the front bull bar ,can you advise if it makes any difference attaching the earth to the body or the earth terminal on the main battery ?????
AnswerID: 527976

Follow Up By: The Bantam - Sunday, Mar 09, 2014 at 18:12

Sunday, Mar 09, 2014 at 18:12
Its not the battery you should be concerned about.

In place of "the greater mass of earth" if the aerial would have been ground standing , what you are connecting your antenna to is "the greater mass of car"....the whole metal mass and surface of the car is a substitute for real ground

SO
you need to ensure there is a solid bond between the autotune base and the bullbar, and between the bullbar and the chasis....and arguably there is a good bond between the chasis and the body....and it would not be excessive to make sure the bonnet is well bonded to the body.

Its about providing a well bonded ground plane, not so much a power supply issue.

cheers
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FollowupID: 810432

Reply By: Allan B (Member, SunCoast) - Sunday, Mar 09, 2014 at 17:43

Sunday, Mar 09, 2014 at 17:43
Pepper,

Either flat braid or circular stranded conductor will be equal for your grounding application.
What is important is the quality of the bond connections at either end of the conductor. It must be clean, strong and reliable to a rigid part of the body mass. It is also important that any body panels adjacent to the antenna be also well bonded.

The cross-sectional area of the grounding conductor need not be huge, simply mechanically strong for reliability. It is after all going to carry no more RF currents than the skimpy centre conductor of your RF antenna feed cable. (Not quite true but near enough)

The subject of "Skin Effect" is often raised in this RF context to support the employment of multi-strand cables benefiting from an enhanced surface area in an RF cable. The physics related to this "skin effect" are quite complex and simply employing stranded conductors in an RF cable is not necessarily appropriate without other considerations. "Skin Effect" is however often the basis for argument by the unqualified or those wishing to financially benefit. Neither understand what they are talking about!

In any case, this is not an RF feed cable, simply a bonding conductor and I'm confidant the earthing cable you have already used will be fine for the purpose.


Cheers
Allan

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AnswerID: 527983

Follow Up By: Member - PJR (NSW) - Monday, Mar 10, 2014 at 20:41

Monday, Mar 10, 2014 at 20:41
Hi Allan. I made just a simple statement and then just sat back and watched peppers brain being fried.

To quote you: "Skin Effect" is however often the basis for argument by the . . . Yep Most definitely true mate.

See I behaved.

Phil
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Reply By: HKB Electronics - Monday, Mar 10, 2014 at 10:45

Monday, Mar 10, 2014 at 10:45
As above stranded cable will do, the other thing I would add is good clean metal to metal contacts. If the auto tune is mounted on the rear door I would also recommend you earth the auto tune to the door, then the vehicles body and then to the vehicles chassis.

Leigh

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