HF aerial - cracks

Submitted: Sunday, Sep 13, 2009 at 18:11

ThreadID: 72237 Views:2165 Replies:4 FollowUps:4

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Member - Shane D (QLD)

I have a multi tap HF aerial that hasn't had a real lot of use recently, so I fitted it up the give the HF a bit of a run so to speak, anyway's, as I was fitting the aerial to its base I noticed lots of cracks running around the shaft, I have always been carefull of low tree branches but have hit some at low speed and have had to bend the aerial down to almost to the height of my roofrack to get under fallen trees and the like,It is mounted on a spring base of course, but it's quite solid, and feel that this may of hyperflexed thus cause cracking

Question:

Are these crack's cause for concern?
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Shane

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Reply By: Member - Kevin B1 (WA) - Sunday, Sep 13, 2009 at 18:40

Sunday, Sep 13, 2009 at 18:40

Have the same cracks occurring on my aerial also. It is about 5 years old and I wouldn`t think is should be cracking at this stage, although it dosn`t appear to affect the operation of it.

AnswerID: 383008

Follow Up By: Member - Shane D (QLD) - Monday, Sep 14, 2009 at 18:37

Monday, Sep 14, 2009 at 18:37

Thanks mate, I bought mine s/hand, age unknown.
Shane

FollowupID: 650751

Reply By: obee1212 - Sunday, Sep 13, 2009 at 18:41

Sunday, Sep 13, 2009 at 18:41

These type of aerials to my knowledge are wound onto a glass fibre rod and then covered with a tough but flexible membrane. It looks like the membrane is getting a bit old and not as good as it usedta.

The winding has its own insulation like the stuff in a motor winding and the central shaft will be as good as ever. I reckon it will see you out but if you want it to look the part then I am sure the manufacturer could replace the membrane no sweat.

Personally I would not worry as long it works.

Owen

AnswerID: 383009

Reply By: Member - joc45 (WA) - Sunday, Sep 13, 2009 at 20:17

Sunday, Sep 13, 2009 at 20:17

Provided that the coating doesn't start flaking away from the pole, you shouldn't have any trouble.
Adding extra insulating tape around the cracks will probably de-tune the antenna slightly; ie, the thickness of the coating is taken into account when the antenna is tuned, so I wouldn't recommend adding any extra tape or heat-shrink tubing.
Gerry

AnswerID: 383023

Follow Up By: PandJ - Wednesday, Sep 16, 2009 at 15:19

Wednesday, Sep 16, 2009 at 15:19

Hi Gerry,

When an antenna is tuned for a resonant frequency the wire is tuned not the heat shrink tubing or plastic coating covering the wire. So by adding more heat shrink over the splits will not alter the resonant frequencies one bit.
Cheers P&J

FollowupID: 651012

Follow Up By: Member - joc45 (WA) - Wednesday, Sep 16, 2009 at 15:28

Wednesday, Sep 16, 2009 at 15:28

Hi P&J,
The dielectric effect of the heat shrink does shift the tuning. Trust me, I've made a few!
However, I will concede that quite short bits of heat-shrink will probably have only a slight effect, given that once each shorting turn is adjusted, I put a small amount of heat shrink over that to lock it in place and the effect is minimal. I certainly wouldn't be recommending that long pieces of heat shrink be put over the cracks.
cheers
Gerry

FollowupID: 651015

Reply By: anglepole - Monday, Sep 14, 2009 at 15:23

Monday, Sep 14, 2009 at 15:23

Hi

If it is an Australian made antenna, send (email ) these photos to them and seek their opinion, they may have a "proper" fix.

Worth a try I would think.

Cheers

AnswerID: 383097