VHF Aerials

[Guest]

When I put my mast up at the begining of the season I noticed that there is a continuous circuit in the aerial between the central core and the sheathing when a tester is put across the cable at the plug to the radio end. This doesn't seem to be right although the radio works OK.

has anybody got any suggestions?

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[Strathglass]

No reason why not. Some VHF aerials have internal matching circuits which present an effective short circuit to DC but also give the correct impedence to a VHF signal. Depends upon the actual aerial.

Iain

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[Guest]

My aerial cable also shows a circuit between sheath and core. The radio works O.K. which probably means that this is normal.

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[JonBrooks]

Whilst in some cases aerials will show a "short circuit" between centre and shield when working correctly, this may not be right for you aerial.
If you do not have the paper work for the aerial a check of the VSWR will tell you if the unit is working correctly.

If you do not have access to a VSWR meter a local marine electronics shop could help or a local Ham radio person.

Hope this is a help.

Regards

<hr width=100% size=1>Jon Brooks Icom UK Ltd. 01227 741741

 

[andy01842]

Most aerials will show zero ohms or open circuit when tested with a multi meter. If a resistant is shown that changes when the wind blows or it rains then you have a problem. A multi meter is dc. An aerial works at rf frequency i.e. vhf is 150 Mhz and thing happen in a vary different way at this frequency. A VSWR meter is the only way to check an aerial. A aerial has Reactance and impedance, it is a tuned circuit not pure resitance.

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[Guest]

Thanks for the help. It's probably OK then as it does seem to work OK.

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