cable question for VHF masthead antenna

[ribbony]

I have a new Banten SS masthead antenna and looking at the install instructions a question arises. The radio end is stripped back with both coax conductors being used in the fitting (insulated from each other). But on the top end of the cable the instructions only show stripping the outer sheaf and leaving the inner with the insultaion on, then it is inserted into the aerial base and only the outer conductor appears to make a connection.

Does this seem correct ?

I can not see how the inner will connect into the whip aerial and what was the point of stripping and soldering the lower end if it does not do anything up top ?

[Tim88]

Ribbony

You are right, you need the outer sheath to connect to the outer and the inner solid/strand to connect to the inner pin without any continuity between the two. Good luck.

[GordMay]

See the instructions for soldering PL-259 Coax Connectors:

Soldering PL-259 Coax Plugs

Soldering PL-259 Coax Connecters

http://www.shakespeare-marine.com/pdf/pl-259-8x.pdf

[MidLandOne]

You will find that in the antenna bottom fitting there is a pin that the centre conductor pushes onto when the cable is inserted into the fitting. As the instructions say, you leave the insulation on the centre conductor but trim the outer sheath and the braid back to the dimensions that should be given in the instructions.

[ribbony]

Thanks, that sorts that out somewhat. The instructions did not describe anything, only some scant sketches on what to do.

What sort of resistance should one be looking at if you run a multimeter across an aerial (disconnected from cable) ?

[MidLandOne]

Originally Posted by ribbony

What sort of resistance should one be looking at if you run a multimeter across an aerial (disconnected from cable) ?

Am not 100% sure for the Banten VHF antennas but they are almost certainly short circuit (zero ohms) to DC at the antenna.

[GordMay]

Either Infinite or Zero.
The results of a DC Continuity test (Ohms between centre conductor & ground shield) will depend upon whether the antenna is a Shunt fed (shorted, low DC resistance), or a Series Fed (open, infinite DC resistance).

[MidLandOne]

Yep, and half wave VHF stainless whips, so somewhere around 1 meter tall, are typically shunt fed (in fact I don't know of any that are not, but that doesn't mean that none exist ) so are zero ohms or close to it DC resistance.

[fairbank56]

Half-wave antenna's made by Larsen, very popular for land mobile applications, especially among hams, are not DC grounded. The base coil has a capacitor to ground and will read open with an ohmmeter. It's always best to test the antenna when new and keep the results in your records so you know what to expect if you ever have to troubleshoot later.

Eric

[ribbony]

Sounds like an open or shut case

Thanks for the tips !

[MidLandOne]

Originally Posted by fairbank56

Half-wave antenna's made by Larsen, very popular for land mobile applications, especially among hams, are not DC grounded. The base coil has a capacitor to ground and will read open with an ohmmeter.

Yes, there are lots of land mobile antennas that are not DC grounded (for example VHF/UHF/cellular, etc vehicle ss whips are often open circuit) but do you know any 1/2 wavelength marine VHF stainless steel whips that are?

I am not sure of this, just assumption on my part, but I think the practice for marine VHF half wave ss whips is that they are designed DC grounded through the matching coil eg no blocking capacitor, as an intentional charge drain because a frequent application is for masthead mounting???

[fairbank56]

Originally Posted by MidLandOne

but do you know any 1/2 wavelength marine VHF stainless steel whips that are?

Yes, the very popular Shakespeare line. Their model 5215 3' 1/2 wave stainless steel whip specially designed for masthead mounting is not DC grounded.

Eric

[MidLandOne]

Well so they are and I even have a new one sitting here - but I did double check it with an ohm meter to make sure that you weren't pulling my leg .