swampthing
Well-Known Member
Before steping mast, id like to test coax and antenae. Is it posible to do this with a multimeter? If so, what sort of resistive values should I check for? Not sure how old the installation is. Thanks
VHF antenae test. Multimeter?
- Thread starter swampthing
- Start date
VicS
Well-Known Member
A resistance test should show a low reading between centre conductor and sheath but that does not guarantee all is well. If you can disconnected cable from antenna then you can check for continuity of both conductors and for shorts between them.
john_morris_uk
Well-Known Member
Most VHF antennas are effectively a short circuit for DC. A multi-meter should give a reading of a couple of ohms or so across inner and outer at the transceiver end of the co-ax.
People will tell you to use a VSWR meter, but remember that water filled coax will give a low VSWR reading just as well as a good bit of co-ax and a good antenna on the end of it. In other words, a low VSWR is not a complete guarantee of a good antenna system.
People will tell you to use a VSWR meter, but remember that water filled coax will give a low VSWR reading just as well as a good bit of co-ax and a good antenna on the end of it. In other words, a low VSWR is not a complete guarantee of a good antenna system.
William_H
Well-Known Member
Vic and John are probably right regarding "most" VHF antenna.
However if it is short ie 17inches possibly steel rod then it is probably a quater wave length dipole using the mast for a ground plane. This type will show no conductivity from outer to inner of the cable but should show a good DC connection to the mast and if yo have a bare steel rod antenna you should have a connection centre of cable to the rod.
The longer antenna in f/g rod are 5/8 wavelength with a coil to match the impedance and negate the need for a ground plane. This type are popular because they can be used on a f/g mobo cabin top.
However if it is short ie 17inches possibly steel rod then it is probably a quater wave length dipole using the mast for a ground plane. This type will show no conductivity from outer to inner of the cable but should show a good DC connection to the mast and if yo have a bare steel rod antenna you should have a connection centre of cable to the rod.
The longer antenna in f/g rod are 5/8 wavelength with a coil to match the impedance and negate the need for a ground plane. This type are popular because they can be used on a f/g mobo cabin top.
captainslarty
N/A
I use an antenna analyser but not the sort of kit the average yottie would have on board. It can even tell the distance up the coax to a short or break.
It is worth changing the coax anytime you have the mast down - it is both cheap and easy to fit. Depending on the layout it can also be straight forward job to replace in situ.
It is worth changing the coax anytime you have the mast down - it is both cheap and easy to fit. Depending on the layout it can also be straight forward job to replace in situ.
swampthing
Well-Known Member
Ok, thanks for tips, and yes its the longer grp type.
