Confused myself about antennas

[IslandJack]

I am hooking up a vhf. Since the mast was raised by me after being refit with a new coax and antenna, I thought I would check the lead before I hooked to the radio. Testing with a multimeter, I get infinite resistance from the conductor to the shield. I was expecting some lesser resistance to wag my meter. Anyone know offhand if the vhf antenna (Raytheon) on a boat is generally a 'no ground plate' or 'ground plate' installation.I hate to climb the mast to find out all is well and the no continuity measurement is normal....and I hate worse to kill a radio by xmiting up a dead end.Along those same lines, I have a little cb i was going to install....it's antenna is ground plate and reads resistance from coax to conductor. What are you guys using for a CB antenna?IslandJack

 

[joe phibbs]

rf vs dc conductivity

There is a world of difference (in potential) between an rf short and a dc short. Some materials are better at rf conductivity, some better at dc conductivity. Your typical rg 8 rg 58 rg 8u and rg 58u cable are very good insulators at radio frequencies. Some fm antennae show a dead short for dc test, but the wave length at FM frequencies shows a null at the tuning point. The only true test is an rf swr (radio frequency standing wave ratio) measurement. If your connections are good, your grounding sound, you should be ok. good luck, joe

 

[Bill Ogilvie]

Antenna testing

Your VHF antenna should look like a very high resistance to a DC meter. If the antenna is new and the connectors are all soldered to the coax and tight there should be no problem. Eventually the connectors fail, either at the top of the mast or at the radio. When a connector fails (open circuit usually) at the radio, transmitting will destroy the RF Amp in the radio. However a broken connection at the top of the mast will not destroy the RF Amp as quickly (or maybe not at all). You should make sure the antenna cable is never left off the radio and that it hasn't opened inside. A VHF SWR/Power meter is handy for testing, but check the connectors first.