Outer Limits 4x4 Board

Should ground independant UHF aerials be open or closed curcuit?

I just purchased one on the weekend and mounted it on the bull bar tonight. Ran the coax through the fire wall, trimed up the coax at the radio end to attach the connection that goes onto the radio and I thought I would quickly check the continuity before soldering anything. The multimeter indicated there was an open circuit of resistance?

Should this be the case or is the aerial stuffed?

I checked the coax and all was in good shape so I soldered the connection on and went for a drive and it was receiving and transmitting quite well but the open curcuit has me baffled?

How did you check for continuity? Just the buzzer setting, or did you try to measure a resistance? If resistance, what range did you use?

Nominally, the impedance should be 50 ohm, but that's measured at RF frequencies. Using a DC source, I would expect you'd be able to measure some resistance, but much higher than 50 ohm - kilohms, or higher. But I've never actually tried it, so I don't know, and I'm probably wrong - again.

I do know that measuring a short between the inner and outer conductors of the antenna cable is a bad thing. But you probably already knew that.

-Scott- wrote:How did you check for continuity?

Come to think of it I didn't actually measure continuity, just resistance between the braid and the inner wire at the at the radio end, which gave a reading of infinite resitance which would mean an open circuit.

I guess it makes sense though if the aerial has an independent ground then the resistance between braid and inner core should be open.

I think I should be measuring continuity (and not resistance between the braid and inner wire) of the entire circuit which should in theory return a zero ohm result?

On the otherhand, my understanding of "ground dependent" is that there should be a circuit of resistance between the braid and the inner core.

It's been a long time since year 12 physics!

It all depends on what antenna it is.
A Dipole will show a short circuit.
A ground independant antenna should show open circuit.

To test these you need to make sure there is no short between the inner and outer braid, Do a continuity check between ground and the braid and also a check between the inner core and the antenna (or base where the antenna screws on) and this should show 0 Ohms (Or a short)

If it is a RFI Ground independant antenna eg CD28's, CD51 Etc you will not be able to do a continuity check as there is no electrical connection between the antenna and the inner core of the coax.

Cheers