How to check a FM ariel

[halb]

Is it possible to check a FM radio ariel using a multimeter, I ask as I'm installing one of the Chinese transponder and have an unused ariel on my mizzen mast, any advice will be gratefully received.

 

[Martin_J]

Unlikely... Some makes of antenna present for example a 10 k ohm resistance so you can at least test them to prove you have no short or open circuit. Not all are like this.
For a real test on a vhf antenna system (antenna, cable and plugs) you really need swr meter that will work at the required frequency...
Maybe someone near you has one and could visit and test..

 

[David2452]

I doubt it would be of any use, an FM radio antenna is not designed to transmit and the coax is generally 75Ω, even a marine VHF antenna is a slight compromise for AIS signal transmission, though more than adequate.

 

[wooslehunter]

This seems to be a question that pops up with remarkable regularity.

If all you're going to do is receive, then if you can receive, it's OK. That's not to say it's optimal or even very good. But if it works then that's fine.

On the other hand, if you intend to transmit, then it needs to be the right antenna & also in good condition. If it's neither of these, then at best it won't work very well and at worst, it could damage the transmitter.

It's not possible to fully check any antenna with a multi-meter. Electrically, the antenna is the whole feeder cable plus the antenna itself & the minimum you really need is a VSWR meter & the test itself is very simple. You don't have to understand what you're actually measuring but juts need to understand how to make the measurement & what to expect from a good/bad antenna. A CB meter may or may not be any good at marine band frequencies. In fact a cheap CB meter probably won't be any good & the only way to check is to use some expensive test equipment. So, anyone doing the VSWR test should get a meter designed for VHF. One supplied for 2m amateur radio use will be fine & they're not really that expensive.

If what you have is a broadcast FM radio antenna, then it's highly unlikely to work at marine VHF frequencies. Get the right antenna for the job.

 

[SHUG]

The Marine VHF band is 156 to 162MHz (approx) and this meter would allow you to test VSWR
http://www.ebay.co.uk/itm/Avair-Maas-SWR-AV-40-RX-40-VSWR-POWER-Meter-Ham-radio-VHF-UHF-/161267805890?pt=UK_Mobile_Phones_Communication_Radio_Meters&hash=item258c4f6ec2

 

[kolster]

If someone is going to check the VSWR what channel should they use? Obviously not 16

 

[nigelmercier]

Is it possible to check a FM radio ariel using a multimeter, I ask as I'm installing one of the Chinese transponder and have an unused ariel ...

Good for washing your clothes

Seriously though, an FM aerial is no use whatsoever for this.

 

[David2452]

If someone is going to check the VSWR what channel should they use? Obviously not 16

I use 20 for new install checks and fault diagnostics, it's mid range so gives a good indication.

 

[vyv_cox]

Easiest way to check that an FM aerial is working is to plug it into the radio. I have not bothered with an aerial for years, a 2 metre length of wire works perfectly well, fed through a nearby locker.

 

[Salty John]

Easiest way to check that an FM aerial is working is to plug it into the radio. I have not bothered with an aerial for years, a 2 metre length of wire works perfectly well, fed through a nearby locker.

I believe the op is hoping to use what he thinks of as an FM aerial for his AIS transponder. Unclear what the aerial in question actually is.

 

[kolster]

I use 20 for new install checks and fault diagnostics, it's mid range so gives a good indication.

Thanks for that David, as a licensed radio amateur I have both HF & VHF / UHF VSWR meters but wanted to make sure which channel to use.

 

[David2452]

Useful video on YouTube by Shakespeare for VHF antenna installation troubleshooting.

 

[vyv_cox]

I believe the op is hoping to use what he thinks of as an FM aerial for his AIS transponder. Unclear what the aerial in question actually is.

Thanks for the clarification. 'Chinese transponder' means nothing to me.