Vhf aerial problem .

[clyst]

Hi all , i think I have an aerial problem ......... I seem to be able to receive but unable to transmit . Iv tried another radio but it appears to be the same . I have a multi meter but not sure how to test the aerial cable ....... any advice would be appreciated . Cheers .

 

[europe172]

Hi all , i think I have an aerial problem ......... I seem to be able to receive but unable to transmit . Iv tried another radio but it appears to be the same . I have a multi meter but not sure how to test the aerial cable ....... any advice would be appreciated . Cheers .

DjfLight Vector Network Analyzer, Nano VNA 50KHz-900MHz, Digital Touching Screen Shortwave MF HF VHF UHF Antenna Analyzer Standing Wave DjfLight Vector Network Analyzer, Nano VNA 50KHz-900MHz, Digital Touching Screen Shortwave MF HF VHF UHF Antenna Analyzer Standing Wave : Amazon.co.uk: Electronics & Photo

I found this type useful if a little complicated to use

 

[Skylark]

A multi meter may not helpful.

What do you mean by “unable to transmit”?

One of the best ways to test is by substitution. A bit of caution is required, though, as radios do not like firing into damaged antennas. All tests should be on low power.

If you have determined that a second radio exhibits the same response, next step is to try another (emergency) antenna.

Test kit usually involves an SWR meter or a NanoVNA. Neither of which is expensive, both widely available and fairly easy to use.

 

[Stemar]

IIRC - and if not, someone will be along shortly to put me right, A multimeter should give close to 0 ohms resistance across the terminals of the cable. That will check continuity, but obviously won't tell you if a stray bit of wire has shorted the core and the shield.

 

[MikeCC]

An antenna may show open or closed circuit depending on design. As mentioned, easiest to use an SWR meter. You can borrow mine, and an antenna too, if you're anywhere near Exmouth.

 

[migs]

We once had a similar sounding problem - excellent reception but only 200m transmission range. The problem turned out to be a faulty right-angled adapter that was plugged into the transmitter’s antenna connector. The adapter’s inner was open circuit and presumably signals were able to ‘jump’ the small gap for reception, but transmissions were blocked. RF is mysterious stuff indeed.

 

[jdc]

...easiest to use an SWR meter. You can borrow mine ... if you're anywhere near Exmouth.

Or mine if anywhere near Falmouth (or I'd measure it for you). NB you do need to allow for the cable between VHF set and antenna.

 

[Dellquay13]

Hi all , i think I have an aerial problem ......... I seem to be able to receive but unable to transmit . Iv tried another radio but it appears to be the same . I have a multi meter but not sure how to test the aerial cable ....... any advice would be appreciated . Cheers .

Do you have a vhf deck plug at the mast base that you can disconnect? The multimeter can test the cable from vhf to the deck plug base, but no further really. Unplug the deck plug and check the resistance across the contacts of the plug at the radio end of the feed, up to the mast base. If that section is good then the resistance should be off the scale of most cheap multimeters.

 

[clyst]

Thanks for all your replies and advice .......... Will try another patch aerial and then maybe an SWR meter if needed . Regards .

 

[oldgit]

Before going all complicated....Check the power going to the radio.
12v needed all the time.
Very little curent draw pn RX.................. a few millivolts.
On TX it needs lots of amps.
Corroded connections will give high resistance and restrict volts/amps.
Check battery connections/bits of old chocolate block and frequently melted fuse holders on lesser quality radios ie anything other than ICOM.
If I had a pound for every faulty radio/ aerial that was bought into our workshop and it turned out simply to be a lack of volts in many cases due to birdnests of bits of added wire.

 

[iamtjc]

I had the same problem and it was nothing to do with the aerial.
Using a multimeter I measures the supply voltage as close to the radio as possible. I got 12.4v, when I pressed transmit it went down to 9.2v. That is too low for the transmitter to work. It confirmed my suspicion that the electrics on my boat were shot and that there was a high resistance in the 12v supply. A rewire of the boat fixed my issue. You may get away with tracking down a bad connection if this is the source of your problem.
It is a quick and easy test to do, so worth a try.

 

[clyst]

Hi guys thanks ,something I'd not considered DOH ! Will check outage today .

 

[mikegunn]

Like others on this thread, i too have suffered a similar problem. Having replaced the aerial and the 12V wiring, all to no avail I eventually sent the radio off to Icom for investigation. They failed to find any defect and respectfully suggested that I go back over the wiring very, very, very carefully and in particular look for signs of arcing. They explained that when pressing the PTT button there is a significant current surge which can cause arcing across dodgy connections. The damage caused by arcing may increase the local resistance to a point where it then blocks any further electrical flow until the next time the tx button is pressed. And so on and so on. That is why I always heard a click, but nothing else when using my handheld to monitor the transmission. I eventually found the culprit. A fuse holder! The only item in the power supply chain that I hadn't replaced. It wasn't gripping the cartidge fuse quite as snugly as it should. Only took me two years to sort that one out.
Mike