VHF help needed

[Grith]

Oops that was help needed! Think predictive text got me again!

Title fixed

Hi All I am in the final rundown to our big Whitsundays Trip and have struck a problem I cannot figure out.
I relocated my fixed VHF, a Uniden Solara Submersible, from my old yacht to my current Imexus. It was working fine previously. The new fit was just out of reach of my existing cable which had been previously shortened.
During the re install the cable was stretched and ultimately a link section was added. The Ariel itself had also seen some service and bashing whilst folded down when towing.
When finished the vhf was receiving fine but didn’t appear to be sending.
Ultimately I blamed my sloppy ariel re install, age, cable extension and cable damage. I purchased a new ariel with 5 metre cable and reinstalled. ( At much effort as the mounts were different and I couldn’t find the old style.)
Testing today again the VHF is transmitting intermittently and very poorly.
Has anyone go any suggestions as to possible fixes before I have to buy a new head unit?
The head unit appears in good condition. ( photo attached) The Ariel now re installed is new and issue free in my view. It is located on the top of my targa bar on the rear of the yacht and is a 1.8 metre Uniden with both single direction tilt and unscrews from the base for trailering to preclude the previous bashing the old one suffered whilst folded down for towing.
The ends are screw on to the Ariel and the unit attachment precluding the need for the fiddly process of stripping back the end and attaching a new screw end.
The power supply is via my lighting circuit and pressing transmit there is a very slight dimming of my led interior lights I noticed tonight. ( power loss? and a need to run a separate line direct from the battery ) this wasn’t previously necessary.
Some other gremlin I haven’t thought of or some stupid mistake I have made?
Thoughts anyone.
PS Testing was carried out with my 10 years older hand held Uniden waterproof portable VHF which I could hear loud and clear on this unit when my partner was transmitting with this from inside our house.
Conversely when I was transmitting on both 5w and 25w with my fixed unit she couldn’t hear me at all in the house and on the verandah only 20 metres from the yacht the transmission was sometimes not happening and sometimes poor and broken up. Help!

[Pete7]

Ok, first off remove it from the lighting circuit and create a new single use circuit for the VHF with decent heavy wires etc, to avoid interference.

Next the VHF plug that you soldered on to the new cable, it was soldered wasn't it? Any chance something went wrong with that join?

Pete

[JPA Cate]

Or, possibly, a loose mike wire? Since it's intermittent.

Pete's suspicion of the coax solder job is a good one.

Do you have an swr meter, either external, or built in to the radio?

You're going to be able to best this, it must be frustrating right now.

Ann

[cr180]

Try testing with an SWR meter. They’re cheap and self explanatory.

[wholybee]

Problems with VHF radios are almost always problems with connectors. You replaced the antenna. What about the coax? How old is it, and id you install the connectors or were they preinstalled?

Having the VHF on the same circuit as lights isn't good, and neither is the lights dimming. A VHF will not perform as well at lower voltages, and the circuit clearly isn't keeping the voltage up. So, as Pete suggested, run a new circuit with heavier wire than is used for the lights.

[Spot]

You could make a simple 1/4 wavelength dipole antenna with a spare piece of coax and see if you can transmit and receive. If switching antenna and/or cable improves it, there is your answer. If not, the mic cord suggestion from Ann makes sense too.

I would not transmit at 25w until 5w is working.

If you know any amateur radio people they will most likely have a SWR meter to lend or invite them out to troubleshoot.

[Tin Tin]

This is informative.

https://www.youtube.com/watch?v=1SyGuzMSXlw

[Grith]

Thanks Tin Tin and others. After trying everything I finally have replaced the head unit and now everything is working correctly. I am going to guess a short when reinstalling the old cable or something similar damaged the transmission side of the VHF.
I am sure it could be opened and fixed but at A$ 207 for a new unit even attempting professional repair seemed not worth it.
I may pull apart the old unit myself and tinker so see if I can find the issue but with leaving to go cruising for 2-3 months next week replacement seemed the simple option at this point.

[deblen]

Originally Posted by Grith

Thanks Tin Tin and others. After trying everything I finally have replaced the head unit and now everything is working correctly. I am going to guess a short when reinstalling the old cable or something similar damaged the transmission side of the VHF.
I am sure it could be opened and fixed but at A$ 207 for a new unit even attempting professional repair seemed not worth it.
I may pull apart the old unit myself and tinker so see if I can find the issue but with leaving to go cruising for 2-3 months next week replacement seemed the simple option at this point.

If you don't have a wattmeter/swr meter-the fact that xmitting causes light dimming suggests the VHF is transmitting at least 10watts or more(drawing 2-5 amps 12vdc),which is sufficient for 10+ miles or more.
Most modern VHF's will not xmit into a bad antenna & coax system.They have a protective shutdown ckt to prevent frying the transmitter. You may hear them for a mile or so sounding weak & scratchy.


Suspect the mike switch or a break in mike cable.
While transmitting,with somebody monitoring at least 1/2 mile away,try gently releasing thumb pressure on the PTT mike switch so that it moves minutely.Does that cause voice break up?
Next,while holding down PTT,pull & stretch the mike cable.Does that cause voice breaks?
The mike & coil cord take the most use/abuse on a radio & require occasional replacement.
Cheers/Len