Testing a new VHF aerial

[IanR]

After taking possession of the new to us boat, we took down the mast and replaced all of the standing rigging and mast wiring including putting up a new aerial cable and a hawk aerial. On refitting the mast I cannot get the VHF to transmit reliably and reception is weak.

I believe it was acceptable prior to mast removal, although this is hearsay as prepurchase.

So the troubleshooting initially defaulted to refitting the mast connector at the base which I made good thinking it was the most likely candidate.

I even went and purchased a new set of gold hyper expensive connectors , no improvement

I then swapped the DSC radio just in case with a spare I was selling (belt n braces) no change

I am now left to believe that the new cable or the connection at the top of the mast or the antenna itself could be faulty.
Given that I do not have an SW meter is there anything else I can do to diagnose without shinning the mast? Even if I got hold of a meter would it help?

I have not changed the under deck cable yet , the mast head cable to the aerial is pre made by the manufacturer and connected by the yard crane operative.

Any thoughts or tests gratefully received.

 

[Martin_J]

SWR / Power meter is very useful in this case. Can be used at the back of the VHF, at the foot of the mast and at any other joins you have. In the right hands it should quickly show where the fault lies.
Where abouts are you in the Solent... ?

I have the necessary test kit and could possibly bring over to you. ..

 

[Martin_J]

Personally, I would have connected that particular antenna to the cable first. ..then put a temporary PL259 plug on the other end and tested. ..then dropped the cable down the mast knowing that the connection at the top was good.

There is a possibility the the cable wasn't pushed fully home into the bottom of the antenna or perhaps a single strand of wire shorting the shield to core... or possibly just badly made up connector below deck. Easy to find with the right test kit. Hopefully we can find time to take a look.

 

[IanR]

Martin

Yes in hindsight it would have been sensible to check all the kit off mast, next time I will.

I have the boat mid river on the Hamble but can bring her to walkashore. If I could gets some instruction on the SWR and borrow one I would be most grateful

I don't like unsolved faults and this is bugging me.

I will send a PM

Thanks

 

[Deleted member 36384]

... or perhaps a single strand of wire shorting the shield to core...

I have found this to be common with me when assembling the VHF plug after raising the mast. I have now installed a cable port on deck such that I do not have to cut the plug off each time the mast is lowered. Last time I used a multi meter to check connectivity before soldering, it took a few attempts to make up the plug correctly. IIRC the last time I had left a silvery coated paper that is between the coax shield and plastic inner conduit too long and that was making the bridge, it to had to be cut well back, so not just strands of shield.

 

[<152587>]

If all else fails try reading the Vitronix instructions. Before you put a SWR meter in circuit ensure you have continuity in the installation, 10k ohms on this item between core and screen. Note that this not always the case with antannaes, depends if DC grounded or not.

 

[Martin_J]

Third engines... Indeed - a good test...

Although the current instructions (online) for the Hawk VHF antenna suggest that you will see a short between centre conductor and screen :ambivalence:

V-Tronix Hawk antenna installation instructions

 

[<152587>]

Although the current instructions (online) for the Hawk VHF antenna suggest that you will see a short between centre conductor and screen :ambivalence:

V-Tronix Hawk antenna installation instructions [/QUOTE]


Interesting, the statement says a small resistance then states a short circuit. It is impossible to have a short circuit if a resistance is present.

Bear in mind the website is a third party, not the manufacturers site. For the definitive answer see vtronix-antennas.com. or refer to the instructions enclosed with the said equipment.

 

[Martin_J]

indeed.. and I seem to think the last few I have measured with a standard multimeter have been approx 10kΩ.

 

[Skylark]

Sounds like quite a few "unknowns" so a bit of detective work and access to some basic electrickery kit is required.

Does the radio work? Patch lead and a temporary antenna should tell you.

Which coax cable (or most probably, plug/socket) is the culprit? Patch lead, 50 ohm dummy load and SWR meter should tell you if you follow a systematic search.

Good luck!

 

[Robin]

It has probably been 15 years but we hada similar problem after fitting a new Hawk Aerial and cable. It tested OK IN the boatyard with a radio check to the CG, but mid Channel it was apparent it was not pulling in the usual babble which was there on the handheld and reappeared on the main set with the emergency spare aerial. I remade all connections assuming it was my installation error but no luck. I called V-tronix who told me how to test it with a multimeter which showed a fault, so they sent me a replacement FOC saying it was probably a duffer. Sure enough the new one was absolutely fine and we thereafter received and transmiited over impressive ranges. .

 

[Petronella]

If this is the push in V-Tronix connector then I would strongly suspect the mast head connection. I never managed to get a good connection there and recently replaced it with a Metz antenna from Salty John. What a difference. A proper PL259 connector, not much more expensive and a thousand times better.

 

[davidpbo]

I am not sure of the make my antenae. It certainly had a very low D.C. RESISTANCE measured with a standard multimeter 1 Ohm or so measured be between core and screen. Because they are both connected to different parts of a short copper wire coil in the base of the aerial.

However at VH frequency the IMPEDANCE will be high I think.

The low resistance surprised me as was not familiar with this design of aerial.

 

[IanR]

Thank you all for the technical and moral support, particularly Martin J who has even offered to come and apply his knowledge on my behalf which is a kind and valuable offer.

I am not a betting man but if I were I would think that the masthead connector is most likely culprit, pity it's at the masthead!

Onwards and no doubt upwards, when we find the issue I will publish back

 

[mcalan]

". I called V-tronix who told me how to test it with a multimeter "

Can some kind soul explain how to do this ?
I have a Simrad RD68 which seems to be working ok but when I transmit instead of showing " Tx "it shows "Ant"in the display according to the handbook this is an error message.?

 

[st599]

". I called V-tronix who told me how to test it with a multimeter "

Can some kind soul explain how to do this ?
I have a Simrad RD68 which seems to be working ok but when I transmit instead of showing " Tx "it shows "Ant"in the display according to the handbook this is an error message.?

It depends on your antenna design. It may not be possible.

 

[Robin]

". I called V-tronix who told me how to test it with a multimeter "

Can some kind soul explain how to do this ?
I have a Simrad RD68 which seems to be working ok but when I transmit instead of showing " Tx "it shows "Ant"in the display according to the handbook this is an error message.?

Had my memory obliged I would have explained what they said, but it was 15 years or more ago and a lot has happened since including a stroke. IIRC it was a surprise to learn that there should be some measureable resistance between core and outer of the cable but that the amount suggested a 'short' that one would normally see as a 'fault'. Someone else here mentioned 'impedance' and that may be the key but is not I think measureable via a multimeter? Beyond my 1960s A Level physics too!

 

[st599]

Had my memory obliged I would have explained what they said, but it was 15 years or more ago and a lot has happened since including a stroke. IIRC it was a surprise to learn that there should be some measureable resistance between core and outer of the cable but that the amount suggested a 'short' that one would normally see as a 'fault'. Someone else here mentioned 'impedance' and that may be the key but is not I think measureable via a multimeter? Beyond my 1960s A Level physics too!

resistance is d.c. impedance. Impedance is frequency dependent.

 

[Robin]

resistance is d.c. impedance. Impedance is frequency dependent.

Thanks! knowledge decreases with age even if wisdom increases!

 

[<152587>]

". I called V-tronix who told me how to test it with a multimeter "

Can some kind soul explain how to do this ?
I have a Simrad RD68 which seems to be working ok but when I transmit instead of showing " Tx "it shows "Ant"in the display according to the handbook this is an error message.?

Firstly determine the construction of the antenna, some are described as DC grounded, if so a resistance value should be specified. With the antenna connected to the cable, remove the plug from the radio, select the appropriate scale on the multimeter and place 1 probe on the centre pin, the other probe on the outer, the meter should indicate the resistance 10,000 ohms in the case of the Hawk. Note that the check should never indicate a short i.e. no resistance.