Testing VHF coax cable

[zoidberg]

I have a mast 'down' and a coax cable snipped off top and bottom, leaving several inches at each end. Is it practicable - or worth the effort - to test this?

I also have a 1m s/s whip antenna with 30-odd feet of coax cable attached. Is there any way to test this to determine if it is worth mounting/fitting to replace the coax already inside the mast?

 

[seaplane]

I believe the major factor would be age. Not yours, the coax! If the cable has been in situ for a good number of years, then replacement whilst the mast is down can only be a good investment. The copper in the cable age hardens becoming easily broken; additionally, the cable can start to allow water ingress. I would also replace the coax connectors at the same time.

Without fancy meters, about the only test you could do on the coax of the other aerial would be continuity of the inner and screen.

 

[William_H]

I believe the major factor would be age. Not yours, the coax! If the cable has been in situ for a good number of years, then replacement whilst the mast is down can only be a good investment. The copper in the cable age hardens becoming easily broken; additionally, the cable can start to allow water ingress. I would also replace the coax connectors at the same time.

Without fancy meters, about the only test you could do on the coax of the other aerial would be continuity of the inner and screen.

As seaplane said. A check with a multimeter on ohms scale (200ohm) should confirm that the centre conductor is intact ie showing less than 1 ohm from one end to the other. Likewise check the screen outer conductor. Then move the ohm meter to 2 meg ohm scale and check the inner to outer should be very high resistance. However this will check it's integrity but will in no way indicate it's likely future life. Ave a noo one.
The whip antenna should show low resistance from the centre conductor at end of cable to the whip itself. It should show very high resistance inner to outer. However there should be a good connection also from the outer shield a tthe base of the antenna to the mount. ie mast. Note these checks do not apply to a fibreglass whip with antenna inside which often have conductivity inner to outer and no connection to the mount ground.
ol'will

 

[Plum]

I have a mast 'down' and a coax cable snipped off top and bottom, leaving several inches at each end. Is it practicable - or worth the effort - to test this?

I also have a 1m s/s whip antenna with 30-odd feet of coax cable attached. Is there any way to test this to determine if it is worth mounting/fitting to replace the coax already inside the mast?

As your vhf is part of your safety kit and will probably be the first thing you grab to call for help, in my opinion, if in any doubt fit a new aerial and cable.

www.solocoastalsailing.co.uk

 

[matthewriches]

With the mast now in a position to have new cable fitted, now is the time to do it. A new bit of decent stranded coax won't cost the earth and is a sensible thing to do.

As mentioned above, you could test using the OHM setting on your multimeter but that'll not account for the fact that there could be 1 strand left hanging on that then decides to break as you are doing up the last bottle screw whilst putting your mast back on!!

I also try and run a couple of coax up when re-rigging as it costs no more in time and just a few quid extra in cable.

 

[zoidberg]

OK. Persuaded.

I'll run some fresh coax with fresh connectors, and dollops of Tefgel.

I'll also keep the above-mentioned whip plus attached coax as a 'spare', if I can find a way to test it for function.

 

[matthewriches]

Might be worth asking about locally to see if anyone has an antenna analyser. Local HAM bloke or something might check it all out for a beer.

OK. Persuaded.

I'll run some fresh coax with fresh connectors, and dollops of Tefgel.

I'll also keep the above-mentioned whip plus attached coax as a 'spare', if I can find a way to test it for function.

 

[SteveNotlob]

Might be worth asking about locally to see if anyone has an antenna analyser. Local HAM bloke or something might check it all out for a beer.

Good idea but make sure they use one that covers Marine VHF frequencies (156+ MHz).
I came across a situation a few years ago where the owner of a Gin Palace was complaining that although his reception / transmission range was good, he thought he could get much better and he was 'confirmed' in his thinking by having his Radio HAM brother test the SWR of the 3 radios / antennas he had - all off which where falling well into the red quadrant....
We tested them and found all installations perfect. This went backwards and forwards until we arrived one day to find his brother yet again checking the SWR, with an SWR meter that was only good for up to 30MHz !!!! How it even read anything, let alone went to red, is beyond me, but is an important lesson to ensure you get someone that does have a bit of a clue as to what they are doing

 

[Daverw]

Doing it with an analyser is very different from using a quite crude SWR meter, it tests without the radio connected and sweeps the selected frequency range. As long as the analyser covers the Ham 2m band it will do the Marine band. Mine will also test cable impedance etc as well.

 

[SteveNotlob]

Doing it with an analyser is very different from using a quite crude SWR meter, it tests without the radio connected and sweeps the selected frequency range. As long as the analyser covers the Ham 2m band it will do the Marine band. Mine will also test cable impedance etc as well.

True. I know what an antenna / transmission line analyser is, i've used them often in the old days when I was an RF Engineer before I became a Marine Electronics Engineer. I was just replying to the mention of getting a Radio HAM to test it - very, very few will have a proper analyser, most will rely (as in the case I mentioned) on a SWR meter.
Anyway, it gave me a chuckle remembering that incident

 

[Bi111ion]

True. I know what an antenna / transmission line analyser is, i've used them often in the old days when I was an RF Engineer before I became a Marine Electronics Engineer. I was just replying to the mention of getting a Radio HAM to test it - very, very few will have a proper analyser, most will rely (as in the case I mentioned) on a SWR meter.
Anyway, it gave me a chuckle remembering that incident

On the contrary, plenty of radio hams will have an antenna analyzer these days as (1) they are pretty cheap now and (2) we radio hams just love test gear. In my case my antenna analyser does not go up to VHF but I have a very neat digital SWR/Power/Frequency meter and it is good for catching potential faults in the VHF antenna feed line. It looks a bit like this https://qrznow.com/tyt-sw-102-vhf-uhf-swr-meter-with-rf-power-meter-and-frequency-counter

Of course some hams are very old school and claim they can tune an antenna by listening to the noise... great skill but ... did I mention... we love test gear.

As OP already said - best to change it while mast is down though.

 

[zoidberg]

Might be worth asking about locally to see if anyone has an antenna analyser. Local HAM bloke or something might check it all out for a beer.

That's an excellent idea, 'matthewr.'

I'm aware of two such geeks within 2-3 miles, so I'll put out the feelers. I've just remembered I have two very long ( circa 16-18' ) GRP marine antennae tucked away in my ( by now almost famous ) polytunnel - one is two-section demountable, the other all of one piece. Perhaps there's a radio ham use for one or other of 'em....

 

[Daverw]

I’m sure they would swap you, we love collecting stuff just to play with, it’s part of the rules of being a radioHam
Regarding analysers, I’ve got three, the last one probebly more advanced thana lot of RF lab test gear

 

[matthewriches]

Even if of no use as an antenna directly, it may tickle someones fancy as a pole to create a long wave antenna for example.

I have two very long ( circa 16-18' ) GRP marine antennae tucked away in my ( by now almost famous ) polytunnel - one is two-section demountable, the other all of one piece. Perhaps there's a radio ham use for one or other of 'em....

 

[lw395]

Even if of no use as an antenna directly, it may tickle someones fancy as a pole to create a long wave antenna for example.

Or a jib stick....

 

[zoidberg]

Youz guys is tempting me to go hunt these bad boys out of where they're hiding, in amongst lots of other piled-up poles and mouldings behind the 20' workbench piled high with accumulated boaty gear, then post some pics so youz can argue over what they were intended for - and what they could be used for now.

 

[weustace]

If you find a particularly sophisticated ham who is willing to a little more work, he could put a connector on the end of the mast coax run, calibrate the effect of say 20m of known good coax out of the measurement, then measure the insertion loss (which is really what you're worried about) in the mast coaxial cable with a network analyser. I'd volunteer, but sadly am manically busy for the foreseeable future... (and not because I'm measuring peoples' coax, either)

William

 

[zoidberg]

If you find a particularly sophisticated ham

Thanks, William. I've determined to hunt down some of the local Wiltshire 'fists' and have a word. I've been able to use HF at various times over the years, from various corners of the globe, without having a licence and without the opportunity to send QSL cards.

Perhaps it's time I changed that.

 

[G12]

I've just replaced my VHF feeder with some M&P Ultraflex 7. I don't have room for a 10mm cable in the mast so the ultraflex gives excellent performance for a much smaller cable (less loss than the 10mm RG213 which is standard on most longer VHF cable runs). I also used the "crystal" version which has a transparent cable jacket so you can see if there is any water ingress in the future.
I use the Metz Manta antenna at the masthead and am very happy with the performance of it, it's a well made bit of kit and will last many years unlike some of the other more common yacht varieties.
The connectors for the ultraflex are about £7.50 each but it is a quality setup and will last years.

https://www.hamradio.co.uk/accessor...13-but-near-to-the-size-of-mini-8-pd-5633.php

 

[zoidberg]

Thanks, 'G12'

I followed your recommendation and link above, and was just about to order when I noticed the charge for carriage...!!! Which is almost the charge for the product....!!!
Looking a little further, I notice the carriage charge made by the manufacturers in Italy, via Ebay, is about half that being charged by Martin Lynch & Sons, from Staines.

Before I speak to them, could you guide me as to what type/spec of connector is appropriate?

Edit: Have now spoken to them, and their webpage shipping cost 'quote' is ambiguous and relates to a typical much larger order.... of around 100m drum.