Dodgy VHF aerial help

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cpedw
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Dodgy VHF aerial help

Postby cpedw » Tue May 26, 2015 10:12 am

We've got a VHF that isn't working well. It's receiving quite well and transmitting over at least 100 yds but radio check with the CG from about 6 miles gets no response.

I suspect the aerial cable which has a joint at the foot of the mast which got corroded last season and replaced. I did this myself so I'm dubious about the quality. I've tried remaking that joint without improving things (no worse though :thumbsup: ).

I'd like to test things before making the dreaded journey up the mast having shelled out for a new aerial. Does anyone know of a service in Argyll that does that? I know there's a meter for aerial testing (SWR?) but I don't have one or know how to use one.

Any suggestions on the best way forward? I contacted BEE in North Connel but they can't come for 2 weeks ...

Derek

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Re: Dodgy VHF aerial help

Postby marisca » Tue May 26, 2015 10:25 am

Derek, a VSWR meter of the correct frequency is indeed one solution though I know of nobody with such a toy. A simpler way is try another aerial plugged into your radio. If you don't have one then buy a cheapy - it's a good thing to have if ever your mast falls down.

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Re: Dodgy VHF aerial help

Postby cpedw » Tue May 26, 2015 11:21 am

Alastair,
Yes i have an emergency aerial that I haven't tried out. I'm fairly confident that the set is OK but I should check (and check the emergency aerial).

I want to know if it's the first bit of cable (VHF set to mast) or the cable up the mast and the aerial that needs to be replaced. Fingers crossed it's the first, but how to know?

Derek

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Re: Dodgy VHF aerial help

Postby marisca » Tue May 26, 2015 11:31 am

May I recommend 2 x PL259 plugs and a barrel connector for the base of your mast? Makes (dis)connection easy when the mast comes down. Then you can plug your spare antenna into the boat bit to eliminate or pinpoint that - if all is good you are going up the mast!

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Re: Dodgy VHF aerial help

Postby mm5aho » Tue May 26, 2015 1:18 pm

I'd go one better and use 2 x N type connectors, and a barrel.
These are much better waterproofing, and fewer impedance issues than PL259.
They cost a little more and are more fiddly to fit, but less likely to fail.
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Re: Dodgy VHF aerial help

Postby claymore » Tue May 26, 2015 2:16 pm

I have tested mine by plugging the handheld into the aerial socket at the base of the mast.
If you are going to be buying another aerial then visit SaltyJohn - he does some great aerials (Metz)
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Re: Dodgy VHF aerial help

Postby marisca » Tue May 26, 2015 2:43 pm

Maplin sell RG58 with tinned conductors at £0.49p a metre - http://www.maplin.co.uk/p/webro-rg58-cu-50-ohm-coax-cable-black-priced-per-metre-a74ra. PL59s @ £2.99ea, adapter for RG58 @ £2.49 ea, female coupler @ £3.49. Hours of fun feeding and soldering and you will feel the satisfaction of a job well done!

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Re: Dodgy VHF aerial help

Postby cpedw » Tue May 26, 2015 5:48 pm

Many suggestions; thanks.

I ordered a BNC to 259 adapter as the mast foot connection is currently BNC; not on deck but inside the saloon so top waterproofness shouldn't be necessary. After that I remembered that BNC was chosen as it will fit through the deck gland. I can postpone that problem till laying up.

The handheld has a smaller fitting. If I could identify it, I would get an adapter so it could be used with the big aerial.

I don't think it will help to get new cable, at least for the stretch from aerial to mast foot; from memory, the joint at the aerial is a strange connector.

Watch this space for news of developments.

Derek

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Re: Dodgy VHF aerial help

Postby mm5aho » Tue May 26, 2015 9:52 pm

For future antenna issues (or current ones)...
I have two instruments that are useful. One is a SWR meter, suitable for HF and VHF (so does marine VHF OK).
The other is an antenna analyser. It can detect a fault in coaxial cable and say at what distance up the cable the fault lies. It will test an antenna remotely (through the coax feeding the antenna), and even measure what frequency the antenna is good for.
If anyone here needs to borrow these at some time, please just ask.
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Re: Dodgy VHF aerial help

Postby DaveS » Wed May 27, 2015 5:19 pm

mm5aho wrote:For future antenna issues (or current ones)...
I have two instruments that are useful. One is a SWR meter, suitable for HF and VHF (so does marine VHF OK).
The other is an antenna analyser. It can detect a fault in coaxial cable and say at what distance up the cable the fault lies. It will test an antenna remotely (through the coax feeding the antenna), and even measure what frequency the antenna is good for.
If anyone here needs to borrow these at some time, please just ask.


I also have a VSWR meter suitable for VHF which is available for borrowers near Craobh. I like the sound of your analyser, though.
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Re: Dodgy VHF aerial help

Postby mm5aho » Wed May 27, 2015 9:04 pm

Geoff.
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Re: Dodgy VHF aerial help

Postby aquaplane » Wed Jul 08, 2015 4:02 pm

So if I can receive OK but can't transmit at all an early check would be to fasten a SWR meter to the beast then?

I have pressed the PTT button and the display changes to indicate that the set thinks it's transmitting.

The mast head aerial has no breaks between the back of the set and the masthead, that was last seen 3 seasons ago when the mast went up.

The emergency aerial on the pushpit doesn't work either but looking at the connections on the outside end I'm not surprised.

It's a Silva S10 DSC VHF but I don't think that's relevant at this stage.
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Re: Dodgy VHF aerial help

Postby DaveS » Wed Jul 08, 2015 4:11 pm

aquaplane wrote:So if I can receive OK but can't transmit at all an early check would be to fasten a SWR meter to the beast then?

I have pressed the PTT button and the display changes to indicate that the set thinks it's transmitting.

The mast head aerial has no breaks between the back of the set and the masthead, that was last seen 3 seasons ago when the mast went up.

The emergency aerial on the pushpit doesn't work either but looking at the connections on the outside end I'm not surprised.

It's a Silva S10 DSC VHF but I don't think that's relevant at this stage.


The SWR meter is connected between the set and the antenna coax cable, most easily arranged using a short length of coax cable with a male plug at each end (if the meter has two female connectors, as mine does). Definitely worth a look since transmitting into an open circuit could damage the set. (OK, I suspect most modern sets are protected, but there's still a potential risk.)
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Re: Dodgy VHF aerial help

Postby sahona » Sun Jul 12, 2015 10:11 pm

Aqua - what happens with the emergency aerial? In the old (CB) days we used to see neon lamps attached to aerials so you could see which car was transmitting - worth a try? I suspect your radio may be broken as it will normally reach as far as the ships handheld even if the masthead aerial is mince. Is there an ammeter aboard - & does it register the current drawn when PTT happens?
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Re: Dodgy VHF aerial help

Postby aquaplane » Sun Jul 12, 2015 10:20 pm

sahona wrote:Aqua - what happens with the emergency aerial? In the old (CB) days we used to see neon lamps attached to aerials so you could see which car was transmitting - worth a try? I suspect your radio may be broken as it will normally reach as far as the ships handheld even if the masthead aerial is mince. Is there an ammeter aboard - & does it register the current drawn when PTT happens?


I don't have a ships HH yet, it's one of the things that we thought would be good to have when we realised we couldn't talk to the lock keepers on the Caley canal. We could hear them OK.

I don't have an ammeter, I have a multimeter which I have only ever used to test continuity or voltage, I think it may do amps but I will have to check. Whether I can or can't measure amps I haven't, but I could borrow a Fluke from work to to check on differences in power draw when I PTT.

The Emergency aerial was THE aerial before I put a SaltyJohn Metz one at the mast head when we moved from Windermere.
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Cheers Bob.


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