VHF Antenna cable connection

[Inselaffe]

Hello,

Trying to get my DSC going. I think it is the anntenna/connection.

At the moment I have new antenna, new cable from antenna to deck connector, but then old (I think very old) deck connector (i.e plug and socket) and cable from deck connector to set.

Since I have no reception (although have only tried to get weather forecast from Jade Trafic so far, tests with neighbours set, emergency antenna etc this weekend) I think it is a good idea to replace old parts of cable since a multimeter gave a closed circuit between outer and inner from set end of cable with deck connector disconnected, although very high resistance of 1500 kohms (but still a different reading than when open circuit on my multimeter).

Anyway, my main Q's are, is it a good idea with VHF to have a deck connector in the cable?

Will this inevitably give probs?

Is it better to have a through deck fitting (ie no break in cable) like:

http://www.bootsradde.de/osc/catalog/product_info.php/products_id/290

(In german but you get the gist)

Then I could drop mast in tabernackle no probs if enough cable slack at mast foot, and at end of season when mast must come right off hopefully the set end of the cable would fit through the dismantled through-deck fitting.

What is best/normal practice?

Thanks

 

[savageseadog]

I find a deck gland better than deck connectors. You will need a join under the deck for which you will need a proper coax connector eg BNC.

 

[Talbot]

If you had reception before, then the likeliest cause is with the pl259 connector on the new cable. disconnect the new from the old cable and repeat your tests with the multimeter to establish whether the problem is with the new cable or the old.
I had the same problem with an open circuit on a new connector.

The need to replace the in-deck element of the cable will depend on how old it is, and what condition it is in. mine was fine

I prefer being able to break the vhf cable close to the mast , but part of that is that it would be difficult to remove the cable inside the boat. using a cable gland does reduce the connection problems by one, but decision is really dependent on the layout in your boat.

 

[Guest]

I have a deck connector for VHF ... and its many years old ... based on BNC deck socket and cable plug. There is a substantial rubber cover that slides down cable over fitting once connected. Works fine.

Previous boat - I used in-line BNC connector above deck - yes above deck - with self-amalgamating tape wrapped to seal it ... lasted about 3 years before I replaced with similar again.

Both above survived mast up / down etc. and connecting - dis-connecting.

Often the problem is corrosion of the internal parts of the connector ... and working of cable ... only takes a slight change and bham - it doesn't work.

Cable without connectors / joints is of course best for continuity - but pain for mast up / down etc.

 

[philip_stevens]

Join the co-ax cables with one of these Shakespeare connectors below deck - via a deck gland - and easy to fit.

I have one on my below deck connection, but had to get it from the USA. There may be somewhere in the UK that stocks them though.

 

[reginaldon]

Had a job soldering the connection to a new deck cable connector, whilst on the mooring - managed it on the 5th attempt after enlarging the access holes to the pin

 

[William_H]

If your cable shows 1500ohms centre to outer with the deck connection disconnected you have the problem in that section of the cable. Problems almost always occur at the connectors so remove the conector from the mast end. Check the resistance centre to outer if it is still showing low resistance then dismantle the set end connector.
If the low resistance is still present then you have a problemn in the cable. This is unusual but possible. Replace the cable. You may find on removal a screw through the outer or some similar damage followed by corrosion.

When I say dismantle the connectors you may be able, depending on connector type, to be able remove the shell leavcing the soldered pin still on. So it can be screwed back together without resoldering. A most common problem is whiskers of wire from the outer escaping and touching the inner so don't be surprised if the problem goes away when you dismantle the connector.
Certainly if you can take the whole cable out when removing the mast then use a deck gland seal. If the cable is behind lining etc then you must have a break connector either at the deck above or below.good luck olewill

 

[PBooth]

I use a soldered joint on the VHF co-ax and leave enough spare cable to remake the joint half a dozen times, I only need to cut back an inch either side to reconnect. the soldered joint is sealed with heatshrink tubing. The cables to the mast lights are jointed in the same way but with heatshrink crimp butt connectors. This method has worked fine for me, it's quick and cheap and you have a new connection each time you lower/raise our mast.

Peter

 

[davidpbo]

Just remember many antennae give a low DC resistance measurement as discussed in a recent thread (1 ohm or so).

So make sure it is disconnected. As I understand it you are trying to check the cable between radio and deck connector and have 1500K Ohm this is a high resistance, but may still cause problems at Radio Frequency.

Is the connector on the cable going up the mast the same as on the radio? If it is I would be tempted to take the radio on deck and plug it staight on to that cable and listen. (using a bit of two core or a battery to power radio). If you receive, try a test call. That would indicate that the problem is the suspected cable.

Moisture in the cable may give you a reading such as you describe.

Have you tried the coathanger in the radio aerial socket suggested in a previous thread. (DO NOT ATTEMPT TO TRANSMIT USING IT).

Good luck

David

 

[William_H]

My appologies I misread 1500K ohms as 1500 ohms. 1.5 meg ohms (1500K) is a difficult number. It may indicate moisture or corrosion especially if the other cable with antenna disconnected does not indicate any discernable resistance (conductance or leakage). Howevewr it may be no fault at all. Be carefull you can easily get 1500K ohms from touching both meter probes with your fingers. Your body can exhibit that sort of resistance or less. So 1500K ohms may mean nothing and be the natural DC resistance of a large length of cable. good luck olewill

 

[Inselaffe]

Thanks for the replies,

I dismantled the deck connector and there was a bit of moisture in it. Now with the deck connector reassambled but disconnected from the cable up the mast and measuring from the set end I have open circuit as should be.

However, a neighbour helped test, and I could still not receive anything with mast top antenna, but loud and clear with the emergency antenna I put together plugged directly into the set (could also transmit with emergency).

I think my next steps will be to try with the emergency antenna plugged into the dck connector to see if the set to deck cable is ok.

If it isnt ok then replace the set to deck part of the cable and try again.

If it is ok drop the mast and plug the emergency antenna in at the mast head. If it works there I reason it must be the new antenna that is faulty. I could check by also trying with the new antenna plugged into the set with a shorter, new cable.