Connecting a severed VHF aerial cable

I

Independence

Well-Known Member
Joined
7 May 2007
Messages
531
Visit site
Whilst disconnecting the wiring at my mast in preparation for it being taken down I realised I had missed the very obvious reason why I was getting poor VHF reception this year.

When buying the boat last year it looks as though the yard from where I purchased the boat (who also prepared it for road transport) severed the VHF aerial cable rather than feed it through the saloon. With lots of other things to focus on this season and noticing that there was an aerial cable connected to the VHF it has just occurred to me that there is no way it could be connected to the aerial at the mast.

Is there anyway of reconnecting the 2 whilst maintaining a degree of reception / transmission?

Thanks
 
pmead50 said:
Whilst disconnecting the wiring at my mast in preparation for it being taken down I realised I had missed the very obvious reason why I was getting poor VHF reception this year.

When buying the boat last year it looks as though the yard from where I purchased the boat (who also prepared it for road transport) severed the VHF aerial cable rather than feed it through the saloon. With lots of other things to focus on this season and noticing that there was an aerial cable connected to the VHF it has just occurred to me that there is no way it could be connected to the aerial at the mast.

Is there anyway of reconnecting the 2 whilst maintaining a degree of reception / transmission?

Thanks
Click to expand...

BNC connector but mine is done with a block connector with no apparent loss.

wait for others who say it that is totally wrong :rolleyes:
 
BNC connector
Click to expand...
Probably have to use 2 plugs and a female coupler between them.

I think UHF PL259 fittings are preferred to BNC.

All available from Maplin anyway.
 
aerial connection

If you tried transmitting with no aerial connected there is a fair possibility you have damaged the output stage of the VHF radio.
The simplest check would be to borrow/buy an emergency aerial and try transmitting to a hand held VHF (also borrowed/bought). If that works then aerial reconnection is worthwhile.
I am told that any joins in the aerial will reduce both transmission and reception quality. About 3dB per join I think. In any case in a marine environment most plug and socket joins do corrode and increase the losses.
I've improved my VHF reception enormously by connecting the aerial directly to the VHF with no joins rather than with a plug and socket joint in the cable. I dont know if the improvement was due to the removal of the joint or because the extension cable had deteriorated.
I have increased the hole sizes in the panels through which the cable runs below decks so that I can remove and replace the cable easily. It is possible to do this inconspicuously in most boats. If you do this then make sure the cable and end plug which are stored with the mast are protected as much as possiblea gainst the weather during the winter.
Using one cable only might mean it's best to buy and fit a complete new aerial. I've done this but it is a pain; particularly with the mast up but it is not in boat terms an expensive job.
If you want to join then use good quality screw together plug and socket of the correct impedance. I think that's 50 ohm but someone will correct me if it isn't.
If at all possible make this joint below deck so it is reasonably protected from the weather.
Consult an instructional manual on how to make the joint between cable and plug
 
VHF aerial cable

Hi Paul, for many years now I have been using a deck plug at the base of my mast, as are all of my other electrics that come from the mast. For me it is just a matter of "unplug" mast down. Next season it is mast up "plug in". My reception is great on my VHF, nav lights are ok and wind instruments funtion fine.
Good luck
Abdiel
 
pmead50 said:
Is there anyway of reconnecting the 2 whilst maintaining a degree of reception / transmission?
Click to expand...

dri-plug-vhf-connector £29.99

VHFconnector-small.jpg
 
Antenna Cable

I doubt that the transmitter has been damaged by transmitting into a broken cable. However if it won't transmit after the antenna cable is fixed then that could be a possibility.

The cable can be joined by simply soldering or even screw connector block however for lowest losses use a proper coaxial cable connector of 50 ohms. Types for TV antenna are 75 ohms but even then you may not notice any difference. Radio performance runs on a logrythmic scale of apparent reduction in performance so huge losses in transmit power may hardly be noticed. Further a large mast with antenna on top using the small RG58 (6mm diameter) cable can lose 40% of power in the cable.

So in the end much depends on whether you want to feel you have the very best performance from the radio as to whether you use proper coax connectors or even as to whether you change to low loss cable (RG8U is about 10mm in outside diameter is usual low loss cable)

Any sort of join will be better than the cut in the cable so you decide. Perhaps water proofing is more important. olewill
 
Deck plug and socket for me too. Been on there since 1985. Never been any trouble. Unplugged when mast lowered every winter. I have managed to keep the cap for the socket and the blanking plug for the plug which are always refitted when the mast is down ... may have helped.

Further to earlier post

2 X UHF PL259 plugs .... Maplin cat no BW 81C
bw81cwhite.jpg

2 x reducers to fit RG58 cable .....Maplin BW 82D
bw82d.jpg

! x UHF Female coupler .... Maplin BW 87U
bw87u.jpg


Total cost under £8
 
VicS said:
Probably have to use 2 plugs and a female coupler between them.

I think UHF PL259 fittings are preferred to BNC.

All available from Maplin anyway.
Click to expand...
PL259 will be fine - but may I correct you and point out that BNC are better (but only if you are able to solder them on properly!)

BNC's are much harder to assemble than PL259's, but in RF terms they are superior. Having said that - I don't expect you will notice the difference in a yacht's VHF.

And the often bandied figure of 3db loss per connection is a load of rubbish. Its a lot less, and a properly made BNC connection should be even lower.

After all 3 db is half the power, and we don't notice that the connectors are getting warm from absorbing 12.5 watts every time we press transmit on the VHF!

Some research that I found showed that the insertion loss at 150 Mhz for a PL259 is more like 0.3 db See the graph below - but remember that the scales are logarithmic.

259iloss.gif


Notwithstanding the above comments, I use the even better 'N' connector at the base of our mast. 'N' connectors are supposed to be waterproof in their own right, but I have a rubber boat and sealant round it as well. The forward loss results for the swept VHF to UHF frequencies are shown in this graph.

nt_iloss.gif
 
Last edited:
"Is there anyway of reconnecting the 2 whilst maintaining a degree of reception / transmission?"

Yes, but you will probably also want to take the opportunity to create a joint that will allow you to take the mast down in future without cutting the cable. You have some choices:
1. Make the joint inside the boat. If you can do this it is the best choice, but you need to select a deck gland that allows you to pass the connector through the deck. Those made by Index Marine are a good choice.
2. Use a deck plug. OK, but don't neglect maintenance.
3. Make the connection between deck and mast. Also OK. The joint is quite bulky so you'll need to stop it banging around. Wrap the joint in self amalgamating tape and secure it at the base of the mast somehow - cable tie?

Because your cable is severed the location of the cut will influence which choice you make.

Determine the type of cable you have - RG58 is nominally 5mm diamenter, RG8X is 6mm and RG8U & RG213 are 10mm - you'll need to know this to get the right connectors.

You can use two PL259's and a double female connector; a TNC set; BNC set (being a bayonet connector you need to be sure the BNC can't disconnect accidentally) or an N type. They are all effective and the insertion loss is low - less than 0.5 dba.

You can actually join the cable by very carefully twisting the centre cores together, insulating them with self amalagamating tape, rejoining the braid cover with plenty of overlap, insulating that and then putting a cover of tape or heat shrink over the whole lot. I couldn't possibly recommend this course of action, however!
 
Salty John said:
"Is there anyway of reconnecting the 2 whilst maintaining a degree of reception / transmission?"

Yes, but you will probably also want to take the opportunity to create a joint that will allow you to take the mast down in future without cutting the cable. You have some choices:
1. Make the joint inside the boat. If you can do this it is the best choice, but you need to select a deck gland that allows you to pass the connector through the deck. Those made by Index Marine are a good choice.
2. Use a deck plug. OK, but don't neglect maintenance.
3. Make the connection between deck and mast. Also OK. The joint is quite bulky so you'll need to stop it banging around. Wrap the joint in self amalgamating tape and secure it at the base of the mast somehow - cable tie?

Because your cable is severed the location of the cut will influence which choice you make.

Determine the type of cable you have - RG58 is nominally 5mm diamenter, RG8X is 6mm and RG8U & RG213 are 10mm - you'll need to know this to get the right connectors.

You can use two PL259's and a double female connector; a TNC set; BNC set (being a bayonet connector you need to be sure the BNC can't disconnect accidentally) or an N type. They are all effective and the insertion loss is low - less than 0.5 dba.

You can actually join the cable by very carefully twisting the centre cores together, insulating them with self amalagamating tape, rejoining the braid cover with plenty of overlap, insulating that and then putting a cover of tape or heat shrink over the whole lot. I couldn't possibly recommend this course of action, however!
Click to expand...
I agree! Sensible and accurate solutions to the original post and if you seem my graphs, the loss is often a LOT less even than 0.5 db

(On a pedantic note do your really mean dba!)
 
"(On a pedantic note do your really mean dba!)"

No, I meant dB. Having been involved in environmental and industrial noise issues, sticking that 'a' on the end is just a bad habit which I really must get out of!
 
I like N connectors as they are easy to screw onto the cable. The guy that did our TV aerial used them, wrapped in self-amalgamating tape, and left them lying in the gutter, covered in water. They never gave any problem all the time they were there.

I can testify to the difficulty of fitting BNC connectors. I had to renew the one for my Garmin sat-nav as it was shorted. I got one from Maplin, which came without instructions. There are about eight bits loose in the packet, so I got application notes from Farnell and RS. When I got the process of having the central core tinned, I found it would not fit into he hole in the central pin. Even un-tinned, the hole was too small and had to be drilled out. After it was fitted, the gland bit refused to hold properly, which makes me think it was not really for RG58 cable.
 
On the subject of Driplugs mentioned above they also do a multi connector which will handle VHF and electrical such as nav lights steaming lights etc. Cost about £62 from

http://driplug.com/products.htm

but reduces the number of through deck holes needed to just one. Comes complete with weatherproof covers for both ends when you take the mast down. A good bit of kit that has stood the test of time (three years now) and still looks as good as new.

Good luck.

Chas
 
Another possibility would be to use F-connectors for the join. These are what are used for connecting satellite TV recievers to the downlead from the dish . Satellite LNBs outputs are at around 1 Ghz, so I would imagine these connectors would be fine down at VHF. They're cheap and easily available, and quite small, which could be handy if you're tucking the join up behind the headlining near the mast base.

Like the PL259 though you'll have to use two plugs and a back to back " barrel" coupler. Check that your cable has a solid central core, not twisted strands as these plugs don't have a central pin, you just leave a stripped section of the core protruding instead. The outer connection is made by pushing the braid back over the insulation and screwing the plug body over it, so you need to get the correct-ish diameter plug for your cable. There are plenty of "How to" guides findable by Google, here's one of them.

http://www.avforums.com/forums/inte...witches/470017-guide-how-fit-f-connector.html
 
Forget UHF (PL-259) connectors and forget F-types they are not good enough for exterior splicing. In fact their **** connectors full stop, not sure why manufacturers still use PL259.

The best would be N-Type, male to female and then seal with self-amalgamating tape. For starters they have rubber glands to seal the cable entry, the centre conductor is soldered and they screw together, by far the best solution. Most wiring on small boats would be RG-58 if it's a short run, larger boats may use RG-213 or RG-214 (double braided).
 
FWIW I cut back the two ends. Solder the cores together and insulate. Then solder the outer sheaf together after twisting them. Then cover the whole lot with a bit of tin foil. Then cover the whole lot with woterproof tape. If you do it neatly then it doesn't add much extra overall bulk to the cable and you can still pull it through holes etc.... Always workd for me and better than introducing connectors in many cases.
 
I'm not an expert in electrics but if you inspect the antennae cable and find the outer mesh is dark brown to almost black you may need to replace the whole cable,as it may have been earthing or shorting out.


£0.02p

ianat182
 
asteven221 said:
FWIW I cut back the two ends. Solder the cores together and insulate. Then solder the outer sheaf together after twisting them. Then cover the whole lot with a bit of tin foil. Then cover the whole lot with woterproof tape. If you do it neatly then it doesn't add much extra overall bulk to the cable and you can still pull it through holes etc.... Always workd for me and better than introducing connectors in many cases.
Click to expand...

May not add to bulk, but it will screw the return loss.
 
You must log in or register to reply here.

Share this page

Top