VHF Aerial Coax

[JSK]

I Recently purchased a mast head VHF aerial and went to fit this today only to find 18mtrs of coax is not enough to reach the bottom of my mast . Can anyone tell me if satalite grade coaxial is ok to use ? if not where would one try to obtain the correct item Thanking you for any information in advance.JSK.

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[discovery2]

I understand that television/satellite co-ax MUST NOT be used undre any circumstances (unless you wish to damage the set). It is essential that the proper co-ax is used - it will also give the best transmission power. Most chandlers/electronics people should be able to supply the length you require.
It is also important that the proper connectors are used for the join.

Good luck.
David

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[roger]

connectors

Do make sure you fit the connectors properly. Its easy to get wrong. There has recently been an article on fitting them but I cant remember where.
Try to ensure that connections are made in a dry place below decks. Deck plugs usually fail quite quickly.

<hr width=100% size=1>Roger

 

[Birdseye]

like as not the coax for the set is 50 ohm (check the set spec) rather than the 75 ohm for tv / satellite and if so you can get good quality coax from maplins, who will also sell you the connectors. Mind you, if the connection is going to be outside I would consider soldering a new one piece length into the aerial rather than joining if poss.

<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.

 

[EdEssery]

The cable you want is RG58 - commonly used in the computer industry...

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[nickjaxe]

Just had to do the same job on our club RIB, got all the bits from maplin mail order, make sure you use the correct connectors, I did find an online CB radio supplier that was cheper just had a look but I cannot find the site ad.and it is and must be RG58 50ohm

Nick.

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by nickjaxe on 10/05/2004 22:28 (server time).</FONT></P>

 

[stevebirch2002]

The cable nyou need must be 50 ohm exterior grade. The perfect grade is a cable called RG58CU Should cost about 50p per metre from usual outlets. Try Maplins, RS, Farnell etc. Any local electronics shop should be able to help. TV and Satellite cable is 75 ohm so not suitable.

<hr width=100% size=1>Albin Vega "Southern Comfort" V1703

 

[andyball]

rg58 is £0.30 per/m + vat from tlc-direct.co.uk

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[john_morris_uk]

The 'RG58' from CB suppliers is not always as of as high a quality as from reputable dealers. For the pence that you save, why not make sure that you've got decent coax?

So, tinned copper for the braid as well as the inner core is better than untinned copper.

If you carefully peel back the outer protection, the braid should completely cover the core insulation. (Compare to cheap TV coax!)

As already posted, be scrupulous with your connections. N Connectors are supposed to be waterproof, but I still wrap them in almalgamating tape...

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[andyball]

screen & core are both tinned from tlc & they're not a cb supplier.....but even if they were, don't see why that means they wouldn't be reputable; have had good & bad from tlc,maplin,farnell, rs- like rs since there's often more technical info. available & huge printed catalogue available by post from the website.

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[William_H]

I would suggest for the sake of reliability that you replace the entire cable rather than put a join in. If you must join for mast removal etc. then do so if possible inside the cabin. Your post says 18 metres that is a tall mast. If you really are looking at a cable run of 20 metres or so you could be bordering on the need for a low loss coax cable RG8U or RG213/U this is about 10 mm in diameter and needs a larger connector to suit the cable but will be more reliable for being simply bulkier and have lower loss. The losses are such that at VHF frequencies I think we are looking at 50% power loss in 50 metres or so (don't quote me) at higher frequencies ie GPS frequencies or TV UHF or mobile phone frequencies the losses are far more dramatic. If you are cheap like me just add more RG58 cable you can just join the centres with solder or even in line crimp then pull the braid over the join of the centre to join the braid and seal the whole lot. Yes you will get some loss no you won't destroy the transmitter (any bad or wrong cable can't be as damging as losing the aerial then transmitting into a piece of cable and this doesn't kill the transmitter)I think you will find it works ok. PS don't forget to have an emergency antenna for if the mast comes down.

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[Birdseye]

Everything said above is correct, but the use you are putting the cable to is not that arduous that you need to frantically search for the ultimate.

It is better that it is 50ohm because that will match the rest of the kit and you will minimise mismatch losses. Its better if the outer braid covers the insulation well, because that makes for good shielding from extraneous noise, and a good supplier will be able to quote you a percentage cover. And it makes sense that the inner conductor has a reasonable surface area so that you lose less of the signal as it goes up the mast - so dont be tempted to get cable less than 5mm od. But RG58 is simply one national spec, albeit a common one, so you can use alternatives.And tinning is less important in this application because if you get moisture into the coax you are stuffed anyway. So it does need to be well sealed at both ends as well as well jointed.

You are more likely to go wrong with poor connections than poor cable. Try to use solder connections (its easy to do, and a 12v soldering iron is useful on board) rather than screw type. Make sure that none of the fine outer cable wires short circuit the connection - very easy to do, and a lot less easy to spot. And make sure any joint is really watertight.


<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.

 

[JonBrooks]

Would suggest you used good standard of RG58.
Maplin is good or you could try www.wsplc.com
One of the leading Ham radio supplies.
You also need to remember that for every join you make in you cable you will get "loss" 1-2db depending on conectors.
Its worth the investment in high grade solder plugs and sockets.

The less you can make the better it is and less to go wrong.

The idea of putting a new full length of cable is by far better if possible.

If you have to put the conection outside then use some self amalgimating tape to seal the joint.

And as I have seen before, never use choc blocks!!!

Hope that helps
Regards

<hr width=100% size=1>Jon Brooks Icom UK Ltd. 01227 741741

 

[Oldhand]

I don't believe making a soldered joint is a good idea at all. Its not just he question of losses. If there is a substantial impedence mis-match at the joint then an appreciable amount of RF power will be reflected back into the transmitter, rather than being radiated at the antenna. This will cause additional heating of the transmitter output stage whcih is likely to be damaged, especially if transmission time is not kept very short. The sytem should be checked for VSWR (voltage standing wave ratio) and should be 2:1 or better.

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[JonBrooks]

As a qualified and experienced radio engineer and installer, solder joints are far far better than any crimp or screw on type, if done correctly

Tining is vital for a good solder conection.
Any young man/woman on his/her first few days at college on an electronics course can tell you that.
If you don't tin you will over heat the insulator in the coax and cause more problems, let along have a poor solder joint.

Most problems I have come across over the years are due to poor DIY joints.

50ohm coax is very important.
Never ever be tempted to uses TV or Sat coax.

If in doubt get someone who "knows" how to do it to do it.
Not just some one who thinks he/she can- a lot of them about.

Radio's are getting cheeper but we can tell, as most most can, what caused you radio to blow up.
Wrong coax or poor VSWR is not covered under warranty.

For those who don't know how to work out your VSWR.
Forward power:- should read about 25w.
Reflected power:- needle should not move ideally, a little is ok.

If in doubt ask.
Your no less of a person if you put your hands up and ask "help"
I do it all the time.

No dig at anyone in particular, just some help and advice.

Regards



<hr width=100% size=1>Jon Brooks Icom UK Ltd. 01227 741741

 

[Oldhand]

Think I must be cracking up, I thought I had read the suggestion of joining co-ax entirely by soldering and not using connectors. However, as an ex-antenna design/development engineer for HM ships and having seen many installations on same, I think I have seen the lot when it comes to joining 2 sections of co-ax, including worse than I have seen on any yacht.

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[Gunfleet]

Aerial Connection NB

Jon - to move sideways slightly, what is the name of the connector on the back of a 706 for an atu? I mean the four pin thing with a vee at one end. I have bought non icom atu (sgc 230) but am baffled as to how to connect the four leads to the unit. Does icom sell the female or do I have to (keep going) bos-eyed trying to find it in Maplins cat?
Thanks
John

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[JonBrooks]

Re: Aerial Connection NB

If you call us here and speak to Chris Ridley 01227 741741
He is our SSB expert he will be able to talk you through it on the phone and advice re the right connectors.

Hope that helps

Regards

<hr width=100% size=1>Jon Brooks Icom UK Ltd. 01227 741741

 

[tome]

<<As a qualified and experienced radio engineer and installer, solder joints are far far better than any crimp or screw on type, if done correctly>>

That's a brave statement. In many industries including ours, soldered joints are not allowed due to reliability issues. This is what ITT-Cannon have to say (they offer both crimp & solder):

"Crimp contacts offer improved electrical performance, strain relief and quality control compared to solder cup contacts. Solder cup contacts are recommended for low volume and prototype applications where the added cost of crimp tools is not justified."

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[steverow]

You must use RG58 or UR67 50 ohm impedance RF coax.
This is absolutely essential to keep a low VSWR which prevents your PA stage from overheating and going into thermal avalanche.

Also your join must be made using proper plug and socket adapters.
Suitable types are PL259 2X plugs and one double female adapter, or BNC types.
They will need soldering to effect a proper join, and the whole lot sealed with self amalgamating tape if left outside in the weather.

Maplin will be a good source for additional cable and plugs and sockets.

Steve.


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