Radio Installation

Rob Jones · 26 December 2005, 15:56

Was wondering if anybody could give me some advice regarding the wiring on my Hummingbird radio.

I have replaced the old antenna with a Vitronix RIB Raider.

The cabling @ the antenna end was corroded and the end thingy fell off.

The new antenna has a 6m cable included, my question is this - what is the best way to fit the new antenna. Would I change the whole cable on the boat? which will entail some fiddly feeding and pulling, or replace the end thingy, if the latter what is the end thingy and where would I get one from?

The new cable seems to have a brass type end - the other is just cut coaxial, which I presume I would add the radio connector.

All advice appreciated

Nos4r2 · 26 December 2005, 16:19

From a safety point of view, change the cable seeing as you've got one. You know the one time it'll stop working is when you're in the shit.

Hightower · 26 December 2005, 16:41

Look for a local amature radio shop or CB shop (if they still exist) you can buy a couple of PL259 plugs and a female connector. This will join up your coax, then you'll have to think about waterprooing it all. Chop a piece of 1" conduit about 10" long slide this over the connector and fill the ends with silkoflex.

Go here: http://www.nevada.co.uk/

daveh · 26 December 2005, 20:49

Definitely change the cable it is usually the source of poor range and reception. It's really not that hard; just attach a thin mousing line - the thin reels of dyneema are pretty good then pull it all through. You might appreciate it one day.

stepheneyre · 26 December 2005, 22:15

hi
i would replace the whole lot just tape the old and new wire together(end to end) and pull through gentley
replacing the wire gives the best waterproof and you know it works
thanks
stephen eyre
sheffield.

Mike C · 26 December 2005, 23:54

Its always best to have one length of cable from the transmitter to the aerial if you can. Any join, even if its a proper plug can corrode. That will cause a mismatch and increase the SWR (Standing Wave Ratio). Basically the amount of signal that gets reflected back into the transmitter instead of radiating out of the aerial! There is always some reflected power but the more you have the less far your signal will go…. And if its too bad you can blow up the transmitter…. Especially the Hummingbird – could be wrong but I don’t think that has much in the way of high SWR protection.

As for waterproofing. The RIB Raider has a fairly good waterproofy connection that goes into it. I just smear a little silicone grease and I’ve had no trouble with that aerial. The PL259 that goes into the transmitter isn’t waterproof but if that’s inside the console then more grease will probably do there. That’s all I have, but I take Hightower’s point

If the cable isn’t long enough to go from TX to Arial then it may be wise to visit an Amateaur Radio shop as Hightower said. Get plenty cable and ask then to wire up the PL259 on one end for you if they will. To my mind they are more difficult to wire than the Vitronix end which just push fits. Then mouse the bare end through your ducting. If it’s wired shorted (at either end) then bye bye Hummingbird.

(Vitronix used to do a longer length cable version once – maybe you could call them and do a swap?)

Happy transmitting!

Mike C (G4OTQ in my Ham Radio days)

Hightower · 27 December 2005, 00:14

Very sound advise Mike

.

steedthrust · 27 December 2005, 07:26

Oops

steedthrust · 27 December 2005, 07:27

Is it okay to shorten a VHF aerial cable? Am worried it may 'tuned'

to a certain length.

Also is it okay to shorten a GPS cable?

Cheers

Rob Jones · 27 December 2005, 10:13

Frustrating morning as I need to get the boat fixed up and I only have today to do it. Of course wake up today and its snowing.

I am getting to grips with the cabling situation - the thingy on the end is a brass hollow nose bullet - which can be pulled off the new wire, which I have done, The pl259 part is the silver screw connection that goes into the radio, but it turns out mine has been threaded so the original still fits but the new does not have enough length to grip the remaining 3 threads.

I have decided a new radio is in order - to that end I pulled the bullet part of and attached it to the old co-axial.

Will now attempt to determine the range by getting my daughter to run with my handheld whilst I sit on a snow covered boat waiting for her chitter chatter.

Thanks All.

Jimbo · 27 December 2005, 10:15

Quote:

Originally Posted by Rob Jones

Will now attempt to determine the range by getting my daughter to run with my handheld whilst I sit on a snow covered boat waiting for her chitter chatter.

I wouldn't broadcast that intention on a public forum!

Mike C · 27 December 2005, 16:34

Quote:

Originally Posted by steedthrust

Is it okay to shorten a VHF aerial cable? Am worried it may 'tuned'

to a certain length.

Also is it okay to shorten a GPS cable?

Cheers

Hi Steedthrust....

Well this is an interesting question.....

I have always said that the length of the co-ax doesn’t matter on the type of sets we use on the boats.... (and the Amateur VHF set I used to run). This came from knowledge secured at the back of my mind when I did my Radio Amateurs Examination…. 25 years ago! But when I thought about it I couldn’t remember why… So I dusted off some of my old books…..

The problem comes with all the different ways you can feed a transmitter. I used to have a ‘Short Wave’ HF Transmitter, which fed to a long aerial that went down the garden. This was a centre fed di-pole using a balanced twin-wire feed. This had to be a length that was a multiple of the wavelength I was transmitting on, (although there were ways round that). But basically, yes it had to be tuned. HF transmission lines are fascinating…. Did you know you can touch them in one place and get a shock… but touch them a few feet further along and there will be no voltage!

Yes, its really complicated….. but fortunately not on a boat.

On a boat we use a

Ground Plane Antenna, fed by co-ax… which is an unbalanced feed. So long as the impedance of your TX output is 50 ohms… and the cable is 50 ohms…. And the antenna is 50 ohms….. (which it will be unless you’ve done something dodgy), you have what’s known as a ‘Non-Resonant Line’. This means everything is matched, all the power is absorbed by the aerial, (in theory) and the length of the feed line doesn’t matter. Its only if you use funny aerials, (di-poles, loops etc) or the wrong impedance co-ax that you will need to mess about with matching by length.

That at least is my understanding from my 25 year old books – but if anyone knows better……!

Designing aerials is a bit like designing boat hulls. I can design you an aerial tomorrow that will work… and a boat hull too….. but don’t expect them to win any awards!

Oh, and I would think the GPS would follow the same argument….

Mike C

PS….

Rob… If you’re going to buy a new VHF… take a look at Icom!

Hightower · 27 December 2005, 17:33

In other words it is safe to alter the length of your coax, right Mike

. Make sure you use some quality connectors though.

PS. I have a Silva S10 which is DSC (Icom never had one in this price range when I was looking) and had no problems but others have had shedfulls of probs. Silva says it has improved it's quality control and the radios are now made in the UK, but is recalling thousands of units to include mine to replace with the NEW ones.

IMHO though I'd go for the Icom as well (safe bet)

Shaggy · 27 December 2005, 17:48

Good advice mike

Shaggy ... G7AYT