testing an aerial

[Phoenix of Hamble]

How do you go about testing a VHF aerial and cabling?

At the weekend, my VHF, while working to sort locking out etc etc wouldn't receive the weather from Walton, even though I was only in Neptune Marina in Ipswich......

I would have thought this easy range?....

So, given that the set clearly works OK for local transmission and receiving, I will start by testing the aerial and associated cabling.... but don't know where to start?

 

[Anonymous]

[ QUOTE ]
....but don't know where to start?

[/ QUOTE ]If that's the case then because of the safety issues I would strongly advise you to employ a professional. It shouldn't take more than 10 mins to 'check' the system but it there is something wrong with the antenna, feed or the radio itself, it would take longer. OTOH, if you know an experienced Radio Amateur with a full licence, they should be perfectly capable of doing at least as much (if not rather more) than the average professional VHF fitter.

 

[Phoenix of Hamble]

Fair enough, but surely there are some basics I can check before engaging a professional?

 

[Anonymous]

Not really. You have already established that you can transmit and receive and that is the 'basics'. The next things to check are the antenna (and its local connection), the feed cable (and its connections), and the output power of the transmitter. It could be that if you take all the connections apart you will find one that has become damaged by water ingress and just needs cleaning or replacing but the most likely one is on top of the mast. If you have an SWR meter you can check how the antenna and feed looks from down below, without going up the mast. If it isn't the connectors or the antenna then a common problem is ingress of water into the screened cable. If that's the case you have to replace the whole feed cable - there is no alternative. I'd bet almost anything that it isn't the radio itself, unless the boat's batteries are very low?????

 

[petercornish]

If anything goes wrong with an areial or the cable or if it is the wrong type of aerial then standing waves will be generated on the cable feeder. To test this you need an SWR meter which is made for the frequency that you are using. The cost of these can be from £40 up to £2000, you generally tend to get what you pay for although the more expensive ones do tend to offer more features and are aimed at people who do it for a living.

Connect it in line with the aerial, calibrate it and then transmit, this will then show the SWR on the meter.

The SWR is shown as a ratio ie 1.2:1. in most cases anything below 1.5:1 is ok although you should remember that if you install the meter at the radio then the SWR will be higher at the antenna. I don't like anything above 2:1.

If you have problems then don't use your radio too much if you suspect the aerial, it can blow the receiver.

 

[Phoenix of Hamble]

Nope, the batteries are tip top... brand new and fully charged!

I'll start then with a visual inspection of the connectors at the bottom side, and given that I have to go up the mast soon anyway, i'll also visually check at the top.... If thats all fails, then its a professional..... thanks!

 

[Anonymous]

Sounds sensible, as long as you have the time. When you check the connectors, make sure that you re-tape the masthead connectors with 'self-amalgamating' tape. You can buy it in chandleries, I think. It looks like thick black pvc tape but it has a backing paper and 'melts' (without heat) into an homogenous seal. Also, take a few small tools and a wire brush up with you. Good luck!

 

[RivalRedwing]

Did you ask anyone at Neptune as to their ability to receive the Walton signal on the day in question - you are inland from the broadcasting antenna with woods and other topographic features in the way of a direct line of sight. If not careful I fear that you may end up chasing your tail on this.

 

[Phoenix of Hamble]

Moonfire,

I didn't and thats a very good point. I did make the assumption that as Walton is perhaps what?... 15 miles by Line of Sight, that it would be OK, but you are absolutely right, there are an awful lot of trees, buildings and other gubbins between Neptune and there that I should consider....

I'll have a word with others in the Marina to see if they get Walton clearly or not.... or maybe there is another Neptune resident on this forum that can confirm one way or the other?

 

[squidge]

Hi Neil , i hope that you are well.

Do you have a multi meter? if not you can pick one up from Maplin for a few pounds.You can use it to test your cable . Remove the connector from the vhf and join the center terminal to the outer with some bare wire,. Take your meter up the mast and put it across the terminals at the top. turn you meter to the buzzer (short) setting and you should get a buzz if not you have a broken cable or dry joint in a connector.If you dont want to buy a meter you could use a torch bulb and a battery at the top of the mast after you have disconnected the aerial. Needless to say dont transmit untill you are sure that the aerial is ok as you can blow the outputs.
Good luck
regards
Squidge

 

[Phoenix of Hamble]

Hi Squidge....

Yes I'm well thanks...

I'll take a good look at the cable anyway when I go up the mast..... and try your tip as an additional test... I guess it will test cable, whereas a visual inspection of the connectors can at best only identify a corroded or similar UHF termination....

Have you got that Moody back in the water yet?

 

[FullCircle]

Neil,
have you got an emergency VHF aerial (you should have!)? Give it a whizz with the emergency connected. If you get the weather, at least that eliminates the set from your investigations.

Jim

 

[Phoenix of Hamble]

Jim,

I don't yet... one of the many additional purchases to yet make!......

First off is a hand held, that I also don't have.....

 

[Benbow]

Well, if you don't have an open circuit with that test ie no buzz - then you know something is wrong, but if you DO, there could still be all sorts of problems with the coax.

SWR meter and/or comparison with the spare antenna you are about to get would be my advice.

 

[squidge]

Hi Neil , Nope , the yard say that they are V Busy and unless a space becomes available i will have to wait another week or so.She's already to go with fenders and lines out just in case.Its gettin a bit close for the B/hol and i dont like doing a long trip straight after launch so i am considering pulling out of the SB trip and going up to Woodbridge instead . I understand that there is some kind of Sea Britian event on and the boys wanted to see Sutton Hoo anyway.
Hows your new toy?

 

[JonBrooks]

Quick and easy test is connect an emergency type antenna ( cheap to buy and worth keeping on the boat) see if the range on this is better than your main set.
If yes time to change your anteena and cable.

If I was changing one I would always the other.
Least that way both are the same age.
Less chance of having to do it all again a bit further down the line.

Regards

 

[Phoenix of Hamble]

New toy is marvellous!...

Loads of fun, especially as the weather has been relatively kind so far!

We are also looking at our options for the bank holiday weekend.... present favourite is Southwold, but weather is key here!

What Sea Britain event is going on up the Deben then?

 

[fireball]

We noticed that we weren't receiving as much traffic around the solent as we expected ... the problem was with a dodgy connection in the cable after it has come through into the cabin - took time out to strip back and re-make the connection and now we can hear the fishermen chattering away .... back to normal!
We then phoned up a friend who was entering into another port and did a quick radio check with him - tested both sets /forums/images/graemlins/smile.gif

 

[Gordonmc]

Bite the bullet and replace both the coaxail cable and the aerial. If the coax has gone and there are no junctions, the aerial will have caused the problem and it will do it again.
My Decca transceiver was curiously quiet toward the end of last Summer while the handheld would chatter away. I checked the terminal going into the back of the set and it was fine. But when I cut away the insulation just below the deck head, the outer shield was non existent and there was much evidence of wet and corrosion.
The aerial and coax were new in 2003 and I had used amalgamating tape on the aerial junction before the mast was stepped.
In conversation with the chandler whence I bought the thing he acknowleged that the type of aerial was prone to letting water from the top, in the joint between the plastic body and SS whip. In my case water had wicked two-thirds the length of the coax.
I was up the mast at the weekend and replaced both aerial and coax.
I would have taken this up with the manufacturer. Unfortunately I dropped the old
aerial into the briny from the masthead.

 

[bruce]

if a friend has a CB swr meter, you can use it, but the reading will be off, but a 3:1 reading in 'CB' is good for a vhf radio and antenna.