Technical VHF Question

Doug Stormforce · 01 November 2006, 09:19

I want a VHF base station at the Centre, primarily so that we can keep in touch with PWC courses on Southampton Water if they have a problem(instructor will carry a hand held, strapped to his shoulder).

Between the centre and S.Water are numerous obstructions effectivly putting the two out of range.

I have a possible solution -my apartment is several stories high and has roof access, from the roof you can see both the centre and Southampton Water.

I dont want a VHF statio at home but is there any way I can install an antenna and repeater on the apratment roof to effectivly provide line of site between the PWC and the centre. Also are there any licensing implications of doing this as the rooftop staion will effectvly have to transmit to the centre.

I am already familiar with licensing requirements for the centre and hand held.

jwalker · 01 November 2006, 09:50

It's fairly common to do this for TV signals in remote places. A normal TV antenna is used for reception and retransmission. The two are simply connected together. One is aligned to receive and the other is aligned to transmit. You could receive on a standard VHF antenna but it would be better to retransmit using a directional antenna. It would be very similar to the old VHF TV aerials and quite sizeable. You could make one reasonably easily. If you consider this, I could work out the element sizes for you.

I've no idea about needing a licence for retransmitting. We're in the UK so probably.

I've got a feeling there is a limit to the gain of an antenna you are allowed to have connected to a transmitting VHF radio.

Jon Brooks · 01 November 2006, 11:25

Doug

If you apply for a private channel then explain to Ofcom the problems you have they may allow you a repeater but would have to say it a tad unlikely.
One of the big issuse is that you will need a duplex channel for the repeater to function and these are very rarely issued.

You could go down the Land Based (PMR) radio route, then again apply for a wide area licence this will give you a duplex channel and allow a reapeter for you.
A number of companies make waterproof PMR radio's now.

Give me a call if I can be of any further help.

Best regards

Jon

The Garfish · 01 November 2006, 11:38

Quote:

Originally Posted by Jon Brooks

Give me a call if I can be of any further help.

i amm givin yew a corl.

noww i downt wont too putt yew onn de fkin spott orr stirr de shitt orr enyfing butt wots de besstist raydio

imoc orr standud orizon

gaRf

Jon Brooks · 01 November 2006, 12:49

One could never say thatyou shit stir Garf!

There are lots of good radio's out there.
There is alsoa hell of a lot of dross so beware.

You will never go to far wrong with anything built in Japan IMHO

Best regards

The Garfish · 01 November 2006, 13:08

Quote:

Originally Posted by Jon Brooks

There are lots of good radio's out there.

fuk mee dat woz a nise likkul shimmy. yew ort too bee a fkin pollytishun

NOW ANSER DE FKIN KWESTIUN YEW NOBBUR

imoc orr standud orizon

gaRf

Doug Stormforce · 01 November 2006, 16:11

Quote:

Originally Posted by Jon Brooks

Doug

If you apply for a private channel then explain to Ofcom the problems you have they may allow you a repeater but would have to say it a tad unlikely.
One of the big issuse is that you will need a duplex channel for the repeater to function and these are very rarely issued.

You could go down the Land Based (PMR) radio route, then again apply for a wide area licence this will give you a duplex channel and allow a reapeter for you.
A number of companies make waterproof PMR radio's now.

Give me a call if I can be of any further help.

Best regards

Jon

Thanks Jon, however unfortunatly life is not that simple.

First problem, is duplex is no good for safetyboat traffic, we need craft and base station all on one frequency, so craft can commumicate with each oter if necassary.

Second problem- Centres I have worked at previously have managed quite happily on a private channel, however we often charter in RIBs etc. Boats we bring in will not have the private channel on their fixed sets.

At the moment we tend to opt for Channel 8 as our unofficial channel between craft. Obviuisly if we had a base station we can not use 8, I was thinking possibly M or M2.

Jon any more suggestions/ideas?

Jimbo · 01 November 2006, 18:29

From a technical point of view, the only thing that springs to mind is possibly using a non RF medium to get the voice comms from the office to the apartment.

The most effective way, I would have thought, would be to have someone design you a web interface for a remote VHF Radio, i.e. you talk into your radio on your pc, it goes through your broadband connection, into the apartment, and is broadcast, and vice versa.

As Jon pointed out, to act as a repeater you'd need a duplex channel ideally, so by making your apartment the only RF transmitter, you remove that problem.

Not sure how that would work from a licensing perspective, or how much it would cost to get someone to knock up a PC interface for a VHF.

jwalker · 01 November 2006, 21:27

I don't understand why you would need duplex.

Connect your VHF to a directional aerial aimed at your apartment roof directional aerial. This aerial will receive the signal and turn it into a current which will travel along the cable to the standard VHF antenna which will retransmit the signal out to sea. The return signal from the sea station travels the other direction through the system.

The reason for a directional aerial is to maximise the gain to compensate for the inevitable losses.

sparkey · 01 November 2006, 22:17

(1) Connecting two antenna together will do nothing. In TV repeaters etc the receive antenna is connected repeater which then re transmits the signal on a different frequency on the other antenna or on the sane antenna with a special unit called a cavity duplexer which prevents the signals mixing.

(2) The reason that duplex ( 2 frequencies ) are required is that if the signal is transmitted on the same frequency as the received one you will get feedback and the system just transmits what it just received. I.E. like having a microphone too close to a speaker.

(3) Another option that you might look at is a telecom leased line between your office and your apartment. You then get your marine VHF modified to remote control use and install in your apartment. This is then linked over the telecom leased line to a remote wired base in your office. All the RX & TX is done in your apartment so eliminates the need for duplex or private channels. The unit in your office is only a slave unit linked by the leased line.

I have installed a number of this type of set up in Ireland but not on marine VHF but on PMR private systems so would have to look into the availability if Marine VHF remote conversion kits.

Jon Brooks · 02 November 2006, 08:40

Most modern repeaters will cover the marine bands, from a technical point of view.
It willcome down to licencing as to if you can do it.

I understand you issue Doug and have to say there is no simple answer for what you need.

Life is never simple.

Oh and Garf, Iwould not go and work for any company if I felt they made crap kit!

Even when I was at Icom, whenasked would sayhow good the kit it here and I stand by that now

As I said there is a lot a dross out there but not out of the Icom or Standard camp!!

Regards

Doug Stormforce · 02 November 2006, 10:11

Thanks everyone

Jimbo and Sparkey

I think both of your ideas sound like they work best and are simply variations of the same theme a remote vhf at the centre would solve the basic problem, I am going to look into this further. It appears to be simple on the licensing front as well

Jimbo I expect you will have some more thoughts on the PC/VHF link. let me nkow if u do.

Poly · 02 November 2006, 17:51

doug - I think this is the sort of thing Jimbo was suggesting - but for am. radio rather than marine use. How easy (or legal) it might be to adapt this for marine use is another thing...

http://www.echolink.org/
http://www.irlp.net/
http://www.eqso.net/