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Geoff_Atkinson
12-05-2006, 09:50 AM
I have just purchased a new VHF radio, AM/FM radio/CD and a set of speakers to supplement the 27 MHZ radio I have in my boat.

I am planning to fit these this weekend, so sorry for the late question, but, if I hook up all three radios to the speakers, will the VHF or 27 MHZ override the AM/FM radio if i am listening to it, or shouldnt I hook up the speakers to those two, or is there a switch I can install which will isolate one or the other?

My other questions concerns aerials. Should I have a separate aerial for each radio or will the AM/FM radio run off the 27 MHZ or VHF aerial which I already have or, once again, is there a switch available which I could fit to switch between one or the other.

I am assuming that the higher I can get the VHF aerial, the better the range?

Many thanks in advance for all those who help

Cheers,

Geoff [smiley=huh2.gif] [smiley=helpa.gif] [smiley=hammer.gif]

MulletMan
12-05-2006, 11:46 AM
Re the VHF antenna height, this equipment operates on line of sight but being a more powerful unit than the 27 MHz, the standard antenna that comes with the VHF should be more than enough around this area. If you get into the trigonometary on angles of reception, you will find that another foot or two doesn't make all that much difference.

I maybe wrong but there is no chance of using the AM/FM radio through the VHF or 27 MHz antennas, totally different concept and incompatible.

Unless you have a fairly big boat, the normal radios have pretty good built in speakers that are more than enough volume for the average boat. I have a 26 footer and no problem hearing them down the back when fishing or when under way.

Are the speakers waterproof? If not they will have to be sheltered I reckon.

Another thought is NOT to go cutting any cables from the supplied length. Leave them as is and just zippy tie the excess out of sight somerwhere.

Ideally, VHF and 27 MHz antenna should be a minimum of one metre apart i.e. one either side of the boat. I'm far from being an ace on this topic but I think it is a good idea to let everything run off its own fittings rather than muck about with transfer switches and cross aerials etc.

Nice to see a guy who carries two marine radios for safety! ;D ;D

Geoff_Atkinson
12-05-2006, 01:43 PM
I have noticed in the shops you can buy an AM/FM VHF or 27MHZ Splitter, which has fittings for both units and join up to the VHF or 27MHZ aerial. What do they do then?

longtail
12-05-2006, 02:57 PM
I maybe wrong but there is no chance of using the AM/FM radio through the VHF or 27 MHz antennas, totally different concept and incompatible.


why not get a band splitter for either 27mhz or vhf , the am/fm radio will work fine on either aerial with a band splitter. ;)

i run my am/fm radio on my vhf aerial through a band splitter , no probs . ;)


cheers
jason

Geoff_Atkinson
12-05-2006, 03:04 PM
Thanks Longtail, thats the way I will go then. the boat would look like a porcupine wit three aerials.

Cheers,

Geoff

MulletMan
12-05-2006, 03:51 PM
Geez Longtail, that is news to me too!
Never even knew you could get such a thing!
:-/ :-/ :-X :-X

Geoff_Atkinson
12-05-2006, 03:56 PM
Of all the places to find one, I found it at BCF

fatandhappy
12-05-2006, 04:08 PM
Gooday guys ... There are a couple of things to note here ...

Re the number of antennas .... I agree with everything said so far in that the only radios you can combine are the 27Mhz and the VHF, but it must be via a band splitter. VHF works between 30Mhz and 300Mhz so depending where you are there will depend on how successful the band splitter will be.

As far as using the same speakers, that could be very dicey as depending on your set up (ie isolation from each individual radio) will depend as to whether you don't finish up blowing each of the radios up ... you may get away with it but probably not in the long term. A simple fix would be to use a double pole, triple throw switch (available from Tandys or Dick Smiths) and wire all three radios into the 2 speakers via that so there will only ever be one single load on any output at the one time.

Re the height thing ... being 27Mhz and VHF, propagation is limited to "line of sight" basically, so unless you can achieve a substantial diference in height with regards alternate mounting of the antenna you will achieve little. As an example, going up in height maybe 10 feet may get you another kilometre or two max ...

The bottom line is simply, if each system is set up individually, you will have a lot less problems as if its not done right , it will prove an expensive mistake.

hope this helps

Geoff_Atkinson
12-05-2006, 05:51 PM
Thanks fatandhappy,

I am now only going to hook the speakers up to the AM/FM radio, so I can hear the cricket and the footy a bit clearer.

Grand_Marlin
12-05-2006, 08:13 PM
The bottom line is simply, if each system is set up individually, you will have a lot less problems as if its not done right , it will prove an expensive mistake.



Spot on.


Hook your radios up to the same speakers and you will blow the radios up, through feedback.

Splitters work ok, but the same as any join in a cable, they inhibit performance. At an estimate 10 - 15%

The built in speakers are fine, but you can also buy extension speakers that plug straight in, if you think it is necessary.

Separate radios, separate power supplies, separate aerials = best performance and best reliability.

1m separation is ideal, but less can be used if necessary. If you were to put them on a rocket launcher ..... put the am/fm in the middle.

Cheers

Pete

fatandhappy
12-05-2006, 08:54 PM
... ;D ;D ... that's the way ... a couple of cold beers, the footy, the cricket and ya boat ... the little missus at home lookin after the dog ... no wait a minute, take that back, bring the dog with ya and all is good .... cheers and happy days ... fatenhappy

Coontakinta
15-05-2006, 09:58 PM
Guys have been reading this post with gr8 interest as I since having my radios installed in my boat I have had nothing but problems running them from separate aerials.

I have a GME GR100 AM/FM receiver and a Navman MCB7270. Each unit is run from its own aerial, with the Navman being the factory supplied and the GR100 having a "rubber ducky" short black rubber stubby, u know the type! The installation and ALL positioning were carried out as per the supplier / installer recommendations.

The problem is that I can not have the GR100 on if I want to transmit from the Navman. If I do I get a loud squeel from the GME. This squeel is the same volume no mater if the unit is on high volume or on mute. the only way to stop this is to turn the unit off all together. Its really pi$$'n me off especially as the installer reckons he dont know what else to do and GME say it 8nt their problem! >:(

Things that have been tried. Moving the aerials further apart, they are about 3ft apart now. (supposedly too close :-? :-/ >:()
Disconnect the Navman and fit a GME, problem still exists. Supposedly have checked earthing etc etc etc >:(

Speaking to GME they say the two units are not compatible, hence trialling with a GME 27meg. Then they say install hotline filters, but no guarantees and then they say if problem still exists could fry the Navman! :-/ :-? >:(

Think I can see I will have to get a report from an acreditied technician and see where the problem lies. I think its the installation myself, but here are some pics, what do u guys think?

Coontakinta
15-05-2006, 10:01 PM
and another

Coontakinta
15-05-2006, 10:10 PM
and another. have a m8 who is involve in the avionics game with a national freight carrier and he reckons it could be the fact that the coaxial cables are interferring with each other and the power from the Navman is being sent back down the aerial cable to the GR100.

Grand_Marlin
15-05-2006, 10:32 PM
Generally interference comes from

a) loose connections / joins
b) poor quality / faulty equipment
c) bad earths
d) common power supply
e) aerials too close.

The first thing I would do is run a separate power & earth cable from the battery to the vhf.

Just do it as a temporary connection first to see if it fixes anything.

Cheers

Pete

Meat
15-05-2006, 10:40 PM
Another important thing to remember about VHF is that, whilst you no longer need a licence to own a VHF radio, you need to be qualified to operate one.

You need a Marine Radio Operators Certificate of Proficiency (MROCP). VMRs run courses which are free for members + the cost of the exam ($48.20). Non-members can do the course at a VMR as well for a few extra $$.

I was told, however, that it is a federally controlled law, which means a fed. has to see you operate the radio to be able to fine you...

That aside, the course is really good. You'll learn a lot of important safety things. Download the handbook free from http://www.amcom.amc.edu.au/handbook/

Meat