High Power VHF Radio (25 watt+)

[CJL]

Evening all,

I'm curious, is there anyway to boost the output of a marine VHF radio on a RIB? (Yes I'm aware there are licensing issues that would accompany any such modification but I'm wondering if it can actually be done before talking to Ofcom and/or buying any kit)

It seems technically feasible to do it for CB radios which are lower output (4w up to 20w) and there are various schematics to home build boosters.

Does nobody offer off the shelf equipment that would not allow higher output?

Chris

[treerat]

Originally Posted by CJL

Evening all,

I'm curious, is there anyway to boost the output of a marine VHF radio on a RIB? (Yes I'm aware there are licensing issues that would accompany any such modification but I'm wondering if it can actually be done before talking to Ofcom and/or buying any kit)

It seems technically feasible to do it for CB radios which are lower output (4w up to 20w) and there are various schematics to home build boosters.

Does nobody offer off the shelf equipment that would not allow higher output?

Chris

I've a booster that I used to use on the CB, same connections so in theroy it should work the same.

Never tried it though.

[ashbypower]

Originally Posted by treerat

I've a booster that I used to use on the CB, same connections so in theroy it should work the same.

Never tried it though.

27Mhz versus 150Mhz, I dont think so... there miles apart!!
You'll need a Ham Band 2m linerea amp for 150Mhz, then though there is still a few Mhz out.

[willk]

An interesting subject. Only of use if you're talking to the CG (or another similarly equipped craft).

You might be best to "optimise" your (legal) setup before trying this. Have you tried all that malarky first?

[Starovich]

questions
if you needed the extra power to contact someone (range?) then how they going to answer back if they don't have the extra power too?

and i'm no expert but wouldn't a taller aerial give more range due to the curvature of the earth and the whole line of sight issue?

[BogMonster]

The easiest road to higher power output would be to use one of the ham band VHFs which are 50-55w and can be opened up to the marine band though that won't be waterproof so no use on an open boat ... I have a collection of ham sets which we use on marine band because the Mrs requires it for her job though of course I always make sure we are transmitting on the middle power rating not on high power

The ones I have are Icom IC-2000, a few IC2100 and an IC2200 plus an Alinco DR140 and an old Icom IC229H at work, they all operate happily in the marine band for transmit and receive, and all except the last one are 50w+

3DB gain on the aerial is worth twice the power output so may be an easier solution? Conversely some crap coax or a dodgy aerial or connections will cut the performance in half just like that.

[GJ0KYZ]

Transmitting with more power than the license specifies is illegal and I doubt OffComm will allow exemptions unless you have good reason. The best way to improve the transmit and receive performance of your VHF is to install a higher gain antenna. As mentioned, a mere 3db gain will double your effective radiated power and provide benefits when receiving the transmissions of other stations. Just buying a new antenna per se will probably help anyway as most of us pay little attention to coax degradation and the quality of our PL259 fixtures.

[treerat]

Originally Posted by ashbypower

27Mhz versus 150Mhz, I dont think so... there miles apart!!
You'll need a Ham Band 2m linerea amp for 150Mhz, then though there is still a few Mhz out.

I think the booster works though by taking in a signal and running it through its board and boosting it up. It should work with the marine as well, actual mhz in shouldn't matter too much.

But I'm no enginier.

[GJ0KYZ]

Originally Posted by treerat

I think the booster works though by taking in a signal and running it through its board and boosting it up. It should work with the marine as well, actual mhz in shouldn't matter too much.

But I'm no enginier.

It won't work. Trust me, I've been a Ham for 25 years; the amplifier needs to be tuned for the frequency band in question.

[m chappelow]

From what i remember the maximum allowed for marine vhf is or was 25 watts,

[BogMonster]

Originally Posted by GJ0KYZ

It won't work. Trust me, I've been a Ham for 25 years; the amplifier needs to be tuned for the frequency band in question.

My father used to be a keen ham radio user in the old days when it was the only way to talk to somebody overseas from here, and he had a 2kw (yes 2 kilowatt...) amplifier for his ham set but I remember 'tuning up' as an endless twiddling of knobs and whistling into the microphone while intently watching dials go up and down until he was happy. Usually took longer than the actual conversation ... so it's not a plug and play exercise but would burn a hole in the world when it was done right

[jyasaki]

Originally Posted by m chappelow

From what i remember the maximum allowed for marine vhf is or was 25 watts,

Not sure about the UK, but in the US, anything over 25W on the water requires a bunch of licenses from the FCC. Operator, unit, and vessel and equipped with unit, I think.

If you need to talk to someone a ways away, well, yachties use Single Side Band sets, don't they? They reach a lot further than VHF (though they may require licensing as well, but the advantage of not needing exemptions from existing regs.)



jky

[Limey Linda]

Originally Posted by willk

. Only of use if you're talking to the CG (or another similarly equipped craft).

?

Please explain why that is

[willk]

Originally Posted by Limey Linda

Please explain why that is

Originally Posted by Starovich

if you needed the extra power to contact someone (range?) then how they going to answer back if they don't have the extra power too?

and i'm no expert but wouldn't a taller aerial give more range due to the curvature of the earth and the whole line of sight issue?

'Cos the CG have "big ears and a loud voice" and Storovich's response applies to the others.

Nice to hear from you, BTW

[Simon B]

Originally Posted by Starovich

questions
if you needed the extra power to contact someone (range?) then how they going to answer back if they don't have the extra power too?

and i'm no expert but wouldn't a taller aerial give more range due to the curvature of the earth and the whole line of sight issue?

Exactly! Hence the 25 watt working power for most sets. Rigging a 50 foot antenna on a rib may reduce the boats performance in other areas!

Linear amplifiers are great until everyone has one,so they are regulated for this reason. Best thing to do is get a good antena and have it fitted correctly and manage performance expectations accordingly. The coast guard have much higher antennas and I think clever repeater antenas for send and recieve.

[two stroke mick]

I have a 27MHZ (CB) SWR meter and it does not work with the VHF (marine) I assume it is because there is too large a gap between the freq

TSM

[Hightower]

Firstly.. you won't get an off the shelf "Burner" for 150MHz band I believe that 25 watts is the most power you can go to on that band of frequencies in most countries and anything else would be illegal to use. But a custom built one could increase the power.

Secondly.. Using more power won't be any more use to you other than to "bleed" over the top of other transmissions. It won't increase your range in normal conditions unless you're using two ruddy tall aerials. Then of course you could use directional aerials to get even further range without increased wattage.

Would there not be increased health risks in increasing the power significantly in a close range application too?

What are you going to be using this set-up on? Or is it just to see if it can be done?

[CJL]

Originally Posted by Hightower

What are you going to be using this set-up on? Or is it just to see if it can be done?

A bit of both and it would be to talk to a CG base station.

Part of the problem is not getting greater distance, it's getting around buildings in Central London that cause black spots. You appear to be able to receive in these black spots from CG stations, just not transmit.

Chris

[Hightower]

I would guess that along the Thames that your mobile phone would be enough in an emergency. You could use the radio to co-ordinate the rescue when the emergency units are on the scene.

I am surprised that you have "black Spots" where you can hear the CG but can't raise them on the VHF. Perhaps you do have a poor aerial or connection that needs looking at? Should your radio setup be OK then perhaps you should map these areas and submit your finding to the CG so that they can improve their coverage.

[CJL]

Originally Posted by Hightower

I would guess that along the Thames that your mobile phone would be enough in an emergency. You could use the radio to co-ordinate the rescue when the emergency units are on the scene.

I am surprised that you have "black Spots" where you can hear the CG but can't raise them on the VHF. Perhaps you do have a poor aerial or connection that needs looking at? Should your radio setup be OK then perhaps you should map these areas and submit your finding to the CG so that they can improve their coverage.

In principle what you suggest is fine but in some places the mobile phones have bad reception areas as well as the radios. We do use a combination of VHF and mobile as it is but I thought a whopping great big powerful VHF might have solved the problem.....it sounds like a no though.

London CG and the PLA already know the black spots on the River if they decide to do something about them, well that's another question!