wipe_out
Well-Known Member
Just curious about the range of a hand held VHF at 1w power.. If the 5w power is supposed to reach 5 miles line of sight then does that translate to 1w being roughly 1 mile line of sight?
Hand held VHF range at 1w?
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mlines
Well-Known Member
The problem is that there are so many variables that it is hard to tell.
Handheld to handheld on land (buildings/trees etc) it can be down to a few hundred metres.
Handheld to handheld over open water - yes a mile or so
Handheld to base station with decent aerial - 5 to 10 miles perhaps
So a handheld will often do fine for inshore ship to shore comms as all the money is spent at the shore station.
Handheld to handheld on land (buildings/trees etc) it can be down to a few hundred metres.
Handheld to handheld over open water - yes a mile or so
Handheld to base station with decent aerial - 5 to 10 miles perhaps
So a handheld will often do fine for inshore ship to shore comms as all the money is spent at the shore station.
vyv_cox
Well-Known Member
The magazines test this on a fairly regular basis. Last one I can find in YM is December 2010. It is very dependent upon make of the set but there is often surprisingly little distance between the two outputs.
AndrewL
Well-Known Member
The Apollo spacecraft used a 20 watt transmitter for voice communication with earth from the moon. Although Nasa were using a 200 foot diameter dish to receive it.
bedouin
Well-Known Member
From a purely numerical point of view I would expect it to be nearer to a square rule (i.e. much less than 1 mile) but that is so simplistic as to be pretty much useless. With clear line of sight I would expect about 1 mile but anything in the way and it could drop to a couple of hundred yards.
BTW forget Apollo - I think Voyager's radio was only about 20W and that could transmit data 12,000,000,000 miles
BTW forget Apollo - I think Voyager's radio was only about 20W and that could transmit data 12,000,000,000 miles
[70521]
Well-Known Member
But that was through a vacuum.BTW forget Apollo - I think Voyager's radio was only about 20W and that could transmit data 12,000,000,000 miles
davidej
Well-Known Member
From a purely numerical point of view I would expect it to be nearer to a square rule (i.e. much less than 1 mile) but that is so simplistic as to be pretty much useless. With clear line of sight I would expect about 1 mile but anything in the way and it could drop to a couple of hundred yards.
BTW forget Apollo - I think Voyager's radio was only about 20W and that could transmit data 12,000,000,000 miles
If it is a simple as the square rule, it would be more than a mile - actually more than two.
just do the maths - the square root of five
Salty John
Well-Known Member
Height above sea level of both transmitter and receiver trumps other considerations. Your horizon distance - how far your signal travels and is available to be received - can be increased by standing up rather than sitting down, or standing on the cabin top rather than in the cockpit. If, however, you were to shinny up the mast your horizon distance may start to become limited by your transmit power.
A masthead antenna significantly increases your radio horizon - even if its connected to a hand held. Radio horizon is 1.4 x root height above sea level. Your communication range is a combination of your radio horizon and your co-respondents radio horizon distance. (Height in feet, distance in nm)
A masthead antenna significantly increases your radio horizon - even if its connected to a hand held. Radio horizon is 1.4 x root height above sea level. Your communication range is a combination of your radio horizon and your co-respondents radio horizon distance. (Height in feet, distance in nm)
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bedouin
Well-Known Member
Would you like to think about that one again
If the radio wave propagated in all directions then the distance would be proportional to the square of the power - so 1W would travel 1/25th of the distance of 5W. In fact even for handhelds with very small antennae the propagation is nothing like omni-directional so they can do much better than that, but certainly not linear.
AntarcticPilot
Well-Known Member
It's worth noting that the 5 mile figure is probably pretty close to the line-of-sight limit for a hand held VHF operating a metre or two above sea-level (the horizon is 4 miles away for a VHF 2 metres ASL). And as others have noted, it does depend as much on what's at the other end as on the handheld itself; the CG have lots of large antennae well above sea-level, which will receive even a weak signal from much further away than the stub antenna on another hand-held will.
st599
Well-Known Member
There are 2 things at play:
1) height of antennas - can they see each other
2) power at the receiver - is it enough to open the squelch and be decodable
Under normal weather conditions then the horizon in km for each is 4.12 x sqrt(height in metres)
Then the receive power is
Prx = Transmit Power + Transmit Antenna Gain - Transmitter Losses - Path Loss + Receive Antenna Gain - Receiver Losses (ALL IN dB)
where path loss is 20log(4 x pi x distance/wavelength)
and the required receive power is radio design dependent.
1) height of antennas - can they see each other
2) power at the receiver - is it enough to open the squelch and be decodable
Under normal weather conditions then the horizon in km for each is 4.12 x sqrt(height in metres)
Then the receive power is
Prx = Transmit Power + Transmit Antenna Gain - Transmitter Losses - Path Loss + Receive Antenna Gain - Receiver Losses (ALL IN dB)
where path loss is 20log(4 x pi x distance/wavelength)
and the required receive power is radio design dependent.
earlybird
Well-Known Member
That doesn't seem correct. It's an inverse square law, so decreasing the transmitting power by a factor of 5 will reduce range by a factor of 2.23 at which the reception power is the same, other things being equal.Would you like to think about that one again
If the radio wave propagated in all directions then the distance would be proportional to the square of the power - so 1W would travel 1/25th of the distance of 5W.
As Davidej said.
lw395
Well-Known Member
In free space.Would you like to think about that one again
If the radio wave propagated in all directions then the distance would be proportional to the square of the power - so 1W would travel 1/25th of the distance of 5W. In fact even for handhelds with very small antennae the propagation is nothing like omni-directional so they can do much better than that, but certainly not linear.
The power is transmitted into a solid angle.
Consider a sphere for simplicity.
The receiver sees a sample of that power based on a certain area, say 1 sq m.
The power in that sqm will be inversely proportional to the area of the sphere, i.e. R^2, and proportional to the Tx power.
So doubling the range requires a four-fold increase in power.
In the 'radio horizon' case, the extra power pushes the horizon as some of the wave diffracts around the surface.
Signal at the receiver can be more like proportional to R than R^2 in this regime, so the 5W becomes more worthwhile.
bedouin
Well-Known Member
Oops yes I seem to be standing on my head
alant
Well-Known Member
Hoover or Dyson?
Momac
Well-Known Member
I usually have mine on low (1W) and in most circumstances calling a shore station there is a range of a mile or so. This is very often where there are some obstructions.
Fendant
Well-Known Member
I am regularly using my handheld at 1 W for communication from the helm station ( lets say 2 m above waterline ) with a friend on his boat ( same 2 m ) when we travel together.
Over open water we manage to communicate loud and clear if the distance is less than 1 km. Even going to 5 Watts does not improve the comm when the distance is over 1 km to 2 km. 5 Watt however on my fixed VHF with antenna on 15 m masthead works quite nice. For ship to shore in locks or ports you are always fine with a 1 W handheld.
Over open water we manage to communicate loud and clear if the distance is less than 1 km. Even going to 5 Watts does not improve the comm when the distance is over 1 km to 2 km. 5 Watt however on my fixed VHF with antenna on 15 m masthead works quite nice. For ship to shore in locks or ports you are always fine with a 1 W handheld.
ronsurf
Well-Known Member
I'd use the 1W setting for communicating with harbourmasters when in harbour, or at the other end of the boat - basically just out of shouting range.
Also good for two people sailing together in separate boats - they can chat without wiping out other communications for (up to, depending on conditions, aerial, atmospheric conditions, battery conditions etc etc) miles around.
Also good for two people sailing together in separate boats - they can chat without wiping out other communications for (up to, depending on conditions, aerial, atmospheric conditions, battery conditions etc etc) miles around.
Dockhead
Well-Known Member
Power is only one of several factors which determines the range over which you can get a readable signal, and far from the most important one.
The most important factor, as any radio amateur will tell you, is the antenna.
I once got a "weak but readable" radio check from Solent Coast Guard, transmitting at 1 watt.
From just outside Cherbourg Harbour, 60 miles away.
That's because I was using an excellent internal dipole antenna 23 metres above the sea, connected to my fixed VHF set by fat low loss RG223 coax with no splices or connectors except at the ends.
The big problem with handhelds is not the power, but the extremely compromised antennae, and of course the height of the antenna. A bit extra power will help overcome these limitations, but not by all that much. I personally don't count on reliable comms between a handheld VHF and an ordinary fixed station at much more than a mile or two, whatever the power setting, although I've had good contacts over 10 miles under the right circumstances (transmitting illegally from land, from a high hilltop, calling the mother ship -- on Ushant, IIRC).
The most important factor, as any radio amateur will tell you, is the antenna.
I once got a "weak but readable" radio check from Solent Coast Guard, transmitting at 1 watt.
From just outside Cherbourg Harbour, 60 miles away.
That's because I was using an excellent internal dipole antenna 23 metres above the sea, connected to my fixed VHF set by fat low loss RG223 coax with no splices or connectors except at the ends.
The big problem with handhelds is not the power, but the extremely compromised antennae, and of course the height of the antenna. A bit extra power will help overcome these limitations, but not by all that much. I personally don't count on reliable comms between a handheld VHF and an ordinary fixed station at much more than a mile or two, whatever the power setting, although I've had good contacts over 10 miles under the right circumstances (transmitting illegally from land, from a high hilltop, calling the mother ship -- on Ushant, IIRC).
Alpha22
Well-Known Member
+1 Dockhead.... its not the power.
Stand on the coach roof and hold your handie in the air, you will probably double the receive range.... well almost.
Many amateurs will tell you you can reach Australia with just a few watts of power. Yes you need a bigger twig than the one on your hand held..... yes you need lower frequencies..... yes you need a bit of luck.... and only with morse code, but!!!! radio waves are not light waves..... even though they are all EM waves.....
The quality of the receiver also plays a big part in VHF marine comms..... my cheap Boefeng Chinese VHF/UHF, all things to all men, £20 radio gives up receiving marine VHF a long time before my half decent Icom handie. Even when connected to an identical antenna.
Stand on the coach roof and hold your handie in the air, you will probably double the receive range.... well almost.
Many amateurs will tell you you can reach Australia with just a few watts of power. Yes you need a bigger twig than the one on your hand held..... yes you need lower frequencies..... yes you need a bit of luck.... and only with morse code, but!!!! radio waves are not light waves..... even though they are all EM waves.....
The quality of the receiver also plays a big part in VHF marine comms..... my cheap Boefeng Chinese VHF/UHF, all things to all men, £20 radio gives up receiving marine VHF a long time before my half decent Icom handie. Even when connected to an identical antenna.
