In your experience, what would you expect for range from a handheld VHF transmitting close to the water?
VHF range
- Thread starter Quoddy
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The range in NM should be the Square Root of the VHF unit above sea level times 1.15. Assuming holding it in cockpit of sailboat it would be roughly 9 Ft above sea level. Sq Rt of 9 =3. 3 x 1.15 = 3.45. Therefore about 3 1/2 NM to horizon. To that add the distance to the other VHF radio. If it to is a handheld, it would have 3 1/2 NM to the horizon. The total distance would be 3.5 + 3.5 or 7 NM. If the other VHF was one with a tower antenna (i.e. Coast Guard), it would be much more. If tower was 144 Ft high, it's distance to horizon would be Sq Rt of 144 =12. Then 12 x 1.15 = 13.8 NM. So in that case total distance would be your 3.5 + their 13.8 = 17.3 NM.
If you are in the Portland area, there is now an automated radio check on 27. I sends back a recording of your voice so you can hear the transmission quality.
I think the service is coming to other areas.
I think the service is coming to other areas.
line of sight, power and antenna play into it, as does the fact that it is FM-simplex
so likely 3-5 miles at sea level...for a handheld....perhaps 60 miles with tall mast mounted antennas and max power.
Depending on wave action, atmospherics, quality of the radio, etc.. of course
so likely 3-5 miles at sea level...for a handheld....perhaps 60 miles with tall mast mounted antennas and max power.
Depending on wave action, atmospherics, quality of the radio, etc.. of course
You can actually get much longer ranges that the math would suggest. 166 MHz is one of those "bendable" frequencies and bounces around the upper atmosphere if conditions are right.
I have gottne NY City? USCG in the Chesapeake Bay several times and rutinly get Norfolk CG from the Route 50 bridge area. In all cases it has been the USCG with their high power that allows this to happen. I've never heard who they where talking to as they have much lower output.
I have gottne NY City? USCG in the Chesapeake Bay several times and rutinly get Norfolk CG from the Route 50 bridge area. In all cases it has been the USCG with their high power that allows this to happen. I've never heard who they where talking to as they have much lower output.
I think that some of you guys should read up on repeaters and trunking radios, etc..
the ranges submitted are quite accurate...the reality is that technology may make it appear that the CG is next door, when in reality they are hundreds of miles away...just a repeater near you that moves the transmission along and then back...
the ranges submitted are quite accurate...the reality is that technology may make it appear that the CG is next door, when in reality they are hundreds of miles away...just a repeater near you that moves the transmission along and then back...
I've done the tests for a UK magazine using my Icom HH VHF with 5 Watts transmitter power.
HH cockpit to cockpit about 2 miles, better if you hold the set above your head! (Okay for receiving not too good for TX!)
HH in cockpit to yacht main VHF set with masthead antenna - about 5 miles.
HH in cockpit to Coastguard antenna height 1000 feet on hill. Communications were still loud and clear both ways at 35 nMiles.
Range from liferaft expected to be about same as above for small wave heights only.
HH cockpit to cockpit about 2 miles, better if you hold the set above your head! (Okay for receiving not too good for TX!)
HH in cockpit to yacht main VHF set with masthead antenna - about 5 miles.
HH in cockpit to Coastguard antenna height 1000 feet on hill. Communications were still loud and clear both ways at 35 nMiles.
Range from liferaft expected to be about same as above for small wave heights only.
Likewise, for about a month every year, I hear transmissions from Ensenada, Mexico in Long Beach, a distance of (air) 125 miles. In fact, one time sailing down the Baja coast, at night, I heard USCG transmissions from San Diego 250 miles away. Since I was unable to raise the marine operator on the SSB, I tried to raise the San Diego VHF marine operator. I got it and had about a five minute talk home before the call dropped. I never thought that would ever happen.
I believe what we are hearing her is the phoneme called tropospheric ducting. Works just like the mirage you see on the road when driving. The different temps of air 'bend" the radio waves back down to earth where you pick them up.
For the record a trunking radio is not what the USCG uses when it talks to civilians. Just plain old simplex radio.
For the record a trunking radio is not what the USCG uses when it talks to civilians. Just plain old simplex radio.
I agree with Bill on the ducting. VHF doesn't propagate much off the atmosphere but if you want to get the most out of your handheld, try a different antenna. Most portables have removable antennas with common connectors. You could mount an antenna at the top of the mast and attach the cable to where your antenna screws on.
For the record,
I spoke with a master chief in the comms shack at Yorktown, VA earlier this week, and I suggest you visit the comms shack at your nearest CG station and ask about Rescue 21 in particular and comms in general. Perhaps trunking is an old style description, but there are certainly MANY transmitters, towers, and receivers and a lot of technology that ties them together for us to use. The receivers "vote" on which one has the best reception for your call and it ...well you can ask about it yourself.
It is not simplex when the CG talks to you, although it may appear to you that way.
In my area alone there are many sites (similar to repeaters) and they "link" St Inigoes, Leonardtown, Sector Baltimore, all in MD, Sector Hampton Roads,VA, Elizabeth City, NC, Curtis Bay, MD and MANY more to a comm center just outside Baltimore.
There is no single super, high watt transmitter that blasts all that CG information. It is multiple everything that they can use to triangulate your transmissions. With backup and failover systems. The broadcasts of information by the coast guard can be across all channels simultaneously, or to a specific geographic area, or specific channels in an area.
Please do the research, as if you continue to believe that your 5 watt handheld, at deck level, to its rubber ducky antenna is going to give you 50-60 miles, you are going to be sadly disappointed and may put your self in jeopardy doing so.
I spoke with a master chief in the comms shack at Yorktown, VA earlier this week, and I suggest you visit the comms shack at your nearest CG station and ask about Rescue 21 in particular and comms in general. Perhaps trunking is an old style description, but there are certainly MANY transmitters, towers, and receivers and a lot of technology that ties them together for us to use. The receivers "vote" on which one has the best reception for your call and it ...well you can ask about it yourself.
It is not simplex when the CG talks to you, although it may appear to you that way.
In my area alone there are many sites (similar to repeaters) and they "link" St Inigoes, Leonardtown, Sector Baltimore, all in MD, Sector Hampton Roads,VA, Elizabeth City, NC, Curtis Bay, MD and MANY more to a comm center just outside Baltimore.
There is no single super, high watt transmitter that blasts all that CG information. It is multiple everything that they can use to triangulate your transmissions. With backup and failover systems. The broadcasts of information by the coast guard can be across all channels simultaneously, or to a specific geographic area, or specific channels in an area.
Please do the research, as if you continue to believe that your 5 watt handheld, at deck level, to its rubber ducky antenna is going to give you 50-60 miles, you are going to be sadly disappointed and may put your self in jeopardy doing so.
Some line of sight calculators:
VHF/UHF
http://www.qsl.net/kd4sai/distance.html
http://www.naval.com/sight/index.htm
RADAR
http://www.mar-it.de/Radar/Horcalc/horcalc.htm
VHF/UHF
http://www.qsl.net/kd4sai/distance.html
http://www.naval.com/sight/index.htm
RADAR
http://www.mar-it.de/Radar/Horcalc/horcalc.htm
The calculations navigator97 did sound right, in a theoretical environment.
This fits my real world experience with my icom handheld quite well. traveling with another boat out to Block Island last year, once I got more than about 5nm ahead of them, we were unable to communicate handheld to handheld. What we did whenever we wanted to raise one another was the calling party went below and got on the ships radio with the mast mounted antenna and hailed the other party. With one party using the ships radio, and the other on the handheld, we were able to communicate clearly until about 8nm separation. Past 8nm (my boat was quite a bit faster) communication with the handheld was receive only, and had to use the ships radio for all outbound communications. This fits the theoretical numbers pretty well also.
As far as talking to someone 100-250nm away on your VHF, that is entirely possible in the right atmospheric conditions (most often happens when it's calm and foggy). In the wireless internet industry (I used to own a wireless internet company) it is known as (atmospheric) thermocline ducting.
There was one particular instance on a serene foggy morning, the kind where you can see the different layers of fog stretch out over the corn fields for miles, we had lots of loss f signal warnings on our equipment, and when diagnosing the situation, I picked up a strong signal from a microwave transmitter belonging to another company that was nearly 100 miles away in the next state. I called their Sr Engineer up and confirmed he was able to very clearly pick up my signal as well.
These transmitters are tower mounted with the antennas normally angled down towards the ground to focus the output power to the ground for an area about 6-7 miles out from the tower, and in normal conditions the signal becomes indecipherable from background noise beyond about 11 or 12 miles.
So the question is how did a signal that normally never travels more than 12 miles pick it up nearly 100 miles away at a signal strength that would lead me to believe his transmitter is only 4-5 miles away? Thermocline Ducting is the answer. The weather that morning was dead calm air, the ground was warm, but the fall sky was cold, and it caused the air to settle in different thermal layers with heavy fog in some, and clear sky in others. Since there was zero wind to stir these layers up, they sat there until the sun came up and warmed everything up. My transmitter happened to be sitting in a clear, more or less fog free layer, in between 2 dense fog layers. Those fog layers went uninterrupted for at least 100 miles and just happened to also be the same layers the other guys transmitter was in. Our signals literally bounced inside that layer with very little signal loss for 100 miles...
These layers, if spaced correctly, will act as a super efficient long range antenna cable, and can transport signals for extremely long distances with amazing efficiency. They don't often last for very long as any wind will normally break them up.
The proper meteorological term is an Inversion layer, in case anyone was wondering.
http://en.wikipedia.org/wiki/Inversion_(meteorology)
VHF Freak long range transmissions
I have this interesting graphical display of freak long range VHF communication.
AIS is on the VHF Marine waveband and ships transmit at 12.5Watts which is half the normal power for a main VHF set. Normally AIS ranges are expected to be between 15 and 25 miles.
I have an antenna in my roof at home about 50' above sea level and live on the Hamble near to Southampton just to the N. of the Isle of Wight.
One evening I saw ships at 204 miles
The attached rather congested picture shows most of the English Channel with the ships to the West at up to 200 miles radius but normal range to the East so nothing showing in the Dover Strait.
Apologies if the detail is blurred but, as usual, SBO has further compressed my original file of 396Kb to 95.5 Kb
I have this interesting graphical display of freak long range VHF communication.
AIS is on the VHF Marine waveband and ships transmit at 12.5Watts which is half the normal power for a main VHF set. Normally AIS ranges are expected to be between 15 and 25 miles.
I have an antenna in my roof at home about 50' above sea level and live on the Hamble near to Southampton just to the N. of the Isle of Wight.
One evening I saw ships at 204 miles
The attached rather congested picture shows most of the English Channel with the ships to the West at up to 200 miles radius but normal range to the East so nothing showing in the Dover Strait.
Apologies if the detail is blurred but, as usual, SBO has further compressed my original file of 396Kb to 95.5 Kb
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