VHF Radio aerial position - impact on effective distance

dylanwinter

dylanwinter

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www.keepturningleft.co.uk
The range without any assistance from atmospheric effects is the distance to the horizon for the antenna height - there are multiple sources for that information - Reeds certainly has a table somewhere in it and I'm sure there are helpful sources on the web. You can often get longer range than that - sometimes much longer range - but that will always be dependent on atmospheric conditions bending and focussing the signal - that is impossible to predict with any accuracy and antenna height will not have much effect.

I'm a radio amateur and used to spend a lot of time around Bordeaux. On one occasion, several years ago, walking on the beach with a hand-held 5w radio, I had a short conversation with an amateur radio expedition on Rockall - well over a thousand miles.

Correction - that should read St. Kilda, not Rockall - still a very long distance.
 
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I can agree with the result in miles, I asume that are nautical miles.
The formula I found also in the ALRS is Distance (in nm)= 2,5 x sqare rout ( high in meter).
In Tenerife the antenna for Tenerife Radio is at 2.100 meter on the Teide.
I got a conversation when aproaching Isla Salvage haf the way to Madeira.
There was a significant noise but Tenerife Radio was good readable.
So the 25 Watt of VHF power are suficiant for a distance of 130 miles.

When I checked the calculator with 1600 meter high, he is showning for appr. 100 nm, but 165 Km.
So I will trust the value in miles.
Wilhelm
AC1WA/DC1WA
 
I said in, response to your previous question about the radio that it was the same as mine. In fact mine is a Sealine II. I bought it in 1984 and it is still in perfect working order.

Yours presumably is a little older.

If yours is in working order then it is a decent radio although of cousre without DSC and GMDSS and all that m'larky.

You might,however, if it concerns you, check that it has channels M1 ( used by some marinas and Yachtclubs ) and M2 ( used by some Yachtclubs) installed

As you will know both are "private channels rather than "international" ones.

I have M1 installed in position P1 on the channel selector . I dont have M2.

A mobile phone would probably be more than adequate for contacting marinas and Yachtclubs so no big deal if you dont have them.

The controls are self explanatory so no problems if you dont have the instruction manual.

DSCF1296.jpg
 
As already pointed out, there isn't a simple answer because it depends on the height of the other fellow's antenna as well as the height of your own. As the other antenna will generally be higher than yours, you will probably get enough range - usually. Of course, the higher the better. Whether it's worth the effort of moving the antenna is debatable, and will doubtless get thoroughly debated in this very forum. I suspect you may have more urgent matters to engage your attention.
 
lw395 said:
http://www.qsl.net/kd4sai/distance.html

VHF will go a bit beyond line of sight, but it's a good guide.
Click to expand...

interesting to run some figures through your link

I compared the yacht at 3m and 10m

and then 3m to 3m which is the distance between fishing boat antenna

then I did 50 m to represent a shore station

putting the antenna at the top of the mast helps - but not a much as I would have expected

I have a handheld so I can do all the chatting to th clubs and marinas malarky with the little raymarine handheld - which has been great so far

putting the thing at the top of the mast is not such a no brainer - for starters the aerial on the radar gantry will survive a dismasting

the run will be shorter to the aerial and I can repair it fairly quickly and easily

lots ot think about

D
 
sarabande said:
usually attached to an external loudspeaker.
Click to expand...

An external speaker can be connected ( there is a socket for one but I have no info on the connections!) The "hail" button then allows the external speaker if suitably placed to be used as a loud hailer. ( presumably for yelling at SWMBO on the foredeck without having to shout)

The red button is a crude form of dual watch. When pressed the set flicks between Ch16 and the selected channel.
 
There is, of course, an argument for having one aerial at the masthead for general use and a second on the gantry for emergency use (hoping the falling mast doesn't wipe out the gantry). Mind you, as you are in the planning stages for sailing around Scotland, at times this will appear irrelevant, as some places are considered dead areas where the surrounding geography masks signals completely. In an emergency, though, should your Mayday not reach the shore station, the further off shore it goes the better in the hope of someone hearing you and providing a relay. As the water laps around the cockpit benches, it's probably best to trigger the epirb so that the satellites can pick it up!

Sod's Law suggests that once you have the perfect antenna arrangements, the VHF will pack up - you might like to consider getting an adaptor to alliow you to connect the handheld to the masthead (or emergency) antenna to extend its range.

Rob.
 
VicS said:
The "hail" button then allows the external speaker if suitably placed to be used as a loud hailer.
Click to expand...

I wondered if it was for a hailer horn, but the set seemed a bit basic for that. I suppose it's just age giving that impression.

Does it use the same speaker for VHF receiving? A VHF speaker up the mast, and a loudhailer speaker in the cockpit, both seem equally useless :)

Pete
 
VHF is generally considered as "line of sight" communication. This uses some basic assumptions and, of course, there are many variables. The fundamental antenna is a dipole and, assuming vertical polarisation, most the radiated power goes horizontally. Table 3(1) Distance of Horizon in Reeds Almanac (pg 44 on 2014 edition). Add the effective horizontal distance between receiving and transmitting antennas based upon their respective height of eye.

Distances way in excess of this are related to propagation anomalies, the most common around early summer (IIRC) is known as Sporadic E. It's where the VHF signal hitches a ride in the E layer of our atmosphere. Distances of 1000 M have been recorded but these are not reliable, or predictable forms of propagation.

If you need new coax, buy decently quality with low loss. There could easily be a scenario that all the benefit of height, and more, could be lost to the coax.
 
there is

prv said:
I wondered if it was for a hailer horn, but the set seemed a bit basic for that. I suppose it's just age giving that impression.

Does it use the same speaker for VHF receiving? A VHF speaker up the mast, and a loudhailer speaker in the cockpit, both seem equally useless :)

Pete
Click to expand...

there is a little speaker attached to a metal rod inside the hatchway

I was wondering what that was for

I am going to buy an aerial for the gantry and then decide if I need more communications

I think money spent on an epirb would be more efficacious that trying to squeeze an extra mile or four out of vhf
 
prv said:
I wondered if it was for a hailer horn, but the set seemed a bit basic for that. I suppose it's just age giving that impression.

Does it use the same speaker for VHF receiving? A VHF speaker up the mast, and a loudhailer speaker in the cockpit, both seem equally useless :)

Pete
Click to expand...

I dont know. I seem to have left the instruction manual on the boat, not that there is much info in there IIRC.

On the back there is a 6 pin socket marked HAIL/EXT SPKR but I am sure there is no info in the manual on what to connect where, I assume that some pins are for a loudhailer ( possibly including a power supply?) while others are for a simple cockpit extension speaker.
 
VicS said:
On the back there is a 6 pin socket marked HAIL/EXT SPKR but I am sure there is no info in the manual on what to connect where, I assume that some pins are for a loudhailer ( possibly including a power supply?) while others are for a simple cockpit extension speaker.
Click to expand...

Ah, makes sense. Presumably two separate speakers, then. My modern GX2100 has the same, though I haven't bothered with the external speaker as the cockpit remote does that job. I doubt I'll use the loudhailer as such, but it also does fog signals which seems useful.

Pete
 
dylanwinter said:
interesting to run some figures through your link

I compared the yacht at 3m and 10m

and then 3m to 3m which is the distance between fishing boat antenna

then I did 50 m to represent a shore station

putting the antenna at the top of the mast helps - but not a much as I would have expected

I have a handheld so I can do all the chatting to th clubs and marinas malarky with the little raymarine handheld - which has been great so far

putting the thing at the top of the mast is not such a no brainer - for starters the aerial on the radar gantry will survive a dismasting

the run will be shorter to the aerial and I can repair it fairly quickly and easily

lots ot think about

D
Click to expand...
Will your gantry really be 3m to the base of the antenna?
I suspect you should probably subtract wave height as well.

Where masthead often really scores is in harbour, which may sound irrelevant, but we used to get a lot of forecasts that way.
 
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