As we all know, VHF communication is a 'line-of-sight' communication. The primary range factor is the heights of both the transmitting and receiving antennae. An easy 'line-of-sight' approximation is the square root of the antenna height on the transmitter added to the square root of the antenna height on the receiving antenna and then multiply that sum by 1.53, this will give you an approximate range for those two antennae. So for two boats with nine foot antennae (above the water), the square root of 9 is 3, so (3+3) X 1.53 = about 9.2 nmiles. Of course if you're both on top of a wave or both in a wave trough can greatly affect the outcome. I don't know how high the USCG mounts their antennae but it must be very high because they get excellent range and their output power is sufficient to walk over any other transmission or static generator. Communicating with the coasties from 25 miles out is reasonable but you are not going to talk to other boaters at more than about 10 miles unless you both have very tall antennae.
Crossroads
CG is way over 100 feet high and have directional antennas that they can train on a signal, so that is why 2 stations can talk to you sometimes.
by the way there is a huge difference in 8' white whip antennas, and chances are , you got sold the cheapest one. check out shakespeares website for the diff. in loading, db gain etc.
nothing like a good radio chack on a side channel every now and then.
by the way there is a huge difference in 8' white whip antennas, and chances are , you got sold the cheapest one. check out shakespeares website for the diff. in loading, db gain etc.
nothing like a good radio chack on a side channel every now and then.
Antenna gain
When you buy an antenna always get the one with the most gain. They sell some antennas with 6 db of gain omni directional like the vertical antennas on your boat. they talk in all directions equally. Higher gain antennas are mostly directional meaning they transmitt in one direction better than another. The more gain the lower angle of radiation from your antenna meaning more of your signal is transmitted down lower not up in the sky so you have better range. Remember this also works in receiving a signal. With luck most of the times with average installation heights of most boats you can talk maybe 15 miles sometimes more and sometimes less. Remember at VHF frequencies like marine radio nothing gives you more range than antenna height. Good fishing.
Charlie
When you buy an antenna always get the one with the most gain. They sell some antennas with 6 db of gain omni directional like the vertical antennas on your boat. they talk in all directions equally. Higher gain antennas are mostly directional meaning they transmitt in one direction better than another. The more gain the lower angle of radiation from your antenna meaning more of your signal is transmitted down lower not up in the sky so you have better range. Remember this also works in receiving a signal. With luck most of the times with average installation heights of most boats you can talk maybe 15 miles sometimes more and sometimes less. Remember at VHF frequencies like marine radio nothing gives you more range than antenna height. Good fishing.
Charlie
This is why I questioned his antenna height with the distress call thread. He was only 20 miles from me and our antenna is around 15' off water level to the tip of it. I should have been able to hear him. My geuss was that he had a disconnected antenna or he had one that was still folded down. We should have been able to hear him from 20 miles away either way and so should have anyone out at southern or hospital if you were out in that area. CG uses high powered antennas so that is probably why they could suck up your transmission. Crabby, check out your antenna and see if it has a good connection to it.
If you want to learn more look in your WEST MARINE Master Catalog. The West Advisor explains it fairly well.
In my boat It's Two raidos Two tall antennas with good power(6db). I'm thinking of replacing an older antennan with a DIGITAL (brand) 8' 9db for some extra range since it needs to be replaced anyway. Has anyone used one of these before?
Thanks Scott
In my boat It's Two raidos Two tall antennas with good power(6db). I'm thinking of replacing an older antennan with a DIGITAL (brand) 8' 9db for some extra range since it needs to be replaced anyway. Has anyone used one of these before?
Thanks Scott
Argo, the antenna was upright, I dont know for certain about integrity of the connection, but Im pretty sure we checked it. Regardless, I think we are going to change the antenna to a longer on, probably the radio as well. ANy recommendations, anybody?
Shakespeare Galaxy Little Giant
I have a T-top and on top of that I have the 4 foot Little Giant. I would guess the tip of it is at least 11 feet above the water. It is supposed to be very high quality (it was not cheap) and designed for use on a T-top. Before I bought it I asked the resident radio expert THOM on the old *** board If I should get it or the longer antenna. He gave a rather long dissertation the bottom line of which was that the difference would be negligible. I just like the idea that the shorter antenna may be more durable mounted so high where it is subjected to so much movement.
I have a T-top and on top of that I have the 4 foot Little Giant. I would guess the tip of it is at least 11 feet above the water. It is supposed to be very high quality (it was not cheap) and designed for use on a T-top. Before I bought it I asked the resident radio expert THOM on the old *** board If I should get it or the longer antenna. He gave a rather long dissertation the bottom line of which was that the difference would be negligible. I just like the idea that the shorter antenna may be more durable mounted so high where it is subjected to so much movement.
Well size does matter with antennas. You caint stack enough elements into a short antenna to really get the gain and besides the extra two feet someday will make a difference. Remember height is the main thing tho. A shorter antenna with less gain will work better higher than a long antenna low. If your buying a new radio get am ICOM.
Charlie
Charlie
One thing that was missing from this thread is the fact that your radio's range also is very dependent on the strength of your battery.
I have only one 12 volt battery for my VHF , the other batt. works the electronics, sounder,GPS, dash lights, running lights ect.
Then i have one other batt that starts the engine.Thats all it does.
Yes 3 batts may be excessive, but, if the engine Batt goes dead then i have two others to start with.
And being redundant offshore is always a good thing.
Also, Speaking of batt. there are some quick-start ,batt. jumper packages out there that not only can jump start your dead batt, they also have a couple of cig. lighter adapters for accesories such as cell phones , got mine at Wal-Mart for $ 60.00 and I would recommend one on every boat bay or offshore.
I have only one 12 volt battery for my VHF , the other batt. works the electronics, sounder,GPS, dash lights, running lights ect.
Then i have one other batt that starts the engine.Thats all it does.
Yes 3 batts may be excessive, but, if the engine Batt goes dead then i have two others to start with.
And being redundant offshore is always a good thing.
Also, Speaking of batt. there are some quick-start ,batt. jumper packages out there that not only can jump start your dead batt, they also have a couple of cig. lighter adapters for accesories such as cell phones , got mine at Wal-Mart for $ 60.00 and I would recommend one on every boat bay or offshore.
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