what size is best for vhf antenna ?

[gtb]

There is a good description of the subject here VHF Marine Antenna Fundamentals

[morin1]

As already mentioned, higher is the better. Do you have navigation lights? As you known the all-round light should be 1 meter above the side-lights. Why not use the same mast for the antenna. I did that on my zodiac LSC-530. I install a GAM SS2 (3db, 35 inch stainless steel antenna) on a folding mast, reception is good but there is a lot of whipping while underway. If I have to do it again, I will install a Shakespeare 5415 (3dB 24 inch) instead. Remember that the best radio and antenna can not properly work with bad cable and connectors.

[pierpressure]

6db VHF whip (about 34") attach the antenna to any metal structure if possible (that give you a ground plane) that will be a great set up.... Now, if you want to go the extra mile, take your antenna and radio to a local radio shop (before installing, measure your cable in the boat), replace the RG-58 cable for low loss cable like LMR-195 and make them cut the cable and match the antenna with channel sixteen 156.8 MHz(they may need to cut the antenna to the right size) if you match the antenna to CH 16 that will give you a 1:1 match on that channel, no loss. all VHF antennas are broadband and match on the center of the band, by the time you get to CH 16 you already are 2:1 such it a way to measure loss signal, but that's another history.

sounds complicated and expensive but may cost you about $30 including labor and the new cable.

Good luck.

[ashbypower]

Really Mmm our anttena end fed base loaded 3dbi whip is between 1:1 and 1.3 on the VSWR and that was straight out of the Box!! As has been said a 6db gain antenna will have a narrower radiation patern which is not always ideal on a boat, hight however is as instringicaly VHF is line of sight. So distance to the Horizon =

SquareRoot(height above surface / 0.5736) = distance to horizon

[thomas]

I had a little Vtronix think on my last boat, could always hear Solent Coastguard from Chichester but hardly ever heard who they were talking to. I have a long whippy thing, pictured, on the new boat and hear everything including Dover and Portland coastguard.

In the past I've had dirty great long plastic things on power boats and smaller ones on the top of masts on sailing boats, I reckon my current set up is once of the best I've had.

[pierpressure]

Originally Posted by ashbypower

Really Mmm our anttena end fed base loaded 3dbi whip is between 1:1 and 1.3 on the VSWR and that was straight out of the Box!! As has been said a 6db gain antenna will have a narrower radiation patern which is not always ideal on a boat, hight however is as instringicaly VHF is line of sight. So distance to the Horizon =

SquareRoot(height above surface / 0.5736) = distance to horizon

1.3 VSWR in what freq? you don't know that until you measure it with a VSWR meter. line of sight is correct. the straight shot with 6db only applies with directional antennas (Yagi's) I'm sure you're setup is more that enough, I was going to the extreme.

[pierpressure]

Originally Posted by thomas

I had a little Vtronix think on my last boat, could always hear Solent Coastguard from Chichester but hardly ever heard who they were talking to. I have a long whippy thing, pictured, on the new boat and hear everything including Dover and Portland coastguard.

In the past I've had dirty great long plastic things on power boats and smaller ones on the top of masts on sailing boats, I reckon my current set up is once of the best I've had.

I agree with that set up, much better than having a fiberglass 8ft.