Antenna placement

There was a thread a while back about antenna placement where it was pointed out that propagation over water is different than over land and that antenna height isn't as important as it is over land. My friend says this is due to ducting in the water vapor layer. The result was that for some typical antenna, all else being equal, the range would decrease from 43 miles to 40 miles if you move your antenna to the stern, if I am remembering correctly. This difference could be easily made up by more antenna gain with a stern mounted antenna, for example one of the 8 ft whips. I have always had my antenna on the stern but this thread got me to thinking and testing and I found that my antenna wasn't very good. I made a new one that has a great VSWR. It is a simple stern pulpit mounted dipole with the center conductor up from the pulpit and the ground half down from the pulpit. It is grounded to the pulpit. I did this because I didn't want a 3 ft whip sticking above my pulpit if I could help it. Next I started wondering if my pattern was any good so I looked for a program to model antennas. I found 4NEC2, a great free program for antenna modeling. I made a stab at modeling the stern mounted antenna as well as a masthead mounted one. I got better gain off a stern mounted antenna than a masthead mounted one and if you consider the small but significant coax loss necessary for a masthead mounted antenna, I think for sure you are better off with a stern mounted antenna. Next I modeled where to put the thing on the pulpit. With it off to the side of the pulpit like I mounted it, you get some gain off to that side but some dead spots in other directions. My conclusion was to center it on the pulpit. Now, it might be good to have gain off to one side so that you could turn your boat and reach further away. However, that wasn't my goal. I am going to move my antenna to the center of the pulpit. This is not very scientific but interesting enough that I thought I would share it with the group in case someone wants to have a reason not to bother with mounting an antenna up on the masthead. I continue to believe you will get better reception over water with the antenna on the pulpit than on the masthead. I would love to see someone with both types of antennas run some experiments with stations 40 miles across water. Allen

Allen Edwards wrote: > > > I got better gain off a stern mounted antenna than a masthead mounted > one and if you consider the small but significant coax loss necessary > for a masthead mounted antenna, I think for sure you are better off > with a stern mounted antenna. Does angle of heel affect your antenna? And I don't remember if you posted a photo last time around. Chris Campbell >

You know, I might have been double counting the cable loss and gain differences so the masthead mounted antenna is probably a little better. In other words, the October analysis stands. The bottom line was that you would get about 10% more range from a masthead antenna. I personally don't think 10% is worth putting an antenna on the top of the mast and risking not having range if you are distasted so my choice remains to use a stern mounted antenna and give up the 10% I did post a picture but if I were to build one again, I would build it differently. I made some drawings that I have attached. I would probably use a barrel and an elbow and then clamp the barrel to the pulpit and run the coax along the pulpit. Allen On Tue, Jan 12, 2010 at 1:49 PM, Chris Campbell < cl… [at] charterinternet.com> wrote: > > > Allen Edwards wrote: > > > > I got better gain off a stern mounted antenna than a masthead mounted one > and if you consider the small but significant coax loss necessary for a > masthead mounted antenna, I think for sure you are better off with a stern > mounted antenna. > > > Does angle of heel affect your antenna? And I don't remember if you posted > a photo last time around. > > Chris Campbell > > > > >

too much precision on the dimensions in the drawings. They don't need to be that close. Allen On Tue, Jan 12, 2010 at 2:04 PM, Allen Edwards <al… [at] gmail.com>wrote: > You know, I might have been double counting the cable loss and gain > differences so the masthead mounted antenna is probably a little better. In > other words, the October analysis stands. The bottom line was that you > would get about 10% more range from a masthead antenna. > > I personally don't think 10% is worth putting an antenna on the top of the > mast and risking not having range if you are distasted so my choice remains > to use a stern mounted antenna and give up the 10% > > I did post a picture but if I were to build one again, I would build it > differently. I made some drawings that I have attached. I would probably > use a barrel and an elbow and then clamp the barrel to the pulpit and run > the coax along the pulpit. > > Allen > > > > > On Tue, Jan 12, 2010 at 1:49 PM, Chris Campbell < > cl… [at] charterinternet.com> wrote: > >> >> >> Allen Edwards wrote: >> >> >> >> I got better gain off a stern mounted antenna than a masthead mounted one >> and if you consider the small but significant coax loss necessary for a >> masthead mounted antenna, I think for sure you are better off with a stern >> mounted antenna. >> >> >> Does angle of heel affect your antenna? And I don't remember if you >> posted a photo last time around. >> >> Chris Campbell >> >> >> >> >> > >

Allen Edwards wrote: > [Attachment(s) <#TopText> from Allen Edwards included below] > > > I did post a picture but if I were to build one again, I would build > it differently. I made some drawings that I have attached. I would > probably use a barrel and an elbow and then clamp the barrel to the > pulpit and run the coax along the pulpit. Can you provide the dimensions? They weren't visible on the attachments. I've got a whole binder of antenna plans for FM broadcast, AM, the whole works. Yours looks like it's two elements secured to a PL-259 connector. I'm happy with my masthead antenna (out of sight, out of mind, plus it keeps birds off the Windex) but it's always fun to experiment. And when I had to buy a new pointer for the Windex, it came with a bird spike anyway. Chris Campbell

The elements are 18 inches for 3 feet overall. The top element is intended to be soldered into the center conductor of the connector and sealed with silicon rubber. The bottom one is intended to be screwed to the part of the connector that usually secures the shield. I have not built one and expect I might have to solder the ground (down) rod to make the loop to screw to the connector. Allen On Wed, Jan 13, 2010 at 9:06 AM, Chris Campbell < cl… [at] charterinternet.com> wrote: > > > Allen Edwards wrote: > > [Attachment(s) <#12628a69ec77a2ea_TopText> from Allen Edwards included > below] > > > I did post a picture but if I were to build one again, I would build it > differently. I made some drawings that I have attached. I would probably > use a barrel and an elbow and then clamp the barrel to the pulpit and run > the coax along the pulpit. > > > Can you provide the dimensions? They weren't visible on the attachments. > I've got a whole binder of antenna plans for FM broadcast, AM, the whole > works. Yours looks like it's two elements secured to a PL-259 connector. > I'm happy with my masthead antenna (out of sight, out of mind, plus it keeps > birds off the Windex) but it's always fun to experiment. And when I had to > buy a new pointer for the Windex, it came with a bird spike anyway. > > Chris Campbell > > >

Allen Edwards wrote: > > > The elements are 18 inches for 3 feet overall. The top element is > intended to be soldered into the center conductor of the connector and > sealed with silicon rubber. The bottom one is intended to be screwed > to the part of the connector that usually secures the shield. I have > not built one and expect I might have to solder the ground (down) rod > to make the loop to screw to the connector. Thank you. And remind me... these are 50 ohms, right? Seems to me that the VHF-FM equipment differs from the standard for broadcast-band FM at 75 ohms. Chris Campbell

Yes, 50 ohms. Allen On Wed, Jan 13, 2010 at 1:38 PM, Chris Campbell < cl… [at] charterinternet.com> wrote: > Allen Edwards wrote: > > > > > > The elements are 18 inches for 3 feet overall. The top element is > > intended to be soldered into the center conductor of the connector and > > sealed with silicon rubber. The bottom one is intended to be screwed > > to the part of the connector that usually secures the shield. I have > > not built one and expect I might have to solder the ground (down) rod > > to make the loop to screw to the connector. > > Thank you. And remind me... these are 50 ohms, right? Seems to me that > the VHF-FM equipment differs from the standard for broadcast-band FM at > 75 ohms. > > Chris Campbell > > > > ------------------------------------ > > Yahoo! Groups Links > > > >