2 M Ham antenna

[cbadmin]

From: DavidAonAnnaLeigh (Original Message) Sent: 2/10/2003 4:39 PM
What is the opinion out there on using a marine VHF antenna for the 2M ham band. Any idea where the SWR would be using an ant designed for 162 MHZ down at 145?? Any recommendations on what would make a good marine 2M rig. Have a Yaesu 1500 in the truck and am used to it.

Getting ready to install the marine and 2M on the new boat.

DavidA

From: Richard Sent: 2/10/2003 8:35 PM
David,

That's hard to say. I am able to use my marine VHF antenna at 146 Mhz with slightly under a 2:1 SWR which is acceptable to me. (See message #10 under the Ham Radio Onboard thread on the C-Brat site). I had first tested a Shakespeare 3' stainless steel marine VHF whip Model 5241-R. I was not surprised that the SWR was sky-high at 146 Mhz. I ended up with the 4' fiberglass model I have now, intending to use it for marine VHF only. While killing a little time in the cabin doing a little wiring and such, I decided to check that particular antenna at 146 Mhz and was quite surprised that the SWR was as low as it was.

It's about impossible to predict the SWR of the various marine VHF antennas at 2m ham frequencies. It's a function of too many variables, the largest being the electrical design of the antenna itself. There are end-feds, collinears, vertical dipoles, etc. and even within those categories there are variations in the fraction of a wavelength at which they are intended to resonate. In other words, that white fiberglass shroud that hides the guts of the antenna really doesn't tell us much. Some of the more verbose catalog descriptions do go so far as to expose the basic electrical design, but even then it would be challenging.

Sorry to say, about your only options are to install a separate antenna for 2-meters, take your chances with a marine VHF whip and return it if it doesn't tune well at 2m, or perhaps follow the experience of another C-Ham who has found a marine whip that will do the job (like me).

Hey, I just thought of something. The slightly older version of the Shakespeare 5241-R 3' stainless steel antenna had a setscrew in the ferrule allowing you to easily remove the whip. If you could locate one of these antennas (and would be happy with the 3db gain), it's possible that you could tune it lower in frequency by lengthening the whip (I don't know how if there is any extra length to the provided whip to allow that) or replacing the whip with a longer one which you could trim to length to resonate at a point somewhere between that of the marine band and the ham 2m band so as to achieve an acceptable SWR on both. I can't guarantee how successful that approach would be, it's just an idea. And unless it tuned quite well on both frequencies you'd have to take into consideration how much mis-match both the 2m rig and the VHF marine are designed to tolerate.

Hope that helps some.

Richard on the TK Grand

From: Fun Patrol Sent: 2/11/2003 12:33 PM
Maybe Mike could move all this topic to one board or the other?

Roy