VHF radios and such

[cbadmin]

From: C-LionRay (Original Message) Sent: 10/23/2003 3:40 PM
Here is a discussion about VHF radios and the like... I hope you like it


From: C-LionRay Sent: 10/23/2003 3:44 PM
A friend gave me a new piece of boat jewlery, an 8' antennae extension.
Are there certain types of enteneas that work with this extension or will the 8' that I just bought work just fine?
I think I should add a support but do I need 2 supports with 16' of antennea whipping around?

I wish I wouldn't have cut my cable so short

From: C-LionRay Sent: 10/23/2003 3:45 PM
And what about towing with this contraption?

From: Sawdust Sent: 10/23/2003 3:56 PM
Ray -

The first thing you should do is have a ham friend or commercial dude measure the SWR (standing wave ratio) of your antenna with the cut cord. That's a no-no, and if SWR is high it will severely limit the output of your transmitter.

Second, for your ocean going use I'd recommend you not put an extension on your 8-ft whip. No real advantage, and the USCG says that they get much better reception from boats with shorter antennas. (I don't have a copy of their antenna project, but will try and locate it) With the boat rockin' and rollin' in any kind of a sea the taller antennas really shift the pattern. Red Fox has my favorite antennas on his jewel -- spendy but good.

Dusty

From: Chuck S Sent: 10/23/2003 5:31 PM
As the Skipper notes, bigger isn't better with VHF antennas, not on small boats anyway. Easiest place to look for the data is the good olde West Marine catalog. They show the radiation patterns from different whip lengths and the short 3dB whip has by far the broadest pattern.

If the boat was sitting on her trailer with the antenna pointed straight to heaven the pattern wouldn't matter. But this isn't how boats operate on water. Boats our size are in constant motion and the narrow concentration of power in a narrow band projects it into the ocean or the sky with the 6dB and higher antennas.

Finally VHF transmission range is line of sight and that's the horizon, which isn't very far when your antenna is 3' off the surface. Your 25w transmitter will push just fine to the horizon with the broader power band and the transmission will be more reliable. These are sometimes called "sailboat" antennas because of the angle of heel on boats under sail. 50' power boat can use a 6dB but we move around too much.

http://groups.msn.com/CDoryOwnersGroup/detailphotos.msnw?action=ShowPhoto&PhotoID=625

-- Chuck

From: C-LionRay Sent: 10/26/2003 12:58 AM
So what kind does RF have?
I thought he would have chined in here by now.
I'd be interested in reading that report.
I was thinking line of sight to the horizon would be increased with the antennea being 8 foot higher?....
What makes the antennea on Gregs boat the best?

From: C-LionRay Sent: 10/28/2003 11:58 PM
Earth to Red Fox, come in Red Fox.... Helloooo

From: Sawdust Sent: 10/29/2003 8:13 AM
Ray -

Sorry to be so late with a reply. The wind has really messed up my provider - I'm on wireless, and his antenna system went up in smoke.

The additional 8 ft. of length means very little as far as range -- the guy you need to talk to at any distance, the USCG, has his antenna way up there. Don't have my book handy, but you can look up the antenna elevation for any station, and it is easy to compute the effective line of sight by using his antenna elevation and yours. On commercial fishing boats and larger vessels that are more stable I like longer vertical antennas. But (without going technical) the way a vertical antenna gets its gain by increasing length is by squashing the signal -- like stepping on a pumpkin. The more it is squashed, the narrower the vertical field becomes, and at the limits, the narrower the vertical field the more vessel movement modulates the signal. The pumpkin, in our case is 25 watts at the transmitter, and these little VHF gadgets are NOT created equal. Some put out much less, and any ham friend can measure the output and SWR (Standing Wave Ratio) for you. Easy to do, and I highly recommend it.

I still have a couple of 8 ft. extensions in my junk pile - I've used them and tossed them.

I have no experience fishing offshore in your area, but in the usual butt and salmon areas off the WA coast and anywhere in Puget Sound the USCG will hear you even if you have a little 5 watt handheld - have communication satellites listening in some areas.

Greg will log on and tell you about his antennas, I'm sure. If not, I can look them up in the catalog. Excellent, and locally made. And spendy.

HTH,

Dusty

From: Redƒox Sent: 10/30/2003 1:05 PM
Sorry bout the delay Ray... I'll go look right now for ya.. there the best!!

From: Redƒox Sent: 10/30/2003 1:16 PM
You betcha Dusty

OK, got it. I have the MORAD 156 HD for the VHF, it's on the 5 ft anodized aluminum mast. One thing I like about Morad is there totally commercial quality! you need the upper mount for them though, there just too heavy. There so strong that I use them to as a hand hold when I have to go up on the bow. I trashed every other make of antenna I ever had, before I went with these puppys.

I also went with the same for the other side of the cabin, the CB. Do you use CB down there?