Re: [Cal_Boats] replacing antenna wiring (correction+)

(delete the word "Not". Meant to type now but it reads better without it). Another point is that if you care about range, you can put a 6dB antenna on the stern (8 ft high) and that would be a very good setup. I happen to have a lot of them and didn't use it on my boat as I don't really care that much about range. I do just fine with my home made stern mounted antenna. Allen On Fri, Dec 3, 2010 at 8:13 PM, Allen Edwards <al… [at] gmail.com>wrote: > I found the old post from a year ago. It comes from Al Waschka. I copied > it below. Note that with a 3dB antenna on the rail, not the masthead, the > range would be 44.4 miles. Not, the CG is going to have a better antenna > than that so the range would be more. > > Allen > > > AREPS is a well-respected tool generated by/for the Navy for predicting > radio communications range, particularly at VHF/UHF and over water. I > modeled a path with one end at either 10 feet above the water (rail-mount) > or at 50 feet (masthead), and calculated the range to a receiving antenna at > 10 feet, 50 feet, or 150 feet (USCG base). I did this for 25 watts, using > the specified receive sensitivity for an Icom M304 (0.22uV). I assumed 3 dB > coax loss for 50 and 150 feet (better quality coax on the USCG tower) 1 dB > loss for the rail mount, and 3 dB gain antennas on both ends. The results > were not what I expected: > > Antenna 1 = 10’ > Power = 25W > Range to 10’ receiver – 29.8 miles > Range to 50’ receiver – 33.1 miles > Range to 150’ receiver – 44.4 miles > > Antenna 1 = 50’ > Power = 25W > Range to 10’ receiver – 31.6 miles > Range to 50’ receiver – 37.3 miles > Range to 150’ receiver – 48.7 miles > > The improvement of masthead mounting is way less than I expected. My > current antenna is a masthead-mounted ½ wave, but given this data, I’m not > sure I’d go to the trouble for a new installation. > > > > On Fri, Dec 3, 2010 at 6:20 PM, scott <ss… [at] yahoo.com> wrote: > >> >> >> http://en.wikipedia.org/wiki/VHF >> >> >> --- On Fri, 12/3/10, Allen Edwards <al… [at] PaloAltoPhoto.com<allen.edwards%40PaloAltoPhoto.com>> >> wrote: >> >> > From: Allen Edwards <al… [at] PaloAltoPhoto.com<allen.edwards%40PaloAltoPhoto.com> >> > >> > Subject: Re: [Cal_Boats] replacing antenna wiring >> > To: Ca… [at] yahoogroups.com <Cal_Boats%40yahoogroups.com> >> > Date: Friday, December 3, 2010, 2:22 PM >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > The VSWR of your antenna will be so much higher >> > than the connector that there is no reason to worry about >> > the connector if it makes it easier on your >> > installation. >> > An even easier solution is to mount the antanna >> > on the stern pulpit. There was a thread on this some time >> > ago and the conclusion was that range goes from something >> > like 43 miles to 40 miles by mounting the antenna on the >> > stern instead of on top of the mast. I don't remember >> > the exact numbers. Also, if you mount on top of the mast >> > make sure you have an antenna that is about 3 feet long as >> > if you have one 18 inches, you will only be able to talk to >> > the moon. Actually, you can probably reach the race >> > committee but you won't get 40 miles out of a 1/4 wave >> > antenna on top of the mast. You need a 1/2 wave one. >> > >> > >> > Allen >> > >> > On Fri, Dec 3, 2010 >> > at 2:00 PM, Chris <cc… [at] lsnm.org <ccampbell%40lsnm.org>> >> > wrote: >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > On 12/3/2010 11:54 AM, Adam Thorp wrote: >> > >> > >> > >> > >> > Greetings, >> > >> > >> > >> > I'm going to be rewiring the antenna >> > on my cal28 this >> > weekend and am looking for any advice. >> > >> > >> > >> > >> > >> > >> > I read Allen's advice and will disagree slightly. >> > >> > >> > >> > On my other boat, I installed a bulkhead feed-through >> > just like the >> > one Allen showed. I did that because the mast gets >> > unstepped and >> > stepped again each year when the boat is hauled in the >> > fall and >> > launched in the spring. It'sa more convenient to >> > just unscrew a >> > PL-259 fitting. However, the arrangement requires two >> > connectors >> > plus the feed-through, and my understanding is that any >> > disruptions >> > in the coax will likely make the standing-wave ratio >> > (SWR) worse. It >> > has to do with the transmitted wave bouncing back >> > instead of being >> > radiated off the antenna. This diminishes your >> > transmitted power. >> > On my boat, I opted for convenience and not for maximum >> > radiation. >> > I don't have an SWR meter that will measure at VHF >> > frequencies so I >> > don't really know how much effect the connector >> > arrangement has. >> > But be aware that, at least in the abstract, you're >> > better off with >> > no discontinuities in your coax. Also be aware that I >> > disregarded >> > my own warning. >> > >> > >> > >> > One way to avoid that would be to make a little >> > walking-cane-shaped >> > deck fitting, basically the bottom half of a sink drain >> > trap. Your >> > coax would come down from the mast, turn upward into >> > the fitting (to >> > make a drip loop), then turn down inside the fitting >> > through the >> > deck. You could add some sealer, but the >> > fitting's mouth would face >> > downward so water would not be inclined to enter unless >> > under >> > pressure. >> > >> > >> > >> > By the way, the feed-through device is long enough to >> > allow you to >> > add a little wooden donut inside, under it. My >> > boat's deck is not >> > cored there, and is relatively thin, so I made the >> > donut to make the >> > mounting more substantial. Donut is varnished & >> > looks spiffy. >> > >> > >> > >> > Chris Campbell >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> >> >> > >