Keith is correct..........and you will see an improvement in the rig....... my 2 cents.... Bill KD5IUD........ham operator M17 - #251 M15 - #158 ----- Original Message ----- From: "Keith Diehl" <kdiehl@xmission.com> To: "For and about Montgomery Sailboats" <montgomery_boats@mailman.xmission.com> Sent: Saturday, March 31, 2007 12:14 PM Subject: Re: M_Boats: VHF boost
I've worked as a system engineer for a major communications corporation for more years than I care to mention. Here's my analysis:
First, are we using the same antenna, but in one case mounting it at deck level and in the other case mounting it at masthead level? If so, then all we are concerned with is the additional line loss. RG8-X type cable is a manageable size and has reasonable loss - about 4 dB per 100 ft at 100 MHz. Marine radio operates at 160 MHz, so losses will be a little higher, let's call it 5 dB per 100ft.
(Don't use RG58 or Radio Shack cable or connectors. Buy quality, name brand, low-loss cable and get help if you're not sure how to install a connector. Weatherproof all connections.)
How high is your mast? 25 ft? Then loss is only 1.25 dB + maybe 0.5 dB for additional connectors to allow removing the mast. Overall, I think you'd see an improvement.
If you're using a handheld radio with a little helical whip antenna, then you'll see a big improvement. Those rubber antennas have a loss relative to a reference dipole of 6 to 10 dB. A 5/8 wave antenna will be close to the gain of a dipole reference. Even with line loss, you should see a net improvement of 3 to 7 dB.
There is a case to be made that you would like your radio to work if you are dismasted. There is also the danger of undetected corrosion or damage to the antenna and line at the masthead where inspection is difficult.
----- Original Message ----- From: "Larry E Yake" <leyake@juno.com> To: <montgomery_boats@mailman.xmission.com> Sent: Friday, March 30, 2007 9:57 PM Subject: Re: M_Boats: VHF boost <<SNIP>>
"I doubt the 3db gain -- double the radio's radiated power -- from a masthead antenna that's about 18 feet higher than the handheld's antenna will give much of an increase in range.
<<SNIP>>
_______________________________________________ http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats