I'm impressed, Keith. What is your opinion of the 24" replacement antenna option? Is the 2 meter band frequency OK, and would it double the range of the stock antenna as claimed? Larry On Sat, 31 Mar 2007 12:14:37 -0600 "Keith Diehl" <kdiehl@xmission.com> writes:
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>>
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Nothing like a prompt reply. A larger whip antenna would help some, but an antenna tuned for the ham bands (146 MHz) probably won't have enough bandwidth to operate properly on marine frequencies (160 MHz). It certainly won't double your range. I don't think anything is going to double your range other than height. Remember that, over water, range is predominately limited by the radio line of sight horizon, which is about 4/3 the optical horizon under "typical" conditions. From memory (might be wrong!), that can be calculated as 4/3 * sqrt(height in feet / .6) If your antenna is 6' off the water, then your radio horizon is about 4 miles. If the station you're talking with has an antenna height of 50', then his horizon is 12 miles. The two of you could be about 16 miles apart and have radio light of sight. Larson used to make some large whips for portable radios that could be ordered at the proper frequency. You may want to give them a call. 1-800-ANTENNA (268-3662) ----- Original Message ----- From: "Larry E Yake" <leyake@juno.com> To: <montgomery_boats@mailman.xmission.com> Sent: Saturday, March 31, 2007 5:08 PM Subject: Re: M_Boats: VHF boost
I'm impressed, Keith. What is your opinion of the 24" replacement antenna option? Is the 2 meter band frequency OK, and would it double the range of the stock antenna as claimed? Larry
On Sat, 31 Mar 2007 12:14:37 -0600 "Keith Diehl" <kdiehl@xmission.com> writes:
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
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