Santiago
Ultra Nomad
Posts: 3512
Registered: 8-27-2003
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VHF Radio problem
I'm really unhappy with my radio reception/broadcasting. I have a Icom radio (25 watts) with a Shakespeare 3' metal antenna attached to the top of my
center console window frame so it must be at least 10' above the water line. I don't think I receive or broadcast over 3 or 4 miles - 5 max. If I'm
at the local islands in BOLA, I don't get the town chatter. Would it help to upgrade to an 8'? What I really want is to be at Isla Guarda and be
able to raise help 20 miles away - is this even possible? I should note that I did shorten the antenna wire on my first install - maybe I screwed up
somehow?
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Johannes
Nomad
Posts: 110
Registered: 9-29-2006
Location: / Loreto/Kenmore,WA
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Mood: I love it in Loreto
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The range of a VHF is the line-of-sight distance to the horizon . To calculate the distance in miles Distance = Squareroot (2*Hf)
where Hf is the height of the antenna in feet . With 10 ft above the water your max distance is somewhere between 4 and 5 miles. To get to 20 miles
you need a sailboat with a very tall mast. Hope that helps.
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Santiago
Ultra Nomad
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Sigh - that pretty much sums it up.
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Russ
Elite Nomad
Posts: 6742
Registered: 7-4-2004
Location: Punta Chivato
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Although Johannes formula is probably a good one it doesn't mean it is always correct. Many times I've received a good signal from boats in the
Guaymas (sp) area. Without any obstructions and good weather you'll get a lot better performance. I had a short antenna that would work at over 10
miles just fine. I replaced it with a cheap 8' one and it was even better. Ask some others around what their range is. 3 to 5 miles is what I'd expect
from a hand held on low power. My hand held does OK all over the Punta Chivato area and not clear line of sight. About 8 miles and more. You have to
figure out why you're not getting better performance for your safety. I would replace the connector at the radio and try it again.
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BajaWarrior
Super Nomad
Posts: 2307
Registered: 9-27-2006
Location: Mission Bay, San Diego. Playa Hermosa, San Felipe.
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Mood: Anxious to get south
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I recently completed our new house below San Felipe. I installed a cheapy Shakesphere antennae on the ridge of the house which is a two story home so
right at 24'. I thought because of the great height alone the reception would be great, but in fact I couldn't even hear Percebu which is only 6 miles
away.
I returned to Boat U.S. in San Diego and explained my problem and they suggested I go with a more quality antennae made by Shakesphere which I did. I
can now hear both sides of every conversation for twenty miles in all directions....
Also my original house on the same property has an even higher quality radio and antennae and I was able to talk to "Steekers" all the way up in El
Dorado on it and he is more than 30 miles north as the crow flies... True story, BajaRob heard at least half of the conversation...
Check into a better antennae, one that will fold down on your boat, also how you connect the plug to the antennae wire makes a big differance, take
your time doing this...
Haven't had a bad trip yet....
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Johannes
Nomad
Posts: 110
Registered: 9-29-2006
Location: / Loreto/Kenmore,WA
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Mood: I love it in Loreto
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Don't forget that if you are on the water and someone else is over the horizon but the tip of his antenna can see the tip of your antenna the range
proximately doubles. From your house, you are up from sea level plus the height of your house. A good antenna can go a little bit further than the
line-of-sight distance to the horizon
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Johannes
Nomad
Posts: 110
Registered: 9-29-2006
Location: / Loreto/Kenmore,WA
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Mood: I love it in Loreto
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At the following site there is a good discussion on how you can increase your range by getting a higher gain antenna and better coax cable to the
antenna
<http://reviews.ebay.com/VHF-Marine-Radio-Antenna-Buying-Guide_W0QQugidZ10000000000015940>
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Pescador
Ultra Nomad
Posts: 3587
Registered: 10-17-2002
Location: Baja California Sur
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Santiago, I have an 8ft, full gain antenna on my center console and I can communicate easily from my house at San Bruno to Tortuga Island which is
over 25 miles away. Russ is correct that we get Saturday morning radio from San Carlos, Sonora, but that is because we pick up radio signals from a
repeater and sailboats that have a good antenna on top of their masts.
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woody with a view
PITA Nomad
Posts: 15939
Registered: 11-8-2004
Location: Looking at the Coronado Islands
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Mood: Everchangin'
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a total "sparky" type would suggest you get a LONG antenae along with a strong VHF and stow them for your worst case. hopefully when you break down
you can calmly set up your Eiffel Tower antenae and reach help way over the horizon.
but what do i know...
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Santiago
Ultra Nomad
Posts: 3512
Registered: 8-27-2003
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Thanks guys - more stuff to buy - goodie.
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55steve
Senior Nomad
Posts: 857
Registered: 4-24-2006
Location: Warner Springs, CA
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Here in San Diego I routinely communicate with boats that are 30+ miles away, sometimes even much further. I have been at the south end of La Guarda
and talked to my buddy at Smith. I have a 17' CC with a good Shakespeare 8' antenna.
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avid
Junior Nomad
Posts: 41
Registered: 7-10-2008
Location: SW Oregon
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Mood: adventurous
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It's all about EIRP. It is a calculation based on Wattage of transmitter, loss in transmission lines and decibel gain of antenna. Here is a very good explanation about the Marine antennas.
At VHF/UHF frequencies feed lines and connectors can make a significant difference in signal strength.
Also get yourself a 17' antenna.
[Edited on 1-28-2009 by avid]
[Edited on 1-28-2009 by avid]
avid
Ashland, OR
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Hook
Elite Nomad
Posts: 9010
Registered: 3-13-2004
Location: Sonora
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Mood: Inquisitive
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Is your UHF/PL-259 antenna center conductor soldered on or is it crimped on? That reduction of the length of the cable is a big no-no. The entire
antenna plays a role in creating a wavelength multiple of the 156-161 mhz wave. Replace the antenna
As of a few days ago, it looks like the San Carlos repeater is down.
[Edited on 1-28-2009 by Hook]
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Udo
Elite Nomad
Posts: 6346
Registered: 4-26-2008
Location: Black Hills, SD/Ensenada/San Felipe
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Mood: TEQUILA!
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Hola Santiago!
I recall from my radio playing days that one can get a huge increase in signal distance by changing their SWR signal.
I'm probably one of the least technical people on this board, however, I recall that the SWR signal was drastically changed by lenghtening or
shortening the antennae wire from the receiver. It also helped to change the wire to the thicker type (RG 58U) of wire.
One attained the ball-park signal strength by connecting an in-line SWR meter (available at Radio Shack or e-bay), then hook up a 25' wire and start
cutting the wire until you achieve the highest SWR signal ratio.
But...what do I know!
Udo
Youth is wasted on the young!
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