I have a standard 3dB Masthead whip antenna on my 34' sailboat. I have noticed that the antenna has two 90 degree bends in it to avoid the Windex windvane. About 4 inches up from the base it bends outward 90 degrees. It extends about 2 inches to create 360 clearence for the Windex and then bends upward 90 degrees. I have never seen this before and do no know if it was done by the original owners or the dealer when the boat was outfitted 3 years ago. I am not an electronics wizzard and have no idea if this will cause any problems with transmission or reception. I can certainly make some fixes, but before I put in that effort I am curious if anyone can advise whether this is actually a problem or not. I am able to transmit and receive, but I do not know if these bends are limiting my radio. I do notice that occassionally I get reception overlaps, although I am not sure if the antenna is the cause. Any thoughts? Rob McClain
Masthead VHF Antenna
- Thread starter Rob McClain
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vhf antenna bends
Rob, it's not a problem-it's a common solution to fitting a lot of stuff onto the masthead. VHF whips are tip emitters, so it doesn't matter if you change the shape-as long as the length remains correct
Rob, it's not a problem-it's a common solution to fitting a lot of stuff onto the masthead. VHF whips are tip emitters, so it doesn't matter if you change the shape-as long as the length remains correct
SWR
CHUCK says that: “VHF whips are tip emitters, so it doesn't matter if you change the shape-as long as the length remains correct”. I’ve never heard of a “tip radiator”. It seems as though you want it both ways: length matters, but only the tip radiates. I'm confused - Could you please offer further explanation? My ( layman’s ) understanding is that bending the VHF Masthead Antenna (to clear obstructions) will increase the amount of energy that’s reflected back to the radio (Standing Wave Ratio), raising the possibility of burning out the final transmitting transistor. Some radios are protected against this possibility by a SWR protection circuit, that automatically reduces the transmitter output when radiation problems are sensed, which obviously reduces performance (reduced transmission wattage). I don’t understand the utility of bending the Antenna, when it would be so easy to mount (either component) on a horizontal stand-off bracket. FWIW
CHUCK says that: “VHF whips are tip emitters, so it doesn't matter if you change the shape-as long as the length remains correct”. I’ve never heard of a “tip radiator”. It seems as though you want it both ways: length matters, but only the tip radiates. I'm confused - Could you please offer further explanation? My ( layman’s ) understanding is that bending the VHF Masthead Antenna (to clear obstructions) will increase the amount of energy that’s reflected back to the radio (Standing Wave Ratio), raising the possibility of burning out the final transmitting transistor. Some radios are protected against this possibility by a SWR protection circuit, that automatically reduces the transmitter output when radiation problems are sensed, which obviously reduces performance (reduced transmission wattage). I don’t understand the utility of bending the Antenna, when it would be so easy to mount (either component) on a horizontal stand-off bracket. FWIW
Shape does matter
Not enough info to say how much in this case. I do not know what a reception overlap is. Best to put an swr meter on it and or plot a radiation pattern which is probably not practical. I say keep it straight - as designed and use a bracket to keep it above and away from other metal parts as best you can. Just like radar, higher is better.
Not enough info to say how much in this case. I do not know what a reception overlap is. Best to put an swr meter on it and or plot a radiation pattern which is probably not practical. I say keep it straight - as designed and use a bracket to keep it above and away from other metal parts as best you can. Just like radar, higher is better.
Does it Transmit?
If you can get a "Radio Check" from someone that is 15-20 miles away, don't worry about it. I bet the SWR doesn't change that much from the shape of the antenna. The total length does matter. Bill
If you can get a "Radio Check" from someone that is 15-20 miles away, don't worry about it. I bet the SWR doesn't change that much from the shape of the antenna. The total length does matter. Bill
It does matter...
if you consider the radiation pattern. I'd bet dollars to donuts that if you put that antenna on a test range and plotted its radiation pattern you'd find some weird anomolies. If it were my boat, I'd replace the bent piece and find another way to get the clearance I need! Oh, and BTW, Chuck, I've been playing with all sorts of antennas for over 20 years and I'm not familiar with the term 'tip emitter'. I was under the impression (perhaps wrong) that a standard 3dB gain VHF antenna as usually found on a sailboat was nothing more than a base-loaded 5/8 wave, wherein the base coil provides impedance matching to the 50 ohm coax and the entire whip acts as the radiator. Care to enlighten me as to the meaning? Thanks, Jeff
if you consider the radiation pattern. I'd bet dollars to donuts that if you put that antenna on a test range and plotted its radiation pattern you'd find some weird anomolies. If it were my boat, I'd replace the bent piece and find another way to get the clearance I need! Oh, and BTW, Chuck, I've been playing with all sorts of antennas for over 20 years and I'm not familiar with the term 'tip emitter'. I was under the impression (perhaps wrong) that a standard 3dB gain VHF antenna as usually found on a sailboat was nothing more than a base-loaded 5/8 wave, wherein the base coil provides impedance matching to the 50 ohm coax and the entire whip acts as the radiator. Care to enlighten me as to the meaning? Thanks, Jeff
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