VHF Antenna

N

nermal

Joined
Feb 28, 2007
Messages
28
Location
Midwest
I'm in a part of the world where I carry a radio more to listen to the weather than for any other reason. There are so few people monitoring the airwaves that I wouldn't even bother with a mayday if I was in trouble and I seriously doubt that they would hear me anyways. There is so much topography in the way that I have trouble listening to weather being broadcast at times.

I spent a portion of the morning talking to marinas in the area, a waste of time, and searching the net, equally frivolous, on boosting the ability of my handheld to receive and transmit. I'm limited to 5W transmitting, but if I could extend my antenna, in my mind, that would be a batter line of sight and also help with my reception.

I could not find information on replacement antennas. Every place I looked always mentioned radio model numbers. I know that you can attach handheld to boat antennas but no one I talked to would confirm this.

Anyone know of a whip antenna, preferrably packable, that can be used with a handheld VHF?
 
nermal said:
Anyone know of a whip antenna, preferrably packable, that can be used with a handheld VHF?
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I've been down that road a bit, with the assistance of a couple amateur radio buffs (HAM's) ... and was even gifted with a rig made professionally. The word from the HAM's was that a whip might extend my range another 5 miles or so, if I am working off the deck of a kayak, and expecting the receiving antenna to be on a power boat or something similar. OTOH, if I could get the whip up a tree while on the beach (comes with a few feet of coaxial cable), that might gain me another 15 miles.

All of this assumes unobstructed line-of-sight conditions to the receiving antenna.

I have never tested my rig so I do not know its capabilities in the field. Basically, I decided that the added range would not make much difference where I paddle, so I do not carry it.

Some of the radio experts who hang out here may be able to suggest better means of doing what you want.
 
What kind of radio do you have --- brand, handheld or fixed mount, etc?

Does it have a removable antenna mount like an SMC or PL-259 --- or is it not designed to easily be connected to other antennas --- FRS radios, by law, have to be incapable of being connected to antennas other than what they come from the factory with, although I'm not sure about type-certified marine rigs.

If you can't easily connect another antenna, it'll really be a hassle to jury-rig a connection and will at least violate your warranty and probably ruin any water-tightness the rig had to start with.

Like Dave said, at VHF frequencies it's all line-of-sight, you don't get skywave propagation like you do with HF frequencies. You can get phenomenal range between low powered VHF rigs as long as their antennas can 'see' each other --- the closer you are to the surface of the water, the closer the horizon is. The point being that you'll probably get more mileage out of somehow raising your antenna, either by climbing on top of the wheelhouse or on a rock (with a handheld), than by putting a bigger antenna on it.
 
I'm talking about a handheld VHF. It's a 5 year old Uniden Atlantis. Yes the antenna is easily removable however I am not familiar with the terminology of connectors so I am unable to identify what type it has.

I was thinking while in my kayak, I could rig a device to hold the antenna to my paddle blade so I could hold it above my head. While on land, I want to be able to throw a line over a tree and hoist the antenna to help get a better line of site.
 
nermal said:
I was thinking while in my kayak, I could rig a device to hold the antenna to my paddle blade so I could hold it above my head.

Very difficult to juggle that arrangment, while bracing, while using the VHF.

While on land, I want to be able to throw a line over a tree and hoist the antenna to help get a better line of site.
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That is your best bet.

As to your antenna connector, odds-on it is a standard BNC connector such as I have on my old ICOM M10A: Quarter turn of a knurled knob releases it, revealing opposing lugs, maybe 2 mm long and 1.5 mm D.

Post the model number (look on the case), and/or google it up. I bet the specs are posted somewhere. Is this it?
202086946.jpg


If so, it is an Atlantis 250, also available in black.
 
Just an indirect comment on radio antennas to help you formualte your questions to an expert. In general the length of a radio antenna is a multiple of the frequencies it operates at. Generally this makes them too long for practical use so they chop the length in half or quarter to make them protable. This still works, but is not as effective as a full length antenna. Forgive the terminalogy here, I am trying to convey a concept from some radio projects I was invovled in, and my have the terms a bit wrong. The concepts I believe are hoever fairly universal across all radios. I don't know VHF very well but I suspect that the use an antenna that is choped down from the perfect full wave length multiple. So it is probably reasonable to find a longer one at the next multiple length. So that is the question you probably want to ask an antenna specialty place. Good luck and let us know how you do...
 
Woodensoul, I think you have the basic idea correct - at least, that's what I understand also (albeit with limited experience also). Another 'trick' that some antennas use is to wind the antenna around something, in order to make the overall length much shorter. I'm guessing that this is done with VHF antennas. So, if you can manufacture another antenna with the same effective length but not 'wound' around anything, you could use the overall length of it to gain altitude and therefore increase its effective range (since it'll be higher above horizon and objects that interfere with it's line of sight).

I don't understand how these work, but sometimes in small R/C aircraft we use 'base loaded' antennas. We operate on a frequency in the 72 mHZ range, so most of our antennae are 36" long or so. Some cheaper receivers cut this in half for smaller, shorter range aircraft - producing an 18" long antenna. Base-loaded antennae can be retrofitted to receivers, producing an antenna that's only a couple of inches long (so you don't need a long antenna wire trailing the plane in flight) but somehow does not deteriorate the range of the transmitter / receiver combination (which is usually well beyond visual range - a few km or so). I wonder if one could use the same 'base loaded' technology to extend the range of a VHF radio somehow...
 
Very difficult to juggle that arrangement, while bracing, while using the VHF.
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Speaking of juggling, If I can stand on the deck of my boat and juggle, then I probably have the balance needed to hold my paddle in the air and talk on a radio. As a guide, I'm rarely in trouble but If I need the radio, I want to be heard.

As to your antenna connector, odds-on it is a standard BNC connector such as I have on my old ICOM M10A: Quarter turn of a knurled knob releases it, revealing opposing lugs, maybe 2 mm long and 1.5 mm D.
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Nope, it is a threaded terminal. The antenna screws on similar to coaxial cable.

I do believe it is the Alantis 250, but I know it was cosmetically changed shortly after I bought it and there is no indication of a model number on the case.
 
Mark, your handheld VHF has a base-loaded antenna, aka a "rubber ducky." Check out the Wikipedia dissertation on such antennas. Farther down, there is a link to "whip antennas" also. Probably a good place to enlarge understanding of how antenna length and makeup vaies for VHF: http://en.wikipedia.org/wiki/Rubber_Ducky_antenna

I am no expert on this stuff, so I defer to Wiki, where I think you will get better info.
 
nermal said:
Nope, it is a threaded terminal. The antenna screws on similar to coaxial cable.
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Can you post a photo? That sounds like the one on my ICOM M88, which is an SMA 50 ohm connector. Could not find a good photo of it.

Here is Uniden's scoop on the Atlantis: http://tinyurl.com/2fy42a Note there is a link to a pdf file of the owner's manual. That might help confirm its identity.
 
I seem to recall that it is the Atlantis 250. The features are the same but the look has definitely changed. I have a combo squelch/volume knob and the battery pack screws into the base of the unit instead of clipping into the rear. Also I recall my unit being waterproof to JIS-7 standards.

So let me recap what I've learned. I can extend my antenna by using coaxial cable to locate it away from me. Longer cable means reduction in transmission power. The antenna itself must be in proportion to the length of the sign wave of the given frequency.

In my current configuration, my radio can broadcast 3.5 miles, or I can be about 7 miles away from another kayaker and still talk to them. If I were to put my antenna on my paddle held aloft, I only add another mile to that equation. On land, if I were to hoist my antenna 50' into a tree, I could talk to a kayaker 13.5 miles away.
 
I forgot to mention that yes, there are losses associated with a longer antenna feedline, particularly at VHF frequencies, but if the extra feedline length means more elevation for your antenna, then it's probably 'worth it' untill lengths in excess of 50 or 100 feet, where the losses then would begin to exced the gains from the higher elevation --- in most cases.
The losses per 100 foot of RG8U are 4 dB/100 feet at 144 mhz (marine band is 158mhz, so not much difference), 3 dB ratio means difference in strength of 50%.
 
nermal said:
So let me recap what I've learned. I can extend my antenna by using coaxial cable to locate it away from me. Longer cable means reduction in transmission power. The antenna itself must be in proportion to the length of the sign wave of the given frequency.

Not quite; it can be one of a couple fractions of the wavelength. There are commercially available "whip" antennas which will do the job. Or, a "J" antenna. You might email the guy who sent me his "J" pole antenna on 30 ft of coax to test (I never tested it): info@noftc.com He no longer sells these units, but he might be helpful. Nice guy.

In my current configuration, my radio can broadcast 3.5 miles, or I can be about 7 miles away from another kayaker and still talk to them. If I were to put my antenna on my paddle held aloft, I only add another mile to that equation. On land, if I were to hoist my antenna 50' into a tree, I could talk to a kayaker 13.5 miles away.
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I think those distances are optimistic, based on my experience. The 3.5 mile figure is about right (under ideal conditions) for kayak-to-kayak communication. Where did the 7.0 come from?

I don't know if you will be able to get TX from the kayaker at 13.5 miles. I have gotten about 8-10 miles when I had line of sight, beach to beach, each broadcaster about 10-15 feet above the water. Based on that, I am dubious a kayaker would be picked up at 13.5 miles from a whip in a tree. He might hear you, but his TX signal might not reach you.
 
For my 7 and 13.5 miles I was taking into account the kayaker's antenna height. If I can broadcast and listen for 3.5, and they can do the same, then at 7 miles, our signals will be overlapping.
 
nermal said:
For my 7 and 13.5 miles I was taking into account the kayaker's antenna height. If I can broadcast and listen for 3.5, and they can do the same, then at 7 miles, our signals will be overlapping.
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Not how it works. His signal reaches out only 3.5 miles, at which distance there must be a receiver. It does not work for his signal to commingle with your signal in the ether and generate reception 3.5 miles distant from the point f commingling.

However, if you had a person 3.5 miles from each of you, all in a staight line, so the outer yakkers are 7.0 miles apart, the central kayaker could communicate with the outer yakkers, but the outer yakkers could not yak at each other. However, their yakking could be relayed through the central yakker if he re-yaks their yakking (verbally repeats theri transmissions). Wheew! Too much yakking! :wink:
 
I use my radio's rubber ducky while on the water, and a telescoping 1/2 wave for extended tx/rx while on land. The particular telescoping antenna I use is the Smiley halfwave 2 meter http://www.smileyantenna.com/product_in ... 0ae4425e0c
It is designed for the ham radio band 144-148 Mhz but it can be used for marine frequencies if it is shortened by one section. Note that the 1/2 wave will corrode if it is not rinsed in fresh water.

Al VA7YAK
 
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