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Antenna for Marine VHF
A kayaking friend was asking me about antennas for marine VHF radios.
Someone recommended this type of antenna. http://www.amateurradio.bz/2m-70cm_v...e_antenna.html I guess my first question is what would this be dual band? Is it because it works over a range from 2 meters to 70 cm? Or is it somehow tuned for both bands at the same time but not a lot in between? This antenna would need to be vertically mounted, so would be a little clumsy sticking three foot up from a kayak. Light weight would be better than heavier. The construction plans call for stainless steel material. Any reason to not use aluminum? Is diameter important? To use aluminum I would want to use something thicker than 1/8 inch and likely hollow. I believe TV antennas are usually made from 1/4 inch tubing with maybe 1/16 inch thick walls. I guess that might make it harder to bend without kinking. Would it be ok to make it with some sort of couplers for the bends? -- Rick C |
Antenna for Marine VHF
On 4/21/2017 12:28 AM, rickman wrote:
A kayaking friend was asking me about antennas for marine VHF radios. Someone recommended this type of antenna. http://www.amateurradio.bz/2m-70cm_v...e_antenna.html I guess my first question is what would this be dual band? Is it because it works over a range from 2 meters to 70 cm? Or is it somehow tuned for both bands at the same time but not a lot in between? This antenna would need to be vertically mounted, so would be a little clumsy sticking three foot up from a kayak. Light weight would be better than heavier. The construction plans call for stainless steel material. Any reason to not use aluminum? Is diameter important? To use aluminum I would want to use something thicker than 1/8 inch and likely hollow. I believe TV antennas are usually made from 1/4 inch tubing with maybe 1/16 inch thick walls. I guess that might make it harder to bend without kinking. Would it be ok to make it with some sort of couplers for the bends? I guess I should ask if the above antenna has much advantage over a commercial VHF antenna about the same length like this one or maybe longer. If the antenna can be lowered when not in use a *much* longer antenna could be used as kayaks are quite long. -- Rick C |
Antenna for Marine VHF
rickman wrote:
A kayaking friend was asking me about antennas for marine VHF radios. Someone recommended this type of antenna. http://www.amateurradio.bz/2m-70cm_v...e_antenna.html I guess my first question is what would this be dual band? Is it This is an amateur radio antenna. For marine VHF, get a marine VHF antenna. Duh. |
Antenna for Marine VHF
On 4/21/2017 5:37 AM, Jeff wrote:
On 21/04/2017 05:28, rickman wrote: A kayaking friend was asking me about antennas for marine VHF radios. Someone recommended this type of antenna. http://www.amateurradio.bz/2m-70cm_v...e_antenna.html I guess my first question is what would this be dual band? Is it because it works over a range from 2 meters to 70 cm? Or is it somehow tuned for both bands at the same time but not a lot in between? This antenna would need to be vertically mounted, so would be a little clumsy sticking three foot up from a kayak. Light weight would be better than heavier. The construction plans call for stainless steel material. Any reason to not use aluminum? Is diameter important? To use aluminum I would want to use something thicker than 1/8 inch and likely hollow. I believe TV antennas are usually made from 1/4 inch tubing with maybe 1/16 inch thick walls. I guess that might make it harder to bend without kinking. Would it be ok to make it with some sort of couplers for the bends? This is an entirely unsuitable for marine VHF on a kayak!! Firstly it is for the wrong frequency, secondly it is unduly complicated as it is designed to work on 2 frequency bands (not anywhere in between), and thirdly if has to be mounted on a pole!!! I didn't find an explanation of the theory of this antenna. How does it work on two bands? As far as not working on the right frequency, that's just a matter of scaling the dimensions, no? 2 meter band is around 146 MHz and VHF marine is around 156 MHz. Looks like a small adjustment to me. This antenna is mounted using a piece of plexiglass. Are you saying the plexiglass is dimensioned to make the pole part of the antenna? I didn't see a mention of that in the construction. I would investigate something like a J-pole for marine band which does not require a ground-plane. The matching section could be enclosed in a tube with a s/s whip on top. S/S because aluminium will corrode with sea water. Who said anything about salt water use? I seem to recall the longer marine VHF antennas are a type called "colinear" where multiple elements are connected essentially end to end. My understanding is the advantage is that they can get more gain by being longer. -- Rick C |
Antenna for Marine VHF
On Fri, 21 Apr 2017 00:28:47 -0400, rickman wrote:
A kayaking friend was asking me about antennas for marine VHF radios. Someone recommended this type of antenna. http://www.amateurradio.bz/2m-70cm_v...e_antenna.html No. The above antenna is tuned for 144 to 148MHz. Marine band transmit is from 156.0 to 157.5Mhz transmit, and 161.975 to 162.6Mhz for AIS and weather. You might be able to retune the Jpole antenna in the above article, but my guess(tm) is that VWSR at the band edges is too high. Another reason you don't see Jpole antennas in marine use is that vertical radiation angle. Jpoles radiate most of their RF at the horizon and above, not down. With fairly low gain, that's not a problem with an antenna on the water line as the boat pitches and rolls. It's a major problem with mast mounted antennas. It would be better if the vertical radiation pattern was roughly symmetrical as in this dual Jpole antenna. It would be interesting to see what a model of this antenna looked like in 4NEC2. I guess my first question is what would this be dual band? Is it because it works over a range from 2 meters to 70 cm? Or is it somehow tuned for both bands at the same time but not a lot in between? Nope. It relys on the 3rd harmonic of 146Mhz being roughly on 440MHz. There's usually a complex matching network on dual band antennas to help keep the VSWR down, but this one apparently lacks even a balun. For example, this is part of the guts of a Diamond X-50 dual band ham antenna (after a friend backed his car into it breaking it in half). http://802.11junk.com/jeffl/antennas/Misc/slides/x50-01.html This antenna would need to be vertically mounted, so would be a little clumsy sticking three foot up from a kayak. Light weight would be better than heavier. The construction plans call for stainless steel material. Any reason to not use aluminum? Aluminum is fine. Anodizing might be a problem. Alodyne 1200 is fine. Most paints are ok. Coat hangers suck. Watch out for dissimilar metals in contact. Is diameter important? Larger outer diameter means wider bandwidth. You can use tubing in order to get light weight. To use aluminum I would want to use something thicker than 1/8 inch and likely hollow. I believe TV antennas are usually made from 1/4 inch tubing with maybe 1/16 inch thick walls. I'm too lazy to measure mine, but I would guess(tm) 0.5" diameter and a very thin 0.031 wall diameter. TV needs all the bandwidth it can get, so fat pipes are needed. The antenna also needs to be light and cheap, so thin wall with seams is standard for TV. I guess that might make it harder to bend without kinking. We used 6061-T6 for antennas. You can bend it in a tight turn if you seal the ends and fill the tubing with sand: http://www.wikihow.com/Bend-Aluminum-Pipe Would it be ok to make it with some sort of couplers for the bends? Sure. The bend does not need to be contiguous. A bar with two holes drilled in it for the two elements should work (and be adjustable). Suggestion: Look at various commercial VHF antennas and build something similar. You'll be amazed at how crude they are inside. One common antenna (I forgot the maker and model) used a fiberglass radome with a length of 1/4" wide copper tape stuck to the inside of the tube for driven elements. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna for Marine VHF
In article , rickman
wrote: A kayaking friend was asking me about antennas for marine VHF radios. Someone recommended this type of antenna. http://www.amateurradio.bz/2m-70cm_v...e_antenna.html I guess my first question is what would this be dual band? Is it because it works over a range from 2 meters to 70 cm? Or is it somehow tuned for both bands at the same time but not a lot in between? This antenna would need to be vertically mounted, so would be a little clumsy sticking three foot up from a kayak. Light weight would be better than heavier. The construction plans call for stainless steel material. Any reason to not use aluminum? Is diameter important? To use aluminum I would want to use something thicker than 1/8 inch and likely hollow. I believe TV antennas are usually made from 1/4 inch tubing with maybe 1/16 inch thick walls. I guess that might make it harder to bend without kinking. Would it be ok to make it with some sort of couplers for the bends? Rick- I did not watch the video. I believe the antenna is "dual band" because it happens to also work on a frequency band that is three times the basic frequency. In other words, 146 and 440. That does not appear to make any difference with regard to the Marine VHF band. You would simply scale the dimensions by the ratio of the Two Meter frequency to the Marine band frequency, 146/156. That said, the antenna in the article does not appear to be the best choice for your application. The "J-Pole" antenna Jeff suggested would be my choice. Do some research on the J-Pole, but remember to design it for 156 instead of 146 MHz. Fred K4DII |
Antenna for Marine VHF
In article , rickman wrote:
A kayaking friend was asking me about antennas for marine VHF radios. Someone recommended this type of antenna. http://www.amateurradio.bz/2m-70cm_v...e_antenna.html I guess my first question is what would this be dual band? Is it because it works over a range from 2 meters to 70 cm? Or is it somehow tuned for both bands at the same time but not a lot in between? The latter... it's a dualbander. Electrically, it's effectively two dipoles mounted side-by-side. The longer arms of the elements are tuned for 2-meter operation, the shorter ones for 70 cm. It would probably not work terribly well on marine VHF - those frequencies are far enough above the 2-meter band that the 2-meter elements on this antenna will be too long. The radio would see a high SWR. In principle you could build a similar dipole, with one set of elements, somewhat shorter than the 2-meter ones on this example, which would be resonant on the marine VHF frequencies. You'd reduce the element lengths by a factor of about 146/157. This antenna would need to be vertically mounted, so would be a little clumsy sticking three foot up from a kayak. Light weight would be better than heavier. The construction plans call for stainless steel material. Any reason to not use aluminum? Fresh-water kayaking, or bay/sea kayaking? Aluminum antenna elements do not survive well around salt water (or salt air near the coast). They corrode, often quickly and enthusiastically and without a word of apology or shame. Maintaining good electrical connections to aluminum is quite difficult under those conditions. Stainless steel is used for marine antennas for the same reason it's used for boat fittings. Is diameter important? To use aluminum I would want to use something thicker than 1/8 inch and likely hollow. The length of the elements will need to be changed somewhat, if you use thicker-diameter tubing. For any given resonant frequency, a very-thin element (wire or rod) needs to be longer; thick tubing needs to be shorter. Thicker-diameter elements tend to give you a broader SWR bandwidth, which is often a good thing - the length becomes less critical. Would it be ok to make it with some sort of couplers for the bends? Yes, but there's no need for bent elements in your case. This antenna uses dual elements (connected via the bend) only because it's a dualband antenna. A single-band antenna can use single pieces of tubing. However - as you note, this antenna design is going to be clumsy for a kayak. Any half-wave dipole for the marine frequencies is going to be almost a yard long. To complicate matters, a center-fed dipole like this needs to be mounted "out to the side", with the feedline running away at a 90-degree angle (as is show in the picture of the antenna mounted on a mast). If you try to mount this up vertically above the kayak, with the feedline running down right next to the lower dipole arm, the feedline will "de-tune" the antenna quite badly and it won't work well. If you really want to build a home-made antenna for this band, consider a "twin-lead J-pole" design. These are just about the same length, overall, but they're fed at the bottom. You can make them from a piece of coax, and a length of old-style 300-ohm "twinlead" antenna cable. A light and simple antenna system would be one of these twinlead J-poles (cut and tuned for the marine VHF frequencies), taped to a simple piece of wooden dowel which is then mounted on the kayak. They're not perfect antennas, but they're easy to make, light, the antenna itself can be rolled up for storage, and they're cheap. https://m0ukd.com/calculators/slim-j...le-calculator/ Just plug in the center frequency (157 MHz should do) and it will show you the dimensions. Or, as others have suggested, buy a commercial marine VHF antenna. |
Antenna for Marine VHF
On 4/21/2017 1:51 PM, Fred McKenzie wrote:
In article , rickman wrote: A kayaking friend was asking me about antennas for marine VHF radios. Someone recommended this type of antenna. http://www.amateurradio.bz/2m-70cm_v...e_antenna.html I guess my first question is what would this be dual band? Is it because it works over a range from 2 meters to 70 cm? Or is it somehow tuned for both bands at the same time but not a lot in between? This antenna would need to be vertically mounted, so would be a little clumsy sticking three foot up from a kayak. Light weight would be better than heavier. The construction plans call for stainless steel material. Any reason to not use aluminum? Is diameter important? To use aluminum I would want to use something thicker than 1/8 inch and likely hollow. I believe TV antennas are usually made from 1/4 inch tubing with maybe 1/16 inch thick walls. I guess that might make it harder to bend without kinking. Would it be ok to make it with some sort of couplers for the bends? Rick- I did not watch the video. I believe the antenna is "dual band" because it happens to also work on a frequency band that is three times the basic frequency. In other words, 146 and 440. That does not appear to make any difference with regard to the Marine VHF band. You would simply scale the dimensions by the ratio of the Two Meter frequency to the Marine band frequency, 146/156. The link is not a video. I appreciate the speculation, but I am researching this and am looking for facts. As others have pointed out, the design is basically a dipole but with J shaped elements 47.3 and 15.9 cm lengths. Someone else has suggested this is essentially a pair of dipoles of the two lengths. Usually a theoretical analysis can be found for any given antenna design, but I have not found anything other than construction projects for this design. They don't seem to cover theoretical aspects. That said, the antenna in the article does not appear to be the best choice for your application. The "J-Pole" antenna Jeff suggested would be my choice. Do some research on the J-Pole, but remember to design it for 156 instead of 146 MHz. Can you explain what would be preferable about the J-pole antenna? One big disadvantage is that it appears to be more like 6 foot long for 2 meter use. That could be rather heavy and clumsy on a kayak. -- Rick C |
Antenna for Marine VHF
On Fri, 21 Apr 2017 18:28:32 +0100, Jeff wrote:
No. The above antenna is tuned for 144 to 148MHz. Marine band transmit is from 156.0 to 157.5Mhz transmit, and 161.975 to 162.6Mhz for AIS and weather. You might be able to retune the Jpole antenna in the above article, but my guess(tm) is that VWSR at the band edges is too high. I think you are misinterpreting what this antenna is. It is not a J-pole. It is basically 2 closely coupled dipoles one on 2m and the other on 70cms. The drawing that looks like a j-pole is one half of the antenna ie an element cut to 2m and the other 70cms. Jeff Oops. Y'er right. It's not a Jpole, although it looks like one. More like a "fan dipole": https://www.google.com/search?q=fan+dipole&tbm=isch The 18.63" is 1/4 wave at 2m and 6.25" is 1/4 wave at 440Mhz. Thanks. Incidentally, I forgot to mumble that one doesn't need two dipoles to operate on just the marine band. Also, I can get similar performance out of an 18" bow tie dipole antenna (and balun), or a biconical porcupine: http://802.11junk.com/jeffl/antennas/biconical/index.html -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna for Marine VHF
On Fri, 21 Apr 2017 00:28:47 -0400, rickman wrote:
Starting over from scratch... A kayaking friend was asking me about antennas for marine VHF radios. What problem is your friend trying to solve? My guess(tm) is that he wants more range from what he's getting on his VHF marine handheld radio. This is a common problem because the typical rubber ducky helical antenna used on handheld radios has very low gain and is lacking a proper counterpoise. The first improvement would be to replace the rubber ducky antenna with a 1/4 wave vertical stiff wire antenna on 156Mhz. It would be about 48cm (18.9 in) long. That will provide a little gain and not be too long and unwieldy. There are various such antenna available that can be cut down to length. I would need to know the radio model and RF connector type in order to be more specific. Then next improvement would be a counterpoise ground element. In ham radio circles, it's called a "tiger tail". http://www.hamuniverse.com/htantennamod.html https://www.google.com/search?q=tiger+tail+antenna&tbm=isch It's just a length of 1/4 wave insulated wire dangling opposite the antenna element. You could get fancy and use 3 or 4 such counterpoise elements, but the improvement over a single element is minimal and not worth the effort. If the kayak was of a larger or ocean going variety, it might be possible to mount a larger marine antenna like this: http://www.n0lx.com/kayak.html It's for HF, but would serve as a suitable mount for a VHF antenna. A key component is the mount: https://www.westmarine.com/antenna-mounts I suggest something like this bolted to a backing plate: https://www.westmarine.com/buy/west-marine--dual-axis-ratchet-mount-nylon--1986645?recordNum=12 The thread fits most larger marine antennas. https://www.westmarine.com/vhf-antennas Light reading: "VHF Marine Antenna Fundamentals" http://www.boat-project.com/tutorials/vhfant.htm -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna for Marine VHF
In article , rickman
wrote: Can you explain what would be preferable about the J-pole antenna? One big disadvantage is that it appears to be more like 6 foot long for 2 meter use. That could be rather heavy and clumsy on a kayak. Rick- You are correct about the size. On the other hand, any separate antenna for the VHF Marine band will be a bit clumsy on a kayak. The "J" end of a J-pole is used to match a cable to the high impedance of the end of a half wave element. One advantage of a vertical half wave entenna is that it directs more energy towards the horizon, compared to a quarter wave ground plane antenna. Jeff Liebermann's analysis sounds like the best approach to VHF on a kayak. But no matter which way you go, you are transmitting from a point close to the water. You are limited to line-of-sight to another kayak. Range to a base station will be mostly determined by the height of the base station antenna. Fred |
Antenna for Marine VHF
On 4/22/2017 12:25 PM, Fred McKenzie wrote:
In article , rickman wrote: Can you explain what would be preferable about the J-pole antenna? One big disadvantage is that it appears to be more like 6 foot long for 2 meter use. That could be rather heavy and clumsy on a kayak. Rick- You are correct about the size. On the other hand, any separate antenna for the VHF Marine band will be a bit clumsy on a kayak. The "J" end of a J-pole is used to match a cable to the high impedance of the end of a half wave element. One advantage of a vertical half wave entenna is that it directs more energy towards the horizon, compared to a quarter wave ground plane antenna. Jeff Liebermann's analysis sounds like the best approach to VHF on a kayak. But no matter which way you go, you are transmitting from a point close to the water. You are limited to line-of-sight to another kayak. Range to a base station will be mostly determined by the height of the base station antenna. That is an issue I have already explored. There is not much hard information available, but it would appear that the rubber ducky antenna is adequate for use from one kayak to another for the most part. BTW, that range is twice the distance to the horizon which is about two nautical miles. Communications to a land station such as the Coast Guard would be much longer given the height of their antennas, unless your transmitted power level is too low to reach them. You might be able to receive their transmissions which are at a higher power, but they might not be able to hear your transmissions. In that case a better antenna might make the difference between rescue and not. I've also considered the possibility of a higher powered unit built into the boat with a small remote control. A cordless remote would be the best option I believe and I expect they are available. A power boost from 5W to 25W would easily beat the performance of a larger antenna. Not sure how much this would weigh with a battery, but I don't think the battery would need to be so large. It's not like 25W has to be used for every transmission. -- Rick C |
Antenna for Marine VHF
On Sat, 22 Apr 2017, Fred McKenzie wrote:
In article , rickman wrote: Can you explain what would be preferable about the J-pole antenna? One big disadvantage is that it appears to be more like 6 foot long for 2 meter use. That could be rather heavy and clumsy on a kayak. Rick- You are correct about the size. On the other hand, any separate antenna for the VHF Marine band will be a bit clumsy on a kayak. The "J" end of a J-pole is used to match a cable to the high impedance of the end of a half wave element. One advantage of a vertical half wave entenna is that it directs more energy towards the horizon, compared to a quarter wave ground plane antenna. Jeff Liebermann's analysis sounds like the best approach to VHF on a kayak. But no matter which way you go, you are transmitting from a point close to the water. You are limited to line-of-sight to another kayak. Range to a base station will be mostly determined by the height of the base station antenna. And with a kayak, the issue is less about "antenna gain" than that there's nothing with height on a kayak, and it's very low in the water. Figure out some sort of "mast" and the problem is close to solved. Once you have height, the actual antenna type matters less. I seem to recall George Dyson put sails on some of his really big kayaks, so that's an option, and the mast would provide some height for the antenna. Michael |
Antenna for Marine VHF
On Sat, 22 Apr 2017 12:43:39 -0400, rickman wrote:
... it would appear that the rubber ducky antenna is adequate for use from one kayak to another for the most part. BTW, that range is twice the distance to the horizon which is about two nautical miles. Conservative radio range on VHF is: Nautical_Miles = 1.225 * sqrt(antenna_ht_feet) Statute_Miles = 1.415 * sqrt(antenna_ht_feet) km = 4.124 * sqrt(antenna_ht_feet) Mo http://www.qsl.net/kd4sai/distance.html Communications to a land station such as the Coast Guard would be much longer given the height of their antennas, unless your transmitted power level is too low to reach them. You might be able to receive their transmissions which are at a higher power, but they might not be able to hear your transmissions. In that case a better antenna might make the difference between rescue and not. When you're on the water line, antenna height does make a big difference. Prepare a roll of coax cable setup as an RF extension cable. Attach connectors and adapters so that they fit the radio and the antenna. If in trouble at sea, lash the antenna to the top of a pole or oar to gain altitude. A separate antenna, such as a common ground plane or coax sleeve antenna at the end of the coax cable would make a better antenna than a rubber ducky. I've also considered the possibility of a higher powered unit built into the boat with a small remote control. A higher power transmitter will help the Coast Guard hear you but will do nothing for you hearing the Coast Guard. More antenna gain, and a higher antenna are better solutions. A cordless remote would be the best option I believe and I expect they are available. A power boost from 5W to 25W would easily beat the performance of a larger antenna. Not sure how much this would weigh with a battery, but I don't think the battery would need to be so large. It's not like 25W has to be used for every transmission. The biggest headache with using a 25 watt radio on battery power is that the receive current drain is rather high thanks to the display backlighting. For example: http://www.standardhorizon.com/indexVS.cfm?cmd=DisplayProducts&ProdCatID=83&encPr odID=1BFCB309CEE0FEE9385740D0F23313FA&DivisionID=3 &isArchived=0 0.45A very low audio 0.8A full audio 5.0A 25 w transmit 1.0A 1 w transmit So, let's say you start off with a 12V 7A-hr SLA battery commonly found in a UPS. You don't want to kill the battery so let's only drain it down to 40% capacity. That would give you: 12V * 7A-hr * 0.6 = 50.4 watt-hrs In 25 watt transmit, that give you: 50.4 watt-hrs / (12v * 5A) = 0.84 hrs * 60 min/hr = 50.4 minutes talk time That's actually quite a long time for a fairly small battery. However, if you leave it running in receive, you get: 50.4 watt-hrs / (12v * 0.45A) = 6.22 hrs listen time That's at low audio. If you wanted to hear something or transmit, it would be much lower. You could do better with a LiIon battery pack. The problem is that most such packs either 3 cells, which yields about 10.8V which is insufficient, or 4 cells, which could be as high as: 4.1v * 4 = 16.4v which might be over the maximum voltage rating for the radio. The Standard GX1600 is rated for 11 to 16.5V operating voltage, so you should be ok with 4 cells. Yep, a 25 watt radio might work. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna for Marine VHF
On Sat, 22 Apr 2017 20:03:49 -0700, Jeff Liebermann
wrote: Conservative radio range on VHF is: Nautical_Miles = 1.225 * sqrt(antenna_ht_feet) Statute_Miles = 1.415 * sqrt(antenna_ht_feet) km = 4.124 * sqrt(antenna_ht_feet) Something is wrong with the km line above. Perhaps the antenna height should be in meters? Or, the constant should be 2.278. |
Antenna for Marine VHF
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Antenna for Marine VHF
On 4/23/2017 10:17 AM, Ralph Mowery wrote:
In article , says... On Sat, 22 Apr 2017 12:43:39 -0400, rickman wrote: I've also considered the possibility of a higher powered unit built into the boat with a small remote control. A higher power transmitter will help the Coast Guard hear you but will do nothing for you hearing the Coast Guard. More antenna gain, and a higher antenna are better solutions. Going from 5 to 25 watts of FM will gain almost nothing. Raising the antenna several feet from the sitting down position will gain a lot. Are you saying that a hand held 5 watt transceiver with a rubber ducky antenna will reach all receivers because of the line of sight limitation? Is that true even for contacting a land station with a 200 foot high antenna? A 3 foot high antenna and a 200 foot high antenna give nearly 20 statute miles of range. Will 5 watts be heard that far away? -- Rick C |
Antenna for Marine VHF
On 4/23/2017 12:00 PM, rickman wrote:
On 4/23/2017 10:17 AM, Ralph Mowery wrote: In article , says... On Sat, 22 Apr 2017 12:43:39 -0400, rickman wrote: I've also considered the possibility of a higher powered unit built into the boat with a small remote control. A higher power transmitter will help the Coast Guard hear you but will do nothing for you hearing the Coast Guard. More antenna gain, and a higher antenna are better solutions. Going from 5 to 25 watts of FM will gain almost nothing. Raising the antenna several feet from the sitting down position will gain a lot. Are you saying that a hand held 5 watt transceiver with a rubber ducky antenna will reach all receivers because of the line of sight limitation? Is that true even for contacting a land station with a 200 foot high antenna? A 3 foot high antenna and a 200 foot high antenna give nearly 20 statute miles of range. Will 5 watts be heard that far away? Opps, make that nearly 20 nautical miles. It's over 22 statute miles. -- Rick C |
Antenna for Marine VHF
rickman wrote:
On 4/23/2017 10:17 AM, Ralph Mowery wrote: In article , says... On Sat, 22 Apr 2017 12:43:39 -0400, rickman wrote: I've also considered the possibility of a higher powered unit built into the boat with a small remote control. A higher power transmitter will help the Coast Guard hear you but will do nothing for you hearing the Coast Guard. More antenna gain, and a higher antenna are better solutions. Going from 5 to 25 watts of FM will gain almost nothing. Raising the antenna several feet from the sitting down position will gain a lot. Are you saying that a hand held 5 watt transceiver with a rubber ducky antenna will reach all receivers because of the line of sight limitation? Is that true even for contacting a land station with a 200 foot high antenna? A 3 foot high antenna and a 200 foot high antenna give nearly 20 statute miles of range. Will 5 watts be heard that far away? Radio amateurs have launched satellites which usually have about 1 to 5 W of power on VHF and UHF. Those can be clearly heard on a portable with a very small antenna even when 2000-3000km away. The loss of signal on line of sight is easy to overcome with narrow band modulation and this kind of power. It is the "beyond line of sight" attennuation that is the problem. Everything you can do to remove that will help a lot more than power. Today I was working at the repeater in our local radio/tv tower. We were at 220m above ground level and it was easy to work over a repeater about 80km away from us using only a handy with 1W of output. Only because at that height this is (almost) line of sight. |
Antenna for Marine VHF
In article , rickman
wrote: A 3 foot high antenna and a 200 foot high antenna give nearly 20 statute miles of range. Will 5 watts be heard that far away? Rick- I have not done the calculations, but think your limit is line-of-sight rather than power. I once talked 50 miles to an aircraft on Two Meters, using a 1 watt handheld with rubber ducky antenna. This assumes the Coast Guard does not have their squelch set too tight. Fred |
Antenna for Marine VHF
On Sun, 23 Apr 2017 07:10:17 -0400, Pat wrote:
On Sat, 22 Apr 2017 20:03:49 -0700, Jeff Liebermann wrote: Conservative radio range on VHF is: Nautical_Miles = 1.225 * sqrt(antenna_ht_feet) Statute_Miles = 1.415 * sqrt(antenna_ht_feet) km = 4.124 * sqrt(antenna_ht_feet) Something is wrong with the km line above. Perhaps the antenna height should be in meters? Or, the constant should be 2.278. Oops and thanks. That should be: Conservative radio range on VHF is: Nautical_Miles = 1.225 * sqrt(antenna_ht_feet) Statute_Miles = 1.415 * sqrt(antenna_ht_feet) km = 4.124 * sqrt(antenna_ht_meters) -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna for Marine VHF
On Sun, 23 Apr 2017 12:00:09 -0400, rickman wrote:
Will 5 watts be heard that far away? Let's see what the Fiis equation says, assuming line of sight, perfect conditions, and no obstructions: http://www.proxim.com/products/knowledge-center/calculations/calculations-system-operating-margin-som Distance = 20 statute miles Operating frequency is about 156MHz Rubber ducky antenna gain is about -3dB Coax cable loss is zero. 5 watts tx power is +37dBm 25 watts tx power is +44dBm Rx sensitivity is 0.18uV = -122dBm/12dB SINAD Plugging into the above calculator, I get for 5 watts: 106.5 dB path loss -75.5 dbm rx signal strength 46.5 dB fade margin In other words, with this arrangement, your receive signal is 46.5dB stronger than the minimum level (12dB SINAD) necessary to hear a fairly weak and noisy signal. You should theoretically have no problems being heard at 20 miles. However, that's theory, not practice. At 156 MHz, the Fresnel zone is rather large. Quite a bit of signal is lost bouncing off the water surface, or being absorbed. There are waves that get in the way. The curvature of the earth raises the wave height at mid span, resulting in more blockage. My experience is about 5 miles maximum for reliable communications between two handhelds over water. Icom sorta suggests 3 to 8 miles: https://www.westmarine.com/WestAdvisor/Selecting-a-VHF-Handheld-Radio Please read the "What are the limits of range and power?" near the bottom of the page. Propagation over water is also full of oddities and anomalies: "The propagation of VHF and UHF radio waves over sea paths " https://pdfs.semanticscholar.org/a6ca/1fe1ca92e96a7e7150217b265816891b102e.pdf I've been in situations where I can see the person or station that I'm trying to communicate but because of inversion layers and surface reflections, the signal was weak, variable, or gone. You mentioned that it's not over salt water. In that case, land topography has a huge effect on propagation. If your friend is in a river canyon, raising the antenna a few feet isn't going to do anything useful. For such situations, land the kayak, climb the walls of the canyon, and try the radio where there's fewer obstacles. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna for Marine VHF
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Antenna for Marine VHF
On 4/23/2017 2:31 PM, Jeff Liebermann wrote:
On Sun, 23 Apr 2017 12:00:09 -0400, rickman wrote: Will 5 watts be heard that far away? Let's see what the Fiis equation says, assuming line of sight, perfect conditions, and no obstructions: http://www.proxim.com/products/knowledge-center/calculations/calculations-system-operating-margin-som Distance = 20 statute miles Operating frequency is about 156MHz Rubber ducky antenna gain is about -3dB Coax cable loss is zero. 5 watts tx power is +37dBm 25 watts tx power is +44dBm Rx sensitivity is 0.18uV = -122dBm/12dB SINAD Plugging into the above calculator, I get for 5 watts: 106.5 dB path loss -75.5 dbm rx signal strength 46.5 dB fade margin In other words, with this arrangement, your receive signal is 46.5dB stronger than the minimum level (12dB SINAD) necessary to hear a fairly weak and noisy signal. You should theoretically have no problems being heard at 20 miles. However, that's theory, not practice. At 156 MHz, the Fresnel zone is rather large. Quite a bit of signal is lost bouncing off the water surface, or being absorbed. There are waves that get in the way. The curvature of the earth raises the wave height at mid span, resulting in more blockage. My experience is about 5 miles maximum for reliable communications between two handhelds over water. Icom sorta suggests 3 to 8 miles: https://www.westmarine.com/WestAdvisor/Selecting-a-VHF-Handheld-Radio Please read the "What are the limits of range and power?" near the bottom of the page. Propagation over water is also full of oddities and anomalies: "The propagation of VHF and UHF radio waves over sea paths " https://pdfs.semanticscholar.org/a6ca/1fe1ca92e96a7e7150217b265816891b102e.pdf I've been in situations where I can see the person or station that I'm trying to communicate but because of inversion layers and surface reflections, the signal was weak, variable, or gone. You mentioned that it's not over salt water. In that case, land topography has a huge effect on propagation. If your friend is in a river canyon, raising the antenna a few feet isn't going to do anything useful. For such situations, land the kayak, climb the walls of the canyon, and try the radio where there's fewer obstacles. I said the particular case I was being asked about was not over salt water. I didn't say it was on a river. The particular case is for use on the Great Lakes. Other uses I might have at other times would likely be on salt water such as the Chesapeake Bay and tributaries or the Atlantic ocean. Your info is helpful. Thanks. -- Rick C |
Antenna for Marine VHF
On 23/04/17 04:03, Jeff Liebermann wrote:
quote ===== When you're on the water line, antenna height does make a big difference. Prepare a roll of coax cable setup as an RF extension cable. Attach connectors and adapters so that they fit the radio and the antenna. If in trouble at sea, lash the antenna to the top of a pole or oar to gain altitude. A separate antenna, such as a common ground plane or coax sleeve antenna at the end of the coax cable would make a better antenna than a rubber ducky. unquote ===== A simple alternative to the J-Pole antenna would be a ground plane antenna made of welding rod material on an SO-239 socket with a 4 hole square flange with a vertical quarter wave radiator and 4 hinged radial elements,the latter under 45 degrees when in use . The SO-239 socket would be connected to a PL-259 connector and a suitable length of coax. The socket + connector would be fixed into a plastic pipe ,with the coax running inside the pipe . The bottom of the pipe would be fixed to a simple platform the latter clamped to the canoe. When antenna is not in use the 4 hinged radials could be pushed in-line with the plastic pipe mast . It is useful to initially make the vertical radiator and radials ,say 10 mm longer than a quarter wave for the mid band frequency (somewhere between 157 and 162 MHz). The radiator can then be shortened (1mm at the time) to achieve lowest SWR for the desired frequency ,using an antenna analyser or SWR meter with the transceiver Lastly the radials can be trimmed accordingly ,checking SWR When all is done ,the exposed SO-239 centre pin to which the 1/4 wave radiator is soldered (or the complete SO-239 socket can be covered with Epoxy or Bluetack (giving excellent protection) Frank , GM0CSZ / KN6WH in IO87AT |
Antenna for Marine VHF
On Sun, 23 Apr 2017 15:16:40 -0400, rickman wrote:
I said the particular case I was being asked about was not over salt water. I didn't say it was on a river. The particular case is for use on the Great Lakes. It's my understanding the propagation over the Great Lakes is similar to that over the ocean. However, I have no experience on the Great Lakes. Your info is helpful. Thanks. Y're welcome. I mentioned the problem to a friend who was into kayaking when he was younger. He said that kayaks often carry push poles to get them off the rocks. These are often used as an improvised distress flag mast. I found this one: https://thesuperstick.com/product/push-pole/ which goes to 17ft extended. Hopefully, there are cheaper models. To attach an antenna, there's the usual roll of coax cable and some kind of temporary mounting clip. Perhaps something like this, but with lower loss coax cable: http://www.dhgate.com/product/nagoya-rb-clp-window-clip-mount-rg-174-u/176624090.html https://www.aliexpress.com/store/product/NAGOYA-RB-CLP-Window-Clip-Mount-RG-174-U-3m-Cable-BNC-for-walkie-talkie-Radio/1295452_32312249435.html Or, just an L-bracket with a connector attached. Or, a big rubber band. Whatever gets the antenna higher. You're on your own on how to keep the push pole mast upright. Vessels sometimes carry "emergency" antennas. The idea is that if the main antenna is in some way lost, the emergency antenna would be substituted. Examples: https://www.westmarine.com/buy/shakespeare--stowaway-emergency-vhf-antenna--519058 http://shakespeare-ce.com/marine/product/sl-156-emergency-vhf-antenna/ They're usually small and have little gain, but might offer some useful ideas. Lunch beckons... -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna for Marine VHF
On 4/23/2017 4:26 PM, Jeff Liebermann wrote:
On Sun, 23 Apr 2017 15:16:40 -0400, rickman wrote: I said the particular case I was being asked about was not over salt water. I didn't say it was on a river. The particular case is for use on the Great Lakes. It's my understanding the propagation over the Great Lakes is similar to that over the ocean. However, I have no experience on the Great Lakes. I believe the issue of salt water came up because of a materials concern, aluminum vs. stainless steel. Your info is helpful. Thanks. Y're welcome. I mentioned the problem to a friend who was into kayaking when he was younger. He said that kayaks often carry push poles to get them off the rocks. These are often used as an improvised distress flag mast. I found this one: https://thesuperstick.com/product/push-pole/ which goes to 17ft extended. Hopefully, there are cheaper models. Not sure who told you about "push poles", but I've never run into kayaker with a push pole. If you get on rocks, you have a paddle. I don't even know where you would stow a push ploe. Much better to not get on the rocks. To attach an antenna, there's the usual roll of coax cable and some kind of temporary mounting clip. Perhaps something like this, but with lower loss coax cable: http://www.dhgate.com/product/nagoya-rb-clp-window-clip-mount-rg-174-u/176624090.html https://www.aliexpress.com/store/product/NAGOYA-RB-CLP-Window-Clip-Mount-RG-174-U-3m-Cable-BNC-for-walkie-talkie-Radio/1295452_32312249435.html Or, just an L-bracket with a connector attached. Or, a big rubber band. Whatever gets the antenna higher. You're on your own on how to keep the push pole mast upright. Vessels sometimes carry "emergency" antennas. The idea is that if the main antenna is in some way lost, the emergency antenna would be substituted. Examples: https://www.westmarine.com/buy/shakespeare--stowaway-emergency-vhf-antenna--519058 http://shakespeare-ce.com/marine/product/sl-156-emergency-vhf-antenna/ They're usually small and have little gain, but might offer some useful ideas. If I find a kayak with a roll down window I'll get one of these and try it. A kayak is not a large fishing vessel. It is a small, narrow boat with little deck space. I had a deck mounted light on a two foot pole and it was always a problem by being in the way, especially when getting in and out of the boat. You wouldn't believe how stupid and crappy many kayaking products are. I seriously doubt any sort of deck mounted antenna will be acceptable to a serious kayaker, but if it is unobtrusive and light enough it might work. There are a number of commercial marine VHF antennas that should do the job. The trick will be finding one that works as well on a kayak deck as a power boat. That's the main reason why kayakers use hand held radios. -- Rick C |
Antenna for Marine VHF
On 4/23/2017 2:34 PM, highlandham wrote:
When all is done ,the exposed SO-239 centre pin to which the 1/4 wave radiator is soldered (or the complete SO-239 socket can be covered with Epoxy or Bluetack (giving excellent protection) Frank , GM0CSZ / KN6WH in IO87AT Frank - Thanks for the Bluetack reference. It looks quite versatile so I have ordered it to try. Cheers, John N1JLS |
Antenna for Marine VHF
On Sun, 23 Apr 2017 20:34:31 +0100, highlandham
wrote: It is useful to initially make the vertical radiator and radials ,say 10 mm longer than a quarter wave for the mid band frequency (somewhere between 157 and 162 MHz). Nope. You want to tune the antenna for lowest VSWR in the transmit range (156.0 to 157.5MHz) and take whatever you can get in the 162MHz receive only region. If you try to tune the antenna for the middle of the 6 MHz split, you'll end up with lousy VSWR at both extremes where you want to operate, and good VSWR where you're not operating. Frank , GM0CSZ / KN6WH in IO87AT -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna for Marine VHF
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Antenna for Marine VHF
On 4/23/2017 8:17 PM, Jeff Liebermann wrote:
On Sun, 23 Apr 2017 20:34:31 +0100, highlandham wrote: It is useful to initially make the vertical radiator and radials ,say 10 mm longer than a quarter wave for the mid band frequency (somewhere between 157 and 162 MHz). Nope. You want to tune the antenna for lowest VSWR in the transmit range (156.0 to 157.5MHz) and take whatever you can get in the 162MHz receive only region. If you try to tune the antenna for the middle of the 6 MHz split, you'll end up with lousy VSWR at both extremes where you want to operate, and good VSWR where you're not operating. Frank , GM0CSZ / KN6WH in IO87AT How lousy? Enough for the transmitter to reduce power to protect itself? Do you have SWR numbers? |
Antenna for Marine VHF
On Sun, 23 Apr 2017 23:06:37 -0500, John S
wrote: On 4/23/2017 8:17 PM, Jeff Liebermann wrote: On Sun, 23 Apr 2017 20:34:31 +0100, highlandham wrote: It is useful to initially make the vertical radiator and radials ,say 10 mm longer than a quarter wave for the mid band frequency (somewhere between 157 and 162 MHz). Nope. You want to tune the antenna for lowest VSWR in the transmit range (156.0 to 157.5MHz) and take whatever you can get in the 162MHz receive only region. If you try to tune the antenna for the middle of the 6 MHz split, you'll end up with lousy VSWR at both extremes where you want to operate, and good VSWR where you're not operating. Frank , GM0CSZ / KN6WH in IO87AT How lousy? Enough for the transmitter to reduce power to protect itself? Do you have SWR numbers? Of course I have numbers. I never go anywhere without a handy NEC model of a marine VHF band ground plane. For your viewing pleasu http://www.11junk.com/jeffl/antennas/Marine%20VHF%20Ground%20Plane/index.html If you want to play with it, the 4NEC2 model is at: http://www.11junk.com/jeffl/antennas/Marine%20VHF%20Ground%20Plane/slides/Marine%20VHF%20Gnd%20Plane.html Argh, you're right. With a Ground Plane, the VSWR is low enough at the band edges (156 - 163MHz) for transmit, if I tune the antenna for mid-band (159MHz). TX reverse power protection usual kicks in at 2:1. Looks like the VSWR at 156 and 162 is about 1.2:1 which is quite safe: http://www.11junk.com/jeffl/antennas/Marine%20VHF%20Ground%20Plane/slides/VSWR.html Lame Excuse: I'm used to dealing with higher gain marine band antennas, where the bandwidth is much less. With these antennas, it's common practice to tune the antenna for the transmit range, and take whatever you can get at the higher receive only frequencies. However, it seems the bandwidth of a common ground plane is sufficiently wide to have low VSWR over the entire VHF marine band. Grumble... -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Antenna for Marine VHF
On Sun, 23 Apr 2017, highlandham wrote:
On 23/04/17 04:03, Jeff Liebermann wrote: quote ===== When you're on the water line, antenna height does make a big difference. Prepare a roll of coax cable setup as an RF extension cable. Attach connectors and adapters so that they fit the radio and the antenna. If in trouble at sea, lash the antenna to the top of a pole or oar to gain altitude. A separate antenna, such as a common ground plane or coax sleeve antenna at the end of the coax cable would make a better antenna than a rubber ducky. unquote ===== A simple alternative to the J-Pole antenna would be a ground plane antenna made of welding rod material on an SO-239 socket with a 4 hole square flange with a vertical quarter wave radiator and 4 hinged radial elements,the latter under 45 degrees when in use . The SO-239 socket would be connected to a PL-259 connector and a suitable length of coax. But on a kayak? It won't do much good lying on the kayak, and unless you get it high enough (which has problems in itself), you'll poke your eye out. Why not go for something that doesn't need horizontal radials. Michael |
Antenna for Marine VHF
On Sun, 23 Apr 2017, rickman wrote:
On 4/23/2017 4:26 PM, Jeff Liebermann wrote: On Sun, 23 Apr 2017 15:16:40 -0400, rickman wrote: I said the particular case I was being asked about was not over salt water. I didn't say it was on a river. The particular case is for use on the Great Lakes. It's my understanding the propagation over the Great Lakes is similar to that over the ocean. However, I have no experience on the Great Lakes. I believe the issue of salt water came up because of a materials concern, aluminum vs. stainless steel. Your info is helpful. Thanks. Y're welcome. I mentioned the problem to a friend who was into kayaking when he was younger. He said that kayaks often carry push poles to get them off the rocks. These are often used as an improvised distress flag mast. I found this one: https://thesuperstick.com/product/push-pole/ which goes to 17ft extended. Hopefully, there are cheaper models. Not sure who told you about "push poles", but I've never run into kayaker with a push pole. If you get on rocks, you have a paddle. I don't even know where you would stow a push ploe. Much better to not get on the rocks. YOu have the length of the kayak. A bamboo pole is light, and making an antenna out of wire won't burden the pole. The real issue, I'd say, is figuring out something to put on the kayak to hold the pole. For emergencies, you can probably just have some fishing line tied to the top of the pole, and hold that as a "guy wire". If there was some way to hold the oar against the kayak, some clip on antenna that used the oar as a mast would be better than nothing, and of course doesn't require an extra pole. A bit of height probably does make an improvement, after that the "mast" has to get higher and higher to be useful. Michael |
Antenna for Marine VHF
On 4/24/2017 3:44 PM, Michael Black wrote:
On Sun, 23 Apr 2017, rickman wrote: On 4/23/2017 4:26 PM, Jeff Liebermann wrote: On Sun, 23 Apr 2017 15:16:40 -0400, rickman wrote: I said the particular case I was being asked about was not over salt water. I didn't say it was on a river. The particular case is for use on the Great Lakes. It's my understanding the propagation over the Great Lakes is similar to that over the ocean. However, I have no experience on the Great Lakes. I believe the issue of salt water came up because of a materials concern, aluminum vs. stainless steel. Your info is helpful. Thanks. Y're welcome. I mentioned the problem to a friend who was into kayaking when he was younger. He said that kayaks often carry push poles to get them off the rocks. These are often used as an improvised distress flag mast. I found this one: https://thesuperstick.com/product/push-pole/ which goes to 17ft extended. Hopefully, there are cheaper models. Not sure who told you about "push poles", but I've never run into kayaker with a push pole. If you get on rocks, you have a paddle. I don't even know where you would stow a push ploe. Much better to not get on the rocks. YOu have the length of the kayak. A bamboo pole is light, and making an antenna out of wire won't burden the pole. The real issue, I'd say, is figuring out something to put on the kayak to hold the pole. For emergencies, you can probably just have some fishing line tied to the top of the pole, and hold that as a "guy wire". If there was some way to hold the oar against the kayak, some clip on antenna that used the oar as a mast would be better than nothing, and of course doesn't require an extra pole. A bit of height probably does make an improvement, after that the "mast" has to get higher and higher to be useful. Bamboo poles are not all that light and they get water logged. Everything on a kayak gets wet. So far I haven't found anything definitive that even shows a better antenna is needed. It would appear if you are trying to contact a station with a high antenna some 20 miles away you might have trouble with range, but the problem isn't that your antenna isn't high enough. Reaching other handheld units is limited by line of sight which would be helped by a higher antenna. I'm not sure which problem was being addressed. Next time I talk to my buddy I'll ask more about this. I think in reality this was prompted by someone recommending a home brew antenna when the nature of the problem wasn't even explored. -- Rick C |
Antenna for Marine VHF
On 4/24/2017 3:39 PM, Michael Black wrote:
On Sun, 23 Apr 2017, highlandham wrote: On 23/04/17 04:03, Jeff Liebermann wrote: quote ===== When you're on the water line, antenna height does make a big difference. Prepare a roll of coax cable setup as an RF extension cable. Attach connectors and adapters so that they fit the radio and the antenna. If in trouble at sea, lash the antenna to the top of a pole or oar to gain altitude. A separate antenna, such as a common ground plane or coax sleeve antenna at the end of the coax cable would make a better antenna than a rubber ducky. unquote ===== A simple alternative to the J-Pole antenna would be a ground plane antenna made of welding rod material on an SO-239 socket with a 4 hole square flange with a vertical quarter wave radiator and 4 hinged radial elements,the latter under 45 degrees when in use . The SO-239 socket would be connected to a PL-259 connector and a suitable length of coax. But on a kayak? It won't do much good lying on the kayak, and unless you get it high enough (which has problems in itself), you'll poke your eye out. Why not go for something that doesn't need horizontal radials. Actually I gave this antenna some thought. If the radials were attached by some sort of hinge for example a heavy braid, they could fold up while still being electrically attached. The antenna could slide into a tube when not in use. It might be a bit complex to rig up, but this is the sort of thing I can give some thought to and maybe come up with something workable. -- Rick C |
Antenna for Marine VHF
In article , rickman
wrote: On 4/24/2017 3:39 PM, Michael Black wrote: On Sun, 23 Apr 2017, highlandham wrote: On 23/04/17 04:03, Jeff Liebermann wrote: quote ===== When you're on the water line, antenna height does make a big difference. Prepare a roll of coax cable setup as an RF extension cable. Attach connectors and adapters so that they fit the radio and the antenna. If in trouble at sea, lash the antenna to the top of a pole or oar to gain altitude. A separate antenna, such as a common ground plane or coax sleeve antenna at the end of the coax cable would make a better antenna than a rubber ducky. unquote ===== A simple alternative to the J-Pole antenna would be a ground plane antenna made of welding rod material on an SO-239 socket with a 4 hole square flange with a vertical quarter wave radiator and 4 hinged radial elements,the latter under 45 degrees when in use . The SO-239 socket would be connected to a PL-259 connector and a suitable length of coax. But on a kayak? It won't do much good lying on the kayak, and unless you get it high enough (which has problems in itself), you'll poke your eye out. Why not go for something that doesn't need horizontal radials. Actually I gave this antenna some thought. If the radials were attached by some sort of hinge for example a heavy braid, they could fold up while still being electrically attached. The antenna could slide into a tube when not in use. It might be a bit complex to rig up, but this is the sort of thing I can give some thought to and maybe come up with something workable. Back to the J-Pole! You can make a light, flexible J-Pole out of 300 Ohm twinlead. Feed it with RG-174 cable. Use some kind of oar or pole to raise it when needed. Fred |
Antenna for Marine VHF
On Mon, 24 Apr 2017, rickman wrote:
On 4/24/2017 3:44 PM, Michael Black wrote: On Sun, 23 Apr 2017, rickman wrote: On 4/23/2017 4:26 PM, Jeff Liebermann wrote: On Sun, 23 Apr 2017 15:16:40 -0400, rickman wrote: I said the particular case I was being asked about was not over salt water. I didn't say it was on a river. The particular case is for use on the Great Lakes. It's my understanding the propagation over the Great Lakes is similar to that over the ocean. However, I have no experience on the Great Lakes. I believe the issue of salt water came up because of a materials concern, aluminum vs. stainless steel. Your info is helpful. Thanks. Y're welcome. I mentioned the problem to a friend who was into kayaking when he was younger. He said that kayaks often carry push poles to get them off the rocks. These are often used as an improvised distress flag mast. I found this one: https://thesuperstick.com/product/push-pole/ which goes to 17ft extended. Hopefully, there are cheaper models. Not sure who told you about "push poles", but I've never run into kayaker with a push pole. If you get on rocks, you have a paddle. I don't even know where you would stow a push ploe. Much better to not get on the rocks. YOu have the length of the kayak. A bamboo pole is light, and making an antenna out of wire won't burden the pole. The real issue, I'd say, is figuring out something to put on the kayak to hold the pole. For emergencies, you can probably just have some fishing line tied to the top of the pole, and hold that as a "guy wire". If there was some way to hold the oar against the kayak, some clip on antenna that used the oar as a mast would be better than nothing, and of course doesn't require an extra pole. A bit of height probably does make an improvement, after that the "mast" has to get higher and higher to be useful. Bamboo poles are not all that light and they get water logged. Everything on a kayak gets wet. I was thinking of the bamboo stakes sold for tying plants to. Those are thin, but so long as the antenna is made of wire, and thus light, would work fine. I've used the stakes, because they were handy, to get a TV loop up a bit higher to scan the channels on the tv set. But I wasn't thinking of the water, and you're right, they wouldn't hold up after being kept wet a few times. How about fibreglass? Those flags seen on bicycles to give some height for oncoming vehicles, one of those might do. Or I have a vague memory of seeing such things sold for kayaks, to be seen a bit sooner than when a bigger boat stumbles on them. If they have them for kayaks, that's a good route to take, they would come with something to use to mount on the kayak. Michael |
Antenna for Marine VHF
On 4/25/2017 1:46 PM, Michael Black wrote:
On Mon, 24 Apr 2017, rickman wrote: On 4/24/2017 3:44 PM, Michael Black wrote: On Sun, 23 Apr 2017, rickman wrote: On 4/23/2017 4:26 PM, Jeff Liebermann wrote: On Sun, 23 Apr 2017 15:16:40 -0400, rickman wrote: I said the particular case I was being asked about was not over salt water. I didn't say it was on a river. The particular case is for use on the Great Lakes. It's my understanding the propagation over the Great Lakes is similar to that over the ocean. However, I have no experience on the Great Lakes. I believe the issue of salt water came up because of a materials concern, aluminum vs. stainless steel. Your info is helpful. Thanks. Y're welcome. I mentioned the problem to a friend who was into kayaking when he was younger. He said that kayaks often carry push poles to get them off the rocks. These are often used as an improvised distress flag mast. I found this one: https://thesuperstick.com/product/push-pole/ which goes to 17ft extended. Hopefully, there are cheaper models. Not sure who told you about "push poles", but I've never run into kayaker with a push pole. If you get on rocks, you have a paddle. I don't even know where you would stow a push ploe. Much better to not get on the rocks. YOu have the length of the kayak. A bamboo pole is light, and making an antenna out of wire won't burden the pole. The real issue, I'd say, is figuring out something to put on the kayak to hold the pole. For emergencies, you can probably just have some fishing line tied to the top of the pole, and hold that as a "guy wire". If there was some way to hold the oar against the kayak, some clip on antenna that used the oar as a mast would be better than nothing, and of course doesn't require an extra pole. A bit of height probably does make an improvement, after that the "mast" has to get higher and higher to be useful. Bamboo poles are not all that light and they get water logged. Everything on a kayak gets wet. I was thinking of the bamboo stakes sold for tying plants to. Those are thin, but so long as the antenna is made of wire, and thus light, would work fine. I've used the stakes, because they were handy, to get a TV loop up a bit higher to scan the channels on the tv set. But I wasn't thinking of the water, and you're right, they wouldn't hold up after being kept wet a few times. How about fibreglass? Those flags seen on bicycles to give some height for oncoming vehicles, one of those might do. Or I have a vague memory of seeing such things sold for kayaks, to be seen a bit sooner than when a bigger boat stumbles on them. If they have them for kayaks, that's a good route to take, they would come with something to use to mount on the kayak. I think the best fiberglass for a marine VHF antenna would be the stuff you can get when you buy a marine VHF antenna. lol If you are talking about a simple wire the paddle would be ok. They are typically around 7 foot long. Clip the wire on the end of the paddle and Bob's your uncle. It's not like you will be transmitting for hours, so you can just hold the paddle up. Yesterday I couldn't think of the term for the antenna style they use in the commercial marine VHF antennas, but I believe it is called "co-linear" or something like that. It is a bunch of coax sections connected inner to outer at specific lengths. I have never seen a Ham recommend using that type. But I guess Hams go more for permanent installations with ground planes of some type. The co-linear needs no ground plane I believe. -- Rick C |
Antenna for Marine VHF
On 4/25/2017 12:07 PM, Fred McKenzie wrote:
In article , rickman wrote: On 4/24/2017 3:39 PM, Michael Black wrote: On Sun, 23 Apr 2017, highlandham wrote: On 23/04/17 04:03, Jeff Liebermann wrote: quote ===== When you're on the water line, antenna height does make a big difference. Prepare a roll of coax cable setup as an RF extension cable. Attach connectors and adapters so that they fit the radio and the antenna. If in trouble at sea, lash the antenna to the top of a pole or oar to gain altitude. A separate antenna, such as a common ground plane or coax sleeve antenna at the end of the coax cable would make a better antenna than a rubber ducky. unquote ===== A simple alternative to the J-Pole antenna would be a ground plane antenna made of welding rod material on an SO-239 socket with a 4 hole square flange with a vertical quarter wave radiator and 4 hinged radial elements,the latter under 45 degrees when in use . The SO-239 socket would be connected to a PL-259 connector and a suitable length of coax. But on a kayak? It won't do much good lying on the kayak, and unless you get it high enough (which has problems in itself), you'll poke your eye out. Why not go for something that doesn't need horizontal radials. Actually I gave this antenna some thought. If the radials were attached by some sort of hinge for example a heavy braid, they could fold up while still being electrically attached. The antenna could slide into a tube when not in use. It might be a bit complex to rig up, but this is the sort of thing I can give some thought to and maybe come up with something workable. Back to the J-Pole! You can make a light, flexible J-Pole out of 300 Ohm twinlead. Feed it with RG-174 cable. Use some kind of oar or pole to raise it when needed. I wouldn't know where to begin in sizing the components. -- Rick C |
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