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NVIS and VHF?
On 5/25/2011 5:17 PM, John KD5YI wrote:
On 5/25/2011 3:51 PM, Jim Lux wrote: On 5/24/2011 5:17 PM, John KD5YI wrote: On 5/24/2011 6:11 PM, Jim Lux wrote: On 5/24/2011 2:54 PM, Dave Platt wrote: I'm using 75' of professionally assembled RG8X which is required to get from the radio to the antenna. That's probably costing you about half of your power (assuming a typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are better than this. The results are all over the map. A piece of Cable TV cable might not be a bad choice, if you can scrounge one. The 75 ohms probably isn't a big deal. At 144 MHz, bigger in diameter almost always beats fancier dielectric (that is, the .405 inch RG-8, RG-213 flavors will usually beat any of the quarter inch cables (RG-6, RG-8X, LMR240, etc.) because dielectric losses aren't a big driver.. it's the IR loss in the center conductor. RG-11, for instance, has less than 1.2dB loss for a matched 75 foot line, and for the 1.5:1 mismatch, the loss only goes up 0.1 dB. (RG-11 type coax has a solid dielectric, and is pretty darn rugged stuff) 75 feet, at 144 MHz LMR240 - 2.2 dB Belden 8215 (RG-6A) - 2.5 dB Belden 9258 (RG-8x) - 3.0 dB Tandy RG-8x - 3.1 dB Belden 8267 (RG-213) - 1.9 dB Wireman CQ110 (RG-213) - 1.6 dB Belden 8237 (RG-8) - 1.7 dB belden 8213 (RG-11) = 1.2dB Huh? 75 ft of RG-11 has almost 8dB of loss at 146MHz. 75 ft of LMR240 has 9.7dB of loss at 146 MHz. I won't go through your entire list. Check out http://www.vk1od.net/calc/tl/tllc.php That's what I used.. Sure you got feet and not meters? B9219, 75ft, 146 MHz = 1.811dB Yes, Jim, Ralph pointed that out to me yesterday and I posted an apology to him. I see that I should also analogize to you for my mistake. ^^^^^^^^^ Thanks to you both. Apologize John |
NVIS and VHF?
On 5/25/2011 3:17 PM, John KD5YI wrote:
On 5/25/2011 3:51 PM, Jim Lux wrote: Yes, Jim, Ralph pointed that out to me yesterday and I posted an apology to him. I see that I should also analogize to you for my mistake. Darn newsreader that didn't have all the messages loaded.. I saw Ralph's comment and your reply. Such is life.. Now, if you want some high loss coax.. can I interest you in some tiny coax made of stainless steel? It's for cryogenic applications so it has very, very low thermal conductivity, but it also has really high loss. I don't think you want to be running kilowatts (or even watts) through it. |
NVIS and VHF?
On 5/25/2011 7:37 PM, Jim Lux wrote:
On 5/25/2011 3:17 PM, John KD5YI wrote: On 5/25/2011 3:51 PM, Jim Lux wrote: Yes, Jim, Ralph pointed that out to me yesterday and I posted an apology to him. I see that I should also analogize to you for my mistake. Darn newsreader that didn't have all the messages loaded.. I saw Ralph's comment and your reply. Such is life.. Now, if you want some high loss coax.. can I interest you in some tiny coax made of stainless steel? It's for cryogenic applications so it has very, very low thermal conductivity, but it also has really high loss. I don't think you want to be running kilowatts (or even watts) through it. Well, thanks, Jim, for your kind offer. However I have plenty of lossy cable now. I only use in the lab because other options are difficult to handle. Cheers, John |
NVIS and VHF?
On 5/24/2011 8:08 PM, Ralph Mowery wrote:
"John wrote in message ... 75 feet, at 144 MHz LMR240 - 2.2 dB Belden 8215 (RG-6A) - 2.5 dB Belden 9258 (RG-8x) - 3.0 dB Tandy RG-8x - 3.1 dB Belden 8267 (RG-213) - 1.9 dB Wireman CQ110 (RG-213) - 1.6 dB Belden 8237 (RG-8) - 1.7 dB belden 8213 (RG-11) = 1.2dB Huh? 75 ft of RG-11 has almost 8dB of loss at 146MHz. 75 ft of LMR240 has 9.7dB of loss at 146 MHz. I won't go through your entire list. Check out http://www.vk1od.net/calc/tl/tllc.php Cheers, John John you need to see where you went wrong. The numbers Jim listed are either correct or very close. I did not bother to do the calculations, but looking at a 100 foot chart, the numbers are very close and no where near the numbers you have. I thought you may have looked at the web page and missed it defauls to meters, but that does not seem to be the case to me. According to the loss calculator at Times Microwave the loss at 144 MHz for a 75 length of LMR 240 is 2.952. 100 METERS is 9.687. Perhaps you misread. tom K0TAR |
NVIS and VHF?
On 5/25/2011 8:44 PM, tom wrote:
On 5/24/2011 8:08 PM, Ralph Mowery wrote: "John wrote in message ... 75 feet, at 144 MHz LMR240 - 2.2 dB Belden 8215 (RG-6A) - 2.5 dB Belden 9258 (RG-8x) - 3.0 dB Tandy RG-8x - 3.1 dB Belden 8267 (RG-213) - 1.9 dB Wireman CQ110 (RG-213) - 1.6 dB Belden 8237 (RG-8) - 1.7 dB belden 8213 (RG-11) = 1.2dB Huh? 75 ft of RG-11 has almost 8dB of loss at 146MHz. 75 ft of LMR240 has 9.7dB of loss at 146 MHz. I won't go through your entire list. Check out http://www.vk1od.net/calc/tl/tllc.php Cheers, John John you need to see where you went wrong. The numbers Jim listed are either correct or very close. I did not bother to do the calculations, but looking at a 100 foot chart, the numbers are very close and no where near the numbers you have. I thought you may have looked at the web page and missed it defauls to meters, but that does not seem to be the case to me. According to the loss calculator at Times Microwave the loss at 144 MHz for a 75 length of LMR 240 is 2.952. 100 METERS is 9.687. Perhaps you misread. tom K0TAR Oops, needed to do this one level up. Should have responded to John. tom K0TAR |
NVIS and VHF?
On May 24, 2:43*pm, (Dave Platt) wrote:
a *very* deep multipath cancellation effect playing out... maybe interference between a edge-diffraction path involving the office building, and reflections from nearby trees. * Not a Sea Story and relevant to my learning an important multipath lesson: In 1974, I was on an aircraft carrier at a pier in Long Beach Shipyard. Ship's TV sigs not so good, so I ran a cable from the CPO lounge TV out and up to a flight deck catwalk. On the catwalk, I mounted a small all-channel antenna on a mast strapped to the rail. The transmitters (Mt. Wilson) were located away from that side. All very good pictures. In about two months, when the ship moved into drydock, it was turned 180, so I rotated our TV antenna to compensate. No good. Signals arriving across the flight deck were all awful. Unwatchable. I suspected reflections from the flight deck, so I moved the antenna all the way aft, where it was receiving through clear air again. Bingo! Even through the added 150' of cable I needed, we got our nice pictures back. "Sal" |
NVIS and VHF?
On May 22, 2:04*pm, 'Captain' Kirk DeHaan
wrote: I'm living in a wooded area and am trying to hit our club repeater reliably. *It's cloudy now so I'm and getting a bit of ducting but I have a lot of trees, mostly poplars, in the direct path. *I would have a line of sight if not for the trees as I'm up enough in altitude. *I can cut the trees, they're mine, but finding the right ones is difficult and i don't want to waste the whole grove. I go from keying the repeater with no intelligible signal to not being able to hit it. *Today I actually have an S meter reading due to the clouds. I am currently using a J-pole and will put up a Yagi soon but wonder if NVIS would work on 2m? *I have only seen references to it being applied in HF. 'Captain' Kirk DeHaan N6SXR Im convinced that my J antenna that I used while camping radiated mostly verticaly. The situation sounds very similar to yours. I couldnt hit the repeater back home with 50 watts using the J- while my wife could make contacts on her HT on the same repeater, Her antenna was either a telescoping .5 wl or 5/8 wl connected directly to her HT. Jimmie |
NVIS and VHF?
Hello Kirk,
I sent you a PM with a result from Radio Mobile. It took a long time to get RMW working, and getting the terrain data into the SW. It is 10 years ago that I used RMW and that computer I don’t have anymore. I had to start from scratch. First checked with Dutch terrain data to see whether the results are meaningful. When you look to the path profile, you have a huge margin (received power -76 dBm). I used 10W into a 2 dBi antenna (on both sides). I attached the path profile as generated by RMW (Personal Mail only). Even reducing your antenna height to 1m AGL gives sufficient margin (Prx -86 dBm). I used 30m AGL for the repeater antenna. You have 1 degree elevation towards the repeater, that is huge (we don't have that in the Netherlands). Assuming the data is correct, it is really strange that you can't hit the repeater. I couldn’t find were to set vegetation and cities, but even this shouldn't be a problem. I hope some other people can confirm the results from RMW. With kind regards, Wim PA3DJS www.tetech.nl |
NVIS and VHF?
On 5/24/2011 11:05 PM, 'Captain' Kirk DeHaan wrote:
Dave Platt said the following on 5/24/2011 2:54 PM: In , 'Captain' Kirk wrote: All of this leads me to think that something else is wrong. I can hit a repeater 20 miles from me with 5 Watts and its antenna is on a 300 ft tower. My antenna (half wave end-fed dipole) is on a 20 ft mast. There may well be something wrong with the antenna. I don't have an SWR meter handy but will try and borrow one from a club member. The J-pole was beat around quite a bit over the years but since the radio has a limiting circuit if the SWR is too far out of whack I am assuming it is fairly close. It will transmit of full power. One of the things to know about the American Legion J-pole (and most vaguely-similar J-poles) is that it has no feedline or mount-point isolation to speak of. The outside of the feedline coax, and any pipe or tower or other metal to which you strap the antenna, become part of the antenna's ground system, and can radiate a significant amount of RF. This can interact with the RF coming from the main radiator, and significantly alter the antenna's pattern... it no longer behaves like an idealized half-wave vertical radiator. In most installations this doesn't seem to matter all that much... but it's possible that you've got some sort of weird interaction (feedline emissions, reflections from the ground or nearby metal, etc.) which is creating a null in the antenna's pattern in just the wrong direction. If this is an issue (not all that likely but perhaps possible) you could insulate the antenna from the mounting mask, and install a choke (e.g. a few ferrite cores) on the feedline just below the antenna. It is mounted on an angle bracket about 12" from a mast 20' above my metal roof. The mast is isolated from roof but is not yet grounded. Also, the American Legion J-poles are subject to a couple of forms of mechanical/electrical failure after a few years. The plastic insulator which spaces apart the radiator and matching arm can degrade (UV from sunlight is the main offendor, I believe) and crack, allowing the two arms to change spacing. More subtly, the connection between the two arms and the metal base can degrade... it's aluminum-to- aluminum using a set-screw, and the connection can loosen and corrode. My spacer basically disintegrated. I replaced it with 1/2" pvc pipe. I measured the spacing at the base and got it as close as possible. I will check out the other connections. There is obvious aluminum oxide on the assembly so it is very possible it is down between the parts. I'll get up on my steep metal roof after the rains stop. :-) It might be worth checking the spacer (replace if necessary), and checking and tuning up the set-screw connections (squirt with Liquid Wrench if necessary, loosen and remove, take out the rods, clean the ends of the rods and the mounting holes in the place, dab with NoAlOx or a similar corrosion-blocker, reassemble and tighten). I'm using 75' of professionally assembled RG8X which is required to get from the radio to the antenna. That's probably costing you about half of your power (assuming a typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are better than this. Thanks for the suggestions. Hey, Kirk - After reading Wim's response, I am more convinced than ever that you have a problem with your antenna, coax, or transceiver. What type of coax are you using? Could it have gotten water inside? Are you using the coax that you used 10 years ago? Try to think of other question similar to these and we'll get to the bottom of this. Cheers, John |
NVIS and VHF?
John KD5YI said the following on 5/26/2011 8:56 PM:
On 5/24/2011 11:05 PM, 'Captain' Kirk DeHaan wrote: Dave Platt said the following on 5/24/2011 2:54 PM: In , 'Captain' Kirk wrote: All of this leads me to think that something else is wrong. I can hit a repeater 20 miles from me with 5 Watts and its antenna is on a 300 ft tower. My antenna (half wave end-fed dipole) is on a 20 ft mast. There may well be something wrong with the antenna. I don't have an SWR meter handy but will try and borrow one from a club member. The J-pole was beat around quite a bit over the years but since the radio has a limiting circuit if the SWR is too far out of whack I am assuming it is fairly close. It will transmit of full power. One of the things to know about the American Legion J-pole (and most vaguely-similar J-poles) is that it has no feedline or mount-point isolation to speak of. The outside of the feedline coax, and any pipe or tower or other metal to which you strap the antenna, become part of the antenna's ground system, and can radiate a significant amount of RF. This can interact with the RF coming from the main radiator, and significantly alter the antenna's pattern... it no longer behaves like an idealized half-wave vertical radiator. In most installations this doesn't seem to matter all that much... but it's possible that you've got some sort of weird interaction (feedline emissions, reflections from the ground or nearby metal, etc.) which is creating a null in the antenna's pattern in just the wrong direction. If this is an issue (not all that likely but perhaps possible) you could insulate the antenna from the mounting mask, and install a choke (e.g. a few ferrite cores) on the feedline just below the antenna. It is mounted on an angle bracket about 12" from a mast 20' above my metal roof. The mast is isolated from roof but is not yet grounded. Also, the American Legion J-poles are subject to a couple of forms of mechanical/electrical failure after a few years. The plastic insulator which spaces apart the radiator and matching arm can degrade (UV from sunlight is the main offendor, I believe) and crack, allowing the two arms to change spacing. More subtly, the connection between the two arms and the metal base can degrade... it's aluminum-to- aluminum using a set-screw, and the connection can loosen and corrode. My spacer basically disintegrated. I replaced it with 1/2" pvc pipe. I measured the spacing at the base and got it as close as possible. I will check out the other connections. There is obvious aluminum oxide on the assembly so it is very possible it is down between the parts. I'll get up on my steep metal roof after the rains stop. :-) It might be worth checking the spacer (replace if necessary), and checking and tuning up the set-screw connections (squirt with Liquid Wrench if necessary, loosen and remove, take out the rods, clean the ends of the rods and the mounting holes in the place, dab with NoAlOx or a similar corrosion-blocker, reassemble and tighten). I'm using 75' of professionally assembled RG8X which is required to get from the radio to the antenna. That's probably costing you about half of your power (assuming a typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are better than this. Thanks for the suggestions. Hey, Kirk - After reading Wim's response, I am more convinced than ever that you have a problem with your antenna, coax, or transceiver. What type of coax are you using? Could it have gotten water inside? Are you using the coax that you used 10 years ago? Try to think of other question similar to these and we'll get to the bottom of this. Cheers, John John, I believe it is either the trees or the antenna. The coax is new and the transceiver worked fine last time I used it. Also works fine with this setup getting into the repeater on Schweitzer , 145.230, with 5 watts and the signal report from a gentleman I spoke to was 59. That is a clear shot and a few miles closer. Although the profiles show there should be a clear shot to the .780 repeater I can gurantee there is a wall of trees on the first little ridge on the profile. I found that my club, which I've only been with for a month, has an SWR meter and an antenna analyzer. I hope to borrow them to see what's up. In the meantime I will pull the J-pole down and clean it up as suggested. There is considerable aluminum oxide on the outside of the parts so there may be some between the base and uprights. When I put it back up I will move it 180 degrees from it current location. That will only move it about 2' but who knows. -- 'Captain' Kirk DeHaan N6SXR "Beam me up Scotty, there's no intelligent life here" |
NVIS and VHF?
On 27 mayo, 21:30, 'Captain' Kirk DeHaan
wrote: John KD5YI said the following on 5/26/2011 8:56 PM: On 5/24/2011 11:05 PM, 'Captain' Kirk DeHaan wrote: Dave Platt said the following on 5/24/2011 2:54 PM: In , 'Captain' Kirk wrote: All of this leads me to think that something else is wrong. I can hit a repeater 20 miles from me with 5 Watts and its antenna is on a 300 ft tower. My antenna (half wave end-fed dipole) is on a 20 ft mast. There may well be something wrong with the antenna. I don't have an SWR meter handy but will try and borrow one from a club member. The J-pole was beat around quite a bit over the years but since the radio has a limiting circuit if the SWR is too far out of whack I am assuming it is fairly close. It will transmit of full power. One of the things to know about the American Legion J-pole (and most vaguely-similar J-poles) is that it has no feedline or mount-point isolation to speak of. The outside of the feedline coax, and any pipe or tower or other metal to which you strap the antenna, become part of the antenna's ground system, and can radiate a significant amount of RF. This can interact with the RF coming from the main radiator, and significantly alter the antenna's pattern... it no longer behaves like an idealized half-wave vertical radiator. In most installations this doesn't seem to matter all that much... but it's possible that you've got some sort of weird interaction (feedline emissions, reflections from the ground or nearby metal, etc.) which is creating a null in the antenna's pattern in just the wrong direction. If this is an issue (not all that likely but perhaps possible) you could insulate the antenna from the mounting mask, and install a choke (e.g. a few ferrite cores) on the feedline just below the antenna. It is mounted on an angle bracket about 12" from a mast 20' above my metal roof. The mast is isolated from roof but is not yet grounded. Also, the American Legion J-poles are subject to a couple of forms of mechanical/electrical failure after a few years. The plastic insulator which spaces apart the radiator and matching arm can degrade (UV from sunlight is the main offendor, I believe) and crack, allowing the two arms to change spacing. More subtly, the connection between the two arms and the metal base can degrade... it's aluminum-to- aluminum using a set-screw, and the connection can loosen and corrode.. My spacer basically disintegrated. I replaced it with 1/2" pvc pipe. I measured the spacing at the base and got it as close as possible. I will check out the other connections. There is obvious aluminum oxide on the assembly so it is very possible it is down between the parts. I'll get up on my steep metal roof after the rains stop. :-) It might be worth checking the spacer (replace if necessary), and checking and tuning up the set-screw connections (squirt with Liquid Wrench if necessary, loosen and remove, take out the rods, clean the ends of the rods and the mounting holes in the place, dab with NoAlOx or a similar corrosion-blocker, reassemble and tighten). I'm using 75' of professionally assembled RG8X which is required to get from the radio to the antenna. That's probably costing you about half of your power (assuming a typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are better than this. Thanks for the suggestions. Hey, Kirk - After reading Wim's response, I am more convinced than ever that you have a problem with your antenna, coax, or transceiver. What type of coax are you using? Could it have gotten water inside? Are you using the coax that you used 10 years ago? Try to think of other question similar to these and we'll get to the bottom of this. Cheers, John Hello Kirk, John, I believe it is either the trees or the antenna. *The coax is new and the transceiver worked fine last time I used it. *Also works fine with this setup getting into the repeater on Schweitzer , 145.230, with 5 watts and the signal report from a gentleman I spoke to was 59. *That is a clear shot and a few miles closer. *Although the profiles show there should be a clear shot to the .780 repeater I can gurantee there is a wall of trees on the first little ridge on the profile. Are you pointing to the trees that are about 160m south of you and below (that are also visible in google earth)? If so, I can't believe that this will put down your signal from about -76 dBm towards unreadable (so in the -117 dBm range). Reason: the first Fresnel zone has a diameter of 36m (118ft) at 160m (525ft) from your antenna and I don't expect all trees are over (for example) 20m (60ft) height. *I found that my club, which I've only been with for a month, has an SWR meter and an antenna analyzer. *I hope to borrow them to see what's up. *In the meantime I will pull the J-pole down and clean it up as suggested. There is considerable aluminum oxide on the outside of the parts so there may be some between the base and uprights. *When I put it back up I will move it 180 degrees from it current location. *That will only move it about 2' but who knows. -- 'Captain' Kirk DeHaan N6SXR "Beam me up Scotty, there's no intelligent life here" Wim PA3DJS www.tetech.nl |
NVIS and VHF?
"'Captain' Kirk DeHaan" wrote in message news:pZCdnVd2h- I believe it is either the trees or the antenna. The coax is new and the transceiver worked fine last time I used it. Also works fine with this setup getting into the repeater on Schweitzer , 145.230, with 5 watts and the signal report from a gentleman I spoke to was 59. That is a clear shot and a few miles closer. Although the profiles show there should be a clear shot to the .780 repeater I can gurantee there is a wall of trees on the first little ridge on the profile. I found that my club, which I've only been with for a month, has an SWR meter and an antenna analyzer. I hope to borrow them to see what's up. In the meantime I will pull the J-pole down and clean it up as suggested. There is considerable aluminum oxide on the outside of the parts so there may be some between the base and uprights. When I put it back up I will move it 180 degrees from it current location. That will only move it about 2' but who knows. I may have missed it, but have you tried riding around with a mobile rig and seeing if you can hit the repeater ? A SWR meter may not tell you much about the antenna. I think you are using rg-8x. The coax will have enough loss at 2 meters to give a very low false reading. YOu can probably unhook the coax from the antenna and only show about a 3:1 swr. |
NVIS and VHF?
On 5/26/2011 11:53 AM, JIMMIE wrote:
On May 22, 2:04 pm, 'Captain' Kirk wrote: I'm living in a wooded area and am trying to hit our club repeater reliably. It's cloudy now so I'm and getting a bit of ducting but I have a lot of trees, mostly poplars, in the direct path. I would have a line of sight if not for the trees as I'm up enough in altitude. I can cut the trees, they're mine, but finding the right ones is difficult and i don't want to waste the whole grove. I go from keying the repeater with no intelligible signal to not being able to hit it. Today I actually have an S meter reading due to the clouds. I am currently using a J-pole and will put up a Yagi soon but wonder if NVIS would work on 2m? I have only seen references to it being applied in HF. 'Captain' Kirk DeHaan N6SXR Im convinced that my J antenna that I used while camping radiated mostly verticaly. The situation sounds very similar to yours. I couldnt hit the repeater back home with 50 watts using the J- while my wife could make contacts on her HT on the same repeater, Her antenna was either a telescoping .5 wl or 5/8 wl connected directly to her HT. Jimmie The antenna itself could not have radiated a significant percentage vertically if used near the design frequency. It is effectively a half wave vertical if properly constructed and fed. Fed being the most critical. If you didn't choke the coax properly and it was parallel to the ground you may have radiated some towards the zenith. But I doubt it was most. tom K0TAR |
NVIS and VHF?
On 27 mayo, 21:30, 'Captain' Kirk DeHaan
wrote: John KD5YI said the following on 5/26/2011 8:56 PM: On 5/24/2011 11:05 PM, 'Captain' Kirk DeHaan wrote: Dave Platt said the following on 5/24/2011 2:54 PM: In , 'Captain' Kirk wrote: All of this leads me to think that something else is wrong. I can hit a repeater 20 miles from me with 5 Watts and its antenna is on a 300 ft tower. My antenna (half wave end-fed dipole) is on a 20 ft mast. There may well be something wrong with the antenna. I don't have an SWR meter handy but will try and borrow one from a club member. The J-pole was beat around quite a bit over the years but since the radio has a limiting circuit if the SWR is too far out of whack I am assuming it is fairly close. It will transmit of full power. One of the things to know about the American Legion J-pole (and most vaguely-similar J-poles) is that it has no feedline or mount-point isolation to speak of. The outside of the feedline coax, and any pipe or tower or other metal to which you strap the antenna, become part of the antenna's ground system, and can radiate a significant amount of RF. This can interact with the RF coming from the main radiator, and significantly alter the antenna's pattern... it no longer behaves like an idealized half-wave vertical radiator. In most installations this doesn't seem to matter all that much... but it's possible that you've got some sort of weird interaction (feedline emissions, reflections from the ground or nearby metal, etc.) which is creating a null in the antenna's pattern in just the wrong direction. If this is an issue (not all that likely but perhaps possible) you could insulate the antenna from the mounting mask, and install a choke (e.g. a few ferrite cores) on the feedline just below the antenna. It is mounted on an angle bracket about 12" from a mast 20' above my metal roof. The mast is isolated from roof but is not yet grounded. Also, the American Legion J-poles are subject to a couple of forms of mechanical/electrical failure after a few years. The plastic insulator which spaces apart the radiator and matching arm can degrade (UV from sunlight is the main offendor, I believe) and crack, allowing the two arms to change spacing. More subtly, the connection between the two arms and the metal base can degrade... it's aluminum-to- aluminum using a set-screw, and the connection can loosen and corrode.. My spacer basically disintegrated. I replaced it with 1/2" pvc pipe. I measured the spacing at the base and got it as close as possible. I will check out the other connections. There is obvious aluminum oxide on the assembly so it is very possible it is down between the parts. I'll get up on my steep metal roof after the rains stop. :-) It might be worth checking the spacer (replace if necessary), and checking and tuning up the set-screw connections (squirt with Liquid Wrench if necessary, loosen and remove, take out the rods, clean the ends of the rods and the mounting holes in the place, dab with NoAlOx or a similar corrosion-blocker, reassemble and tighten). I'm using 75' of professionally assembled RG8X which is required to get from the radio to the antenna. That's probably costing you about half of your power (assuming a typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are better than this. Thanks for the suggestions. Hey, Kirk - After reading Wim's response, I am more convinced than ever that you have a problem with your antenna, coax, or transceiver. What type of coax are you using? Could it have gotten water inside? Are you using the coax that you used 10 years ago? Try to think of other question similar to these and we'll get to the bottom of this. Cheers, John John, I believe it is either the trees or the antenna. *The coax is new and the transceiver worked fine last time I used it. *Also works fine with this setup getting into the repeater on Schweitzer , 145.230, with 5 watts and the signal report from a gentleman I spoke to was 59. *That is a clear shot and a few miles closer. *Although the profiles show there should be a clear shot to the .780 repeater I can gurantee there is a wall of trees on the first little ridge on the profile. *I found that my club, which I've only been with for a month, has an SWR meter and an antenna analyzer. *I hope to borrow them to see what's up. *In the meantime I will pull the J-pole down and clean it up as suggested. There is considerable aluminum oxide on the outside of the parts so there may be some between the base and uprights. *When I put it back up I will move it 180 degrees from it current location. *That will only move it about 2' but who knows. -- 'Captain' Kirk DeHaan N6SXR "Beam me up Scotty, there's no intelligent life here" Hello Kirk, Did you receive my PM with the path profile and propagation prediction from RMW? I now added clutter because of trees (I used 30m high trees with 80% density). The predicted signal strength goes down from -76 dBm to -81 dBm (10W transmitters into 2 dBi antennes, your height 10m, repeater heigth 30m). Jeff (AE6KS) sent me a .kml file with the path profile from you to the repeater on the hill, there is good agreement between the data I used in RMW. So before going to the paper/plywood production plant, you may search for some other problem. With kind regards, Wim PA3DJS www.tetech.nl |
NVIS and VHF? (Update)
'Captain' Kirk DeHaan said the following on 5/22/2011 11:04 AM:
I'm living in a wooded area and am trying to hit our club repeater reliably. It's cloudy now so I'm and getting a bit of ducting but I have a lot of trees, mostly poplars, in the direct path. I would have a line of sight if not for the trees as I'm up enough in altitude. I can cut the trees, they're mine, but finding the right ones is difficult and i don't want to waste the whole grove. I go from keying the repeater with no intelligible signal to not being able to hit it. Today I actually have an S meter reading due to the clouds. I am currently using a J-pole and will put up a Yagi soon but wonder if NVIS would work on 2m? I have only seen references to it being applied in HF. 'Captain' Kirk DeHaan N6SXR I am still working on finding where the problem is. I pulled the J-pole down and checked the resistance of the separate connections. I didn't want to pull it apart if not necessary. Everything showed 0.0 to 0.1 ohms. Seems fine to me. I then cleaned the connector as throughly as possible using emory cloth inside and dremeled the outside with a fine wire brush. There was a small amount of oxidation and it appeared much cleaner and brighter after. I also straightened the two elements but they were not really that bent. You had to look down the long axis to see any deviation. They are as straight as they are going to get but I can't believe that would make much difference. After all this I put it back up to it's original height. There was not discernible change. I was almost unreadable at the repeater. Next I pushed up my mast a few feet more. It is a 50' pushup that normally requires guy wires. I am not using any so I am leaving considerable overlap of the sections. I would estimate it is up around 32'. Even in high winds here I saw little deflection with just the J-pole. The 3 or 4 feet I pushed it up gave me a little bit of improvement. When I win the lottery I'll get a 100' tower put up. Guess I'm stuck with this then :-) I still think it is the trees and have taken a picture from the roof peak towards the repeater so you can see what I am dealing with. http://www.ncc-1701a.net/Ham Radio/ForestObstruction.jpg It is deceiving as there are many more trees behind this line on my neighbors property. I wouldn't even think of asking him to cut any. They are money in the bank for him. -- 'Captain' Kirk DeHaan N6SXR "Beam me up Scotty, there's no intelligent life here" |
NVIS and VHF? (Update)
On 6/1/2011 4:48 PM, 'Captain' Kirk DeHaan wrote:
'Captain' Kirk DeHaan said the following on 5/22/2011 11:04 AM: I'm living in a wooded area and am trying to hit our club repeater reliably. It's cloudy now so I'm and getting a bit of ducting but I have a lot of trees, mostly poplars, in the direct path. I would have a line of sight if not for the trees as I'm up enough in altitude. I can cut the trees, they're mine, but finding the right ones is difficult and i don't want to waste the whole grove. I go from keying the repeater with no intelligible signal to not being able to hit it. Today I actually have an S meter reading due to the clouds. I am currently using a J-pole and will put up a Yagi soon but wonder if NVIS would work on 2m? I have only seen references to it being applied in HF. 'Captain' Kirk DeHaan N6SXR I am still working on finding where the problem is. I pulled the J-pole down and checked the resistance of the separate connections. I didn't want to pull it apart if not necessary. Everything showed 0.0 to 0.1 ohms. Seems fine to me. I then cleaned the connector as throughly as possible using emory cloth inside and dremeled the outside with a fine wire brush. There was a small amount of oxidation and it appeared much cleaner and brighter after. I also straightened the two elements but they were not really that bent. You had to look down the long axis to see any deviation. They are as straight as they are going to get but I can't believe that would make much difference. After all this I put it back up to it's original height. There was not discernible change. I was almost unreadable at the repeater. Next I pushed up my mast a few feet more. It is a 50' pushup that normally requires guy wires. I am not using any so I am leaving considerable overlap of the sections. I would estimate it is up around 32'. Even in high winds here I saw little deflection with just the J-pole. The 3 or 4 feet I pushed it up gave me a little bit of improvement. When I win the lottery I'll get a 100' tower put up. Guess I'm stuck with this then :-) I still think it is the trees and have taken a picture from the roof peak towards the repeater so you can see what I am dealing with. http://www.ncc-1701a.net/Ham Radio/ForestObstruction.jpg It is deceiving as there are many more trees behind this line on my neighbors property. I wouldn't even think of asking him to cut any. They are money in the bank for him. Hi, Kirk - It looks more formidable than I had imagined. I am sure the picture will generate some comments. Nobody can say you aren't making maximum effort, for sure. When will be that club meeting? 73, John - KD5YI |
NVIS and VHF? (Update)
On 6/1/2011 4:48 PM, 'Captain' Kirk DeHaan wrote:
I am still working on finding where the problem is. I pulled the J-pole down and checked the resistance of the separate connections. I didn't want to pull it apart if not necessary. Everything showed 0.0 to 0.1 ohms. Seems fine to me. I then cleaned the connector as throughly as possible using emory cloth inside and dremeled the outside with a fine wire brush. There was a small amount of oxidation and it appeared much cleaner and brighter after. I also straightened the two elements but they were not really that bent. You had to look down the long axis to see any deviation. They are as straight as they are going to get but I can't believe that would make much difference. After all this I put it back up to it's original height. There was not discernible change. I was almost unreadable at the repeater. Next I pushed up my mast a few feet more. It is a 50' pushup that normally requires guy wires. I am not using any so I am leaving considerable overlap of the sections. I would estimate it is up around 32'. Even in high winds here I saw little deflection with just the J-pole. The 3 or 4 feet I pushed it up gave me a little bit of improvement. When I win the lottery I'll get a 100' tower put up. Guess I'm stuck with this then :-) I still think it is the trees and have taken a picture from the roof peak towards the repeater so you can see what I am dealing with. http://www.ncc-1701a.net/Ham Radio/ForestObstruction.jpg It is deceiving as there are many more trees behind this line on my neighbors property. I wouldn't even think of asking him to cut any. They are money in the bank for him. Kirk - Do you have parts on hand such as extra coax, connectors, wire, etc? Although you have done a thorough job of examining your installation, it behoove you to make a test separate from your present antenna installation. For example, you could simply strip 1/4WL from the end of a coax feeder and put that end on the roof temporarily. I know, not the best match, common mode currents down the line, signal launches upward, etc. But, it is simple and might tell you something. Maybe a quick, thrown-together ground plane? Just a thought. 73, John |
NVIS and VHF? (Update)
On Jun 1, 2:48*pm, 'Captain' Kirk DeHaan
wrote: 'Captain' Kirk DeHaan said the following on 5/22/2011 11:04 AM: I'm living in a wooded area and am trying to hit our club repeater reliably. It's cloudy now so I'm and getting a bit of ducting but I have a lot of trees, mostly poplars, in the direct path. I would have a line of sight if not for the trees as I'm up enough in altitude. I can cut the trees, they're mine, but finding the right ones is difficult and i don't want to waste the whole grove. I go from keying the repeater with no intelligible signal to not being able to hit it. Today I actually have an S meter reading due to the clouds. I am currently using a J-pole and will put up a Yagi soon but wonder if NVIS would work on 2m? I have only seen references to it being applied in HF. 'Captain' Kirk DeHaan N6SXR I am still working on finding where the problem is. *I pulled the J-pole down and checked the resistance of the separate connections. *I didn't want to pull it apart if not necessary. *Everything showed 0.0 to 0.1 ohms. *Seems fine to me. *I then cleaned the connector as throughly as possible using emory cloth inside and dremeled the outside with a fine wire brush. *There was a small amount of oxidation and it appeared much cleaner and brighter after. *I also straightened the two elements but they were not really that bent. *You had to look down the long axis to see any deviation. *They are as straight as they are going to get but I can't believe that would make much difference. I don't think anybody asked you: How much power are you putting out? How well do you hear the repeater; are there times when it fades below squelch while you're listening to other people? (No, I don't have a 2m PA that I'm trying to unload.) Sal |
NVIS and VHF? (Update)
Sal M. Onella said the following on 6/1/2011 10:37 PM:
On Jun 1, 2:48 pm, 'Captain' Kirk wrote: 'Captain' Kirk DeHaan said the following on 5/22/2011 11:04 AM: I'm living in a wooded area and am trying to hit our club repeater reliably. It's cloudy now so I'm and getting a bit of ducting but I have a lot of trees, mostly poplars, in the direct path. I would have a line of sight if not for the trees as I'm up enough in altitude. I can cut the trees, they're mine, but finding the right ones is difficult and i don't want to waste the whole grove. I go from keying the repeater with no intelligible signal to not being able to hit it. Today I actually have an S meter reading due to the clouds. I am currently using a J-pole and will put up a Yagi soon but wonder if NVIS would work on 2m? I have only seen references to it being applied in HF. 'Captain' Kirk DeHaan N6SXR I am still working on finding where the problem is. I pulled the J-pole down and checked the resistance of the separate connections. I didn't want to pull it apart if not necessary. Everything showed 0.0 to 0.1 ohms. Seems fine to me. I then cleaned the connector as throughly as possible using emory cloth inside and dremeled the outside with a fine wire brush. There was a small amount of oxidation and it appeared much cleaner and brighter after. I also straightened the two elements but they were not really that bent. You had to look down the long axis to see any deviation. They are as straight as they are going to get but I can't believe that would make much difference. I don't think anybody asked you: How much power are you putting out? How well do you hear the repeater; are there times when it fades below squelch while you're listening to other people? (No, I don't have a 2m PA that I'm trying to unload.) Sal Sal, My TM-721A is putting out 35 watts. At least that is the spec. The repeater is always scratchy and barely readable. I've only had one time when it even showed up on the S meter. That was low clouds so I assume it was cloud bounce. -- 'Captain' Kirk DeHaan N6SXR "Beam me up Scotty, there's no intelligent life here" |
NVIS and VHF?
On 27 mayo, 21:30, 'Captain' Kirk DeHaan
wrote: John KD5YI said the following on 5/26/2011 8:56 PM: On 5/24/2011 11:05 PM, 'Captain' Kirk DeHaan wrote: Dave Platt said the following on 5/24/2011 2:54 PM: In , 'Captain' Kirk wrote: All of this leads me to think that something else is wrong. I can hit a repeater 20 miles from me with 5 Watts and its antenna is on a 300 ft tower. My antenna (half wave end-fed dipole) is on a 20 ft mast. There may well be something wrong with the antenna. I don't have an SWR meter handy but will try and borrow one from a club member. The J-pole was beat around quite a bit over the years but since the radio has a limiting circuit if the SWR is too far out of whack I am assuming it is fairly close. It will transmit of full power. One of the things to know about the American Legion J-pole (and most vaguely-similar J-poles) is that it has no feedline or mount-point isolation to speak of. The outside of the feedline coax, and any pipe or tower or other metal to which you strap the antenna, become part of the antenna's ground system, and can radiate a significant amount of RF. This can interact with the RF coming from the main radiator, and significantly alter the antenna's pattern... it no longer behaves like an idealized half-wave vertical radiator. In most installations this doesn't seem to matter all that much... but it's possible that you've got some sort of weird interaction (feedline emissions, reflections from the ground or nearby metal, etc.) which is creating a null in the antenna's pattern in just the wrong direction. If this is an issue (not all that likely but perhaps possible) you could insulate the antenna from the mounting mask, and install a choke (e.g. a few ferrite cores) on the feedline just below the antenna. It is mounted on an angle bracket about 12" from a mast 20' above my metal roof. The mast is isolated from roof but is not yet grounded. Also, the American Legion J-poles are subject to a couple of forms of mechanical/electrical failure after a few years. The plastic insulator which spaces apart the radiator and matching arm can degrade (UV from sunlight is the main offendor, I believe) and crack, allowing the two arms to change spacing. More subtly, the connection between the two arms and the metal base can degrade... it's aluminum-to- aluminum using a set-screw, and the connection can loosen and corrode.. My spacer basically disintegrated. I replaced it with 1/2" pvc pipe. I measured the spacing at the base and got it as close as possible. I will check out the other connections. There is obvious aluminum oxide on the assembly so it is very possible it is down between the parts. I'll get up on my steep metal roof after the rains stop. :-) It might be worth checking the spacer (replace if necessary), and checking and tuning up the set-screw connections (squirt with Liquid Wrench if necessary, loosen and remove, take out the rods, clean the ends of the rods and the mounting holes in the place, dab with NoAlOx or a similar corrosion-blocker, reassemble and tighten). I'm using 75' of professionally assembled RG8X which is required to get from the radio to the antenna. That's probably costing you about half of your power (assuming a typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are better than this. Thanks for the suggestions. Hey, Kirk - After reading Wim's response, I am more convinced than ever that you have a problem with your antenna, coax, or transceiver. What type of coax are you using? Could it have gotten water inside? Are you using the coax that you used 10 years ago? Try to think of other question similar to these and we'll get to the bottom of this. Cheers, John John, I believe it is either the trees or the antenna. *The coax is new and the transceiver worked fine last time I used it. *Also works fine with this setup getting into the repeater on Schweitzer , 145.230, with 5 watts and the signal report from a gentleman I spoke to was 59. *That is a clear shot and a few miles closer. *Although the profiles show there should be a clear shot to the .780 repeater I can gurantee there is a wall of trees on the first little ridge on the profile. *I found that my club, which I've only been with for a month, has an SWR meter and an antenna analyzer. *I hope to borrow them to see what's up. *In the meantime I will pull the J-pole down and clean it up as suggested. There is considerable aluminum oxide on the outside of the parts so there may be some between the base and uprights. *When I put it back up I will move it 180 degrees from it current location. *That will only move it about 2' but who knows. -- 'Captain' Kirk DeHaan N6SXR "Beam me up Scotty, there's no intelligent life here" Hello Kirk, If you have access to both ends of the cable and have access to some VSWR measurement equipment, you may measure following things (and post them overhere): VSWR of cable when terminated with a dummy load VSWR of cable when open VSWR of cable when short-circuited VSWR of cable with J-pole antenna Now reduce the output power of your transceiver to avoid damage VSWR when nothing connected to the output of the VSWR meter VSWR when output of VSWR meter is shorted. Make sure to check the reference (forward) reading after every change in load, as this may change due to varying load as seen by the transceiver. You may also do these measurements with the antenna analyser (preferably both antenna analyser and VSWR meter). Regarding the trees, it looks dense. Sadly to mention, if it are the trees, you have to live with this as tree attenuation at 2m is relatively low and first fresnel zone is relatively large at 160m. You need to remove lots of them to get remarkable improvement and you mentioned that you couldn't remove lots of them because of financial reasons. With kind regards, Wim PA3DJS www.tetech.nl Don't forget to instruct your racing pigeon to remove abc before letting him cross the Ocean. |
NVIS and VHF? (Update)
On Jun 2, 8:23*am, 'Captain' Kirk DeHaan
wrote: Sal M. Onella said the following on 6/1/2011 10:37 PM: snip How much power are you putting out? How well do you hear the repeater; are there times when it fades below squelch while you're listening to other people? My TM-721A is putting out 35 watts. *At least that is the spec. *The repeater is always scratchy and barely readable. *I've only had one time when it even showed up on the S meter. *That was low clouds so I assume it was cloud bounce. -- 'Captain' Kirk DeHaan You indicated that you're working other repeaters with ease. Blaming the trees sounds right. I think a 2m beam is the way to go. I've used one at Field Day for ten or so years from south of San Diego and easily worked 100 miles into Los Angeles, simplex, obviously. The improvement in performance is dramatic with 15 dBi gain, compared to approx 2 dBi gain of an end- fed dipole, your j-pole. My two beams were less than 50 dollars apiece at ham swap meets. Mount with elements vertical. I just did an experiment and, as I expected, a 10 dB increase in signal strength took me from unreadable to Q5 copy with tolerable background hiss. (I used switchable attenuators to set up the signal test conditions and a distant repeater as the test signal.) If the repeater is no worse than "barely readable," 10 dB should fix you up. By the way, the gain effect is not so great that you'd lose the other repeaters, unless one just happened to hit a deep null by bad luck. "Sal" |
NVIS and VHF?
On 5/23/2011 5:53 PM, 'Captain' Kirk DeHaan wrote:
This is the repeater I am trying to access, 146.780, K7JEP. I have been playing with Google Earth and getting coordinates so I can go over to my neighbors property and stand on the ridge between our properties and see if I can see the repeater and my house. Hopefully that will help me locate the suspect trees. Suspend a heavy object from a rope over level ground. If I have plugged in the correct numbers, the repeater will be on a line drawn by the shadow of the rope at 12:55. That is, the repeater will be directly below the sun at that time. Maybe you can get an idea of the path to the repeater that way. 73, John |
NVIS and VHF?
On 5/24/2011 8:47 AM, Wimpie wrote:
On 24 mayo, 05:06, John wrote: On 5/23/2011 5:10 PM, Wimpie wrote: On 22 mayo, 20:04, 'Captain' Kirk wrote: I'm living in a wooded area and am trying to hit our club repeater reliably. It's cloudy now so I'm and getting a bit of ducting but I have a lot of trees, mostly poplars, in the direct path. I would have a line of sight if not for the trees as I'm up enough in altitude. I can cut the trees, they're mine, but finding the right ones is difficult and i don't want to waste the whole grove. I go from keying the repeater with no intelligible signal to not being able to hit it. Today I actually have an S meter reading due to the clouds. I am currently using a J-pole and will put up a Yagi soon but wonder if NVIS would work on 2m? I have only seen references to it being applied in HF. 'Captain' Kirk DeHaan N6SXR Hello, As you can see from the replies, we are in the speculation phase. If you would like to receive more specialized feedback, you should provide us with more details about the path, antenna height, nearby obstacles, vegetation in between, etc (maybe some pictures). As we are discussing 2 m wavelength, obstacles that may be optically in the path may introduce less attenuation then expected, but obstacles that are outside the optical path can still introduce attenuation. At 10m (33ft) from your antenna, the first Fresnel zone is about 9m (30 ft) wide. In addition, the tree attenuation at these frequencies is not that high. I think of 0.15 dB/m (I hope somebody can confirm this). It can be less due to diffraction (bending) of the waves around and over the trees. I am almost sure, removing some poplar treetops at 10m from your antenna or more will not change the situation from marginal to good (because of the relative low attenuation). Just to be curious, what type of poplar do you have at your site. With kind regards, Wim PA3DJS www.tetech.nl According to his lat/lon numbers, he is 19 miles from the repeater and its bearing is 185 degrees (ref true north) from him. The repeater is about 2000 feet above him (not including the tower height). He is in a valley that has little altitude variation until his signal reaches the mountain. This info is available from Google Earth using his numbers. All of this leads me to think that something else is wrong. I can hit a repeater 20 miles from me with 5 Watts and its antenna is on a 300 ft tower. My antenna (half wave end-fed dipole) is on a 20 ft mast. I have tons of deciduous trees between me and the repeater but the signal is always solid with no noise on it (I don't have an S-meter) and I have never had a report of noise on my signal until I tried to carry on a conversation with 200 mw output power. Cheers, John Hello John, With Google maps, results (distance and bearing) are similar (based on the data given by Kirk). If the trees south of his antenna are the problem (I am not convinced), he needs to cut lots of them. They are about 150m from his antenna, and at that distance first Fresnel zone width is about 30m (100ft). It seems flat when looking to the activities in the valley. I hope somebody can make a path profile and loss simulation to see what is the real obstacle. With kind regards, Wim PA3DJS Well, I have applied some numbers today and I am changing my mind that the trees are not the problem. If my numbers are correct: The repeater, 19 miles away, is 1900 feet above his elevation. At that distance, the antenna will appear be about 240 feet lower than actual due to earth curvature. That makes the antenna appear to be about 0.954 degrees above the horizon. That is equivalent to 60 feet at 3600 feet. In other words, 60 foot trees closer in will be completely in the way. The hurtful part of this is that his antenna at 45 feet will have a lowest angle of radiation (take-off angle) of .7 degrees, right into the near trees. The next lobe above that is at 2.2 degrees. Between those two lobes is a null. In short, I think his antenna is in a null. I think the only answer for his present situation is to raise the antenna another 10 feet. What do you think? 73, John |
NVIS and VHF?
On Sat, 04 Jun 2011 12:26:33 -0500, John S
wrote: On 5/23/2011 5:53 PM, 'Captain' Kirk DeHaan wrote: This is the repeater I am trying to access, 146.780, K7JEP. I have been playing with Google Earth and getting coordinates so I can go over to my neighbors property and stand on the ridge between our properties and see if I can see the repeater and my house. Hopefully that will help me locate the suspect trees. Suspend a heavy object from a rope over level ground. If I have plugged in the correct numbers, the repeater will be on a line drawn by the shadow of the rope at 12:55. That is, the repeater will be directly below the sun at that time. Maybe you can get an idea of the path to the repeater that way. 73, John Clever trick, but methinks I have an easier way. I've sighted 1 degree beamwidth microwave dishes this way: 1. Place a road map on a flat surface[1]. If you can't find a road map, print a Google Maps or equivalent road map on a piece of paper[2]. 2. Pound a nail or push pin into the map at your location. 3. Find a distant mountain, that's also visible. Pound a nail into the map at its location and sight between the two nails to the distant mountain. 4. Without moving the map, find the distant repeater location on the map and pound in a 3rd nail or push pin. 5. Sight from the nail at your location, to the nail at the repeater location. What you see is where it's located. [1] Yes, the earth really is flat. [2] When I didn't have a printed map handy, I've used my laptop LCD screen and 3ea flat head screws. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
NVIS and VHF?
On 6/4/2011 5:31 PM, Jeff Liebermann wrote:
On Sat, 04 Jun 2011 12:26:33 -0500, John wrote: On 5/23/2011 5:53 PM, 'Captain' Kirk DeHaan wrote: This is the repeater I am trying to access, 146.780, K7JEP. I have been playing with Google Earth and getting coordinates so I can go over to my neighbors property and stand on the ridge between our properties and see if I can see the repeater and my house. Hopefully that will help me locate the suspect trees. Suspend a heavy object from a rope over level ground. If I have plugged in the correct numbers, the repeater will be on a line drawn by the shadow of the rope at 12:55. That is, the repeater will be directly below the sun at that time. Maybe you can get an idea of the path to the repeater that way. 73, John Clever trick, but methinks I have an easier way. I've sighted 1 degree beamwidth microwave dishes this way: Easier than what I suggested? Actually, all he has to do is step outside at 12:54 and look at the Sun's location. (I admit it is more accurate to do this in the winter.) 1. Place a road map on a flat surface[1]. If you can't find a road map, print a Google Maps or equivalent road map on a piece of paper[2]. 2. Pound a nail or push pin into the map at your location. 3. Find a distant mountain, that's also visible. Pound a nail into the map at its location and sight between the two nails to the distant mountain. 4. Without moving the map, find the distant repeater location on the map and pound in a 3rd nail or push pin. 5. Sight from the nail at your location, to the nail at the repeater location. What you see is where it's located. [1] Yes, the earth really is flat. [2] When I didn't have a printed map handy, I've used my laptop LCD screen and 3ea flat head screws. I am afraid I cannot tell whether items [1] and [2] are just screwing with me or that you are sincere. John |
NVIS and VHF?
On 6/4/2011 5:39 PM, John S wrote:
On 6/4/2011 5:31 PM, Jeff Liebermann wrote: By the way, Jeff, you have a great deal to offer the group by way of your vast experience. If I have been disrespectful of that, then I apologize. 73, John |
NVIS and VHF?
On 4 jun, 23:26, John S wrote:
On 5/24/2011 8:47 AM, Wimpie wrote: On 24 mayo, 05:06, John *wrote: On 5/23/2011 5:10 PM, Wimpie wrote: On 22 mayo, 20:04, 'Captain' Kirk wrote: I'm living in a wooded area and am trying to hit our club repeater reliably. *It's cloudy now so I'm and getting a bit of ducting but I have a lot of trees, mostly poplars, in the direct path. *I would have a line of sight if not for the trees as I'm up enough in altitude. *I can cut the trees, they're mine, but finding the right ones is difficult and i don't want to waste the whole grove. I go from keying the repeater with no intelligible signal to not being able to hit it. *Today I actually have an S meter reading due to the clouds. I am currently using a J-pole and will put up a Yagi soon but wonder if NVIS would work on 2m? *I have only seen references to it being applied in HF. 'Captain' Kirk DeHaan N6SXR Hello, As you can see from the replies, we are in the speculation phase. If you would like to receive more specialized feedback, you should provide us with more details about the path, antenna height, nearby obstacles, vegetation in between, etc (maybe some pictures). As we are discussing 2 m wavelength, obstacles that may be optically in the path may introduce less attenuation then expected, but obstacles that are outside the optical path can still introduce attenuation. At 10m (33ft) from your antenna, the first Fresnel zone is about 9m (30 ft) wide. In addition, the tree attenuation at these frequencies is not that high. I think of 0.15 dB/m (I hope somebody can confirm this). It can be less due to diffraction (bending) of the waves around and over the trees. I am almost sure, removing some poplar treetops at 10m from your antenna or more will not change the situation from marginal to good (because of the relative low attenuation). Just to be curious, what type of poplar do you have at your site. With kind regards, Wim PA3DJS www.tetech.nl According to his lat/lon numbers, he is 19 miles from the repeater and its bearing is 185 degrees (ref true north) from him. *The repeater is about 2000 feet above him (not including the tower height). *He is in a valley that has little altitude variation until his signal reaches the mountain. This info is available from Google Earth using his numbers. All of this leads me to think that something else is wrong. *I can hit a repeater 20 miles from me with 5 Watts and its antenna is on a 300 ft tower. My antenna (half wave end-fed dipole) is on a 20 ft mast. I have tons of deciduous trees between me and the repeater but the signal is always solid with no noise on it (I don't have an S-meter) and I have never had a report of noise on my signal until I tried to carry on a conversation with 200 mw output power. Cheers, John Hello John, With Google maps, results (distance and bearing) are similar (based on the data given by Kirk). If the trees south of his antenna are the problem (I am not convinced), he needs to cut lots of them. *They are about 150m from his antenna, and at that distance first Fresnel zone width is about 30m (100ft). It seems flat when looking to the activities in the valley. I hope somebody can make a path profile and loss simulation to see what is the real obstacle. With kind regards, Wim PA3DJS Well, I have applied some numbers today and I am changing my mind that the trees are not the problem. If my numbers are correct: The repeater, 19 miles away, is 1900 feet above his elevation. At that distance, the antenna will appear be about 240 feet lower than actual due to earth curvature. That makes the antenna appear to be about 0.954 degrees above the horizon. That is equivalent to 60 feet at 3600 feet. In other words, 60 foot trees closer in will be completely in the way. The hurtful part of this is that his antenna at 45 feet will have a lowest angle of radiation (take-off angle) of .7 degrees, right into the near trees. The next lobe above that is at 2.2 degrees. Between those two lobes is a null. In short, I think his antenna is in a null. I think the only answer for his present situation is to raise the antenna another 10 feet. What do you think? 73, John Hello John, This link: http://www.tetech.nl/divers/Kirk_Repeater_USA_1.png shows the path profiles with and without trees (from Radio Mobile, VE2DBE). I will keep it there for some weeks. I used 30m (98ft) high trees (so they are easy to see). The trees cover some additional part of the first fresnel zone, but the average canopy will be lower and the absorption loss is not that high at 146 MHz. So yes, there is influence from the trees, but not that much I think. If you want to get some increase in signal, you need to remove lots of them, and he don't want to do that. Note that the first trees are 160m away from his antenna (info from google earth, based on data provided by Kirk). With kind regards, Wim PA3DJS www.tetech.nl |
NVIS and VHF?
On Sat, 04 Jun 2011 17:39:03 -0500, John S
wrote: Easier than what I suggested? Actually, all he has to do is step outside at 12:54 and look at the Sun's location. (I admit it is more accurate to do this in the winter.) Well, your method only works at exactly 12:54PM, requires remembering daylight savings time, requires dark glasses to avoid blindness, works badly in fog, need to get it right the first time, and offers no way to document the results. At 12:54PM, the sun is almost directly over head with no point of reference, as you would have at the horizon. Manually translating the sun's overhead direction, to azimuth at the horizon, requires considerable guesswork. A plumb line might helpful. Incidentally, trees are a very real problem with antenna sighting: http://802.11junk.com/jeffl/pics/DBS/index.html That's my view of the DirecTV bird at 101 degrees. The photos were taken during the bi-annual solar outage, where the sun gets behind the satellite belt. http://en.wikipedia.org/wiki/Solar_outage Note the branch shadows on the dish, which are blocking the signal. [1] Yes, the earth really is flat. [2] When I didn't have a printed map handy, I've used my laptop LCD screen and 3ea flat head screws. I am afraid I cannot tell whether items [1] and [2] are just screwing with me or that you are sincere. As far as this measurement is concerned, the earth is essentially flat over fairly small areas. No spherical geometry required. Even the United Nations has adopted the flat earth map for its flag. http://upload.wikimedia.org/wikipedia/commons/2/2f/Flag_of_the_United_Nations.svg Antarctica is a collection of icicles around the outer edge. The 2nd item is for real. I was on top of a mountain, trying to aim a dish without a map. I had Street Atlas USA v5 on my then ancient Toshiblah 100CS laptop, which I used for my initial bearing. Other than having a difficult time holding the laptop, problems viewing the screen in the sunlight, and too short a base line, it worked. By the way, Jeff, you have a great deal to offer the group by way of your vast experience. If I have been disrespectful of that, then I apologize. Thanks and not a problem. You have a long way to go before such comments become a problem. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
NVIS and VHF?
On 6/4/2011 6:20 PM, Wimpie wrote:
On 4 jun, 23:26, John wrote: On 5/24/2011 8:47 AM, Wimpie wrote: Well, I have applied some numbers today and I am changing my mind that the trees are not the problem. If my numbers are correct: The repeater, 19 miles away, is 1900 feet above his elevation. At that distance, the antenna will appear be about 240 feet lower than actual due to earth curvature. That makes the antenna appear to be about 0.954 degrees above the horizon. That is equivalent to 60 feet at 3600 feet. In other words, 60 foot trees closer in will be completely in the way. The hurtful part of this is that his antenna at 45 feet will have a lowest angle of radiation (take-off angle) of .7 degrees, right into the near trees. The next lobe above that is at 2.2 degrees. Between those two lobes is a null. In short, I think his antenna is in a null. I think the only answer for his present situation is to raise the antenna another 10 feet. What do you think? 73, John Hello John, This link: http://www.tetech.nl/divers/Kirk_Repeater_USA_1.png shows the path profiles with and without trees (from Radio Mobile, VE2DBE). I will keep it there for some weeks. I used 30m (98ft) high trees (so they are easy to see). The trees cover some additional part of the first fresnel zone, but the average canopy will be lower and the absorption loss is not that high at 146 MHz. So yes, there is influence from the trees, but not that much I think. If you want to get some increase in signal, you need to remove lots of them, and he don't want to do that. Note that the first trees are 160m away from his antenna (info from google earth, based on data provided by Kirk). With kind regards, Wim PA3DJS www.tetech.nl In that case, perhaps it is due to his antenna being at a height that puts the target into a null. Along with low repeater output power, I suppose that could cause it. Thanks, Wim. 73, John - KD5YI |
NVIS and VHF?
On 6/5/2011 10:59 AM, John S wrote:
On 6/4/2011 6:20 PM, Wimpie wrote: On 4 jun, 23:26, John wrote: On 5/24/2011 8:47 AM, Wimpie wrote: Well, I have applied some numbers today and I am changing my mind that the trees are not the problem. If my numbers are correct: The repeater, 19 miles away, is 1900 feet above his elevation. At that distance, the antenna will appear be about 240 feet lower than actual due to earth curvature. That makes the antenna appear to be about 0.954 degrees above the horizon. That is equivalent to 60 feet at 3600 feet. In other words, 60 foot trees closer in will be completely in the way. The hurtful part of this is that his antenna at 45 feet will have a lowest angle of radiation (take-off angle) of .7 degrees, right into the near trees. The next lobe above that is at 2.2 degrees. Between those two lobes is a null. In short, I think his antenna is in a null. I think the only answer for his present situation is to raise the antenna another 10 feet. What do you think? 73, John Hello John, This link: http://www.tetech.nl/divers/Kirk_Repeater_USA_1.png shows the path profiles with and without trees (from Radio Mobile, VE2DBE). I will keep it there for some weeks. I used 30m (98ft) high trees (so they are easy to see). The trees cover some additional part of the first fresnel zone, but the average canopy will be lower and the absorption loss is not that high at 146 MHz. So yes, there is influence from the trees, but not that much I think. If you want to get some increase in signal, you need to remove lots of them, and he don't want to do that. Note that the first trees are 160m away from his antenna (info from google earth, based on data provided by Kirk). With kind regards, Wim PA3DJS www.tetech.nl In that case, perhaps it is due to his antenna being at a height that puts the target into a null. Along with low repeater output power, I suppose that could cause it. Thanks, Wim. 73, John - KD5YI Okay. I take that back. I just ran a simulation with EZNEC and it shows twice as much uV available at the receiver than Radio Mobile, so my conclusion is that a pattern null is not involved. I'm stumped. 73, John |
NVIS and VHF? Solved!
'Captain' Kirk DeHaan said the following on 5/22/2011 11:04 AM:
I'm living in a wooded area and am trying to hit our club repeater reliably. It's cloudy now so I'm and getting a bit of ducting but I have a lot of trees, mostly poplars, in the direct path. I would have a line of sight if not for the trees as I'm up enough in altitude. I can cut the trees, they're mine, but finding the right ones is difficult and i don't want to waste the whole grove. I go from keying the repeater with no intelligible signal to not being able to hit it. Today I actually have an S meter reading due to the clouds. I am currently using a J-pole and will put up a Yagi soon but wonder if NVIS would work on 2m? I have only seen references to it being applied in HF. 'Captain' Kirk DeHaan N6SXR I purchased a 10 element 2m Yagi and installed it today. I can now hit the repeater in question full quieting. The other benefit is I can hit the one other repeater that I could not even hear before. I am quite happy now. :-) Now I don't have to cut down any more trees, other than those I am selling. Thanks for all the input from everyone. Problem is solved! -- 'Captain' Kirk DeHaan N6SXR "Beam me up Scotty, there's no intelligent life here" |
NVIS and VHF? Solved!
On 6/17/2011 8:03 PM, 'Captain' Kirk DeHaan wrote:
'Captain' Kirk DeHaan said the following on 5/22/2011 11:04 AM: I'm living in a wooded area and am trying to hit our club repeater reliably. It's cloudy now so I'm and getting a bit of ducting but I have a lot of trees, mostly poplars, in the direct path. I would have a line of sight if not for the trees as I'm up enough in altitude. I can cut the trees, they're mine, but finding the right ones is difficult and i don't want to waste the whole grove. I go from keying the repeater with no intelligible signal to not being able to hit it. Today I actually have an S meter reading due to the clouds. I am currently using a J-pole and will put up a Yagi soon but wonder if NVIS would work on 2m? I have only seen references to it being applied in HF. 'Captain' Kirk DeHaan N6SXR I purchased a 10 element 2m Yagi and installed it today. I can now hit the repeater in question full quieting. The other benefit is I can hit the one other repeater that I could not even hear before. I am quite happy now. :-) Now I don't have to cut down any more trees, other than those I am selling. Thanks for all the input from everyone. Problem is solved! Glad to hear it, Kirk. Good work on your part. 73, John - KD5YI |
NVIS and VHF? Solved!
On 18 jun, 03:03, 'Captain' Kirk DeHaan
wrote: 'Captain' Kirk DeHaan said the following on 5/22/2011 11:04 AM: I'm living in a wooded area and am trying to hit our club repeater reliably. It's cloudy now so I'm and getting a bit of ducting but I have a lot of trees, mostly poplars, in the direct path. I would have a line of sight if not for the trees as I'm up enough in altitude. I can cut the trees, they're mine, but finding the right ones is difficult and i don't want to waste the whole grove. I go from keying the repeater with no intelligible signal to not being able to hit it. Today I actually have an S meter reading due to the clouds. I am currently using a J-pole and will put up a Yagi soon but wonder if NVIS would work on 2m? I have only seen references to it being applied in HF. 'Captain' Kirk DeHaan N6SXR I purchased a 10 element 2m Yagi and installed it today. *I can now hit the repeater in question full quieting. *The other benefit is I can hit the one other repeater that I could not even hear before. *I am quite happy now. *:-) *Now I don't have to cut down any more trees, other than those I am selling. Thanks for all the input from everyone. *Problem is solved! -- 'Captain' Kirk DeHaan N6SXR "Beam me up Scotty, there's no intelligent life here" Hello Kirk, Thanks for the feedback on the outcome of your experiments, and to hear that there is no problem anymore. Wim PA3DJS www.tetech.nl |
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