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NVIS and VHF?
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 |
NVIS and VHF?
'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. Wait for winter and use a beam antenna to locate the tree(s) that need to be trimmed. If a 10 element beam won't "blast" through the trees in the summer, it should get you down to a line of 1 or two trees that need to be cut. A more radio oriented project would be to put a 6m or 10m input on the repeater. 10m should groundwave over the trees anyway. It's easy enough to test. 10m inputs are IMHO neat, at the top of the sunspot cycle, they give your repeater worldwide input. At that point a 10m output would be good too, but for now, it's not much of a problem. Geoff. -- Geoffrey S. Mendelson N3OWJ/4X1GM It's amazing how many people have no clue what the word "contiguous" means. :-( |
NVIS and VHF?
On 22 mayo, 20:04, '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 Hello, The repeater antenna will probably have most of its radiation in the horizontal plane and 145 MHz is far above the critical frequency, so your rays will leave earth. Did you monitor the signal for several time (also winter and rain) to assess the real influence of the trees? Do you have any possibility to move the J-pole to another place? As you can open the repeater now and then, some 10 dB additional gain will certainly help you to get above the FM-knee (assuming that you can get the beam at same height as the J-pole. Nice thing is, it will also improve reception. With kind regards, Wim PA3DJS www.tetech.nl remove abc first in case of PM |
NVIS and VHF?
On May 22, 11:04*am, '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 I can't see that NVIS has any VHF backers. Can you exploit Google Maps, satellite view, to establish a precise line bearing from your antenna to the repeater site? If you need even more help than you get from your new yagi, then such a line bearing will help identify your "trouble trees." I had to do it for a new FD site a few years ago. We're in San Diego and I wanted to work 2m into Los Angeles. First, I used a protractor to determine LA was X-degrees True (whatever it was) from us; next, on a close-up print of the FD site, I plotted that same line bearing from the antenna site to obvious local landmarks which we then used on the the ground for pointing the 2m beam. This is not the only approach, but it got me what I needed. "Sal" (KD6VKW) |
NVIS and VHF?
On 5/22/2011 1:04 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 Your yagi may fix your problem completely. Other things to consider: * Try moving your existing antenna. Even a small movement may cure the problem as you may have cancelling reflections at times. There is almost always a "sweet spot" somewhere in the vicinity. * Try tilting your antenna to 45 degrees and see if that helps. It might improve reception due to the random polarization of the incoming signal caused by the trees. Note: do this on a day when the signal is either weak or non-existent. You can always apologize for kerchunking. Or, use your S-meter if you have one. Cheers & Good Luck, John KD5YI |
NVIS and VHF?
On 5/22/2011 1:04 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 Addendum: If you can add even a foot or two your antenna height, it may make a world of difference. Cheers, John KD5YI |
NVIS and VHF?
On Sun, 22 May 2011 18:29:03 +0000 (UTC), Geoffrey S. Mendelson wrote:
10m inputs are IMHO neat, at the top of the sunspot cycle, they give your repeater worldwide input. s/input/QRM/ |
NVIS and VHF?
On Sun, 22 May 2011 11:04:10 -0700, 'Captain' Kirk DeHaan
wrote: I'm living in a wooded area and am trying to hit our club repeater reliably. I live in a dense mostly redwood forest. Signals vary from full quieting to not copyable. We also have two co-channel repeaters sharing the frequency, that also vary radically in strength. I can often point my 5 element 2m beam in a totally insane direction, and improve the signal. 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. I just love technical posting with no numbers. It would be helpful if you would offer a clue as to the distance you're trying to cover, what manner of impervious to RF dirt is along the line of sight, antenna at the repeater, power levels, etc. For extra credit, if you disclose these plus your exact location, the repeater's exact location, and I will contrive a Radio-Mobile path profile from you to the repeater. That should give you a clue as to what challenges you are facing. http://www.cplus.org/rmw/english1.html It will look something like this: http://802.11junk.com/jeffl/coverage/RST/RST-KCRA.jpg As for a seat-of-the-pants guess as to a solution, I don't like J-pole antennas. Actually, the antenna is fine, but the way most people build, tune, and position them, is what I find disgusting. The lack of any commercially manufactured J-pole antennas (other than the American Legion J-poles) should offer a clue. Plenty of plans: http://www.google.com/search?q=j-pole+antenna&hl=en&prmd=ivns&tbm=isch but nothing from a commercial antenna manufactory. In my never humble opinion, if you can barely talk to the repeater with a J-pole, then a yagi will offer a substantial improvement. The problem is how much gain is going to be needed to make it reliable. My guess(tm) is that the J-pole has a gain of about 2.5dBi (opinions vary on the gain), and that you'll need about 5dB more gain to get a decent link. That means you'll need a yagi with about 7.5dBi of gain. That can be done with a 5 element 2m yagi. Obviously, more gain is better as is more altitude. Good luck. -- 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 Sun, 22 May 2011 17:55:16 -0500, John KD5YI
wrote: * Try moving your existing antenna. Even a small movement may cure the problem as you may have cancelling reflections at times. There is almost always a "sweet spot" somewhere in the vicinity. I beg to differ. I have about 30 years experience in dealing with propogation through a dense redwood forest (Ben Lomond CA). The trees in my area are about 120ft high. While moving the antenna around may temporarily improve the signal quality by reducing frequency selective fading, multipath, reflections, and just plain bad luck, they do not tend to remain improved. Trees grow and move around. What works well now, will probably not work well tomorrow. I gave up on fixed antenna mounts for my rooftop verticals. (Well, I have one mounted on a tripod, but that was before I realized what was happening). Most of my verticals are mounted on 2x12 planks, held down to the roof with sand bags, concrete blocks, and buckets full of water. Every few months, I move the antennas around to see if I can improve the signals to specific repeaters. * Try tilting your antenna to 45 degrees and see if that helps. It might improve reception due to the random polarization of the incoming signal caused by the trees. I beg to differ again. Tree trunks are mostly water and do an impressive job of simulating a slot type polarization filter at 2m and 440Mhz frequencies. Leaves and branches will pass RF fairly well, but not tree trunks. I've played with both polarizations, circular polarization: http://802.11junk.com/jeffl/circular-polarization/ and some diversity reception. Empirically, signals are about 6dB stronger going through the trees vertically polarized, than horizontal. The effect continues up to at least 2.4GHz. Above that, at 5.7GHz, the signals seem to be going through the holes between the leaves. I must admit that I haven't actually tried 45 degrees on 2m or 440Mhz, but I don't think it will help much. Still, it's an easy thing to try. Note: do this on a day when the signal is either weak or non-existent. You can always apologize for kerchunking. Or, use your S-meter if you have one. Do it on a windy day, when the trees are moving around, so you can see how much it will change. Cheers & Good Luck, John KD5YI -- 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 5/22/2011 8:26 PM, Jeff Liebermann wrote:
On Sun, 22 May 2011 17:55:16 -0500, John wrote: * Try moving your existing antenna. Even a small movement may cure the problem as you may have cancelling reflections at times. There is almost always a "sweet spot" somewhere in the vicinity. I beg to differ. I have about 30 years experience in dealing with propogation through a dense redwood forest (Ben Lomond CA). The trees in my area are about 120ft high. While moving the antenna around may temporarily improve the signal quality by reducing frequency selective fading, multipath, reflections, and just plain bad luck, they do not tend to remain improved. Trees grow and move around. What works well now, will probably not work well tomorrow. You may be right, Jeff. But he may not have 120ft redwoods around and, after all, this is a temporary fix until his yagi comes in. I gave up on fixed antenna mounts for my rooftop verticals. (Well, I have one mounted on a tripod, but that was before I realized what was happening). Most of my verticals are mounted on 2x12 planks, held down to the roof with sand bags, concrete blocks, and buckets full of water. Every few months, I move the antennas around to see if I can improve the signals to specific repeaters. Good for you! Pat yourself on the back. * Try tilting your antenna to 45 degrees and see if that helps. It might improve reception due to the random polarization of the incoming signal caused by the trees. I beg to differ again. Tree trunks are mostly water and do an impressive job of simulating a slot type polarization filter at 2m and 440Mhz frequencies. Leaves and branches will pass RF fairly well, but not tree trunks. I've played with both polarizations, circular polarization: http://802.11junk.com/jeffl/circular-polarization/ and some diversity reception. Empirically, signals are about 6dB stronger going through the trees vertically polarized, than horizontal. The effect continues up to at least 2.4GHz. Above that, at 5.7GHz, the signals seem to be going through the holes between the leaves. I must admit that I haven't actually tried 45 degrees on 2m or 440Mhz, but I don't think it will help much. Still, it's an easy thing to try. You spent more words debunking the suggestion than admitting that you don't really know whether it could help or not. Good move. And, by the way, I have experience to the contrary at both 144 and 444 MHz. It all depends on the location of the source and the receiver. At 2 meters, some rotation of the antenna can sometimes be helpful. Note that we are not concerned with GHz. John |
NVIS and VHF?
On Sun, 22 May 2011 20:56:52 -0500, John KD5YI
wrote: You may be right, Jeff. But he may not have 120ft redwoods around and, after all, this is a temporary fix until his yagi comes in. 30 years of trying to maintain a stable signal to several distant repeaters is sufficient to convince me. Trees move and grow, causing signals to change. Also, temporary is a rather useless term. In my experience, if it works, it's permanent. Good for you! Pat yourself on the back. Thank you for the traditional contentious remark. You spent more words debunking the suggestion than admitting that you don't really know whether it could help or not. True. I spent more words explaining why I suspect it will not work, what I expect will happen, and a bit of substantiation. I consider this a substantial improvement over the traditional one-line pontification. Good move. And, by the way, I have experience to the contrary at both 144 and 444 MHz. It all depends on the location of the source and the receiver. At 2 meters, some rotation of the antenna can sometimes be helpful. Perhaps it would be helpful if you read what I had written. I said that rotating the antenna might help temporarily, but that movements of the trees, tree growth, swaying branches in the wind, and possibly sources of reflections, will soon negate any temporary benefits. If the yagi is going to arrive shortly, then tilting the antenna is probably a useful exercise. Note that we are not concerned with GHz. Topic drift follows: Since you mentioned GHz, one of the other problems with living in the deep dark forest is that DBS satellite dish reception is a problem. I hacked an 8ft diameter hole in the tree canopy by lopping off some branches at about the 80ft level, through which I point my DirecTV dish. Every year, the trees grow a little, requiring that I move the dish around my roof. During the twice annual solar satellite outage: http://en.wikipedia.org/wiki/Sun_outage Twice a year, I photograph the sunlight shining through the hole and onto the dish and roof. If there are shadows of branches on the dish, I move it to a better location. http://www.11junk.com/jeffl/pics/DBS/ Note the shadow at 12 o'clock on the dish. -- 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 22/05/2011 19:04, '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 If you have line of sight to the repeater I find it hard to believe that a few trees will cause you problems at 2m. NVIS will not work at vhf it is an HF mode. 2m signals go straight through the atmosphere they are not reflected back down. You don't say how far away the trees are, but if they *really are* the cause of you problems, if they are at any distance then they will probably all have to go to give any sort of Fresnel zone clearance at 2m. A simple map and compass will give you the bearing to the repeater, but perhaps you would be better off running a propagation prediction program such as Radiomobile to see if it is actually the terrain rather than the trees that are the problem. 73 Jeff |
NVIS and VHF?
On Sun, 22 May 2011 20:56:52 -0500, John KD5YI
wrote: You may be right, Jeff. But he may not have 120ft redwoods around and, after all, this is a temporary fix until his yagi comes in. Ummm... I don't think the yagi is on order. http://www.k7jep.org/node/107 #Begin speculation(); His area has a variety of repeaters available: http://www.k7jep.org/node/107 I would guess(tm) N7JCT 145.230 on Schweitzer Mtn. Idaho. http://www.repeaterbook.com/beta/repeaters/details.php?ID=64&state_id=16 Plugging the coordinates 48.367500 -116.628326 into Google Earth gives me a view of the area. It seems to be in the middle of a ski resort, that has been cleared of most trees and is full of trails. Plenty of trees both up and down the slope, but not around the probable location of the repeater. I can't identify the trees from the photo, but my guess(tm) is Lodgepole Pine at about 60ft. The location is not at the top of the hill and also has hills shading the view for about 270 degrees. I don't think this is going to be a foliage penetration issue. KML file for Google Earth: http://802.11junk.com/jeffl/kml/N7JCT possible location.kml JPG for those without Google Earth: http://802.11junk.com/jeffl/kml/N7JCT possible location.jpg Blundering forward, N6SXR is shown as getting his snail mail in Sandpoint ID a distance of about 7 miles. However, there's quite a bit of dirt in the way, which will be a problem. http://802.11junk.com/jeffl/kml/N6SXR to N6JCT.jpg At 7 miles, it should be possible on VHF, even with 450ft of dirt in the way. My guess(tm) is that there's something wrong with the home made J-pole, coax, radio, or all the aformentioned. Again, this is a guess(tm) of both the repeater and it's location and just might be totally wrong. #End speculation(); -- 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 5/22/2011 11:26 PM, Jeff Liebermann wrote:
On Sun, 22 May 2011 20:56:52 -0500, John wrote: You may be right, Jeff. But he may not have 120ft redwoods around and, after all, this is a temporary fix until his yagi comes in. 30 years of trying to maintain a stable signal to several distant repeaters is sufficient to convince me. Trees move and grow, causing signals to change. Also, temporary is a rather useless term. In my experience, if it works, it's permanent. The OP already said he will be putting up a yagi. Anthing he does between now and then is temporary. Good for you! Pat yourself on the back. Thank you for the traditional contentious remark. You earned it. You spent more words debunking the suggestion than admitting that you don't really know whether it could help or not. True. I spent more words explaining why I suspect it will not work, what I expect will happen, and a bit of substantiation. I consider this a substantial improvement over the traditional one-line pontification. I find it more useful to encourage experimentation rather than the opposite. Good move. And, by the way, I have experience to the contrary at both 144 and 444 MHz. It all depends on the location of the source and the receiver. At 2 meters, some rotation of the antenna can sometimes be helpful. Perhaps it would be helpful if you read what I had written. I said that rotating the antenna might help temporarily, but that movements of the trees, tree growth, swaying branches in the wind, and possibly sources of reflections, will soon negate any temporary benefits. If the yagi is going to arrive shortly, then tilting the antenna is probably a useful exercise. I did read what you had written. So? Note that we are not concerned with GHz. Topic drift follows: Since you mentioned GHz, *You* are the one who brought it up: "The effect continues up to at least 2.4GHz. Above that, at 5.7GHz, the signals seem to be going through the holes between the leaves." Perhaps you should read what you wrote. John |
NVIS and VHF?
On 5/23/2011 10:46 AM, Jeff Liebermann wrote:
On Sun, 22 May 2011 20:56:52 -0500, John wrote: You may be right, Jeff. But he may not have 120ft redwoods around and, after all, this is a temporary fix until his yagi comes in. Ummm... I don't think the yagi is on order. Now you are just being argumentative. I never said it was on order. The OP said he was planning to put one up. Therefore, it will most likely come in some day. I'll bet you are still waiting for your boat to come in. |
NVIS and VHF?
On Mon, 23 May 2011 11:46:58 -0500, John KD5YI
wrote: On 5/23/2011 10:46 AM, Jeff Liebermann wrote: On Sun, 22 May 2011 20:56:52 -0500, John wrote: You may be right, Jeff. But he may not have 120ft redwoods around and, after all, this is a temporary fix until his yagi comes in. Ummm... I don't think the yagi is on order. Now you are just being argumentative. Not really. Methinks that you're being overly defensive. My litmus test is "duz it answer the OP's question"? If not, you're wasting your bytes. By asking for help with the design and contruction of a yagi, it appears that the author is planning to build his own yagi. I haven't seen any mention of a structure, pole, or tower, so that will also need to be constructed. Perhaps also a rotator. Methinks temporary might be a long time. I never said it was on order. The OP said he was planning to put one up. Therefore, it will most likely come in some day. At this point, I think were suppose to debate the definition of temporary. I think I'll pass. I'll bet you are still waiting for your boat to come in. Nope, no waiting. I let the computah do that for me. http://www.marinetraffic.com/ais/ The station I'm slightly involved with is at: http://www.marinetraffic.com/ais/stationdetails.aspx?station_id=112 Watching the VHF propagation effects are fascinating. -- 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 5/22/2011 3:11 PM, Sal M. Onella wrote:
On May 22, 11:04 am, '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 I can't see that NVIS has any VHF backers. Can you exploit Google Maps, satellite view, to establish a precise line bearing from your antenna to the repeater site? If you need even more help than you get from your new yagi, then such a line bearing will help identify your "trouble trees." I had to do it for a new FD site a few years ago. We're in San Diego and I wanted to work 2m into Los Angeles. First, I used a protractor to determine LA was X-degrees True (whatever it was) from us; next, on a close-up print of the FD site, I plotted that same line bearing from the antenna site to obvious local landmarks which we then used on the the ground for pointing the 2m beam. For this kind of thing "RadioMobile" from VE2DBE is the application of choice. It will load the SRTM terrain DEMs, etc. and plot out the path quite nicely. http://www.cplus.org/rmw/english1.html But, if you can get in sometimes, but not others, the next question is, "can you hear it"? How long is your coax? If more than 20 ft, are you running a preamp? Getting 10-15 dB gain over a jpole would be easy with a moderate length Yagi. A M2 2M4 (4 elements, $115) is about 10dBi. A 2M9($240) is about 14dBi |
NVIS and VHF?
On 22 mayo, 20:04, '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 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 |
NVIS and VHF?
Jeff Liebermann said the following on 5/23/2011 8:46 AM:
On Sun, 22 May 2011 20:56:52 -0500, John wrote: You may be right, Jeff. But he may not have 120ft redwoods around and, after all, this is a temporary fix until his yagi comes in. Ummm... I don't think the yagi is on order. http://www.k7jep.org/node/107 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. #Begin speculation(); His area has a variety of repeaters available: http://www.k7jep.org/node/107 I would guess(tm) N7JCT 145.230 on Schweitzer Mtn. Idaho. This repeater is 59 on signal. I have direct line of site with no obstructions. http://www.repeaterbook.com/beta/repeaters/details.php?ID=64&state_id=16 Plugging the coordinates 48.367500 -116.628326 into Google Earth gives me a view of the area. It seems to be in the middle of a ski resort, that has been cleared of most trees and is full of trails. Plenty of trees both up and down the slope, but not around the probable location of the repeater. I can't identify the trees from the photo, but my guess(tm) is Lodgepole Pine at about 60ft. The location is not at the top of the hill and also has hills shading the view for about 270 degrees. I don't think this is going to be a foliage penetration issue. KML file for Google Earth: http://802.11junk.com/jeffl/kml/N7JCT possible location.kml JPG for those without Google Earth: http://802.11junk.com/jeffl/kml/N7JCT possible location.jpg Blundering forward, N6SXR is shown as getting his snail mail in Sandpoint ID a distance of about 7 miles. However, there's quite a bit of dirt in the way, which will be a problem. http://802.11junk.com/jeffl/kml/N6SXR to N6JCT.jpg Addresses here are not all they seem. My physical address is 14 miles north even though the postal idiots label it in Sandpoint. Approx location... lat 48.494070 lon -116.447788. You'll see my crazy driveway and the house. The J-pole sits about 30' above the house. Plenty of trees in sight. At 7 miles, it should be possible on VHF, even with 450ft of dirt in the way. My guess(tm) is that there's something wrong with the home made J-pole, coax, radio, or all the aformentioned. Again, this is a guess(tm) of both the repeater and it's location and just might be totally wrong. #End speculation(); -- 'Captain' Kirk DeHaan N6SXR "Beam me up Scotty, there's no intelligent life here" |
NVIS and VHF?
Jeff Liebermann said the following on 5/22/2011 6:05 PM:
On Sun, 22 May 2011 11:04:10 -0700, 'Captain' Kirk DeHaan wrote: I'm living in a wooded area and am trying to hit our club repeater reliably. I live in a dense mostly redwood forest. Signals vary from full quieting to not copyable. We also have two co-channel repeaters sharing the frequency, that also vary radically in strength. I can often point my 5 element 2m beam in a totally insane direction, and improve the signal. 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. I just love technical posting with no numbers. It would be helpful if you would offer a clue as to the distance you're trying to cover, what manner of impervious to RF dirt is along the line of sight, antenna at the repeater, power levels, etc. For extra credit, if you disclose these plus your exact location, the repeater's exact location, and I will contrive a Radio-Mobile path profile from you to the repeater. That should give you a clue as to what challenges you are facing. The repeater, 146.780, in on Gold Mtn., 48.219713, -116.482883 I do not know the specs of the repeater. I am at 48.494070, -116.447788, at 2300' using an American Legion J-pole. It has worked very well in the past but this is the first time it has been up in 15 years. It hits the 145.230 repeater on Schweitzer 59. I'm running a Kenwood 721 at 25 watts trying to hit the 780 repeater. Schweitzer can be hit at 5 watts no problem. http://www.cplus.org/rmw/english1.html It will look something like this: http://802.11junk.com/jeffl/coverage/RST/RST-KCRA.jpg As for a seat-of-the-pants guess as to a solution, I don't like J-pole antennas. Actually, the antenna is fine, but the way most people build, tune, and position them, is what I find disgusting. The lack of any commercially manufactured J-pole antennas (other than the American Legion J-poles) should offer a clue. Plenty of plans: http://www.google.com/search?q=j-pole+antenna&hl=en&prmd=ivns&tbm=isch but nothing from a commercial antenna manufactory. In my never humble opinion, if you can barely talk to the repeater with a J-pole, then a yagi will offer a substantial improvement. The problem is how much gain is going to be needed to make it reliable. My guess(tm) is that the J-pole has a gain of about 2.5dBi (opinions vary on the gain), and that you'll need about 5dB more gain to get a decent link. That means you'll need a yagi with about 7.5dBi of gain. That can be done with a 5 element 2m yagi. Obviously, more gain is better as is more altitude. Good luck. -- 'Captain' Kirk DeHaan N6SXR "Beam me up Scotty, there's no intelligent life here" |
NVIS and VHF?
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 |
NVIS and VHF?
On 24 mayo, 05:06, John KD5YI 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 |
NVIS and VHF?
Wimpie said the following on 5/24/2011 6:47 AM:
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). I was up on my neighbors property along the path to the repeater and the quantity of trees is a lot more than I had remembered. Since this is tree growing/logging country it is not feasible for me to be cutting huge amounts of trees. The deciduous can go but there are to many conifers on both properties to cut just for signal. You are correct on the distance to the grove and it is the, I believe, the only impediment. 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. I download the Radio Mobile SW that someone suggested but am still trying to figure out how to use it. With kind regards, Wim PA3DJS -- 'Captain' Kirk DeHaan N6SXR "Beam me up Scotty, there's no intelligent life here" |
NVIS and VHF?
John KD5YI said the following on 5/23/2011 8:06 PM:
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. 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. I'm using 75' of professionally assembled RG8X which is required to get from the radio to the antenna. 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. Not to make light, one of these poplars is tons in itself. They are easily 70' tall and 24" diameter. I truly appreciate all the help from everyone. Cheers, John -- 'Captain' Kirk DeHaan N6SXR "Beam me up Scotty, there's no intelligent life here" |
NVIS and VHF?
On Mon, 23 May 2011 15:53:28 -0700, 'Captain' Kirk DeHaan
wrote: You'll see my crazy driveway and the house. The J-pole sits about 30' above the house. Plenty of trees in sight. That's quite a drive. Thanks for the numbers. I've ignored the antenna heights as they don't seem to make much difference. 31 km (19 mile) path length. The K7JEP repeater seems to be on a wide flat part of a hilltop. Pointing downward, it may not clear the edge of the flat part if the antenna isn't high enough. Difficult to tell without photos or numbers. Not much you can do at your end to fix that. Any chance you have a photo of the K7JEP repeater antenna location? Otherwise, the path is line-o-sight, and should be quite usable with your American Legion J-Pole. Of course, a yagi would be better, but I think tinkering with your J-pole, coax, connectors, and radio may be a better solution (assuming the repeater is working properly). KML file: http://802.11junk.com/jeffl/kml/N6SXR-to-K7JEP.kml JPG image: http://802.11junk.com/jeffl/kml/N6SXR-to-K7JEP.jpg Hint: In Google Earth, enable 3D. When you have the KML file displayed, stomp on the MIDDLE mouse button to tilt the image. -- 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 Tue, 24 May 2011 08:17:46 -0700, 'Captain' Kirk DeHaan
wrote: I download the Radio Mobile SW that someone suggested but am still trying to figure out how to use it. Radio-Mobile will give you the expected coverage area and signal strengths from your location. However, it's a tricky program to master and will require some patience and practice. There are tutorials. For example: http://www.pizon.org/radio-mobile-tutorial/index.html http://www.bcwireless.net/moin.cgi/RadioMobile/Tutorial http://radiomobile.pe1mew.nl/ etc. Also check YouTube for various video tutorials. -- 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 Tue, 24 May 2011 08:24:09 -0700, 'Captain' Kirk DeHaan
wrote: 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. The American Legion J-pole is rather critical, especially the dual band flavor. The vertical section of electrical wire between the coax connector and the part where it's wound around the driven element is the tuning adjustment. Move it slightly and it's mistuned. You'll need a VSWR meter to re-tune it. I'm using 75' of professionally assembled RG8X which is required to get from the radio to the antenna. RX-8x is 4.5dB loss per 100ft. Half your power is being lost in the coax. -- 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?
Jeff Liebermann said the following on 5/24/2011 8:47 AM:
On Mon, 23 May 2011 15:53:28 -0700, 'Captain' Kirk DeHaan wrote: You'll see my crazy driveway and the house. The J-pole sits about 30' above the house. Plenty of trees in sight. That's quite a drive. Thanks for the numbers. I've ignored the antenna heights as they don't seem to make much difference. 31 km (19 mile) path length. The K7JEP repeater seems to be on a wide flat part of a hilltop. Pointing downward, it may not clear the edge of the flat part if the antenna isn't high enough. Difficult to tell without photos or numbers. Not much you can do at your end to fix that. Any chance you have a photo of the K7JEP repeater antenna location? Otherwise, the path is line-o-sight, and should be quite usable with your American Legion J-Pole. Of course, a yagi would be better, but I think tinkering with your J-pole, coax, connectors, and radio may be a better solution (assuming the repeater is working properly). I have heard from a club member that the repeater is weak and it has been overrun by one on the coast! He is much farther away than me and in a much less desirable location, signal wise. I have been out of HAM radio for about 15 years so am having to relearn quite a lot. Had a brain injury, doh!, so lot's of what I knew went bye bye. Lot's of holes in the memory. I will find out about the repeater during the next club meeting. Specs and all. KML file: http://802.11junk.com/jeffl/kml/N6SXR-to-K7JEP.kml JPG image: http://802.11junk.com/jeffl/kml/N6SXR-to-K7JEP.jpg Hint: In Google Earth, enable 3D. When you have the KML file displayed, stomp on the MIDDLE mouse button to tilt the image. -- 'Captain' Kirk DeHaan N6SXR "Beam me up Scotty, there's no intelligent life here" |
NVIS and VHF?
In article ,
John KD5YI 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. I wonder whether he might have his antenna sitting in a particularly deep multipath cancellation null. I help run a repeater located about 4 miles from my house, which is up at about 80' AGL on a hospital roof. There's an office building blocking direct line-of-sight path from my house to the repeater. For a few weeks, several years ago, I found myself unable to successfully open up the repeater using my base station, even while transmitting 50 watts of power from a good-quality commercial 2-meter antenna located a few feet above my roofline. Had no trouble with any other repeater in the area, or with simplex operations. The feedline/antenna system measured out just fine... no reflected power worth speaking about. I moved the antenna mast about 2' to one side, and was then able to open up the repeater full-quieting with 100 milliwatts. All I can figure is that there must have been a *very* deep multipath cancellation effect playing out... maybe interference between a edge-diffraction path involving the office building, and reflections from nearby trees. Moving the antenna a fraction of a wavelength changed the path lengths enough to eliminate the cancellation (or reduce it by a large factor). -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
NVIS and VHF?
In article ,
'Captain' Kirk DeHaan 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. 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. 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. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
NVIS and VHF?
On 5/24/2011 4:23 PM, 'Captain' Kirk DeHaan wrote:
I have heard from a club member that the repeater is weak and it has been overrun by one on the coast! He is much farther away than me and in a much less desirable location, signal wise. I have been out of HAM radio for about 15 years so am having to relearn quite a lot. Had a brain injury, doh!, so lot's of what I knew went bye bye. Lot's of holes in the memory. I will find out about the repeater during the next club meeting. Specs and all. Sounds great, Kirk. I'll bet they will fix you up right away. Hang in there. Cheers, John |
NVIS and VHF?
On Tue, 24 May 2011 14:23:20 -0700, 'Captain' Kirk DeHaan
wrote: I have heard from a club member that the repeater is weak and it has been overrun by one on the coast! He is much farther away than me and in a much less desirable location, signal wise. Ok. Might be a sick repeater. That would explain quite a bit. I have been out of HAM radio for about 15 years so am having to relearn quite a lot. Had a brain injury, doh!, so lot's of what I knew went bye bye. Lot's of holes in the memory. I have a slight idea of what's that's like. I had a triple bypass operation in 2002. They're not sure what happened but the result is that my memory around that time is like Swiss cheese. It's a mix of things that happened that I don't remember, and things I remember that never happened. Fortunately, things got better after about a year for me. Hopefully, you'll do as well. Also, my neighbor had a brain tumor removed. She's fine, but has the same scrambled memory problem. I gave up ham radio from about 1975 to 1992. I was working designing radios and working in commercial 2way. The last thing I needed was ham radio after hours. Welcome back. I will find out about the repeater during the next club meeting. Specs and all. Good idea. I assumed that you had already done that. If the specs on the repeater (tx power, feed line losses, antenna gain, antenna height, lat-long) were known on the repeater, I can calculate the signal strength you should expect at your end. -- 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 5/24/2011 4:43 PM, Dave Platt wrote:
In , John 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. I wonder whether he might have his antenna sitting in a particularly deep multipath cancellation null. I help run a repeater located about 4 miles from my house, which is up at about 80' AGL on a hospital roof. There's an office building blocking direct line-of-sight path from my house to the repeater. For a few weeks, several years ago, I found myself unable to successfully open up the repeater using my base station, even while transmitting 50 watts of power from a good-quality commercial 2-meter antenna located a few feet above my roofline. Had no trouble with any other repeater in the area, or with simplex operations. The feedline/antenna system measured out just fine... no reflected power worth speaking about. I moved the antenna mast about 2' to one side, and was then able to open up the repeater full-quieting with 100 milliwatts. All I can figure is that there must have been a *very* deep multipath cancellation effect playing out... maybe interference between a edge-diffraction path involving the office building, and reflections from nearby trees. Moving the antenna a fraction of a wavelength changed the path lengths enough to eliminate the cancellation (or reduce it by a large factor). That is always a possibility, Dave. I have seen similar situations and I am not surprised at your findings. It is one reason I suggested moving his antenna, even slightly. His latest post may also indicate that there is a repeater problem. So, I hope he posts his findings after his meeting with his club. Cheers, John |
NVIS and VHF?
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 |
NVIS and VHF?
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 Cheers, John |
NVIS and VHF?
"John KD5YI" 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. |
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. You are correct, Ralph, and I apologize to the group for my error. I did indeed put meters rather than feet into the calculator. Again, my apologies, and thanks, Ralph, for correcting me. Cheers, John |
NVIS and VHF?
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. -- 'Captain' Kirk DeHaan N6SXR "Beam me up Scotty, there's no intelligent life here" |
NVIS and VHF?
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 |
NVIS and VHF?
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. John |
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