Re: Topband: Low band antenna project questions
On 3/7/2016 3:11 PM, Jim Brown wrote: The vertical pattern of any antenna is produced by the reinforcement of the direct wave by the first reflection from the earth. That reflection is MUCH stronger, and is strong at a lower angle, if the "earth" at the point of reflection is sea water. Sea water will NOT improve signal strength in directions where the first reflection is over land. 73, Jim K9YC Not quite. The reinforcement of vertically polarized waves from a perfect ground plane is 3 dB. For a real ground, the worst that can happen is that you lose the whole 3 dB and get down to the free space value ... as long as you are talking about angles above the pseudo-Brewster angle. For angles below the pseudo-Brewster angle, the reflection amplitude is the same for both a perfect ground and a lousy ground. The difference is that for lousy ground the PHASE of the reflection is inverted. This results in near perfect cancellation at low angles. As we all know, this effect is much greater than 3 dB. For a ground mounted vertical, I don't think the idea of doing ray tracing to see if the "point of reflection" is over sea water is very useful, because the vertical does not model as a source at a definable height, AFAIK. It's probably more like the wave has to be over salt water not just at a point of reflection, but continuously from the antenna out to some critical radius. In this region, it is still a ground wave. Possibly, this radius corresponds to the point where the ray has reached a critical height such that the wave has been "launched" and can be considered to be a skywave. I don't know if this critical height is a function of take off angle or ground conductivity. For example, if the take off angle is 30 degrees, and the critical height is a half-wavelength, the critical radius (in terms of wavelength) is half of the square root of 3 (0.866...). This is just trig. I don't claim these are the actual numbers. If there really were a single "point of reflection", then I could put some half wave reflector wires on the ground a long distance from the antenna and generate a huge signal at a particular low angle. If this worked, I suspect it would have been discovered long ago and exploited. The over the horizon radar people may have figured this out. They use huge ground screens to actually try to simulate the vertical on the beach paradigm. Rick N6RK _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Low band antenna project questions
On Mon,3/7/2016 2:37 PM, Bill N6MW wrote: The V7 version with 2 drooping T wires and 2 elevated radials for each band was just okay on 160 but good on 80, Drooping Tee wires will reduce the effective height of the antenna by a significant fraction of their droop. probably limited by trees proximity and restricted geometry, although some might claim enhanced by being on a beach with adjacent ocean. Verticals near the beach need an effective radial/counterpoise. Only if the feed is directly over water and the coax return makes very good contact with it will sea water serve as a counterpoise. The vertical pattern of any antenna is produced by the reinforcement of the direct wave by the first reflection from the earth. That reflection is MUCH stronger, and is strong at a lower angle, if the "earth" at the point of reflection is sea water. Sea water will NOT improve signal strength in directions where the first reflection is over land. 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Low band antenna project questions
On Mon,3/7/2016 12:37 PM, NC3Z Gary wrote: My 160M dipole is actually a 160/80M fan and resonates well on both bands, For several years after I moved to W6 ten years ago, I had a loaded 160 dipole that was also resonant on 80M up at about 120 ft. Even at that height, its a low dipole on 160M, and 90% of the time, my 85 ft Tee vertical beat it, often by a lot. When it had to come down for repair several years ago I removed the 160M loading coils and extension wires. I did not think I could do that with a T top. That would solve issues. Would a cage of vertical wires be better than if I could use 2.5 to 1.5" aluminum masting? Anything that would increase the height of the vertical section would improve radiation efficiency a bit, but wide spaced wires would make the tuning broader. Luckily in our rural local club we have 2 hams that sell some neat products, one is the Air-boss launcher A guy in the SF Bay area developed the compressed air tennis ball launcher that I've seen at least ten years ago. It's very slick, works quite well. K2RD brought his over to my QTH soon after I moved here, and with his first shot, cleared the tallest redwood on my property by at least 10 ft. That tree is about 200 ft tall. and the other is the Antenna Tensioner. That looks very good for trees of moderate size, but I'd like something a bit more robust for the tall ones we have out here. :) 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Low band antenna project questions
OK, this has me intrigued. So the T top would look like this if looking straight up (or straight down) with the vertical portion at the xx? x x x xx xx xx xx x x xx x x xx xx xx xx x x x My 160M dipole is actually a 160/80M fan and resonates well on both bands, I did not think I could do that with a T top. That would solve issues. Would a cage of vertical wires be better than if I could use 2.5 to 1.5" aluminum masting? Luckily in our rural local club we have 2 hams that sell some neat products, one is the Air-boss launcher and the other is the Antenna Tensioner. The tensioner has proven its self here in the eastern NC winds. And being a boating area I have several West Marine stores nearby. Gary Mitchelson NC3Z/4 Pamlico County, NC FM15 On 07-Mar-16 12:48, Jim Brown wrote: > Hi Gary, > > The antenna you describe should work quite well on both bands, but I'll > suggest a couple of tweaks to make the matching easier. First, make it a > Tee -- if you have a catenary, you can support a Tee as easily as an L. > Second, make the top section a fan (like a fan dipole) with short > elements to resonate it on 80 and longer ones for 160. Third, don't > worry about remoting the tuner unless you feedline is very long. Unless > the match is really bad, feedline loss on 80 and 160 is pretty low, > especially if you use RG8. Also, you can make the tuning more broadband > (and electrically lengthen the vertical section by 1-2 percent) by using > two parallel runs spaced 12-18 inches, tied together top and bottom. Do > a simple NEC model to get dimensions. > > Finally, use as many radials as you can, don't worry a lot about length, > just think more is better. :) BTW -- 50 ft on the ground will be close > to a quarter wave on 80, 100 ft on 160. > > As to physical details -- get a good pulley at each end, tie one end > down, put a weight on the other end, and use some sort of "mechanical > fuse" at the feedpoint so that wind doesn't break it. I use a mating > pair of Pomona connectors -- when the wind blows, they simply un-mate. > For the fan spreaders, cut short lengths (12-18 inches is great) of > 1/2-in PVC conduit, drill holes about 3/4-in from each end to pass the > wires through. Make this antenna as physically robust as possible to > withstand the wind. At a minimum, #10 THHN for the long top sections > that carry the stress. #12 or #14 is fine for the shorter top sections. > Don't make any soldered connections -- they don't weather well, and wire > tends to break at a soldered joint. Instead, use split-bolt copper clamp > connectors sized to fit the wire you're using. For support rope, use > 5/16-in rope from http://www.synthetictextilesinc.com/supportham.html > It's resold by lots of ham vendors, but Synthetic Textiles is a bit > cheaper. Smaller rope is sufficient for strength, but you'll appreciate > the larger size when you're trying to pull on it to maximize tension, > which pulls it higher. :) Don't use hardware store pulleys -- instead, > use marine pulleys (good) or this excellent "rescue" pulley, which is > also easy to rig. > > http://www.ropescoursewarehouse.com/catalog1/advancedwebpage.aspx?cg=1851&cd=4&SKUTYPE=202&SKUFLD=SKU&DM=1250&WEBID=914&gclid=CKfCobGOr8sCFQWUfgod5DUOHQ > > > Out here in CA, the West Marine is the place to buy marine pulleys. > > 73, Jim K9YC > > On Mon,3/7/2016 5:50 AM, NC3Z Gary wrote: >> Now I want to be able to use this antenna for 80M as well as the non-DX >> portion of 160M. I can house a autotuner at the base (or make my own >> network but that would require control lines). My thinking is to make >> the 160M a 5/16 WL vs 1/4 to be more beneficial to 80M tuning without >> loosing anything on 160M. > > _ > Topband Reflector Archives - http://www.contesting.com/_topband > . > _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Low band antenna project questions
Good recommendations. I did a couple of things differently for my 160 T hung to 3 trees, I use Lewmar or Ronstan or Harken small swivel blocks, cheaper, more durable in tough environments and the swivel helps keep lines from tangling or twist from messing things up. Don't use 3 strand rope. Whichever I can find cheapest in 30mm or so. http://www.mauriprosailing.com/us/product/LEW29925001BK.html?gclid=CLC7qJefr8sCFYRrfgodbeYH_Q http://www.fisheriessupply.com/lewmar-30mm-synchro-control-blocks For any serious load the ball bearing blocks are terrific. I loop my hoist line thru the block to the tie off (or weight or bungee), so if the antenna wire breaks, I still have a line through the pulley. I use a separate line over the tree branch for the pulley and after a while the tree grows around it and it won't come down. The wind oscillation should be in the antenna hoist line, not the pulley line to minimize chafe. Let the block sheave do the moving. With a loop the hoist line can be replaced with a new one with a careful splice/tape to go thru the block. 1/4" braid dacron from Synthetic is awesome and plenty strong enough, and ok on the hands with gloves to what I can pull (100# +). For the top T wire, I use Davis RF 13ga copperweld stranded with the poly cover, no stretch, less weight, high strength, and less corrosion http://www.davisrf.com/antenna-wire/polystealth.php I always use a bowline knot and Scotch 33 tape the bitter end after another half hitch. It's a great knot but I've seen them shake out under cyclic loads. I use a 50::25 ohm TLT which is a very good match for my antenna, easy, broad band and zilch loss. My T is tuned low in the band and then use series caps to cover the band to 1980 or so. Grant KZ1W On 3/7/2016 9:48 AM, Jim Brown wrote: Hi Gary, The antenna you describe should work quite well on both bands, but I'll suggest a couple of tweaks to make the matching easier. First, make it a Tee -- if you have a catenary, you can support a Tee as easily as an L. Second, make the top section a fan (like a fan dipole) with short elements to resonate it on 80 and longer ones for 160. Third, don't worry about remoting the tuner unless you feedline is very long. Unless the match is really bad, feedline loss on 80 and 160 is pretty low, especially if you use RG8. Also, you can make the tuning more broadband (and electrically lengthen the vertical section by 1-2 percent) by using two parallel runs spaced 12-18 inches, tied together top and bottom. Do a simple NEC model to get dimensions. Finally, use as many radials as you can, don't worry a lot about length, just think more is better. :) BTW -- 50 ft on the ground will be close to a quarter wave on 80, 100 ft on 160. As to physical details -- get a good pulley at each end, tie one end down, put a weight on the other end, and use some sort of "mechanical fuse" at the feedpoint so that wind doesn't break it. I use a mating pair of Pomona connectors -- when the wind blows, they simply un-mate. For the fan spreaders, cut short lengths (12-18 inches is great) of 1/2-in PVC conduit, drill holes about 3/4-in from each end to pass the wires through. Make this antenna as physically robust as possible to withstand the wind. At a minimum, #10 THHN for the long top sections that carry the stress. #12 or #14 is fine for the shorter top sections. Don't make any soldered connections -- they don't weather well, and wire tends to break at a soldered joint. Instead, use split-bolt copper clamp connectors sized to fit the wire you're using. For support rope, use 5/16-in rope from http://www.synthetictextilesinc.com/supportham.html It's resold by lots of ham vendors, but Synthetic Textiles is a bit cheaper. Smaller rope is sufficient for strength, but you'll appreciate the larger size when you're trying to pull on it to maximize tension, which pulls it higher. :) Don't use hardware store pulleys -- instead, use marine pulleys (good) or this excellent "rescue" pulley, which is also easy to rig. http://www.ropescoursewarehouse.com/catalog1/advancedwebpage.aspx?cg=1851&cd=4&SKUTYPE=202&SKUFLD=SKU&DM=1250&WEBID=914&gclid=CKfCobGOr8sCFQWUfgod5DUOHQ Out here in CA, the West Marine is the place to buy marine pulleys. 73, Jim K9YC On Mon,3/7/2016 5:50 AM, NC3Z Gary wrote: Now I want to be able to use this antenna for 80M as well as the non-DX portion of 160M. I can house a autotuner at the base (or make my own network but that would require control lines). My thinking is to make the 160M a 5/16 WL vs 1/4 to be more beneficial to 80M tuning without loosing anything on 160M. _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Low band antenna project questions
On 3/7/2016 11:05 AM, John Pescatore via Topband wrote: It is resonant on 160, with about 16 radials out now, so don't need a tuner there. I've tried it on other bands with a tuner in the shack, and performance is horrible. Could have been so much loss in the coax that a base of the antenna tuner might change things but I wouldn't want that to be my only HF antenna. 73 John K3TN If it is series resonant on 160, it is likely to be approximately parallel resonant on 80 and 40, with a very high drive impedance. This severe mismatch will give you a lot of loss in the coax, even though it might be low loss when matched. A tuner at the base of the antenna will solve this problem and you should have excellent results. The tuner, however, will have to be one that can match an impedance in many 100's or maybe 1000's of ohms. Not just any tuner. Rick N6RK _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Low band antenna project questions
Gary, Though our conditions are different, I also have a top height of somewhere around 50-60'. I don't know exactly, I run a sloper over the top of the tallest tree I can find from my radial plate. I'm at the edge of a marsh and every hurricane takes down trees and I need to get them up over what is left. The only tuner I have is in the k3 and I pretty much use that only to make the radio happy with the input of the amplifier. Half my radials are on the marsh and the other 1/2 are in the woods. Unlike your situation, I have a lot of excessively long radials about 130' each. I also have a 350' run of coax to the remote switchbox. I have the 129' long 160M sloper, an 80M Inv-L, 40M vert wire, 30M Vert wire and a butternut in the middle of the radial plate that I use for 20 only. Right before the radial plate is the distal end of an Ameritron RC5-8V coax switch. I don't need any tuner to have a good match on all of the HF bands with this: 160M = Sloper 80M = 80M vert 40M = 40M vert 30M = 30M vert 20M - Butternut 17M = 80M vert 15M = 40M vert 12M = 80M vert & 160 Sloper 10M = 160M Sloper You've gotten some great advice on specifically what to do from others, I am including this less specific info to try to demonstrate how it's worth experimenting with the info you've been given and you will surely find something that works well with your 50' height limit. 73, Gary KA1J _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Low band antenna project questions
Gary - I've had a 51' T up for 6 or 7 years now and it is a very good transmit antenna on 160. It is resonant on 160, with about 16 radials out now, so don't need a tuner there. I've tried it on other bands with a tuner in the shack, and performance is horrible. On most bands, it heard/talked worse than a mutliband vertical I had up for a while and is many dB below my 135' OCF dipole at the same height on every band other than 160. I think I modeled it once using one of the online programs and you can see a very spiky pattern. Could have been so much loss in the coax that a base of the antenna tuner might change things but I wouldn't want that to be my only HF antenna. 73 John K3TN _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Low band antenna project questions
Hi Gary, The antenna you describe should work quite well on both bands, but I'll suggest a couple of tweaks to make the matching easier. First, make it a Tee -- if you have a catenary, you can support a Tee as easily as an L. Second, make the top section a fan (like a fan dipole) with short elements to resonate it on 80 and longer ones for 160. Third, don't worry about remoting the tuner unless you feedline is very long. Unless the match is really bad, feedline loss on 80 and 160 is pretty low, especially if you use RG8. Also, you can make the tuning more broadband (and electrically lengthen the vertical section by 1-2 percent) by using two parallel runs spaced 12-18 inches, tied together top and bottom. Do a simple NEC model to get dimensions. Finally, use as many radials as you can, don't worry a lot about length, just think more is better. :) BTW -- 50 ft on the ground will be close to a quarter wave on 80, 100 ft on 160. As to physical details -- get a good pulley at each end, tie one end down, put a weight on the other end, and use some sort of "mechanical fuse" at the feedpoint so that wind doesn't break it. I use a mating pair of Pomona connectors -- when the wind blows, they simply un-mate. For the fan spreaders, cut short lengths (12-18 inches is great) of 1/2-in PVC conduit, drill holes about 3/4-in from each end to pass the wires through. Make this antenna as physically robust as possible to withstand the wind. At a minimum, #10 THHN for the long top sections that carry the stress. #12 or #14 is fine for the shorter top sections. Don't make any soldered connections -- they don't weather well, and wire tends to break at a soldered joint. Instead, use split-bolt copper clamp connectors sized to fit the wire you're using. For support rope, use 5/16-in rope from http://www.synthetictextilesinc.com/supportham.html It's resold by lots of ham vendors, but Synthetic Textiles is a bit cheaper. Smaller rope is sufficient for strength, but you'll appreciate the larger size when you're trying to pull on it to maximize tension, which pulls it higher. :) Don't use hardware store pulleys -- instead, use marine pulleys (good) or this excellent "rescue" pulley, which is also easy to rig. http://www.ropescoursewarehouse.com/catalog1/advancedwebpage.aspx?cg=1851&cd=4&SKUTYPE=202&SKUFLD=SKU&DM=1250&WEBID=914&gclid=CKfCobGOr8sCFQWUfgod5DUOHQ Out here in CA, the West Marine is the place to buy marine pulleys. 73, Jim K9YC On Mon,3/7/2016 5:50 AM, NC3Z Gary wrote: Now I want to be able to use this antenna for 80M as well as the non-DX portion of 160M. I can house a autotuner at the base (or make my own network but that would require control lines). My thinking is to make the 160M a 5/16 WL vs 1/4 to be more beneficial to 80M tuning without loosing anything on 160M. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Low band antenna project questions
Gary, Given the 50' maximum height of a presumably level catenary line supported at its ends, there are two things you can do to significantly improve the performance of the 50' vertical wire hanging below. 1. Obtain a stout piece of bamboo. Try to make at least a 10' long pole, and this may require using two bamboo pieces butted together. Make two rope bridles. Attach the ends of both to opposite ends of the bamboo pole. Make sure that the length of each bridle is such that when both are pulled taut from each bridle's center, a square pattern is formed. Using a goodly quantity of light-weight wire (#26 stranded copper that has a modest coating of pvc insulation is a suggestion), make yourself a reasonably dense top-hat by running lengths of the chosen wire out in rays, with each ray extending to the perimeter of the rope bordered square that you've formed. Then run the same gauge of wire around the square perimeter of the rope square. Using lead-free solder (recommended is 96% Sn, 4% Ag), solder all the rays together at their center, together with the top end of your vertical antenna wire, and each junction of the ray ends to the perimeter wire. Use GE's pure silicone black caulk, daubing some on every soldered joint. All this work can be easily done at ground level, after having first driven in a couple of ground stakes at the center of each rope bridle to keep the bridles taut in their intended square configuration. Break your catenary line at the point where you want your vertical wire to hang. Attach each inner end of the catenary line to the center of each bridle rope. Elevate! 2. Use a much shorter bamboo pole and appropriately shorter rope bridles. Attach a self-supporting length of light-weight aluminum tubing to the center of the pole and connect that to the top of your vertical antenna wire. Fasten the bridles to the split catenary rope as in no. 1. My preference is for no. 1. This because the taller a vertical antenna, the more it needs longer radials to harvest radiation splashed off the ground for recycling back to the antenna's feedpoint. Because you are limited in the length of your radials, a shorter capacitance top-loaded vertical will play better than a >50' tall vertical. Have a look in the QST archives for the picture of Jerry Sevick's eight-foot tall 40-meter vertical wearing a very large top hat. 73, Charles, W2SH > From: n...@outlook.com > To: topband@contesting.com > Date: Mon, 7 Mar 2016 15:28:08 + > Subject: Re: Topband: Low band antenna project questions > > That is the highest I can get support for. I am in far eastern NC and > right on the sound where we get hurricanes and nor'easters so I am not > putting up the towers I had at the old QTH. > > > Gary Mitchelson > NC3Z/4 Pamlico County, NC FM15 > > On 07-Mar-16 09:49, Robert Harmon wrote: > > Gary, > > Are you restricted to 50 feet high max ? > > > > Bob > > K6UJ > > > > On 3/7/16 5:50 AM, NC3Z Gary wrote: > >> OK, still working on my permanent low band antenna and what I can fit > >> for an effective antenna. The space I have is a recently cleared forest > >> area. I had originally considered a full size loop but the best I could > >> do is 50' high, although that would be a bit higher than my temporary > >> dipole it is not much in the scheme of things. And I keep getting talked > >> out of it. > >> > _ > Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Low band antenna project questions
That is the highest I can get support for. I am in far eastern NC and right on the sound where we get hurricanes and nor'easters so I am not putting up the towers I had at the old QTH. Gary Mitchelson NC3Z/4 Pamlico County, NC FM15 On 07-Mar-16 09:49, Robert Harmon wrote: > Gary, > Are you restricted to 50 feet high max ? > > Bob > K6UJ > > On 3/7/16 5:50 AM, NC3Z Gary wrote: >> OK, still working on my permanent low band antenna and what I can fit >> for an effective antenna. The space I have is a recently cleared forest >> area. I had originally considered a full size loop but the best I could >> do is 50' high, although that would be a bit higher than my temporary >> dipole it is not much in the scheme of things. And I keep getting talked >> out of it. >> _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Low band antenna project questions
Gary, Are you restricted to 50 feet high max ? Bob K6UJ On 3/7/16 5:50 AM, NC3Z Gary wrote: OK, still working on my permanent low band antenna and what I can fit for an effective antenna. The space I have is a recently cleared forest area. I had originally considered a full size loop but the best I could do is 50' high, although that would be a bit higher than my temporary dipole it is not much in the scheme of things. And I keep getting talked out of it. I have walked the back many times with the tape measure and lines to see what I can fit, and what I can fit is a catenary line to support a T or L at 50' above ground. And after reading numerous articles the consensus was not to use radials much longer than the vertical height. I can easily fit 32 radials @ up to 75' each. Now I want to be able to use this antenna for 80M as well as the non-DX portion of 160M. I can house a autotuner at the base (or make my own network but that would require control lines). My thinking is to make the 160M a 5/16 WL vs 1/4 to be more beneficial to 80M tuning without loosing anything on 160M. With the above limitations is this an effective solution? T or L ? Am I missing anything? Working on a RX antenna later. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Low band antenna project questions
Gary, I have an inverted L similar to this setup and it does a decent job on 160 through 20 meters. I put up an inverted L supported in trees because it fit he backyard layout. It is 5/16 long with a 50-55 foot vertical component. I have 30 radials 70 feet long and 4 130 foot radials because this is what it into the yard. I only run 100 watts and use an MFJ-929 autotuner. I first started out with a 160 meter dipole at 50 feet and this inverted L performs much better. I use one set of halyards for the supports over the trees and a second set of pulleys to support the L. The L support lines have wood stump counterweights to allow for sway. I can easily lower the inverted L to prepare for a major storm. Good luck with the installation. Mike N2MS - Original Message - From: NC3Z Gary To: topband@contesting.com Sent: Mon, 07 Mar 2016 13:50:29 - (UTC) Subject: Topband: Low band antenna project questions OK, still working on my permanent low band antenna and what I can fit for an effective antenna. The space I have is a recently cleared forest area. I had originally considered a full size loop but the best I could do is 50' high, although that would be a bit higher than my temporary dipole it is not much in the scheme of things. And I keep getting talked out of it. I have walked the back many times with the tape measure and lines to see what I can fit, and what I can fit is a catenary line to support a T or L at 50' above ground. And after reading numerous articles the consensus was not to use radials much longer than the vertical height. I can easily fit 32 radials @ up to 75' each. Now I want to be able to use this antenna for 80M as well as the non-DX portion of 160M. I can house a autotuner at the base (or make my own network but that would require control lines). My thinking is to make the 160M a 5/16 WL vs 1/4 to be more beneficial to 80M tuning without loosing anything on 160M. With the above limitations is this an effective solution? T or L ? Am I missing anything? Working on a RX antenna later. -- Gary Mitchelson NC3Z/4 Pamlico County, NC FM15 _ _ Topband Reflector Archives - http://www.contesting.com/_topband