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HF Log Periodic WTB
Hello Folks
I would like to get a HF log periodic antenna 13 - 30 mcs can anyone recommend one? opinions please??? Lee. |
"Lee." wrote in message ... Hello Folks I would like to get a HF log periodic antenna 13 - 30 mcs can anyone recommend one? opinions please??? Lee. Check out www.SteppIR.com . I was looking for a log once. Bought the SteppIR yagi. 73 H. NQ5H |
"H. Adam Stevens, NQ5H" wrote in message ... "Lee." wrote in message ... Hello Folks I would like to get a HF log periodic antenna 13 - 30 mcs can anyone recommend one? opinions please??? Lee. Check out www.SteppIR.com . I was looking for a log once. Bought the SteppIR yagi. 73 H. NQ5H Yeah but the spacing don't change. Course either does a standard quad. hi. Tennadyne make a nice looking LP. Haven't used one tho. Dan/W4NTI |
I used a Tennadyne T8 for years.
Lee. wrote: Hello Folks I would like to get a HF log periodic antenna 13 - 30 mcs can anyone recommend one? opinions please??? Lee. |
Dear "Lee"
You do not tell us where you are nor whether you wish the antenna for amateur radio or commercial radio. In different parts of the world, different answers might be appropriate. http://www.tennadyne.com/ These people make a series of LPDAs that are competently designed and executed. However, if you are in the ice "zone" you need to know that at about 7 mm of ice the elements almost point straight down. As is often the case with antenna manufacturers who are selling mostly to radio amateurs, the safety factor on the wind rating is optimistic. This should be of interest only if you are hit by very destructive winds or if you are to place the antenna in the clear in an area of clear fields. (The usual urban area significantly reduces wind load.) Two hints: one needs the optional rear boom reinforcement and the optimum way to connect to the antenna is to connect a piece of coax to the front of the boom (obvious part) and run the same coax under the bottom boom (the antenna uses a twin boom) to the insulated boom to mast clamp. At that clamp, wind the coax on a uv stable plastic tube to form a choke and bridge the clamp with the choke. Do not put the choke out at the end of the boom. Let us know what you decide. 73 Mac N8TT -- J. Mc Laughlin - Michigan USA Home: "Lee." wrote in message ... Hello Folks I would like to get a HF log periodic antenna 13 - 30 mcs can anyone recommend one? opinions please??? Lee. |
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The Tennadyne LPDA was developed in Colorado to withstand 100 MPH
winds, snow and ice. They offer T-6, T-8, T-10 and T-12 element models from 12' to 30 booms. They have been in TX about 5 years now. Prices include UPS Ground service in lower 48 states. (The KMA is basically a T-8.) GL, Jim, K4SQR "J. McLaughlin" wrote in message ... Dear "Lee" You do not tell us where you are nor whether you wish the antenna for amateur radio or commercial radio. In different parts of the world, different answers might be appropriate. http://www.tennadyne.com/ These people make a series of LPDAs that are competently designed and executed. However, if you are in the ice "zone" you need to know that at about 7 mm of ice the elements almost point straight down. As is often the case with antenna manufacturers who are selling mostly to radio amateurs, the safety factor on the wind rating is optimistic. This should be of interest only if you are hit by very destructive winds or if you are to place the antenna in the clear in an area of clear fields. (The usual urban area significantly reduces wind load.) Two hints: one needs the optional rear boom reinforcement and the optimum way to connect to the antenna is to connect a piece of coax to the front of the boom (obvious part) and run the same coax under the bottom boom (the antenna uses a twin boom) to the insulated boom to mast clamp. At that clamp, wind the coax on a uv stable plastic tube to form a choke and bridge the clamp with the choke. Do not put the choke out at the end of the boom. Let us know what you decide. 73 Mac N8TT -- J. Mc Laughlin - Michigan USA Home: "Lee." wrote in message ... Hello Folks I would like to get a HF log periodic antenna 13 - 30 mcs can anyone recommend one? opinions please??? Lee. |
Dear Jim:
Note the careful wording that I used. One person's 100 mph wind is not what an engineer considers 100 mph wind. If one considers the average density of air at sea level (kg/m^3) and assumes that it is impacting a flat plate while traveling at a steady speed (m/s) one will estimate a resultant pressure (newtons/m^2), which is proportional to the square of the speed. If one then assumes a discounting factor for a round element with respect to the just mentioned flat plate and multiplies the distributed element area times the factor times the pressure one will produce a distribution of force along the element. Making assumptions about the mechanical properties of the element, one can calculate an estimate of when the element will be loaded to the yield point somewhere along the element. The steady-wind-speed-to-yield (suggested by the above scheme) is significantly higher than that suggested by good engineering practice. Good engineering practice applies safety factors to the steps just described. One of two major safety factors is the use of a higher safety factor than one in the pressure calculation. This safety factor takes into account the fact that real world wind is not steady ( it also takes into account the increased likelihood of faster wind on taller antennas). The second major safety factor has to do with the strength of the element material. It is bad engineering to take material to theoretical yield. This is especially inappropriate with antenna elements that are able to flex in wind gusts. It might be true that an antenna element that has been very carefully assembled from selected materials could be placed in a wind tunnel, have the wind speed slowly increased to a laminar 100 mph, and have the element just have a permanent bend. Note that I have said that the LPDAs are competently designed - both electromagnetically and mechanically. They are good value. However, the mechanical ratings, as is common with most antennas sold to radio amateurs, are optimistic. The standard of care for the mechanical design of non-amateur antennas includes the use of safety factors. It is reasonable to expect that most radio amateurs will effect this class of antenna in an urban area to a height of no more than about 70 feet. Under such conditions, the probability of damaging winds is small. Ice, in the North country, is the most likely agent that will kill an antenna. However, antennas of this class that are placed in clear, rural sites at serious heights will be much more likely to fail from wind than their counterparts in town. What I would like to see is a standard to rate amateur antennas in terms of pressure. 73 Mac N8TT -- J. Mc Laughlin - Michigan USA "Jim" wrote in message om... The Tennadyne LPDA was developed in Colorado to withstand 100 MPH winds, snow and ice. They offer T-6, T-8, T-10 and T-12 element models from 12' to 30 booms. They have been in TX about 5 years now. Prices include UPS Ground service in lower 48 states. (The KMA is basically a T-8.) GL, Jim, K4SQR |
Mac,
I understand your line of work is a patent attorney but it easily could have been one as a mechanical engineer. Your description of antenna mechanical design is outstanding. As far as designing to a yield point, Rohn did that with the fold over tower and from experience after selling a few did some retroactive strengthening ( I calculated it out myself when my one failed ) On antennas I have for years resorted to the use of fishing poles covered with aluminum foil. With respect to cost and survivability it easily beats the traditional aluminum designs which are rapidly getting beyond the amateurs reach. Do the math, fishing poles cost $1 a foot for a $800 commercial antenna you get how many feet of aluminum that you have to lift to the tower top ! Regards Art "J. McLaughlin" wrote in message ... Dear Jim: Note the careful wording that I used. One person's 100 mph wind is not what an engineer considers 100 mph wind. If one considers the average density of air at sea level (kg/m^3) and assumes that it is impacting a flat plate while traveling at a steady speed (m/s) one will estimate a resultant pressure (newtons/m^2), which is proportional to the square of the speed. If one then assumes a discounting factor for a round element with respect to the just mentioned flat plate and multiplies the distributed element area times the factor times the pressure one will produce a distribution of force along the element. Making assumptions about the mechanical properties of the element, one can calculate an estimate of when the element will be loaded to the yield point somewhere along the element. The steady-wind-speed-to-yield (suggested by the above scheme) is significantly higher than that suggested by good engineering practice. Good engineering practice applies safety factors to the steps just described. One of two major safety factors is the use of a higher safety factor than one in the pressure calculation. This safety factor takes into account the fact that real world wind is not steady ( it also takes into account the increased likelihood of faster wind on taller antennas). The second major safety factor has to do with the strength of the element material. It is bad engineering to take material to theoretical yield. This is especially inappropriate with antenna elements that are able to flex in wind gusts. It might be true that an antenna element that has been very carefully assembled from selected materials could be placed in a wind tunnel, have the wind speed slowly increased to a laminar 100 mph, and have the element just have a permanent bend. Note that I have said that the LPDAs are competently designed - both electromagnetically and mechanically. They are good value. However, the mechanical ratings, as is common with most antennas sold to radio amateurs, are optimistic. The standard of care for the mechanical design of non-amateur antennas includes the use of safety factors. It is reasonable to expect that most radio amateurs will effect this class of antenna in an urban area to a height of no more than about 70 feet. Under such conditions, the probability of damaging winds is small. Ice, in the North country, is the most likely agent that will kill an antenna. However, antennas of this class that are placed in clear, rural sites at serious heights will be much more likely to fail from wind than their counterparts in town. What I would like to see is a standard to rate amateur antennas in terms of pressure. 73 Mac N8TT -- J. Mc Laughlin - Michigan USA "Jim" wrote in message om... The Tennadyne LPDA was developed in Colorado to withstand 100 MPH winds, snow and ice. They offer T-6, T-8, T-10 and T-12 element models from 12' to 30 booms. They have been in TX about 5 years now. Prices include UPS Ground service in lower 48 states. (The KMA is basically a T-8.) GL, Jim, K4SQR |
Dear Art: Indeed, fishing poles are a main stay of amateur radio - and
very good value. As you have pointed out, I am a patent attorney (who is not looking for additional work). I am also a licensed professional engineer in Michigan. These two professions facilitate my "day job." As a follow on to your note about a certain Rohn tower (with an aside that their commercial products always conformed to standards - I have checked some of their calculations) I note that Heights Tower once included in their literature an accurate account of how to calculate "strength" and wind effects on their line of welded aluminum towers. It was clear from what they presented just what assumptions were being made. Such a full disclosure is commendable. 73 Mac N8TT -- J. Mc Laughlin - Michigan USA Home: "Art Unwin KB9MZ" wrote in message . .. Mac, I understand your line of work is a patent attorney but it easily could have been one as a mechanical engineer. Your description of antenna mechanical design is outstanding. snip |
Dear Art: Indeed, fishing poles are a main stay of amateur radio - and
very good value. As you have pointed out, I am a patent attorney (who is not looking for additional work). I am also a licensed professional engineer in Michigan. These two professions facilitate my "day job." As a follow on to your note about a certain Rohn tower (with an aside that their commercial products always conformed to standards - I have checked some of their calculations) I note that Heights Tower once included in their literature an accurate account of how to calculate "strength" and wind effects on their line of welded aluminum towers. It was clear from what they presented just what assumptions were being made. Such a full disclosure is commendable. 73 Mac N8TT -- J. Mc Laughlin - Michigan USA Home: "Art Unwin KB9MZ" wrote in message . .. Mac, I understand your line of work is a patent attorney but it easily could have been one as a mechanical engineer. Your description of antenna mechanical design is outstanding. snip |
The Tennadyne antennas are well built, perform quite nicely and are ruggedly
built. My T-10 withstood 5 major ice storms in central Iowa before I moved. I replaced it with a smaller T-6 at the new I moved. I am VERY pleased with its performance and the customer service at Tennadyne has been superb. Two additional positive factors: The Tennadynes are light weight and low wind-load, and at the same time rugged. The price is exceptional. I made some relatively careful meaurements of F/B on the T-10 with a step attenuator, and found the Front to Back ratio was never less than 17 dB from 13 through 30 Mhz, and I had no trouble working anyone in any pileup that I entered. I have not made similar measurements on the T-6, which is lower (50 ft instead of 70 ft), but I have yet to not be able to work someone in a pileup that I wanted. Obviously the forward gain of a yagi is going to be better than a comparbly sized LP. The frequency agility and price performance however, are unmatched, except for the most die hard contester. I like what the SteppIR continuously tuned yagis offer, but I don't like their unproven (over decades) mechanical reliability nor their high price. If I was starting over, and could afford triple the price of the LP, AND felt certain that the SteppIR would work reliably in all sorts of weather conditions for at least 10 years, I would be sorely tempted. This is not to dump on the reliability of the SteppIR...they just haven't been up long enough, much less long enough in difficult environments. It sure looks like a wonderful concept. ....hasan, N0AN "Lee." wrote in message ... Hello Folks I would like to get a HF log periodic antenna 13 - 30 mcs can anyone recommend one? opinions please??? Lee. |
Well Mac the fold over was simple to check, they had just one tube in
tension when using the fold over. I kept that piece of tubing for ages since the necking shape was so well defined. And why I mentioned it was that I believe stress aplied was in the region just below and in the plastisation area below the Y.P. Either way they quickly beefed up that area with welded plates. On the patent area I can really understand your reluctance to seak new work. I had a couple of forays into that area and found it most fraustrating since it now seems to come down to a battle of words and in one case a throw out because I had used a continental 7 which had a cross on it ! I have one more to write , for my own satisfaction, where even if the claims are not protectable the completion of the subject will give me closure plus another area for antenna experts to be derisive of. I once spoke to a miltary patent attorney from Washington regarding the direction the patent office was going and he told me that most of their patents were hnow being rejected however the 15 minuite appeal was being used with great success. So cost cutting aproaches appears to be financially successful in one section by overloading another section ! Cheers Art "J. McLaughlin" wrote in message ... Dear Art: Indeed, fishing poles are a main stay of amateur radio - and very good value. As you have pointed out, I am a patent attorney (who is not looking for additional work). I am also a licensed professional engineer in Michigan. These two professions facilitate my "day job." As a follow on to your note about a certain Rohn tower (with an aside that their commercial products always conformed to standards - I have checked some of their calculations) I note that Heights Tower once included in their literature an accurate account of how to calculate "strength" and wind effects on their line of welded aluminum towers. It was clear from what they presented just what assumptions were being made. Such a full disclosure is commendable. 73 Mac N8TT -- J. Mc Laughlin - Michigan USA Home: "Art Unwin KB9MZ" wrote in message . .. Mac, I understand your line of work is a patent attorney but it easily could have been one as a mechanical engineer. Your description of antenna mechanical design is outstanding. snip |
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