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Log Periodic ant
Hi All.....
I have just bought a Yaesu VR5000 receiver/scanner and while looking round for a wideband antenna came across the good old log periodic but what a price!!!, circa £200+...... I have a discone but it`s not a lot of use up around the 2gig area (or anywhere else!!) so i thought i might have a go at making my own, the magloops are working great as is the QFH 137megs weathersat ant, thanks to everyones assistance!..... Is there any software around to design a log periodic to around 2400megs??.....i`ve found some but is there any better?.. Regards... Lee......de G6ZSG.... |
Log Periodic ant
On Tue, 29 Aug 2006 07:43:15 GMT, "Lee"
wrote: Hi All..... I have just bought a Yaesu VR5000 receiver/scanner and while looking round for a wideband antenna came across the good old log periodic but what a price!!!, circa £200+...... I have a discone but it`s not a lot of use up around the 2gig area (or anywhere else!!) so i thought i might have a go at making my own, the magloops are working great as is the QFH 137megs weathersat ant, thanks to everyones assistance!..... Is there any software around to design a log periodic to around 2400megs??.....i`ve found some but is there any better?.. Regards... Lee......de G6ZSG.... Hi Lee, Simply build a discone to the scale of 2GHz. The reason why the present one might not work is that if it is designed for a very lower base frequency, it is TOO BIG. Discones can be as wide banded as over a 10:1 frequency range, but this is for matching (certainly useful, but this does not necessarily make it usable). For instance, if you have a discone that has a low frequency design of 450 MHz and claims to go as high as 2GHz; then it may well match at those frequency extremes. On the other hand, at 450 MHz it is looking out at the horizon, BUT at 2GHz it is looking into the sky. The higher the frequency, the more the most favored direction climbs up. In other words it becomes deaf unless you want to hear an overhead satellite. This may be the source of your disdain for your current discone. Build a Discone whose lowest frequency would be around 1.2 GHz. How do you know what the lowest frequency is? Measure one of the skirt elements (the skeletal part of the cone). It should be a quarter wave of the lowest frequency of intended use. In this case, 1.2GHz, that would be 6 cm or so. The high end would then comfortably range up to 2.4 GHz, match, and still look at the horizon. Of course, the simple ground plane at 2GHz would work as well, unless you really need widebandedness (and it would probably work even then). Simply observe the simple geometry of keeping the element no longer than 5/8ths wavelength at the HIGHEST frequency you plan to monitor. If you still want a log periodic, simple scaling will always work. However, remember that scaling must be applied to ALL physical dimensions (this means element diameters too). 73's Richard Clark, KB7QHC |
Log Periodic ant
"Richard Clark" wrote in message ... On Tue, 29 Aug 2006 07:43:15 GMT, "Lee" wrote: Hi All..... I have just bought a Yaesu VR5000 receiver/scanner and while looking round for a wideband antenna came across the good old log periodic but what a price!!!, circa £200+...... I have a discone but it`s not a lot of use up around the 2gig area (or anywhere else!!) so i thought i might have a go at making my own, the magloops are working great as is the QFH 137megs weathersat ant, thanks to everyones assistance!..... Is there any software around to design a log periodic to around 2400megs??.....i`ve found some but is there any better?.. Regards... Lee......de G6ZSG.... Hi Lee, Hi Richard.... Simply build a discone to the scale of 2GHz. The reason why the present one might not work is that if it is designed for a very lower base frequency, it is TOO BIG. Discones can be as wide banded as over a 10:1 frequency range, but this is for matching (certainly useful, but this does not necessarily make it usable). For instance, if you have a discone that has a low frequency design of 450 MHz and claims to go as high as 2GHz; then it may well match at those frequency extremes. On the other hand, at 450 MHz it is looking out at the horizon, BUT at 2GHz it is looking into the sky. The higher the frequency, the more the most favored direction climbs up. In other words it becomes deaf unless you want to hear an overhead satellite. This may be the source of your disdain for your current discone. Build a Discone whose lowest frequency would be around 1.2 GHz. How do you know what the lowest frequency is? Measure one of the skirt elements (the skeletal part of the cone). It should be a quarter wave of the lowest frequency of intended use. In this case, 1.2GHz, that would be 6 cm or so. The high end would then comfortably range up to 2.4 GHz, match, and still look at the horizon. Of course, the simple ground plane at 2GHz would work as well, unless you really need widebandedness (and it would probably work even then). Simply observe the simple geometry of keeping the element no longer than 5/8ths wavelength at the HIGHEST frequency you plan to monitor. Yes, thanks for the info but i would like a little more gain than a standard discone gives...going to a parabolic discone would be the alternate option but a little too involved.... 73... Lee ....de G6ZSG... |
Log Periodic ant
On Tue, 29 Aug 2006 11:27:10 GMT, "Lee"
wrote: Yes, thanks for the info but i would like a little more gain than a standard discone gives...going to a parabolic discone would be the alternate option but a little too involved.... Parabolic discone??!!!?? Involved is not the word. Hi Lee, Everyone wants more gain. You don't say why and that may negate wanting gain. At the frequency you are desiring, performance is very much limited to line of sight and even 2M handhelds with rubber duckies can work the Space Shuttle an hundred miles up. Consider the downside of gain: you are a tourist at the Grand Canyon and you put a telephoto lens on your camera (high gain). When you get home and show your pictures to friends, they might ask why you went to the Grand Canyon but took pictures only of the river bed at the bottom, or a cactus on the ridge. Too much gain for the intended use which was to show the ENTIRE canyon in one shot. This would take a wide-angle lens (very low gain). Anyway, simple scaling works. Just research the model of antenna that gives you the gain characteristics you want, and scale to your band of interest. The downside here is you may find that you have designed yourself into a corner because you cannot find the right stock that supports the dimensions. For a log periodic, this might not matter so much, and especially for a receiver, but latitude is not generous. 73's Richard Clark, KB7QHC |
Log Periodic ant
"Richard Clark" wrote in message ... On Tue, 29 Aug 2006 11:27:10 GMT, "Lee" wrote: Yes, thanks for the info but i would like a little more gain than a standard discone gives...going to a parabolic discone would be the alternate option but a little too involved.... Parabolic discone??!!!?? Involved is not the word. Hi Lee, Everyone wants more gain. You don't say why and that may negate wanting gain. At the frequency you are desiring, performance is very much limited to line of sight and even 2M handhelds with rubber duckies can work the Space Shuttle an hundred miles up. Consider the downside of gain: you are a tourist at the Grand Canyon and you put a telephoto lens on your camera (high gain). When you get home and show your pictures to friends, they might ask why you went to the Grand Canyon but took pictures only of the river bed at the bottom, or a cactus on the ridge. Too much gain for the intended use which was to show the ENTIRE canyon in one shot. This would take a wide-angle lens (very low gain). I have a wide angle lens (low gain) it`s known as a discone !!! freq range to 3000megs, supposedly 0db ref dipole that has heard one or two weak signals just outside its range....now i need a telephoto lens to make out what it is.......a wideband antenna with gain -- a log periodic!!!! With respect Richard, i have a scanning radio receiver that scans up to 2500megs - that`s a lot of coverage which requires more gain the higher you go....a discone just doesn`t cut it gainwise so i need a wideband antenna with more directional gain to work alongside the discone...a yagi with one meg bandwidth isn`t much use either...imagine how many i would have lying around!!! besides, i know how to design those....... :-) Anyway, simple scaling works. Just research the model of antenna that gives you the gain characteristics you want, and scale to your band of interest. The downside here is you may find that you have designed yourself into a corner because you cannot find the right stock that supports the dimensions. For a log periodic, this might not matter so much, and especially for a receiver, but latitude is not generous. If i knew how to scale or re-engineer an existing design, i wouldn`t be on this NG asking how to do it ... Thanks for the advice Richard ...... 73... Lee......G6ZSG...... |
Log Periodic ant
On Wed, 30 Aug 2006 06:19:09 GMT, "Lee"
wrote: I have a wide angle lens (low gain) it`s known as a discone !!! freq range to 3000megs, Hi Lee, Simply because it has a "frequency range to 3000megs" does not mean it is usable to 3000megs - only that it matches to 3000megs. Matching and usability are not strictly related. supposedly 0db ref dipole that has heard one or two weak signals just outside its range Antennas don't have "ranges." You may experience poor performance due to the combination of transmit power, path loss, and receiver sensitivity, but none of this has anything to do with the antenna (unless its poor construction adds loss). If you have too much path loss, not enough transmit power, or poor receive sensitivity, then, yes, a gain antenna will make up for those problems (as long as S+N/N is sufficient in the end) - but this still does not confer a range specification to an antenna. This would be whole lot simpler if you simply told us the model number of this discone. If i knew how to scale or re-engineer an existing design, i wouldn`t be on this NG asking how to do it ... You don't offer enough parameters like frequency span, gain, F/B, how long a feedline, what kind of feedline (lot of potential loss there) for someone to whip out a design here, and that wouldn't be a modest enterprise if you did. Scaling is the easiest solution, perhaps you should buy a log periodic. Google would be another solution, your problem would not be unique - would it? 73's Richard Clark, KB7QHC |
Log Periodic ant
"Richard Clark" wrote in message ... On Wed, 30 Aug 2006 06:19:09 GMT, "Lee" wrote: SNIP!!!! Richard, all i want is design software to build a LPA!!!! do you or don`t you know of any????? Lee.....G6ZSG....... |
Log Periodic ant
On Wed, 30 Aug 2006 07:04:08 GMT, "Lee"
wrote: Richard, all i want is design software to build a LPA!!!! do you or don`t you know of any????? EZNEC 73's Richard Clark, KB7QHC |
Log Periodic ant
"Richard Clark" wrote in message ... On Wed, 30 Aug 2006 07:04:08 GMT, "Lee" wrote: Richard, all i want is design software to build a LPA!!!! do you or don`t you know of any????? EZNEC Why didn`t you say that in the first place?? Thankyou... G6ZSG... 73's Richard Clark, KB7QHC |
Log Periodic ant
On Tue, 29 Aug 2006 07:43:15 GMT, "Lee"
wrote: I have just bought a Yaesu VR5000 receiver/scanner and while looking round for a wideband antenna .... Scanners are notorious for a lack of front end selectivity and resultant high intermodulation products / noise. Sometimes they depend on narrow band antennas to supplement their meagre front end selectivity. In the absense of external front end selectivity, you may find that the realisable sensitivity is quite a deal higher (tens of dB worse) than specification, depending on your own RF environment. Owen -- |
Log Periodic ant
"Owen Duffy" wrote in message ... On Tue, 29 Aug 2006 07:43:15 GMT, "Lee" wrote: I have just bought a Yaesu VR5000 receiver/scanner and while looking round for a wideband antenna ... Scanners are notorious for a lack of front end selectivity and resultant high intermodulation products / noise. Yes i am taking a bit of a chance with a wideband antenna Owen but if i can resolve a signal, it is a start.....i have built a bow tie can-tenna for 23cms which seems to work okay, now, i`ll build one for 13 cms with a corner reflector, only because i know something is there!!!. Sometimes they depend on narrow band antennas to supplement their meagre front end selectivity. Agreed!!. In the absense of external front end selectivity, you may find that the realisable sensitivity is quite a deal higher (tens of dB worse) than specification, depending on your own RF environment. That is where i will need a narrow filter pre-amp which will be bought (or built) when needed..... Thanks for your input Owen, the Yaesu is certainly a great deal better than the AOR 2002 which is as wide as a barn door, but served its purpose!!!..... Regards.. Lee....G6ZSG.... |
Log Periodic ant
ARRL Antenna Handbook gives all the LPDA design equations.
However, LPDAs do not have high gain!! They have typical gain of 6 to 8 [+/-] dBd and broad bandwidth. They typically function as either a three or four element driven array. They are driven arrays, not parasitic [i.e. Yagi principle] designs. Also, LPDAs for 3,000 MHz will have a L/D ratio issues with element geometry and general construction will require fairly precise measurements. Unlike a Yagi, a long boom length LPDA does not equate into higher gain. /s/ DD Lee wrote: "Richard Clark" wrote in message ... On Wed, 30 Aug 2006 06:19:09 GMT, "Lee" wrote: SNIP!!!! Richard, all i want is design software to build a LPA!!!! do you or don`t you know of any????? Lee.....G6ZSG....... |
Log Periodic ant
"Dave" wrote in message . .. ARRL Antenna Handbook gives all the LPDA design equations. However, LPDAs do not have high gain!! They have typical gain of 6 to 8 [+/-] dBd and broad bandwidth. They typically function as either a three or four element driven array. They are driven arrays, not parasitic [i.e. Yagi principle] designs. Also, LPDAs for 3,000 MHz will have a L/D ratio issues with element geometry and general construction will require fairly precise measurements. Unlike a Yagi, a long boom length LPDA does not equate into higher gain. /s/ DD Yes thanks Dave i am aware of the functions of a LPA i just need a little directivity and a little more gain than a discone offers, plus design software!!... Regards... Lee....G6ZSG...... |
Log Periodic ant
On Wed, 30 Aug 2006 08:16:12 GMT, "Lee"
wrote: EZNEC Why didn`t you say that in the first place?? Hi Lee, Because of various clues in your discussion, and your claim If i knew how to scale or re-engineer an existing design, i wouldn`t be on this NG asking how to do it ... Re-engineering goes to the heart of a successful outcome and is part and parcel to modeling. On the other hand, the trivial work for simple scaling will always give a solution. EZNEC, although probably the best modeler for the occasion, is one that does require deep knowledge of design elements and program operation in this case. Modeling an LPDA is not trivial. 73's Richard Clark, KB7QHC |
Log Periodic ant
Lee wrote:
Yes thanks Dave i am aware of the functions of a LPA i just need a little directivity and a little more gain than a discone offers, plus design software!!... If you're looking for software to design an antenna for you, EZNEC isn't it. EZNEC will analyze an antenna you design, but it won't design it for you. Roy Lewallen, W7EL |
Log Periodic ant
On Tue, 29 Aug 2006 07:43:15 GMT, "Lee"
wrote: Hi All..... I have just bought a Yaesu VR5000 receiver/scanner and while looking round for a wideband antenna came across the good old log periodic but what a price!!!, circa £200+...... I have a discone but it`s not a lot of use up around the 2gig area (or anywhere else!!) so i thought i might have a go at making my own, the magloops are working great as is the QFH 137megs weathersat ant, thanks to everyones assistance!..... Is there any software around to design a log periodic to around 2400megs??.....i`ve found some but is there any better?.. http://members.aon.at/hwabnig/ input your numbers.... |
Log Periodic ant
"Helmut Wabnig" *_.-_- wrote in message ... On Tue, 29 Aug 2006 07:43:15 GMT, "Lee" wrote: Is there any software around to design a log periodic to around 2400megs??.....i`ve found some but is there any better?.. http://members.aon.at/hwabnig/ input your numbers.... Thankyou Helmut, very much apreciated....... Lee.......G6ZSG..... |
Log Periodic ant
Why try to design and build one if you can get a 900 to 2600MHz version
for US$12 or a 2 to 11GHz version for US$6. See Ebay items 300021857426 and 300021856873. How about 400 to 900MHz for US$24, item 300021857046. Cheers! Bob Lee wrote: "Helmut Wabnig" *_.-_- wrote in message ... On Tue, 29 Aug 2006 07:43:15 GMT, "Lee" wrote: Is there any software around to design a log periodic to around 2400megs??.....i`ve found some but is there any better?.. http://members.aon.at/hwabnig/ input your numbers.... Thankyou Helmut, very much apreciated....... Lee.......G6ZSG..... |
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