Re: [Xastir] Portable Digipeater Antenna?
> Was it a very old (about 35 years ago) QST article that headlined "My > Dipole Has A Gain Of 79dB"? Just the thought of Curt with a 79dB antenna is scary... here's my favorite version of the J-Pole... http://www.wb8erj.com/bike-ant.htm It's a good use for all that old 58 ohm lan cable... 73 Bill - WA7NWP ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Portable Digipeater Antenna?
On Mon, 2 Jul 2007, Ray Wells wrote: > Was it a very old (about 35 years ago) QST article that headlined "My > Dipole Has A Gain Of 79dB"? > > The crux of the article was that you need to know what you're comparing > with. In the magazine article the comparison was with a dummy load!! That's great! I may have to slip that into some conversations every now and then for fun. -- Curt, WE7U. APRS Client Comparisons: http://www.eskimo.com/~archer "Lotto:A tax on people who are bad at math." -- unknown "Windows: Microsoft's tax on computer illiterates." -- WE7U "The world DOES revolve around me: I picked the coordinate system!" ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Portable Digipeater Antenna?
The J-Antenna is an end-fed 1/2 wave with a 1/4 wave matching section. The bottom is tied together forming a "hairpin". The coax is moved up from the bottom to reach the 50 ohm point and secured. The feedpoint is actually balanced so there can be some issues feeding the antenna with coax, which is by design is unbalanced. As a matter of convention, the shield is tied to the short piece and the center conductor is tied to the long side. The matching section does not do much radiating because the signals are cancelled out, leaving the 1/2 wave section in the clear to do the radiating as vertical dipole. This antenna does have some gain associated with it over a ground plane antenna and it is a great way to start an argument. The nice thing about the J is that you do not need a ground or ground plane to work against. Ray Wells wrote: Jason Winningham wrote: On Jul 1, 2007, at 7:59 AM, Richard Polivka, N6NKO wrote: I have just now created a vertical 1/2 wave dipole. I tune it with an MFJ box. A roll-up J-pole is slightly more complex to build (but not much!) and doesn't need a tuner. A J-pole has noticeably more gain than a dipole, too. -Jason kg4wsv Given that a J-pole is only a dipole with an alternative feed method (i.e. at the end rather than the centre), I have to wonder where this gain comes from. Ray vk2tv ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Portable Digipeater Antenna?
Jason Winningham wrote: On Jul 1, 2007, at 4:23 PM, Ray Wells wrote: Given that a J-pole is only a dipole with an alternative feed method (i.e. at the end rather than the centre), I have to wonder where this gain comes from. beats me, but when we fly 'em on the balloons, the J-pole has a better range. Could be that the lack of a balun isn't so bad with a J-pole than with a dipole. Could be some other construction issue, too. -Jason kg4wsv Was it a very old (about 35 years ago) QST article that headlined "My Dipole Has A Gain Of 79dB"? The crux of the article was that you need to know what you're comparing with. In the magazine article the comparison was with a dummy load!! When you run them in a balloon, do you hang the J-pole down from the balloon? The reason I ask is that a dipole has maximum radiation at right angle to the element. An end-fed dipole is no different, providing the pattern isn't being disturbed by "something". The J-pole, being an end-fed dipole "should" be the same. Here's the "but". If the feed section of a J-pole radiates (and it often does), it radiates out of phase with the dipole element, causing the radiation pattern to move away from being at right angles to the element. With an inverted J-pole, i.e. one hanging down from the ballon, the antenna pattern would have downward tilt, a desirable characteristic given the height a balloon can achieve. This could be a case of having the antenna pattern where you want it rather than the absolute gain of the antenna, a case where your particular antenna does indeed work better than some others. Ray vk2tv ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Portable Digipeater Antenna?
On Jul 1, 2007, at 4:23 PM, Ray Wells wrote: Given that a J-pole is only a dipole with an alternative feed method (i.e. at the end rather than the centre), I have to wonder where this gain comes from. beats me, but when we fly 'em on the balloons, the J-pole has a better range. Could be that the lack of a balun isn't so bad with a J-pole than with a dipole. Could be some other construction issue, too. -Jason kg4wsv ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Portable Digipeater Antenna?
Jason Winningham wrote: On Jul 1, 2007, at 7:59 AM, Richard Polivka, N6NKO wrote: I have just now created a vertical 1/2 wave dipole. I tune it with an MFJ box. A roll-up J-pole is slightly more complex to build (but not much!) and doesn't need a tuner. A J-pole has noticeably more gain than a dipole, too. -Jason kg4wsv Given that a J-pole is only a dipole with an alternative feed method (i.e. at the end rather than the centre), I have to wonder where this gain comes from. Ray vk2tv ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Portable Digipeater Antenna?
On Sun, 01 Jul 2007 14:42:41 -0500, Gerry Creager wrote: >3. If you were to expand the braid and double it back over the jacket >of the coax, you'd achieve the decoupling you're trying to get with the >(effectively HF) choke. A similar decoupler can theoretically (meaning, >I've not tried this yet) with a piece of 1/2 in pvc and aluminum or >copper tape bonded (electrically) to the shield and also .52 wave long. > >This is a good idea for a short-term, temporary, quickie antenna. What you're talking about is basically this: http://athensarc.org/sleevedipole.asp The feed needs to be offset from the center because of the end effect of the dipole element interacting with the coax. They can be made with coax as you describe above, I've seen them called a "coaxial dipole" in the past. -- Jim Shorney -->.<--Put complaints in this box jshorney (at) inebraska.com Ham Radio NU0C Lincoln, NE, USA EN10ps http://incolor.inetnebr.com/jshorney/ ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Portable Digipeater Antenna?
On Sunday 01 July 2007 15:42:41 Gerry Creager wrote: > Couple of thoughts here. > > 1. Coax-seal is evil and messy. > > > 2. For short-term protection against the elements, I recommend Scotch > 23 or 130 rubberized splicing tape plus or minus ScotchKote. > > 3. If you were to expand the braid and double it back over the jacket > of the coax, you'd achieve the decoupling you're trying to get with the > (effectively HF) choke. A similar decoupler can theoretically (meaning, > I've not tried this yet) with a piece of 1/2 in pvc and aluminum or > copper tape bonded (electrically) to the shield and also .52 wave long. > > This is a good idea for a short-term, temporary, quickie antenna. > > gerry > are we talking short term in a pinch workable antennae?? a coax works well enough, but if we are talking about an antennae that is already made up to take out in the field and work with for events, camping trips, ect. then why not build a copper J pole? they are simple enough, work well enough -- my voice rig here at the house is working one thats stood up in the corner of my home office (its not been mounted in the attic its future perminate home) and are rugged enough to be just thrown in the back of a pickup or car and hauled anywhere. my suggestion -- Chris Thompson ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Portable Digipeater Antenna?
Couple of thoughts here. 1. Coax-seal is evil and messy. 2. For short-term protection against the elements, I recommend Scotch 23 or 130 rubberized splicing tape plus or minus ScotchKote. 3. If you were to expand the braid and double it back over the jacket of the coax, you'd achieve the decoupling you're trying to get with the (effectively HF) choke. A similar decoupler can theoretically (meaning, I've not tried this yet) with a piece of 1/2 in pvc and aluminum or copper tape bonded (electrically) to the shield and also .52 wave long. This is a good idea for a short-term, temporary, quickie antenna. gerry Richard Polivka, N6NKO wrote: Here is a quick and dirty one. We all have coax, wire ties, and a good pitching arm. Sometimes a mast is not the easiest thing to install but if you have tall overhanging objects, this helps. I always carry a spool of mason's twine (either pink or electric green/yellow). The antenna is made out of RG-58. I strip back about 22 inches to expose the center conductor, making sure that the outer shield does not short against the exposed center conductor. I also put a little coax-seal at that point to seal the cable against the elements. I form a loop at the end of the center conductor so the length is .52 meters. At the same distance down the coax from the strip point, I put about six-eight turn coil about 3-4 inches in diameter, straight wind, not scatter wind. I hold the inductor together with the plastic wire ties. I have just now created a vertical 1/2 wave dipole. I tune it with an MFJ box. Tuning is accomplished with it hanging in an accessible spot off the ground and adjusting where the coil is and the length of the exposed copper center conductor. The antenna works either inside or out. It may not be a gain antenna, but it is simple, easy to store, easy to use, and costs are just for the coax, connector and wire ties. A nice safety aspect of this is that there are no radials sticking out. It can be used inside in a building ( a pin in the wall to hang it on or in a suspended ceiling from a paperclip) or outside from a tree or lamp post. Don't use power lines as a hanger. You could get away using a cable TV cable or phone cable, but not power lines. 73 from 807, Richard, N6NKO Gerry Creager wrote: Steve Friis wrote: Jim Tolbert wrote: When considering adding a portable digipeater to a kit, what does an antenna mast buy you and what is the relationship between height and effectiveness? What is antenna height & specifications and equipment specifications that should be considered for a permanent antenna, centrally located in the county? We are in Burnett County, Wisconsin . according to the U.S. Census Bureau, the county has a total area of 2,280 km² (880 mi²). 2,128 km² (822 mi²) of it is land and 152 km² (59 mi²) of it (6.69%) is water. There are small elevation changes in the county (800 feet to 1440 feet above mean sea level) and the land is largely forested. Many thanx . jt My experience shows that doubling the height is equal to multiplying the power by 4. This is especially true if you can get above the tree-tops. Here in the desert, you can really increase the range by adding height. I bring a 25' pole to mount both the HF antenna on plus the dual band VHF/UHF antenna. My portable repeater exploits suggest that an antenna should be between 20-40 feet as a minimum... or else just left on the car. You see benefits with antenna height above local terrain that cannot be compensated for by either power or preamplification. I tend to shoot for one of several 30 foot portable masts I have available. One of the simplest is a "bull-float" handle available from concrete supply stores (but probably not Home Depot). they're ~1-3/4" diameter threaded poles, 10 ft long. I've put up to 4 together with 3-way, single level guying and had the antenna up for as long as a week. Easy to carry and handle, and total cost of the mast was less than $80. Very rugges... they have to be to survive the concrete business. gerry -- Gerry Creager -- [EMAIL PROTECTED] Texas Mesonet -- AATLT, Texas A&M University Cell: 979.229.5301 Office: 979.458.4020 FAX 979.862.3983 MAIL: AATLT, 3139 TAMU Physical: 1700 Research Parkway, Suite 160, College Station, TX 77843-3139 ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Portable Digipeater Antenna?
I agree about the windup j-pole. My complaint is that 300 ohm twinlead is not stable in construction or materials. I have had the geometries of a J change when rolled up, messing up the tunings. You also have to use a coax balun or beads on a J since it is a balanced antenna being fed from an unbalanced coax. Just personal preference. Coax is more easily had than twinlead in an emergency 73 from 807, Richard, N6NKO Jason Winningham wrote: On Jul 1, 2007, at 7:59 AM, Richard Polivka, N6NKO wrote: I have just now created a vertical 1/2 wave dipole. I tune it with an MFJ box. A roll-up J-pole is slightly more complex to build (but not much!) and doesn't need a tuner. A J-pole has noticeably more gain than a dipole, too. -Jason kg4wsv ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Portable Digipeater Antenna?
On Jul 1, 2007, at 7:59 AM, Richard Polivka, N6NKO wrote: I have just now created a vertical 1/2 wave dipole. I tune it with an MFJ box. A roll-up J-pole is slightly more complex to build (but not much!) and doesn't need a tuner. A J-pole has noticeably more gain than a dipole, too. -Jason kg4wsv ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Portable Digipeater Antenna?
Here is a quick and dirty one. We all have coax, wire ties, and a good pitching arm. Sometimes a mast is not the easiest thing to install but if you have tall overhanging objects, this helps. I always carry a spool of mason's twine (either pink or electric green/yellow). The antenna is made out of RG-58. I strip back about 22 inches to expose the center conductor, making sure that the outer shield does not short against the exposed center conductor. I also put a little coax-seal at that point to seal the cable against the elements. I form a loop at the end of the center conductor so the length is .52 meters. At the same distance down the coax from the strip point, I put about six-eight turn coil about 3-4 inches in diameter, straight wind, not scatter wind. I hold the inductor together with the plastic wire ties. I have just now created a vertical 1/2 wave dipole. I tune it with an MFJ box. Tuning is accomplished with it hanging in an accessible spot off the ground and adjusting where the coil is and the length of the exposed copper center conductor. The antenna works either inside or out. It may not be a gain antenna, but it is simple, easy to store, easy to use, and costs are just for the coax, connector and wire ties. A nice safety aspect of this is that there are no radials sticking out. It can be used inside in a building ( a pin in the wall to hang it on or in a suspended ceiling from a paperclip) or outside from a tree or lamp post. Don't use power lines as a hanger. You could get away using a cable TV cable or phone cable, but not power lines. 73 from 807, Richard, N6NKO Gerry Creager wrote: Steve Friis wrote: Jim Tolbert wrote: When considering adding a portable digipeater to a kit, what does an antenna mast buy you and what is the relationship between height and effectiveness? What is antenna height & specifications and equipment specifications that should be considered for a permanent antenna, centrally located in the county? We are in Burnett County, Wisconsin . according to the U.S. Census Bureau, the county has a total area of 2,280 km² (880 mi²). 2,128 km² (822 mi²) of it is land and 152 km² (59 mi²) of it (6.69%) is water. There are small elevation changes in the county (800 feet to 1440 feet above mean sea level) and the land is largely forested. Many thanx . jt My experience shows that doubling the height is equal to multiplying the power by 4. This is especially true if you can get above the tree-tops. Here in the desert, you can really increase the range by adding height. I bring a 25' pole to mount both the HF antenna on plus the dual band VHF/UHF antenna. My portable repeater exploits suggest that an antenna should be between 20-40 feet as a minimum... or else just left on the car. You see benefits with antenna height above local terrain that cannot be compensated for by either power or preamplification. I tend to shoot for one of several 30 foot portable masts I have available. One of the simplest is a "bull-float" handle available from concrete supply stores (but probably not Home Depot). they're ~1-3/4" diameter threaded poles, 10 ft long. I've put up to 4 together with 3-way, single level guying and had the antenna up for as long as a week. Easy to carry and handle, and total cost of the mast was less than $80. Very rugges... they have to be to survive the concrete business. gerry ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Portable Digipeater Antenna?
Steve Friis wrote: Jim Tolbert wrote: When considering adding a portable digipeater to a kit, what does an antenna mast buy you and what is the relationship between height and effectiveness? What is antenna height & specifications and equipment specifications that should be considered for a permanent antenna, centrally located in the county? We are in Burnett County, Wisconsin . according to the U.S. Census Bureau, the county has a total area of 2,280 km² (880 mi²). 2,128 km² (822 mi²) of it is land and 152 km² (59 mi²) of it (6.69%) is water. There are small elevation changes in the county (800 feet to 1440 feet above mean sea level) and the land is largely forested. Many thanx . jt My experience shows that doubling the height is equal to multiplying the power by 4. This is especially true if you can get above the tree-tops. Here in the desert, you can really increase the range by adding height. I bring a 25' pole to mount both the HF antenna on plus the dual band VHF/UHF antenna. My portable repeater exploits suggest that an antenna should be between 20-40 feet as a minimum... or else just left on the car. You see benefits with antenna height above local terrain that cannot be compensated for by either power or preamplification. I tend to shoot for one of several 30 foot portable masts I have available. One of the simplest is a "bull-float" handle available from concrete supply stores (but probably not Home Depot). they're ~1-3/4" diameter threaded poles, 10 ft long. I've put up to 4 together with 3-way, single level guying and had the antenna up for as long as a week. Easy to carry and handle, and total cost of the mast was less than $80. Very rugges... they have to be to survive the concrete business. gerry -- Gerry Creager -- [EMAIL PROTECTED] Texas Mesonet -- AATLT, Texas A&M University Cell: 979.229.5301 Office: 979.458.4020 FAX 979.862.3983 MAIL: AATLT, 3139 TAMU Physical: 1700 Research Parkway, Suite 160, College Station, TX 77843-3139 ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Portable Digipeater Antenna?
Jim Tolbert wrote: When considering adding a portable digipeater to a kit, what does an antenna mast buy you and what is the relationship between height and effectiveness? What is antenna height & specifications and equipment specifications that should be considered for a permanent antenna, centrally located in the county? We are in Burnett County, Wisconsin . according to the U.S. Census Bureau, the county has a total area of 2,280 km² (880 mi²). 2,128 km² (822 mi²) of it is land and 152 km² (59 mi²) of it (6.69%) is water. There are small elevation changes in the county (800 feet to 1440 feet above mean sea level) and the land is largely forested. Many thanx . jt My experience shows that doubling the height is equal to multiplying the power by 4. This is especially true if you can get above the tree-tops. Here in the desert, you can really increase the range by adding height. I bring a 25' pole to mount both the HF antenna on plus the dual band VHF/UHF antenna. Steve/WM5Z ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
[Xastir] Portable Digipeater Antenna?
When considering adding a portable digipeater to a kit, what does an antenna mast buy you and what is the relationship between height and effectiveness? What is antenna height & specifications and equipment specifications that should be considered for a permanent antenna, centrally located in the county? We are in Burnett County, Wisconsin . according to the U.S. Census Bureau, the county has a total area of 2,280 km² (880 mi²). 2,128 km² (822 mi²) of it is land and 152 km² (59 mi²) of it (6.69%) is water. There are small elevation changes in the county (800 feet to 1440 feet above mean sea level) and the land is largely forested. Many thanx . jt -- Jim & Peggy Tolbert [EMAIL PROTECTED] ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
