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#1
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Best 144/440 Antenna for Attic Installation
The Arrowantennas.com OSJ 146/440 J Pole antenna should work great for you.
They're small and very inexpensive. Mine works great. Rollie |
#2
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Best 144/440 Antenna for Attic Installation
I will second the OSJ 146/440. It is a "side by side" dual band
J-pole so it is only the height of a basic 2 meter J-pole, very sturdy, and does not require a ground plane. Mine is on the roof, but I have a good friend who has his installed in the attic of a condo. He hears and transmits very well. -- Alan WA4SCA |
#3
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Best 144/440 Antenna for Attic Installation
Rollie wrote:
The Arrowantennas.com OSJ 146/440 J Pole antenna should work great for you. They're small and very inexpensive. Mine works great. Rollie I built a replica, since he provides the dimensions, and it works very well. Just make sure you decouple the feedline with a choke. tom K0TAR |
#4
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Best 144/440 Antenna for Attic Installation
On 20-Jul-2009, "Rollie" wrote: The Arrowantennas.com OSJ 146/440 J Pole antenna should work great for you. They're small and very inexpensive. Mine works great. Rollie I see that they have a 4.8/5 rating on eham.net. I will definitely look into them. From the picture, it looks like one of the poles has a SO239 connector, but the others don't. Are the two other poles passive? What's the radiation pattern? Another antenna I've been looking at is the Diamond X50A. |
#5
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Best 144/440 Antenna for Attic Installation
I see that they have a 4.8/5 rating on eham.net. I will definitely look
into them. From the picture, it looks like one of the poles has a SO239 connector, but the others don't. Are the two other poles passive? The Arrow is an "open-sleeve" J-pole design. The other poles aren't actively fed, but make up a critical part of the antenna design. A standard (traditional) J-pole is an extended zepp. It consists of a half-wave end-fed radiator, connected to a transmission-line matching section (nominally a quarter-wavelength). The matching section is usually made up of an extension to the radiator, and a second element located an inch or two away. The matching section is usually shorted at the bottom, and fed at a tap point an inch or two above the short... a point at which the high impedance of the end-fed half-wave radiator has been transformed down by the transmission line to something close to 50 ohms. An "open sleeve" J-pole (which Cebik calls a "nontraditional" J-pole on his web site) is a bit different. It's somewhat shorter (the long arm is less than 3/4 wavelength), the short arm is longer than 1/4 wavelength, and it's fed differently (at the bottom, with one arm being grounded and the other being insulated from ground and fed directly from the feedline). Cebik's website has a very nice discussion of it. The Arrow OSJ is actually two open-sleeve dipoles, in parallel. The longest arm and the shortest arm are grounded, and the medium-length arm is connected to the hot side of the feedline. On 2 meters, the long and medium arms form an OSJ and are active... the short arm is simply a grounded stub which carries very little current and doesn't radiate much. On 70 cm, the medium and short arms form an OSJ and carry most of the current. The long arm probably carries a small amount of current, but since it's a couple of wavelengths long its radiation resistance is high and its current flow and radiation are only a small percentage of the total. What's the radiation pattern? Very similar to any other half-wavelength radiator... 0 dBd, plus or minus a few fidgets. The Arrow OSJ is not actively decoupled from the feedline (there's no balun) and thus there may be a small amount of RF current flowing on the outside of the feedline, and some amount of disturbance of the pattern. The amount of current on the feedline will depend on the details of the individual installation (e.g. the length of the feedline). I don't think the effect will be significant in most installations; reflections from the ground, building structures, etc. are likely to alter the pattern just as much or even more. You may, if you choose, mount the Arrow on an insulated mast, and include some sort of choke in the feedline (e.g. a small loop of a few turns in the coax, or some ferrites) in order to reduce the effect of feedline radiation. I think that the Arrow is a good performer and a good value. You can even make 'em yourself if you wish - Arrow sells the parts individually and (last time I looked) had complete construction dimensions and plans somewhere on their web site. -- 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! |
#6
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Best 144/440 Antenna for Attic Installation
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#7
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Best 144/440 Antenna for Attic Installation
The Arrow is an "open-sleeve" J-pole design. The other poles aren't
actively fed, but make up a critical part of the antenna design. What are the pros and cons of an Arrow J-pole versus a Diamond X50A pole? The Diamond X50A has a somewhat higher gain than the Arrow on 2 meters (about 2 dB higher, if I'm reading the stats correctly) and a significantly higher gain than the Arrow on 70 cm (about 5 dB higher). The Arrow is about 6" shorter than the Diamond (might fit into an attic space where the Diamond will not), has been tested at power levels of up to a kilowatt (the Diamond is rated for 200 watts), and costs only 40% as much as the Diamond. The Diamond has decoupling radials, and I infer that it's less likely to have a feedline-RF situation than the Arrow - its actual pattern may be more consistently like its theoretically-calculated pattern. The Diamond looks more like a traditional antenna... the Arrow is more likely to get "What the bleep is that thing?" questions, if mounted outdoors. The Arrow may be easier to field-repair, since it's mostly just aluminum angle and rod stock. -- 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! |
#8
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Best 144/440 Antenna for Attic Installation
Dave Platt wrote:
The Arrow is an "open-sleeve" J-pole design. The other poles aren't actively fed, but make up a critical part of the antenna design. What are the pros and cons of an Arrow J-pole versus a Diamond X50A pole? The Diamond X50A has a somewhat higher gain than the Arrow on 2 meters (about 2 dB higher, if I'm reading the stats correctly) and a significantly higher gain than the Arrow on 70 cm (about 5 dB higher). The Arrow is about 6" shorter than the Diamond (might fit into an attic space where the Diamond will not), has been tested at power levels of up to a kilowatt (the Diamond is rated for 200 watts), and costs only 40% as much as the Diamond. . . Wow, 5 dB extra gain for an extra quarter wavelength, and 2 dB for an extra 7/100 wavelength of size. That's quite a trick! Do you maybe mean to say that the Diamond has a somewhat higher *claimed* gain than the Arrow? If we're looking for high claimed gains (and claimed power handling capability for that matter), some of the CB whips should take the prize. Roy Lewallen, W7EL |
#9
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Best 144/440 Antenna for Attic Installation
In article ,
Roy Lewallen wrote: Wow, 5 dB extra gain for an extra quarter wavelength, and 2 dB for an extra 7/100 wavelength of size. That's quite a trick! Do you maybe mean to say that the Diamond has a somewhat higher *claimed* gain than the Arrow? If we're looking for high claimed gains (and claimed power handling capability for that matter), some of the CB whips should take the prize. You're quite correct. I'm going by "claimed" gain figures, and those that Diamond cites do sound a trifle high to be believable. -- 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! |
#10
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Best 144/440 Antenna for Attic Installation
On 23-Jul-2009, Roy Lewallen wrote: The Diamond X50A has a somewhat higher gain than the Arrow on 2 meters (about 2 dB higher, if I'm reading the stats correctly) and a significantly higher gain than the Arrow on 70 cm (about 5 dB higher). The Arrow is about 6" shorter than the Diamond (might fit into an attic space where the Diamond will not), has been tested at power levels of up to a kilowatt (the Diamond is rated for 200 watts), and costs only 40% as much as the Diamond. . . Wow, 5 dB extra gain for an extra quarter wavelength, and 2 dB for an extra 7/100 wavelength of size. That's quite a trick! Do you maybe mean to say that the Diamond has a somewhat higher *claimed* gain than the Arrow? If we're looking for high claimed gains (and claimed power handling capability for that matter), some of the CB whips should take the prize. I don't know what the actual gain is, but Diamond has been in business a long time, and I've never seen any reports of them misreporting gains. Does the Arrow have any gain? I thought it was close to 0.0. If it does, how do you know it's correct? The overall rating for the X50A on eHam.net is 4.7/5. The average rating for the Arrow J-pole is 4.8/5. It sounds like both products are highly regarded. |
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