2.4 GHz antenna for 5GHz?

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h4x0r
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PostPosted: Fri Aug 20, 2010 23:03    Post subject: 2.4 GHz antenna for 5GHz? Reply with quote
I need to upgrade the adapter in my desktop to support dual band n and I am thinking about the WMP600N. However, right above the PCI slot I have the PCI-E slot, which is occupied by the video card and there is a stiff VGA cable with a huge plug. Thus I have to turn the antennas sideways. I want to replace the external antennas for ones that have an extension cord (no more than a foot) and a stand, so that I can put it on top of the desktop. Here is my question: Can I use antennas rated for 2.4GHz for 5GHz? As far as I can see, the adapter has standard 2dBi antennas, nothing fancy. So will my performance suffer if instead I install a 7dBi antenna, however one rated for 2.4 GHz, or maybe it doesn't even matter?

Another reason I want to install antennas on a stand is so that the signal doesn't have to go through the whole computer (The front of the tower faces the router and the antennas are on the back.)
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h4x0r
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PostPosted: Fri Aug 20, 2010 23:28    Post subject: Reply with quote
Anybody? Any Ideas?
barryware
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PostPosted: Sat Aug 21, 2010 0:23    Post subject: Reply with quote
h4x0r wrote:
Anybody? Any Ideas?


Nope.. 2.4 ghz antenna's will not work @ 5ghz. I know this from trying it.

It will work close, but your range will be 1/4 or less what it is now with the 5ghz antenna's

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h4x0r
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PostPosted: Sat Aug 21, 2010 17:42    Post subject: Reply with quote
barryware wrote:
h4x0r wrote:
Anybody? Any Ideas?


Nope.. 2.4 ghz antenna's will not work @ 5ghz. I know this from trying it.

It will work close, but your range will be 1/4 or less what it is now with the 5ghz antenna's


How does a dual band adapter work? Do they just put 2.4GHz antennas on it or do they put 5GHz antennas? From the pictures of the adapter, those antennas look like standard 2dBi antennas. Should I even replace them, or will the stock ones be fine? Also does the position of the antennas matter? (Meaning will there be a difference between a vertical antenna and a horizontal antenna?)
barryware
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PostPosted: Sat Aug 21, 2010 18:22    Post subject: Reply with quote
I modded a wrt350n with a 5ghz card and used 2.4 ghz antenna's. Range sucked..

I have no idea what dual band adapter you are talking about..

Yes indeed. Antenna orientation can make a big diff. My 600, twisting & turning the antenna's makes all the diff in the world. 2.4 is not as touchy as 5ghz.

My wndr3300, I got it standing up and turned about 160 degrees.. Looks like shit next to the rest of my stuff but works well.

The 610 (e3000).. It is hard to get that one turned right but I have had it orientated where it worked well. I am not running it now..

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Peabody
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PostPosted: Sun Aug 22, 2010 0:53    Post subject: Reply with quote
2.4 ghz antennas and 5 ghz antennas are completely different and not interchangeable. Yes, they use 5ghz antennas on a 5ghz router, connected to a separate radio, and don't simply put 2.4ghz antennas there because they have a bunch....
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davel
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PostPosted: Sun Aug 22, 2010 2:07    Post subject: Reply with quote
I think as long as you use an antenna that is a the proper fraction of the original wavelength of the signal you should be ok, but yes I'm sure it will need to be tweaked. I might be wrong.

all my 5 ghz tx are about 1/2 range as my 2.4. Not really seeing this an issue since I trying to use a band thats not as crowded. I think due to the short wavelength its going to make more power to make 5 match 2.4 range.

ok firesuit on.....
h4x0r
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PostPosted: Sun Aug 22, 2010 22:46    Post subject: Reply with quote
I am talking about the WMP600N which is a dual band adapter but it come with only one pair of antennas and it doesn't say that you should change antennas when switching frequencies.
barryware
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PostPosted: Sun Aug 22, 2010 23:05    Post subject: Reply with quote
h4x0r wrote:
I am talking about the WMP600N which is a dual band adapter but it come with only one pair of antennas and it doesn't say that you should change antennas when switching frequencies.


Your thread started asking about using external 2.4ghz antenna's on the 5ghz band. You have your answers..

Without checking out your adapter.. I'll bet there are other antennas on the pcb. The externals, are for 2.4ghz (just a guess based on other hardware I have worked with)

Post back if your experimentation turns out diff..

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nn5i
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PostPosted: Mon Aug 23, 2010 1:35    Post subject: Reply with quote
Either that, or there are two antennas in the plastic housing.

At 5 GHz, an antenna cut for 2.4 GHz will be nearly thw worst possible length and will present a load impedance that the transmitter cannot feed -- off by a factor of not just two, but sometimes a factor of thousands. Won't work worth a flip. If the transmitter were not such a wimpy flea-power affair, it would also destroy the transmitter; but these tiny transmitters don't produce enough power to melt themselves down.

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barryware
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PostPosted: Mon Aug 23, 2010 12:56    Post subject: Reply with quote
barryware wrote:
h4x0r wrote:
I am talking about the WMP600N which is a dual band adapter but it come with only one pair of antennas and it doesn't say that you should change antennas when switching frequencies.


Your thread started asking about using external 2.4ghz antenna's on the 5ghz band. You have your answers..

Without checking out your adapter.. I'll bet there are other antennas on the pcb. The externals, are for 2.4ghz (just a guess based on other hardware I have worked with)

Post back if your experimentation turns out diff..


Checking the FCC pics of the device, there are no antennas etched into the pcb.. The antenna's look identical to the antennas used on my DMA2200 extender. The DMA is also a dual band device. So.. I dunno.

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nn5i
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PostPosted: Mon Aug 23, 2010 13:49    Post subject: Reply with quote
There could easily be two antennas in the plastic husing. All it costs to design it that way is an inch of wire.
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LOM
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PostPosted: Mon Aug 23, 2010 14:00    Post subject: Reply with quote
Should be possible to use the same antenna for 2.4GHz and 5GHz, they are not perfectly tuned in routers intended for short distance coverage.

A full-wave dipole for 5GHz will also work as a half-wave dipole on 2.5GHz which is near enough to 2.4Ghz.

(It may be a bit trickier to get a 2.4Ghz full-wave dipole to work efficiently on 5GHz though, since it will be a double-wave dipole there)

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nn5i
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PostPosted: Mon Aug 23, 2010 14:08    Post subject: Reply with quote
Ever try to feed a full-wave dipole? Its impedance at midpoint is extremely high. Same goes for a half-wave monopole, of course. In each case the feedpoint would be at a current null.
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LOM
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PostPosted: Mon Aug 23, 2010 14:42    Post subject: Reply with quote
nn5i wrote:
Ever try to feed a full-wave dipole? Its impedance at midpoint is extremely high. Same goes for a half-wave monopole, of course. In each case the feedpoint would be at a current null.


I'm sure you're right, its such a long time ago that I have forgotten..
So what about a trap dipole like W3DZZ or dual band dipole, must be possible also for microwave bands?

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