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jedon
EVDO Newbie
Joined: 23 May 2008
Posts: 7
Location: Nevada City, CA
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 Posted: Mon Jun 02, 2008 11:29 am Post subject: Using a 10ft parabolic C-Band as an 800mhz EVDO antenna |
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I am able to get 35% EVDO signal at around -0.96db using a 3 watt amp and a 12" mag mount antenna. I found someone giving away an old C-Band ( maybe eKu? ) parabolic that looks to be at least 10ft wide. The dish is plastic/fiberglass not metal mesh.
Is this possible?
What should I put where the LMB is?
Dipole? Bi-Quad? the mag mount? 24" omni with built in ground plane? ( it looks like the marine antenna but it's black ).
Is the plastic okay as a reflector or do I need to line it with foil or?
I can't seem to find anyone else who has done this, the net has failed me 
Thanks!!
-Jedon |
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xrayman
EVDO Junkie
Joined: 23 Feb 2007
Posts: 293
Location: Kansas City
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| Posted: Mon Jun 02, 2008 12:36 pm Post subject: |
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The C band dish you are looking at has metal mesh embedded inside the fiberglass. For DIY Bi-Quad checkout the link below. You will need to re-calculate the length of each "side" of the element for a quarter of a wavelength of the frequency you want to receive. Others may be able to give you expert antenna building advice when it comes to specific frequency dimensions for the element. A factory made panel directional type antenna with a short low loss cable may get the signal you require without all the work of a DIY project.
http://martybugs.net/wireless/biquad/ |
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jedon
EVDO Newbie
Joined: 23 May 2008
Posts: 7
Location: Nevada City, CA
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| Posted: Mon Jun 02, 2008 2:05 pm Post subject: |
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Thank you for the info about the metal mesh inside the dish, I didn't know that.
I have been to that website and my brother made a wifi bi-quad using it but I am a little hazy on how to adapt the measurements.
There is also something about not having the bi-quad on a parabolic have too much gain I think?
I did find a 24db mesh parabolic for $250, I guess my time is worth something? I'd rather have 30+db for free... |
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n6gn
EVDO Junkie
Joined: 22 Aug 2006
Posts: 384
Location: Northern California
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| Posted: Mon Jun 02, 2008 2:52 pm Post subject: |
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| jedon wrote: | There is also something about not having the bi-quad on a parabolic have too much gain I think?
I did find a 24db mesh parabolic for $250, I guess my time is worth something? I'd rather have 30+db for free... |
Yes, probably almost anything simple to build has too much gain for a typical C band dish. These antennas normally had about a .375 F/D and need a very broad (low directivity, low gain) feed for optimum performance.
You could probably get a lot of gain from one using a dipole mounted ~.2 wavelengths in front of a reflector though.
At PCS, you need pay only $50 for a 24 dBi grid antenna. The same reflector with a different feed, more or less as above, will probably give you almost 18 dBi at 850 MHz though.
Mounting a 10' C band dish high enough to clear local clutter and keeping it pointed at the horizon might start to be a problem in windy conditions...
n6gn |
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xrayman
EVDO Junkie
Joined: 23 Feb 2007
Posts: 293
Location: Kansas City
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| Posted: Mon Jun 02, 2008 3:44 pm Post subject: |
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jedon,
What n6gn said about using a $50 24 dBi grid antenna and changing the feed to 850 MHz, sounds like an excellent idea to me. That old C band dish is very heavy and will require a very strong mast to hold up to the wind load. Much info about the grid antenna can be found on this forum using search. This link is a good starting point.
Using a frequency to wavelength calculator at this link may be of help if you go the DIY route. |
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jedon
EVDO Newbie
Joined: 23 May 2008
Posts: 7
Location: Nevada City, CA
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| Posted: Mon Jun 02, 2008 4:58 pm Post subject: |
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Verizon EVDO in my area uses 800mhz only, not 1900mhz so would a 2.4ghz grid really work? If I was to modify one to work at 800mhz how would I go about doing that?
I had read that other thread already, but it was about 1900mhz.
The frequency calculator is interesting but I don't know enough to make it useful ( yet? ). |
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n6gn
EVDO Junkie
Joined: 22 Aug 2006
Posts: 384
Location: Northern California
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| Posted: Mon Jun 02, 2008 5:27 pm Post subject: |
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| jedon wrote: | Verizon EVDO in my area uses 800mhz only, not 1900mhz so would a 2.4ghz grid really work? If I was to modify one to work at 800mhz how would I go about doing that?
I had read that other thread already, but it was about 1900mhz.
The frequency calculator is interesting but I don't know enough to make it useful ( yet? ). |
The reflector part of it will work fine. The reason for lower gain at 850 MHz is that the area of the antenna is a bit less than one fourth of what it is at PCS ( one fourth the area would be about - 6 dB; 24-6 = 18 dBi).
Wavelength in inches is about 11,811/Frequency(MHz). This gives about 13.9" at 850MHz and about 6.2 inches at 1900 MHz.
However, a dipole will be somewhat less than .5 wavelength long, depending upon it's thickness. Furthermore, it is necessary to use a balancing device to properly feed a dipole from an unbalanced transmission line like coaxial cable. That device is usually called a "Balun".
While it's not impossible to make a balun and dipole work blind - without any measuring equipment, the odds are pretty good that it won't work optimumly.
There's a picture of a dipole and balun in front of a corner reflector (you'd want to use a planar reflector for a dish feed) that I put up previously at http://www.sonic.net/~n6gn/corner.pdf however, as I said, I don't think I'd recommend tackling a feed for a dish without at least setting up some rudimentary measuring equipment first.
If you really want to learn about DIY antennas, you can look for amateur radio publications for antenna construction at www.arrl.org (Admin, this is a non profit organization, hopefully posting this URL is OK) as well. Otherwise, I'm sure that our hosts can give you some recommendations.
n6gn |
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jedon
EVDO Newbie
Joined: 23 May 2008
Posts: 7
Location: Nevada City, CA
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| Posted: Wed Jun 04, 2008 8:48 pm Post subject: |
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I replied about a 15db parabolic for $240 and a 14db yagi for $170 but the spam filter ate it. I'm starting to thing those would be a better idea? What is the advantage of the grid parabolic over the yagi besides 1db?
Thanks!
-Jedon |
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n6gn
EVDO Junkie
Joined: 22 Aug 2006
Posts: 384
Location: Northern California
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| Posted: Wed Jun 04, 2008 10:53 pm Post subject: |
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| jedon wrote: | I replied about a 15db parabolic for $240 and a 14db yagi for $170 but the spam filter ate it. I'm starting to thing those would be a better idea? What is the advantage of the grid parabolic over the yagi besides 1db?
Thanks!
-Jedon |
The main difference is probably that the parabolic reflector is closer to achieving what it claims than is the Yagi. A 5' yagi can produce 15-16 dBi if everything is done well. See
http://www.sonic.net/~n6gn/antenna/oldyagi.pdf
This antenna does about as well as a Yagi of it's size can do (original work on the design was from the National Bureau of Standards -now National Institute of Science and Technology). If someone tells you that an antenna smaller than that has as much gain you'd better question their numbers. Also be sure to notice the difference in gain specifications between "dBd" and "dBi" - they are about 2.1 dB part with "dBi" giving the higher value.
However, it is *really* easy for a Yagi not to work as well as an antenna of it's size might. The parabola is much less finicky, broader band and more likely to achieve close to the theoretical gain for an antenna of it's size.
Even so, the difference between the two, even if it were 5 dB or so, might easily be made up or lost by mounting, pointing and a little extra foliage or obstruction. Thus, paying top dollar for the last (actual) dBi is perhaps counterproductive. Reducing cable loss between antenna and phone or amplifier is just as useful and perhaps cheaper. Placing the antenna higher or better locating it is often a very big win, and can produce many dB of improvement in both signal level and in reduction of variation of level vs. time/temperature/season etc.
n6gn |
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jedon
EVDO Newbie
Joined: 23 May 2008
Posts: 7
Location: Nevada City, CA
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| Posted: Thu Jun 05, 2008 10:09 am Post subject: |
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n6gn,
Thank you so much for all your help and advice. The one local shop in my town has a Yagi they let people borrow to see if it will work for them and then will sell you one if it does so I'll see if I can do that before paying out cash. I tried putting my marine type antenna on top of a 20ft 2x4 at the location where I got the best signal but it didn't seem to help any.
I got a KPC680 so I"ll see how that does compared to my tethered VX8100.
-Jedon |
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khordale
EVDO Newbie
Joined: 12 Jun 2008
Posts: 4
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| Posted: Thu Jun 12, 2008 3:32 pm Post subject: |
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Jedon,
I would try using a spare DirecTV dish. You probably don't need that huge dish to get a reliable signal.
About 8 months ago I was going through what you are now. I was a total novice so I did a lot of research. I ended up getting an inside repeater (I got a zboost, but 3g sells one also, a wilson brand I think). It came with a 12" omni. With the omni mounted outside the signal was better, but not good. It disconnected all the time and was slow. about half the time I got Rxtt instead of EVDO.
I was also wary of trying to make my own antenna. I might be capable, but it didn't seem like fun to me. I don't mind tinkering a little though so when I saw a guy had used an old directv dish, I figured I would give it a try. It worked great! I now get EVDO all the time and I haven't had a disconnect in weeks. Verydependable connection now at around 500-700 downloads (which is fast for my rural area) Here is a picture of my set-up:
(Ok I give up on trying to post a link. I read how to do it and sometimes it works and sometimes it doesn't. The words in the post are what;s important though, so I'll just leave the pictures off for now. IF you want a picture just e-mail me and I'll send 'em to ya' )
Good luck with whatever you decide.
-Erik |
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alhanson
EVDO Fledgling
Joined: 10 Jul 2007
Posts: 11
Location: South West Wisconsin
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| Posted: Thu Jun 12, 2008 4:25 pm Post subject: dish antenna set up |
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jedon
I would be interested in seeing you picture of your dish antenna set up. but i do not have enough post to IM you my email address. 
alhanson
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alhanson |
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jedon
EVDO Newbie
Joined: 23 May 2008
Posts: 7
Location: Nevada City, CA
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| Posted: Fri Jun 20, 2008 5:17 pm Post subject: |
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Well I am pretty disappointed with the KPC680 when it comes to my remote area. In town in works great, I can get peaks of 2550 kbps. Out where I am building my house though I was able to get 300kbps with my VX81000 tethered to my laptop and the VX8100 hooked to an amp plus a 12" mag mount omni. Now with the same setup hooked to the KPC680 I can't connect at all. I tried both antenna ports even and it didn't help.
I'll bring my old DISH ( not a KA or C-Band, just a little modern one ) and see if that helps. |
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khordale
EVDO Newbie
Joined: 12 Jun 2008
Posts: 4
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| Posted: Tue Jul 08, 2008 1:14 pm Post subject: |
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I was going to use one of those old C-band dishes also, until I ran the idea by my wife and she vetoed having one of those things anywhere near our house, haha
I got really good results from just an old directv dish. I removed the LNB from the arm and replaced it with a 12" omni antenna. I drilled a hole in the arm and bolted it right in place. I then pointed the antenna in the direction of the nearest tower (about 7 miles- I live in a rural area). Bingo! It has improved my reception dramatically.
Here is a picture:
It is mounted temporarily to the pole behind it with duct tape. I will figure out a more permanent mounting solution when I have more time. I don't have the increase in signal measured in RSSI or bars, but before with just the omni in the same spot, I got frequent disconnects and sometimes went to Rx speeds (really slow, slightly better than dialup.)
With the dish+ omni I haven't had a disconnect in days and I consistently get download speeds of 500-700 (for where I am that is FAST). Amazing improvement with very little work.
Good luck!
-Erik |
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