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MattFS218
EVDO Newbie
Joined: 19 Nov 2007
Posts: 3
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 Posted: Thu Nov 22, 2007 10:15 pm Post subject: Does a TV Antenna Work? |
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| This may sound like a stupid question, but my resources at my current location are limited. But would a TV antenna work to increase EVDO reception? |
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fordrhs41
EVDO User
Joined: 29 Jan 2007
Posts: 92
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| Posted: Fri Nov 23, 2007 7:28 am Post subject: Re: Does a TV Antenna Work? |
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| MattFS218 wrote: | | This may sound like a stupid question, but my resources at my current location are limited. But would a TV antenna work to increase EVDO reception? |
No idea what the tv antenna will do for you but I am trying a 19 inch dish with a feed added and it dropped (increased) my signal from -80dbm to about -60dbm and it was a fast/2 setup and I expect better when I get the dish properly mounted and using low loss coax. The feed is described on this forum and is easy to build |
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rickster
EVDO Junkie
Joined: 27 Aug 2005
Posts: 216
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| Posted: Fri Nov 23, 2007 7:47 am Post subject: Re: Does a TV Antenna Work? |
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| MattFS218 wrote: | | This may sound like a stupid question, but my resources at my current location are limited. But would a TV antenna work to increase EVDO reception? |
Possibly, if you can stand the commercial breaks!  |
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n6gn
EVDO Junkie
Joined: 22 Aug 2006
Posts: 369
Location: Northern California
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| Posted: Fri Nov 23, 2007 1:11 pm Post subject: Re: Does a TV Antenna Work? |
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| MattFS218 wrote: | | This may sound like a stupid question, but my resources at my current location are limited. But would a TV antenna work to increase EVDO reception? |
I don't think it's a stupid question but it's not any easy one to answer except by trying it.
It turns out that one usually has to go to considerable effort to make *any* reasonably sized assemblage of metal ( bigger than, say, a quarter wavelength) hooked to a transmission line work either a lot better or a lot worse than a dipole.
If the feedline is OK, there's a liklihood that at least in some direction(s) and polarization a TV antenna works as well as a dipole or typical omni.
If by TV antenna you mean a vhf/uhf antenna of the type traditionally mounted above the roof, as contrasted to a DBS antenna, and if the antenna has decent feedline (even 300 ohm twinlead properly installed is pretty good) then if you are comparing phone performance to a much worse location, you might see some improvement. A well situated TV antenna could easily be mounted in a 20 dB better location, compared to in indoor room. Of course you might not see any improvement, as well 
If you have a way of adapting from the phone's external input to the TV line, try it in and see what happens.
If you meant "DBS antenna" for TV antenna above, you'll probably not have as much luck unless you build a new feed that works at PCS or 850 MHz. If you're willing to do that, a DBS antenna can work pretty well.
n6gn |
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MattFS218
EVDO Newbie
Joined: 19 Nov 2007
Posts: 3
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| Posted: Sun Nov 25, 2007 1:56 am Post subject: |
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OK, so one more question.
I have a C-Motech ccu-650 EVDO modem, which has an external antenna port, on a proprietary (I think) connector. Would I be able to strip the TV antenna cord, and simply place the stripped wire into the small connector on my usb evdo modem?
The whole is small enough that I'm sure there will be contact.
--matt |
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fordrhs41
EVDO User
Joined: 29 Jan 2007
Posts: 92
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| Posted: Sun Nov 25, 2007 7:04 am Post subject: |
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| MattFS218 wrote: | OK, so one more question.
I have a C-Motech ccu-650 EVDO modem, which has an external antenna port, on a proprietary (I think) connector. Would I be able to strip the TV antenna cord, and simply place the stripped wire into the small connector on my usb evdo modem?
The whole is small enough that I'm sure there will be contact.
--matt |
Try it, but remember to be careful about introducing static electricity as solid state equipment can be unforgiving and static voltages can be very high. |
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Capt Ron
EVDO Heavy User
Joined: 01 Feb 2007
Posts: 139
Location: Central Florida Connected Using Razr & CTR350
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| Posted: Sun Nov 25, 2007 10:36 am Post subject: |
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It may very well show some improvement in received signal, but the problem is the transmission. The antenna must be matched to get good results.
I wouldn't try it, because if you should short the leads it could blow the transmitter.
_________________
Ron |
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n6gn
EVDO Junkie
Joined: 22 Aug 2006
Posts: 369
Location: Northern California
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| Posted: Sun Nov 25, 2007 3:07 pm Post subject: |
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| MattFS218 wrote: | OK, so one more question.
I have a C-Motech ccu-650 EVDO modem, which has an external antenna port, on a proprietary (I think) connector. Would I be able to strip the TV antenna cord, and simply place the stripped wire into the small connector on my usb evdo modem?
The whole is small enough that I'm sure there will be contact.
--matt |
Matt,
It's important to understand that the transmission line between the modem and the antenna has two conductors; it's either coaxial with a center surrounded by some insulation and then by a conductive shield, or it's balanced, having two lines separated by insulation.
The modem almost certainly is coaxial and is intended for use with a connector which goes onto coaxial cable. Furthermore, there is probably a mechanical switch internal to the modem which disables the internal antenna when the connector center pin is inserted properly.
If you want to try the TV antenna, you still need to properly connect to the modem and switch the internal antenna out of service. At a minimum, I think you will want to have an adapter cable that does this.
Once you have an adapter cable, you may be able to connect to it's free end from a piece of TV coaxial cable well enough to try things out but you'll need to take care of connecting both center and shield and you'll want to do this without adding any significant length of non-coaxial conductor. That is, you won't want to just strip back the coax a couple of inches and twist the shields and centers together as though were wiring a table lamp or something. Rather, you want to maintain the coaxial nature of the structure all the way.
If your situation does allow you to connect all in coax, you should be aware that you are probably connecting a 50 ohm modem to a 75 ohm TV coax. This isn't the end of the world but it won't improve performance.
The fact that there is significant mismatch has equal negative effect on both transmit and receive but as noted before, the antenna is already such an unknown that this is probably the least of your issues.
This is a very non-optimum arrangement but as I noted, it still *could* produce useful results; at least to let you know that a good antenna in the same location as the TV antenna and fed by proper feedline could work well. If your TV antenna test doesn't produce positive results you probably don't know much more than you did before but I doubt that it will hurt anything. The modem can probably connect to either an open or a short without doing itself any damage- - though this isn't 100% guaranteed.
Implicit in all this is the assumption that the TV feedline really does connect directly to the external antenna and not to something else, like a preamplifier or distribution system (splitter for example).
If your TV feedline is balanced rather than coax you can still try it, with further degradation due to more impedance mismatch (likely) and balanced-to-unbalanced problems.
As I said previously, this is a pretty bad arrangement but you won't know for sure what it will do unless you try it.
n6gn |
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meteoro
EVDO Newbie
Joined: 18 Dec 2007
Posts: 6
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| Posted: Tue Dec 18, 2007 10:06 pm Post subject: |
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| TV freqs are in the 100Mhz range, and 700Mhz for the ultra high freqs. EVDO rides on the 1.9Ghz networks typically. TV antennas are not tuned for such high freqs, I doubt you will get any gain out of them. |
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n6gn
EVDO Junkie
Joined: 22 Aug 2006
Posts: 369
Location: Northern California
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| Posted: Tue Dec 18, 2007 10:51 pm Post subject: |
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| meteoro wrote: | | TV freqs are in the 100Mhz range, and 700Mhz for the ultra high freqs. EVDO rides on the 1.9Ghz networks typically. TV antennas are not tuned for such high freqs, I doubt you will get any gain out of them. |
Because the TV antenna is probably significantly larger than a half wavelength, it's actually likely that there *will* be gain relative to a dipole. The problem (at least one problem) is that the direction at which this occurs is quite hard to predict with this arrangement. It may very likely be away from the horizon where the cell site is probably located.
However, it's also not unlikely that such a non-optimum antenna is no more than -10 dB relative to a dipole. It's actually difficult to make any reasonably sized chunk of conductor behave a *lot* worse than a dipole. (It also takes effort to make one work a lot better!) If the antenna is well located relative to the previous location and if the feedline is decent (admittedly two significant IFs) then there is a chance that there will actually be more signal than with a PCS antenna located in the house right at the modem/phone. This is particularly true if the house lication has significant shielding or obstruction.
There's no question that this is not the way to make things work well but there's at least a slim chance that it will work or at least give some useful information. At the least, I doubt that it is very likely to hurt anything.
n6gn |
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meteoro
EVDO Newbie
Joined: 18 Dec 2007
Posts: 6
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| Posted: Tue Dec 18, 2007 11:00 pm Post subject: |
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the other factor is that most tv antennas are set up for horizontal polarization. All service providers use vertical polarization.
I guess you could turn the antenna to vertically polarize..... |
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n6gn
EVDO Junkie
Joined: 22 Aug 2006
Posts: 369
Location: Northern California
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| Posted: Tue Dec 18, 2007 11:12 pm Post subject: |
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| meteoro wrote: | the other factor is that most tv antennas are set up for horizontal polarization. All service providers use vertical polarization.
I guess you could turn the antenna to vertically polarize..... |
That's true but the TV antenna/feedline combination is so different at PCS from it is at design center that there's no guarantee that polarization is even maintained. It may very well be circularly polarized at PCS.
In any case, I bet it isn't more than 15 dB down from a vertical dipole. Not optimum by any means but perhaps still better than an indoor antenna that is down by 25 dB due to it's location.
n6gn |
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skizzorhandz
EVDO Newbie
Joined: 09 Jul 2008
Posts: 8
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| Posted: Tue Jul 22, 2008 8:24 pm Post subject: |
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| through out my house i have little antenna ports where you plug a cable into the wall then into the back of your tv to use for getting TV. the antenna is in our attic. The port on the wall just looks like the port on the back of a t.v. used for "bunny ears" type antennas. I have a UTStarcom UM150 with alltel and i was wondering what cable i would need or if it was even possible to hook my internet up to the big antenna. PLEASE reply i am getting -75dBm and this isnt good enough for me to play my Xbox on. |
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n6gn
EVDO Junkie
Joined: 22 Aug 2006
Posts: 369
Location: Northern California
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| Posted: Tue Jul 22, 2008 9:50 pm Post subject: |
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| skizzorhandz wrote: | through out my house i have little antenna ports where you plug a cable into the wall then into the back of your tv to use for getting TV.
PLEASE reply i am getting -75dBm and this isnt good enough for me to play my Xbox on. |
If you're seeing -75 dBm, more signal isn't likely to help any problem you are experiencing.
To verify this you can drive next the tower and see what happens.
Perhaps others can suggest better network configurations but I don't think you should spend more time on signal.
n6gn |
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skizzorhandz
EVDO Newbie
Joined: 09 Jul 2008
Posts: 8
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| Posted: Tue Jul 22, 2008 11:54 pm Post subject: |
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| well thn how can i lower my latency. |
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