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bcsman
EVDO Fledgling
Joined: 13 Jul 2007
Posts: 22
Location: Michigan's Thumb
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 Posted: Thu Jul 19, 2007 10:27 am Post subject: Omni Antenna question |
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| If I install an omni antenna on my roof to pull in a fringe signal does it matter where my desktop and PCMCIA card are inside my house?? I know with no external antenna, placement inside my house is important to pull in the strongest signal as the card has the antenna also. But if I have the omni does it negate the computer placement?? The reason I ask is my desktop is on the north side of my house and the tower is located south of me. With no omni installed I'm sure I would pull in a better signal if my computer was relocated on the tower side of my house. |
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jfulmer
EVDO Heavy User
Joined: 30 Jun 2007
Posts: 125
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| Posted: Thu Jul 19, 2007 10:30 am Post subject: |
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It doesn't matter, but the longer the cable from the PC to the antenna, the more signal you will lose. Also, good quality cable is somewhat expensive, so there is that as well.
Otherwise, it makes very little difference, IMHO. |
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Alex
Site Admin
Joined: 19 Sep 2006
Posts: 1945
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| Posted: Thu Jul 19, 2007 10:30 am Post subject: |
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| only thing to keep in mind is that you want to keep antenna cable length as short as possible. running a long antenna cable to far end of house is likely to result in less signal strength than relocating desktop closer to where antenna cable enters the house. |
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dan1101
EVDO User
Joined: 17 May 2007
Posts: 60
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| Posted: Thu Jul 19, 2007 11:34 am Post subject: |
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| Alex wrote: | | only thing to keep in mind is that you want to keep antenna cable length as short as possible. running a long antenna cable to far end of house is likely to result in less signal strength than relocating desktop closer to where antenna cable enters the house. |
How difficult is it to shorten the ~8 foot cable that comes with the Omni antenna? |
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Alex
Site Admin
Joined: 19 Sep 2006
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| Posted: Thu Jul 19, 2007 12:39 pm Post subject: |
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| dan1101 wrote: | | How difficult is it to shorten the ~8 foot cable that comes with the Omni antenna? |
its actually a 12ft cable, and for a fee, we can special order one with shorter cable.
I think price is $12-15 more. cost of new connector plus labor/handling.
also adds at least a day to delivery time. |
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Walter
EVDO Junkie
Joined: 14 Sep 2005
Posts: 307
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| Posted: Thu Jul 19, 2007 12:39 pm Post subject: |
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Difficult enough that you don't want to bother. You'd have to cut the cable to the length you want and then attach a new connector. You're probably more likely to make things worse than better. 8ft of cable is not going to have much drop. I'd leave it alone IIWY.
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Walter
EVDO Junkie
Joined: 14 Sep 2005
Posts: 307
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| Posted: Thu Jul 19, 2007 12:41 pm Post subject: |
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Or you can spend $15 dollars extra and special order from Alex. 
I'd still stick with the standard length myself. It works fine.
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Reach, Connect, Celebrate, Grow, Serve. |
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bcsman
EVDO Fledgling
Joined: 13 Jul 2007
Posts: 22
Location: Michigan's Thumb
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| Posted: Thu Jul 19, 2007 10:09 pm Post subject: |
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If I mount the antenna on my rooftop I'm looking at about 40' of cable to go from my 2 story farmhouse to my first story computer. Can I order the omni antenna without the cable and put one on myself or would I just extend the 8' attached cable?? I have some pretty good RG-6 cable.
Also where does the law of diminishing returns happen as far as extending the antenna higher to reach more signal compared to how much signal loss in the cable?? There must come a point where more height actually gives you less signal at your computer. In other words with how much cable length normally do you find an amp necessary especially in a fringe area?? |
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Alex
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Joined: 19 Sep 2006
Posts: 1945
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| Posted: Thu Jul 19, 2007 10:19 pm Post subject: |
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omni can be special ordered a number of different ways.
the key to deciding how long is too long, is far more dependent on how good the signal is that you have when you actually put the antenna where you think it will do the most good.
in other words... if you place an antenna where it gets -70 signal, you are obviously going to be able to run cable farther and still have benefit on other end... compared to if you only get -85 signal at the antenna.
its really impossible to create a perfect guideline for cable length other than to say something like:
"you can go as long as you want, so long as the signal at the end is as good as you're hoping for"
see how hokey that sounds? |
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bcsman
EVDO Fledgling
Joined: 13 Jul 2007
Posts: 22
Location: Michigan's Thumb
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| Posted: Thu Jul 19, 2007 10:44 pm Post subject: |
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| Is there usually enough variance in signal strength that would make it worthwhile to take the antenna up on my roof and move it around while someone could monitor the computer for signal?? Or just mount it somewhere on the peak of my roof? I've heard that a few feet in either direction can make a noticeable difference. At least in some cases. I know it works with a TV antenna but not sure about this frequency range. |
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Alex
Site Admin
Joined: 19 Sep 2006
Posts: 1945
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| Posted: Thu Jul 19, 2007 10:46 pm Post subject: |
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| bcsman wrote: | | Is there usually enough variance in signal strength that would make it worthwhile to take the antenna up on my roof and move it around while someone could monitor the computer for signal?? Or just mount it somewhere on the peak of my roof? I've heard that a few feet in either direction can make a noticeable difference. At least in some cases. I know it works with a TV antenna but not sure about this frequency range. |
absolutely worthwhile to test in as many positions as possible.
and make sure that data is actually moving thru connection, during testing. |
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bcsman
EVDO Fledgling
Joined: 13 Jul 2007
Posts: 22
Location: Michigan's Thumb
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| Posted: Thu Jul 19, 2007 10:50 pm Post subject: |
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Thanks Alex-learning alot tonight!!
Time to let it all sink in now and retire for the evening! |
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n6gn
EVDO Junkie
Joined: 22 Aug 2006
Posts: 347
Location: Northern California
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| Posted: Thu Jul 19, 2007 11:31 pm Post subject: |
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| bcsman wrote: |
Also where does the law of diminishing returns happen as far as extending the antenna higher to reach more signal compared to how much signal loss in the cable?? There must come a point where more height actually gives you less signal at your computer. In other words with how much cable length normally do you find an amp necessary especially in a fringe area?? |
That's a good question.
Another way of examining the question is to ask how much worse a lower, non LOS location is than one that is totally in view of the base. The general answer is "a lot". It is common to see excess attenuation exceeding 40 dB over and above the LOS (freespace) value.
At one mile two omni antennas (dipoles) will have almost 100 dB of path loss at PCS. But since the base can run run 10-20 watts (+43 dBm) with 12 dB of antenna gain (giving 55 dBm EIRP) , even with the pilot power (what's measured by RSSI) down ~ 9 dB below full power, (46 dBm EIRP) the RSSI indicator on a handset would indicate (+46-100 = -54 dBM. That's quite a strong EVDO signal. In bad locations it's not impossible to see 60 dB or more excess attenuation (which would drop the reading above to -116 dBm) which is why one isn't guaranteed of EVDO at 1 mile with an omni antenna.
For good quality cable the short answer is that almost anything you do that gets you closer to LOS will be more than worth the effort. Times Microwave LMR400 cable is about 6 dB/100' at PCS. For most terrestrial situations going even several 100's of feet straight up, if it gets you to LOS, will be worth it.
If you are using bad cable the balance is tipped somewhat but for many locations the first level of improvement, say going from inside a building to the roof, is almost always worth doing and can easily net one 20 dB of improvement. Even rather poor cable is likely to be able to get you to the roof with less loss than that, unless perhaps if you live in a really tall, obstructed highrise.
n6gn |
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bcsman
EVDO Fledgling
Joined: 13 Jul 2007
Posts: 22
Location: Michigan's Thumb
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| Posted: Fri Jul 20, 2007 7:43 am Post subject: |
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| n6gn wrote: |
That's a good question.
Another way of examining the question is to ask how much worse a lower, non LOS location is than one that is totally in view of the base. The general answer is "a lot". It is common to see excess attenuation exceeding 40 dB over and above the LOS (freespace) value.
n6gn |
Wow n6gn really good info, thanks for the input!
As I said above I would probably be running around 40' of cable from the top of my roof and I have some RG-6, which is a little better than RG-58. I do have numerous trees in my LOS for the tower I would hope to connect to. I think even on top of my 2 story house the antenna would still not have a clear LOS so my situation could be iffy at best. The Sprint maps say I'm just outside the broadband area so all I can do is try. And if I do get a signal with an omni hopefully I can amplify it either with a booster or 3 watt amp! |
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mooch
EVDO User
Joined: 02 Dec 2006
Posts: 40
Location: sunbury, ohio
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| Posted: Fri Jul 20, 2007 9:24 am Post subject: |
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I have a lot of high quality Belken quad shield RG-6 that has solid copper conductor and is rated at 3 ghz...but I was for some reason under the impression that RG-6 was not a good cable to use for a long run to a wireless antenna when compared to something like LM400.
Am I mistaken? Heck, if I could use the RG-6 I've already got, I could save a few bucks. |
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