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cmon69
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setting TX Power

Mon Oct 22, 2007 6:31 am

I am currently using a 532a on a tower with (1) SR2, 400mW and (1) Senao 2511MP 200mW. The SR2 is set to AP/Bridge, and the Senao 2511MP is set to station. The network connection is supplied threw the Senao 2511MP, and my "Tx/Rx Signal Strength is -82" "Distance 6 Miles" I'm guessing that this is not good enough. The Senao 2511MP is attached to a 24db grid and if I'm correct I can go up to 250mW and still remain legal on a Point-to-Point. My question is, if I replaced the Senao 2511MP with a SR2, what would I set my TX power setting to? "All rates fixed 24dBm?" and will I have any issues running a 532a with (2) SR2's cards?
Christapher James Hasher
Waseca Wireless

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Equis
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Re: setting TX Power

Mon Oct 22, 2007 2:11 pm

Yes, it will work with sr2 cards.

But dude, 6miles and -82, are you sure you have the antenna connected? /jokes but it should be -60 something with what you have now.
 
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cmon69
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Re: setting TX Power

Mon Oct 22, 2007 5:55 pm

I have always had problems! I suspect that there is a lot of interference in my area. I have one main tower and it’s only around 60' high, and it’s a TinyWiFi AP with StarOS. That’s my first mistake. I wish I had found out about MikroTik a long time ago! I plan on replacing out the TinyWiFi AP with a 532a just as soon as I have all my other 8 towers that are associated to the TinyWiFi with AP1000’s switched to 532a's, I only have 2 left to go! I love MikroTik, once I tried a 532a I couldn’t believe how reliable it’s been. My TinyWiFi that I paid $1500. For has been nothing but trouble since I got it.




Q= Quality
S= Signal
N= Noise

65’ Tower TinyWiFi AP (200mW – 15dB Omni)

2.9 miles - Breck 80’ Silo – AP1000 (32mW- 24dB Grid) "Q -17/-22 S -82/-78 N -93/*"
Buscho 95’ Silo – 532a (200mW – 24dB Grid) 3.8 miles to Breck "Q S N"
Kuhns 95’ Silo – AP1000 (200mW 15dB Panal) 3.0 miles to Harguth "Q S N"
4.4 miles - Harguth 95’ Silo – 532a (200mW – 24dB Grid) "Q -22/-28 S -83/-78 N -98/*"
2.2 miles - Singlestad 100’ Elevator – 523a (200mW – 24dB Grid) "Q -25/-38 S -68/-68 N */*"
.5 miles - Fairgrounds 105’ Tower – 532a (200mW – 15dB Grid) "Q -36/-39 S -64/-66 N */*"
3.9 miles - Haley 110’ Elevator – 532a (200mW – 24dB Grid) "Q -23/-30 S -76/-77 N */*"
6.8 miles - Brase 90’ Silo – 532a (200mW – 24dB Grid) Q -19/-26 S -81/-82 N -98/*
Christapher James Hasher
Waseca Wireless

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Re: setting TX Power

Tue Oct 23, 2007 1:42 am

Do you have enough resorces to try that link at 5ghz?
 
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cmon69
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Re: setting TX Power

Tue Oct 23, 2007 3:19 am

My whole network is setup for B only. Once I replace out the equipment on my three remaining towers I should be able to use G.
Christapher James Hasher
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Re: setting TX Power

Tue Oct 23, 2007 3:25 am

G is worse IMHO more interference.
 
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cmon69
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Re: setting TX Power

Wed Oct 24, 2007 5:25 am

That brings me back to my original question, if I replaced the Senao 2511MP with a SR2, what would I set my TX power setting at, to achieve 250mW? "All rates fixed 24dBm?"
Christapher James Hasher
Waseca Wireless

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galaxynet
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Re: setting TX Power

Sun Nov 18, 2007 4:54 pm

cmon69 -
No - you can't use 'all rates fixed' @ 24db. The SR card max at 54mbps is 17 (If I remember correctly). @ 48 it's 19db, @36 I think it's 22db and the rest are 26db. 26db is 400mw.... So 250mw would be close to 24db....

And - right now unless the latest release of ROS has changed this behavior - you have to set the card to 10 less than you want, i.e. you want 24db out then set the power at that data rate to 14db.

I am not sure where you are but if you are in the US then you can go above 250mw on a Point-to-Point link at the input of the antenna connector. I don't remember the exact power level but 400mw keeps popping in to my head and I don't remember if this was the PtMP or the PtP level.
Do you have enough resorces to try that link at 5ghz?
This quote from Equs - he was asking you if you had sufficent resources to swap your backhauls out to 5Ghz instead of using two 2.4ghz channels.... Thus keeping a little more spectrum for your own use.... Because using two 2.4ghz channels is always a challenge when they are (physically) close together. And since you are using two 2.4ghz channels - hopefully you are using 1 & 11 at the sites - a larger frequency spread between the two channels will give you a better chance at maximizing your throughput. Remeber there are only three non-overlapping channels 1, 6, and 11, 2412, 2442 and 2462.........any other selection will overlap and cause you issues.

So back to you original question - no you don't set the power out to 'all fixed rates', instead you'll have go look up the SR card specs, and set the power you want / and or can achieve minus 10 for each data rate you want to use.

Lastly - you can set the RB to B/G mode - the AP will connect to a client at whatever rate / protocol (B or G) that it can support and the data speed that it can connect at.....

Good luck out there!
Thom Lawless
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RapidWiFi, LLC
thom.lawless [at] rapidwifi.com
 
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cmon69
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Re: setting TX Power

Mon Nov 19, 2007 6:13 pm

I haven’t used 5.8 GHz before, and wonder if I would get the same distance as I currently do with 2.4 GHz. I have heard that 900MHz would provide greater distance. What are your thoughts? I guess I could also try using a different polarity in the 2.4 GHz
Christapher James Hasher
Waseca Wireless

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galaxynet
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Re: setting TX Power

Mon Nov 19, 2007 9:54 pm

cmon69 -
5Ghz does fade faster in the air than 2.4ghz, but the flip side is you can use a higher gain anntenna and they are a lot smaller than the same gain antenna in 2.4ghz As in a 24db gain 5ghz antenna is about the same size as a 19db 2.4ghz antnenna (patch panel antenna).

The adavantge of 900mhz is really in it's ability to make links that are not LOS (NLOS). I don't know the RF climate you are in, but a lot of older cell phone towersand emergency services use either 900mhz band or close by frequencies and the first harmonic of the ever popular high power (50 watts or more) the 455mhz band. So really it's use is limited. I use it in PtP applications - I shoot a high gain link through the trees to a neighborhood, there I use a 2.4ghz AP (or more than one AP) and 're-distribute' the feed there.

Switching polarities can get you 10db or more of isolation between the antennas.

OK - there you have it...

Thom
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cmon69
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Re: setting TX Power

Sun Nov 25, 2007 7:12 pm

Galaxynet

Thank you for helping me with my load balancer issue, now I’m on to my signal issue.

During our conversations in the forum that dealt with my load balancing issues I mentioned that I had plans on replacing my StarOS AP with a RB532a board. What I have since planned should make migration of my existing customers, and AP’s easier for me.
I plan on adding another tower “Taller one” next to the existing one that is used for my StarOS AP.

I have a few decisions to make and I thought you might be able to give me some input.

On my new tower I plan on having (1) 2.4 VPOL 15db omni for customers associated to the new AP. Below the 2.4 VPOL 15db omni I would like to add (3) 120 degree sector antennas dedicated to my towers only.

Existing towers use either SR2 or Senao 2511MP Plus cards, all set to 2.4GHz-B

Decisions to be made:

2.4 GHz or 5.8 GHz?
“ If I use 2.4 GHz I don’t have to switch out (8) receiving antennas on my towers.” If I will see a significant gain using 5.8 GHz I would be willing to make that switch.

VPOL or HPOL?
“If I stick to 2.4 GHz I will have to use HPOL!” (In this case I’m hoping that all I will have to do is turn my 2.4 GHz grid antennas 90 degrees to achieve HPOL.)

90 or 120 degree sector antennas?
Since I plan on using a RB532a with (4) cards, 1 used for a 2.4 omni, that would leave me with the ablity to use 3 cards for my AP’s, so I guess (3) 120 degree sectors are my only option!

If I do go the route of using 5.8 do you have any thoughts on which card and antenna combo I should use. I want the maximum the law will allow!
Christapher James Hasher
Waseca Wireless

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cmacneill
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Re: setting TX Power

Mon Nov 26, 2007 12:17 am

In the US your maximum EIRP on a PtP link is 36dB or 4W. EIRP is the combined gain of the antenna and output power of the wireless card minus any cable/connector losses.

If you are going to use a 29dB antenna, assuming zero cable loss, the maximum transmit power of your wireless to stay legal is only 7dB. For every 1db of cable loss you can increase the transmit power by 1dB. So if you're transmitting at 17dB or more, you are actually exceeding the legal limit 10 fold!

Throwing more power at a problem is not the solution, what is more power to you is more noise to everyone else.

Just because you want to create a link, that doesn't mean it's feasible to do so within legal limits. Use a link loss calculator to determine if a specific link is feasible. There is a link loss calculator in the MikroTik Wiki http://www.mikrotik.com/test_link.php. Remember to enter receiver sensitivity as negative values and gain/cable loss/transmit power as positive values.

You guys in the US should think yourselves lucky, in Europe we are restricted to a maximum EIRP of 20dB or 100mW @ 2.4GHz, we have no choice but to use 5.8GHz for links of any significant length where we have the same EIRP limits as the US.
 
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Re: setting TX Power

Mon Nov 26, 2007 2:05 pm

cmon69 -
On almost any backhaul I use the 5Ghz band. Now 5Ghz doesn't get quite the distance that 2.4Ghz gets but there is a lot less 'consumer' grade electronics interference with this band. The antennas are far smaller than 2.4Ghz. You have a lot more channels to choose from and all are non-overlapping (standard channels). Use Horizontal or linear polarity - less likey to pick up interference. Final is that your backhaul won't interfere with your own 2.4Ghz client equipment.

As to equipment....the R52H and the XR5 are my favorites. I use 23-24db antennas usually, I have few long links that I use 1 and 1.5 meter dish antennas on - it just depends on the application whether or not there are multiple radios in a box and what band(s) I am using. There are a few 24db antennas that are antenna/enclosure combinations (ARC Wireless comes to mind), PAC Wireless makes a great 23.5 db panel antenna. There are several more - you'll need to find what works for you.

You do have to pay antenntion to the regulatory restrictions - you should go look up part 15 in the FCC rules regarding the bands your are interested in using. Higher power does not mean better, focused systems create less 'noise', are more frequency efficient, require less 'raw' power, and are less prone to interference.

cmacneill is almost right regarding the power output limits here in the US. 36 EIRP is the maximum with PtMP setups. PtP EIRP I believe is either 44 or 48db. Now a funny thing this PtP defination here. A CPE pointing to an AP is considered a PtP. The AP looking at several CPEs is considered a PtMP. Thus your CPE can have a higher combined EIRP than your AP that serves the several locations. With that in mind you may want to rethink how you are going to reach your remote sites from your new tower.... It is almost cost effective for you to hit each remote site with a PtP link in the 5Ghz band using seperate antennas. You could easily stuff two good high power radios per box with two seperate antennas at your main site...something to think about.....
Thom Lawless
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RapidWiFi, LLC
thom.lawless [at] rapidwifi.com
 
pixitha
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Re: setting TX Power

Wed Dec 19, 2007 6:45 am

A really simple and easy overview of the US FCC rules on radio power in the ISM bands:

http://www.fab-corp.com/pages.php?pageid=1

Talks about PtMP and PtP

-pix
 
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Re: setting TX Power

Wed Dec 19, 2007 10:00 am

You must use "default tx power" for the best stability.

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