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iDirect 3000 series TX Power Adjustment

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Jan 28th, 2008 at 7:06am  
is it possible that i can increase the tx power at the modem.... and after rebooting the said power adjustment is still there?

thanks...
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Reply #1 - Jan 28th, 2008 at 8:52am  
Hi polpan,

Are you tring to set the TX from the hub or remote end?  Usually the initial and max TX power of the NM is set by your hub.  Thus you will only be able to drive the NM to the max set by the hub.  I take it you need to increase the TX past the maximum set in the option file?
You may be able to do this manually by opening the option file as a text documentn changing the max TX power and then reloading it on the NM.
Let me know how you get on.

Thanks,

Lukio ;.)
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Reply #2 - Jan 28th, 2008 at 9:17am  
yes.... i want to increase the tx power at the modem.... because sometimes ther is no cellphone signals at remote sites so normally i would be the one to adjust the power....

anyway... you mean i will try to edit the option file then upload it again to the modem?

which part of it....

thanks
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Eric Johnston
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Reply #3 - Jan 28th, 2008 at 11:21am  
Don't change the modem output power setting locally.  If you have service problems ask the hub to investigate and let them make appropriate changes, if necessary.

The modem output power setting needs to be correct, neither too high nor too low.  Increasing it without the hub monitoring may interfere with the service of other people, increase the bit error rate and damage your BUC.

Best regards, Eric.
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Reply #4 - Jan 28th, 2008 at 11:27am  
i always install at mountains....remote places... no way to contact the hub most of the time and maybe i will just raise it for about -5dbm only....sometimes this is the only way to be connected to the  network

how should i do it...step by step...

thanks to all...

Cheesy
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Eric Johnston
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Reply #5 - Jan 28th, 2008 at 11:48am  
Be careful..

If the BUC has 55 dB gain and you put -20 dBm into it then output power should be +35 dBm or +5 dBW or 3.2 watts.

1 watt = +30 dBm or +0 dBW
2 watts = +33 dBm or +3 dBW
4 watts = +36 dBm or +6 dBW
8 watts = +39 dBm or +9 dBW
10 watts = +40 dBm or +10 dBW

Unless you have a very long cable, a modem level of -5 dBm is likely to overload the BUC and cause severe interference to return link services on adjacent frequencies. It will also degrade your own carrier as it will be distorted.

BUCs must be operated at or below their -1dB compression point, which is the rated power.

In other words don't try to transmit more than 2 watts with a 2 watt BUC.

Once the hub has control they should adjust for the correct level.

Ideally the hub should put the transmit into CW mode and increase the drive in 1 dB steps while measuring the output.  Once the graphed line becomes non-linear and there is a 1 dB vertical gap between the projected straight line and the actual output curve, the BUC is at its 1 dB gain compression point.  The drive level for the 1 dB gain compression point should be recorded for reference as a "never-to-exceed" value. ( opt file. max power )

...
This image shows how altering the modem tx power altered the receive level at the hub. Note that during the last three adjustments it goes non linear and at the final measurement the gain is 1 dB below what the straight line projects.  This is the rated 2 watt output maximum at the -1dB compression point.

Cross pol measurement and adjustment should made if necessary.  With modulation back on the Eb/No should be set to nominal, assuming clear sky conditions at the time.

It gives confidence if you then experimentally and temporarily reduce the power 4 dB (at Ku band) and check everything continues to work normally under faded conditions.  This shows you have a decent rain margin.   Reducing the power by 10 dB should make it fail.  If such a reduction actually improves the service be alert to the possibility that the BUC might have been operating in grossly overloaded way.

Best regards, Eric.
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« Last Edit: Jan 30th, 2008 at 3:18pm by Eric Johnston »  
 
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TDMAMike
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Reply #6 - Jan 28th, 2008 at 12:14pm  
Adjusting power in telnet will only briefly adjust power on the modem as the NMS UCP config will bring you back down to the configured nominal C/N for your network.  

Dependent on the iDS, the Uplink Control Parameters (UCP) for a specific beam is set at the inroute level.   (Older iDS's 6.x and below are set at the network level).  

When the beam is commissioned the HNO will determine TDMA Nominal C/N for the upstreams and that is considered the "sweet spot" UCP for the beam/network.  After setting the Nominal C/N he sets the fine and course adjusts. Normally Fine is set to one dB either side of the sweet spot and course adjusts are 3dB on either side of the 1dB fine adjusts.  It will look like this.

|  3dB  |1dB| 9dB C/N |1dB| 3dB |

So, dependent on where your burst arrives, you may or may not get a power adjustment.  If you do not, then you are meeting the UCP. If your modem is being told to pull power then you are arriving too hot.  If you are being told to push power, you are arriving too low.  The params above can be heavily skewed if you have different C/Ns (from multiple  modems) arriving at the hub.  That is why it is extremely important to ensure all VSATs operating in the beam are commissioned correctly and their Tx values are set to arrive within the UCP.

A lot of operators use a common set of inital and max power values for commissioning and they forget to follow up after node acquistion (and take a clear sky bseline) and revisit the configured params.  Using "common" parameters is dangerous, as variopus nodes sit in different EIRP contour lines.
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« Last Edit: Jan 28th, 2008 at 2:28pm by TDMAMike »  

Regards, &&&&M
 
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Reply #7 - Jan 28th, 2008 at 12:55pm  
Eric Johnston wrote on Jan 28th, 2008 at 11:48am:
a modem level of -5 dBm is likely to overload the BUC



i mean...raise it  at increment of -5dbm only...from -25dbm to -20bm only example.....

do i need to edit the options file in notepad then upload it again... how should i do it...

Cheesy
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TDMAMike
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Reply #8 - Jan 28th, 2008 at 11:22pm  
Manipulating the options file doesnt do anything for you as the modem will still adapt itself to the configured UCP parameters.  

For example: if the UCP is configured for 9dB C/N (Nominal) your modem will use whatever power necessary to stay right at 9dB C/N.  It is the sole purpose of the UCP.  So, adjusting in telnet, in the options file, or even sending a probe from iMonitor, will only temporarily adjust the power.  The NMS will send it power offset statements to bring you right back in line with the configured UCP.
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« Last Edit: Jan 29th, 2008 at 2:36am by TDMAMike »  

Regards, &&&&M
 
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Reply #9 - Jan 30th, 2008 at 3:12pm  
pol,

there are two power settings in your opt file. max power and initial power.

max power should only be set by the hub as described above with respects to your compression point. if thats too low then you uplink chain is starting to degrade. whether because parts or merely antennae alignment. start with a peak and pole to maximize alignment.

if your issue is that the modem's initial power is too low, such as the modem wont come back into the network until you raise power, then have the hub set your initial power higher and push down the reset. typically this should be set 2-3db above your normal operating power.

nigel
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