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Intermodulation for TETRA ETSI standard - RF Cafe Forums

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RDO-RF
 Post subject: Intermodulation for TETRA ETSI standard
Posted: Mon Mar 22, 2010 2:59 pm 
 
Captain
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Joined: Wed Apr 08, 2009 7:53 am

Posts: 17

Hello RF-Cafe folks!:

I have two questions regarding the ETSI TS 101 789-1 V1.1.2 (ETSI standard for TETRA Repeaters).

On point 5.5.2.3, we the Limit Values for the intermodulation Attenuation.

Te text says: “The level of intermodulation product shall be less than -60 dBc. In any case not requirement greater than -36dBm shall apply”. I can't quite understand this phrase, so I have the following two questions:

1) If I have a repeater of 2x32dBm output power. The maximum intermodulation level needed to apply ETSI is -36dBm (-68dBc) or -28dBm (32dBm-60dBc) ?

2) If I have a repeater of 2x15dBm output power. The maximum intermodulation level needed to apply ETSI is -36dBm (-51dBc) or -45dBm (15dBm-60dBc) ?

Thank you!

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Jose Arrina
 Post subject: Re: Intermodulation for TETRA ETSI standard
Posted: Tue Mar 23, 2010 10:59 am 
 
Captain
User avatar

Joined: Thu Mar 30, 2006 9:01 am

Posts: 12

The spec means your intermods have to be at least -60 dBc, and also cannot be any greater than -36 dBm in absolute power.

So your first example would produce intermods at -28 dBm when down 60 dB from the +32 dBm. That is 8 dB too high.

In the second example the intermods are at -45 dBm when 60 dB down from the +15 dBm carriers, so you're below the max absolute level of -36 dBm.

Example 1 fails, example 2 passes.

Hope that helps.

Jose'

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RDO-RF
 Post subject: Re: Intermodulation for TETRA ETSI standard
Posted: Tue Mar 23, 2010 1:21 pm 
 
Captain
User avatar

Joined: Wed Apr 08, 2009 7:53 am

Posts: 17

Hello Jose, thank you for your quick response.

Your add helps a lot, but I´m still not convinced yet.

If the standard was "Intermods have to be at least -60 dBc, and also cannot be any greater than -36 dBm in absolute power" it will be more than clear.

But it says:

"...In any case not requirement greater than -36dBm shall apply", it doesn't clearly says that the absolute power can´t be greater that -36dBm, it also can be understood that they are not asking for requirement grater that -36dBm... and the question will be: what is a grater requirement? -37dBm or -35dBm???? I believe that -37dBm is a grater requirement than -36dBm.

That is why I´m not convinced yet... on one hand, I can understand what Jose said, but on the other hand I can also understand that they ask for -60dBc but that there is no need for a lower IMD than -36dBm.

What can´t be greater than -36dBm, the absolute IMD tones or the requirement?? I cant clearly understand that from the standard...

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