Selectivity & adjacent parameters - RF Cafe Forums

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evgkru

Post subject: Selectivity & adjacent parameters

Posted: Wed Dec 16, 2009 8:37 am

Lieutenant

Joined: Wed Dec 16, 2009 8:28 am
Posts: 2

Hi guys,

I have a question about Selectivity & adjacent paremeters.

What is deference between receiver selectivity and adjacent parameters?

Glad for any help.

SunshineDesign

Post subject: Re: Selectivity & adjacent parameters

Posted: Fri Dec 18, 2009 11:54 am

Colonel

Joined: Sat Nov 08, 2008 11:35 pm
Posts: 30
Location: Ramona, CA

evgkru - can you be more specific as to what exactly you are asking. I presume filter/band selectivity of the receiver and adjacent channel power?

Receiver selectivity is the ability to receive the desired signal without inteference from other adjacent signals and the filter selectivity and sensitivity (i.e. noise figure and gain) of the receiver play a part in this as does the receivers ability to not be sensitive to the adjactent channel effecting the receiver gain of the desired signal (desense as this effect is called).

The Adjacent Channel power is the integrated band power of any signals adjacent to the desired channel being received.

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evgkru

Post subject: Re: Selectivity & adjacent parameters

Posted: Sun Dec 20, 2009 6:54 am

Lieutenant

Joined: Wed Dec 16, 2009 8:28 am
Posts: 2

Hi,

Thank you for your reply.
I am looking for receiver with 60dB selectivity @±50KHz
On one of the data sheets http://www.radiometrix.com/node/343 I see only Adjacent channel parameter (Adjacent Channel: -70dBm)
Can I refer to this parameter as selectivity?

happy Xmas

SunshineDesign

Post subject: Re: Selectivity & adjacent parameters

Posted: Mon Dec 21, 2009 10:47 pm

Colonel

Joined: Sat Nov 08, 2008 11:35 pm
Posts: 30
Location: Ramona, CA

The two are related but not equal. Adjacent Channel Power or Rejection is a band integrated power measurement. Selectivity is a point to point power comparison to some set /RBW or /Hz. You would define the primary band and the adjacent band and then compare min, max, average and/or defined frequency points. For instance, a filter I worked on had a passband min to a band trap adjacent in upper sideband. I had to have so many dBc rejection or selectivity. On the other hand for CDMA I might have +15dBm/CDMA Band power compared to -32dBm/CMDA Adjacent channel power in the upper channel for a 47dB Adjacent Channel Rejection. So you could estimate but not equate from the info you have. You would have to test.

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Posted 11/12/2012

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