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Selectivity & adjacent parameters - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.

 Post subject: Selectivity & adjacent parameters
Posted: Wed Dec 16, 2009 8:37 am 

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.

 Post subject: Re: Selectivity & adjacent parameters
Posted: Fri Dec 18, 2009 11:54 am 

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.

Sunshine Design Engineering Services

 Post subject: Re: Selectivity & adjacent parameters
Posted: Sun Dec 20, 2009 6:54 am 

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

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

happy Xmas

 Post subject: Re: Selectivity & adjacent parameters
Posted: Mon Dec 21, 2009 10:47 pm 

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.

Sunshine Design Engineering Services

Posted  11/12/2012
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