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Design >> RF Design >> abot superheterodyne receiver
https://designers-guide.org/forum/YaBB.pl?num=1237130352

Message started by mydreamhouse on Mar 15^th, 2009, 8:19am

Title: abot superheterodyne receiver
Post by mydreamhouse on Mar 15^th, 2009, 8:19am

i am designing a superheterodyne receiver, but i wonder my IF VGA. (first IF :180MHZ), i found if IF VGA has third order intermodulation, and it will mix with third order distortion of LO, which will locate in bands,is this a serious problem?, who can give me some advice or refernces?

Title: Re: abot superheterodyne receiver
Post by mydreamhouse on Mar 16^th, 2009, 10:05am

who can give me some advice

Title: Re: about superheterodyne receiver
Post by pancho_hideboo on Mar 16^th, 2009, 10:11am

mydreamhouse wrote on Mar 15^th, 2009, 8:19am:

i found if IF VGA has third order intermodulation, and it will mix with third order distortion of LO, which will locate in bands,is this a serious problem?

???????????????
Maybe there is no one who can understand a meaning of your sentences.

mydreamhouse wrote on Mar 16^th, 2009, 10:05am:

who can give me some advice

Again If you want someone to answer your post,
you have to describe your questions regarding situation and condition in detail and correctly using industrial standard terminologies.

This is very very true for all your posts too.
http://www.designers-guide.org/Forum/YaBB.pl?num=1235494642/0#0
http://www.designers-guide.org/Forum/YaBB.pl?num=1229879167/0#0
http://www.designers-guide.org/Forum/YaBB.pl?num=1235493325/0#0
http://www.designers-guide.org/Forum/YaBB.pl?num=1236016393/0#0

Title: Re: abot superheterodyne receiver
Post by mydreamhouse on Mar 18^th, 2009, 11:01am

thanks.
what i worry about is the third order distortion of IF signal mixes that of the second LO. for instance, the IF is 200MHZ, after external LC BPF or SAW filter, an on chip IF VGA is following. due to the third order intermodulation of IF VGA, third order distortion will be appears before the second mixer. so 3IF-3LO will be in band(dual conversion superheterodyne receiver),which will degrade the sensitivity.

Title: Re: about superheterodyne receiver
Post by pancho_hideboo on Mar 18^th, 2009, 5:24pm

mydreamhouse wrote on Mar 18^th, 2009, 11:01am:

what i worry about is the third order distortion of IF signal mixes that of the second LO.
for instance, the IF is 200MHZ, after external LC BPF or SAW filter, an on chip IF VGA is following.
due to the third order intermodulation of IF VGA, third order distortion will be appears before the second mixer.
so 3IF-3LO will be in band(dual conversion superheterodyne receiver),which will degrade the sensitivity.

Still there is no one who can understand a meaning of your sentences.

I can't know your system is double super heterodyne until now.

And third order harmonic distortion is different from distortion due to third order intermodulation.
Do you understand third order intermodulation correctly ?

Again If you want someone to answer your post,
you have to describe your questions regarding situation and condition in detail and correctly using industrial standard terminologies.

Title: Re: abot superheterodyne receiver
Post by loose-electron on Mar 18^th, 2009, 10:25pm

Suggest: Post a block diagram of your system and some details of the frequencies, and other numeric specifics of what you are doing.