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Image Anf IF Rejection - RF Cafe Forums

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Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


jab
Post subject: Image anf IF rejection Posted: Thu Mar 23, 2006 1:24 pm

Lieutenant

Joined: Wed Mar 08, 2006 8:18 am
Posts: 3
Guys - any idea on how to measure the image frequency and IF rejection ratio say your in band is 98MHz.

Thanks.
JAB


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yendori
Post subject: Posted: Thu Mar 23, 2006 5:05 pm

General


Joined: Thu Sep 25, 2003 1:19 am
Posts: 50
Location: texarcana
Measure your desired IF signal. Apply the image frequency at the input and then measure the image IF.

RK


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nubbage
Post subject: Image anf IF RejectionPosted: Fri Mar 24, 2006 11:18 am

General


Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
More specifically if the IF is 10.7MHz, then set the sig gen to 98MHz and note a reference level immediately after the IF filter stage. Avoid taking a level any further down the IF chain, as the presumably FM receiver will have a nonlinear limiter.

Set the generator frequency to 21.4 MHz above or below the 98MHz channel, eg 76.6MHz and increase the level of the generator until it reaches the previous level. Note the attenuator level setting difference. This is the Image Rejection ratio in dB

Set the generator to 10.7MHz and repeat the measurement. The attenuator difference is the IF rejection.

All best
Trev


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jab
Post subject: Posted: Tue Apr 04, 2006 8:54 am

Lieutenant

Joined: Wed Mar 08, 2006 8:18 am
Posts: 3
Thank you Guys.
I dont have the attenuator so this is what I did.
First measure the direct inject sensitivity at operating freq. and inject the image - the difference is my ratio. same thing on 10.7MHz for IF.

Thanks again.
JAB



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