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  1. #1
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    improve radio selectivity

    hi
    i have a radio which use CXA1619BS IC.problem is radio selectivity.strong local stations didn't let to receive adjacent channels so i want to use another filter
    i extract schematic from radio board and i want to replace SFU455B ceramic filter with CFWLA455KGFA-B0
    can i do this?and just replace new filter with the old filter? or circuit need chanes?

    here is extracted schematic(just IF parts)(NPN transistor is S9018):

    http://s8.picofile.com/file/8341918792/SFU455.jpg

    Click image for larger version. 

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    here is SFU455B datasheet:
    https://drive.google.com/open?id=1pp...IBcBegu0aysJOm

    here is CFWLA455KGFA-B0 datasheet:
    https://drive.google.com/open?id=1XE...NhBCWLiOr_aNGu

    and CXA1619BS datasheet:
    https://drive.google.com/open?id=1g-...aQraO_-RLgtYXh
    Last edited by BradtheRad; 7th November 2018 at 04:49. Reason: Converted image to Edaboard attachment

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  2. #2
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    Re: improve radio selectivity

    Strong Radio Channels don't impact directly the IF Frequency only, they do impact also LNA so interference signal(s) may cause Harmonic Distortion due to Limited Linearity of the LNA.
    So, using a Narrower Band Ceramic Filter may improve the selectivity but not it's not only one who perturbs the selectivity.


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  3. #3
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    Re: improve radio selectivity

    Quote Originally Posted by BigBoss View Post
    Strong Radio Channels don't impact directly the IF Frequency only, they do impact also LNA so interference signal(s) may cause Harmonic Distortion due to Limited Linearity of the LNA.
    So, using a Narrower Band Ceramic Filter may improve the selectivity but not it's not only one who perturbs the selectivity.
    for example a local station that is 20 KM away from me on 1188 KHz is heard even on 1320 KHz so i think using that filter solve this problem and radio can receive stations between 1181 to 1320 KHz.is that right?
    and i have another question is CFWLA455KGFA-B0 narrower than SFU455B and does it solve problem?



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    Re: improve radio selectivity

    If you really want to improve selectivity on the 455kHz IF, you have to go with a Mechanical filter.
    Follow ebay and sometime you find cheap ones.
    https://www.ebay.com/itm/Collins-Mec...pJ92:rk:2:pf:0

    You have to search for a filter with bandwidth between 6kHz and 9kHz (looks like you are looking for AM bands).
    Depending on the existing IF amplifier, using mechanical filters is possible to need an extra amplifier to compensate for their insertion loss.
    Those amplifiers helps also for their impedance matching, which is totally different than that of ceramic filters (or crystal filters).


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  5. #5
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    Re: improve radio selectivity

    Quote Originally Posted by vfone View Post
    If you really want to improve selectivity on the 455kHz IF, you have to go with a Mechanical filter.
    Follow ebay and sometime you find cheap ones.
    https://www.ebay.com/itm/Collins-Mec...pJ92:rk:2:pf:0

    You have to search for a filter with bandwidth between 6kHz and 9kHz (looks like you are looking for AM bands).
    Depending on the existing IF amplifier, using mechanical filters is possible to need an extra amplifier to compensate for their insertion loss.
    Those amplifiers helps also for their impedance matching, which is totally different than that of ceramic filters (or crystal filters).
    thank you
    but i dont't want spend 90$ for a filter while many 60$ radios have good selectivity without any mechanical filter
    do you see CFWLA455KGFA-B0 datasheet?it's a 6 element ladder type filter ,so you think it's not a suitable filter for improve selectivity?



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    Re: improve radio selectivity

    CFWLA455KGFA-B0 is a new generation filter from Murata and should be fine for a 60 bucks radio.

    Mechanical filters were designed for professional radios, having out-of-band rejection up to 90dB.
    But more important than the rejection, mechanical filters have a very flat out-of-band spurious response, when ceramic filters have a lot of "bumps" in that region.


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  7. #7
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    Re: improve radio selectivity

    Quote Originally Posted by vfone View Post
    CFWLA455KGFA-B0 is a new generation filter from Murata and should be fine for a 60 bucks radio.

    Mechanical filters were designed for professional radios, having out-of-band rejection up to 90dB.
    But more important than the rejection, mechanical filters have a very flat out-of-band spurious response, when ceramic filters have a lot of "bumps" in that region.
    you'r absolutely right about mechanical filter and their price against these murata filters says everything.
    i want improve my radio selectivity by spend under 10 dollars.
    in this situation i think that murata filter is the best solution.am i right?
    and again my important question is should i just replace new filter with old one or another components need changes?



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