Ok so are you just after suppression of anything coming out of your radio and suppression of out of ban spurious emissions or after better receive audio?
I ask because depending on what is more important there are several ways to cook this bird or skin this cat.
First it would be easy to get much more narrow 8-15 element crystal filter and install in the radio pricey I know. You could get 2-3 crystals of much lower cost and use them in each stage in the radio sharpening selectivity/rejection and making the skirt much steeper. Remember the "Channel Guard" from CBC International back in the 1990's? Like that idea only built on the existing IF stages in circuit instead of on a separate board.
On the output side of things keeping your radio from being a splatter box is easy and not over driving your amp and filtering it's output is easy enough to do passively with passive components. In fact avoiding transformer coupling altogether and going with a tuned input is fantastic medicine plus it always improves efficiency over transformer coupled input and broad band designs.
Everything Bellow is off topic could be fun to try anyways!!!
Audio filtering could remove some trash so you do not hear it at the very least.
I think I recall you in the past mentioning NPC and various forms of audio and rf clipping in the past. While not strictly a filter not in the sense you desire if I understand you right it could be made to clean up the receive audio. Depending on where you put it in the radio you could in theory pass the receive signal through it just like you do audio prior to the rf stage on tx. So it would work in receive just as it does on transmit. The same thing applies to any gadget we normally associate with putting between the mic and radio so eq's noise gates, downward expanders clippers/compressors split band audio processing etc....All of thee things can be used on the receive side of things as well and can be switched in and out. The Cherokee 150 Night Rider even had what it called an "Expander" that switched on receive. It was a separate board that mounted inside.
I know it sounds stupid for me to say the above I am sure but we do stuff like this all the time to tx audio . I have never tried it but I am going to try it now soon. I have 3 kids one going off to college and 2 are Freshmen in High School so as my Great Grandfather used to say " I am as busy as a one legged man in an butt(self censored) kicking contest!". I do not get on here often. I hope some of these idea's even if not directly helpful spur some creative thought on the matter!
I just yanked out my handy dandy 1999 ARRLHandBook and have not found any gems inside of it yet that would relate to this idea.
Since most CB and Export radio audio starts to drop off at or before 2500hz it would be easy to filter anything above that. I think combining the enhanced crystal filtering and the audio idea's you could get to a point where the combination of selectivity and audio processing produce fantastic results.
I know none of those idea's keep the emissions from getting from your antenna to the radio or keep emissions from getting from your radio out to the antenna. I just thought they where cool.
I ask because depending on what is more important there are several ways to cook this bird or skin this cat.
First it would be easy to get much more narrow 8-15 element crystal filter and install in the radio pricey I know. You could get 2-3 crystals of much lower cost and use them in each stage in the radio sharpening selectivity/rejection and making the skirt much steeper. Remember the "Channel Guard" from CBC International back in the 1990's? Like that idea only built on the existing IF stages in circuit instead of on a separate board.
On the output side of things keeping your radio from being a splatter box is easy and not over driving your amp and filtering it's output is easy enough to do passively with passive components. In fact avoiding transformer coupling altogether and going with a tuned input is fantastic medicine plus it always improves efficiency over transformer coupled input and broad band designs.
Everything Bellow is off topic could be fun to try anyways!!!
Audio filtering could remove some trash so you do not hear it at the very least.
I think I recall you in the past mentioning NPC and various forms of audio and rf clipping in the past. While not strictly a filter not in the sense you desire if I understand you right it could be made to clean up the receive audio. Depending on where you put it in the radio you could in theory pass the receive signal through it just like you do audio prior to the rf stage on tx. So it would work in receive just as it does on transmit. The same thing applies to any gadget we normally associate with putting between the mic and radio so eq's noise gates, downward expanders clippers/compressors split band audio processing etc....All of thee things can be used on the receive side of things as well and can be switched in and out. The Cherokee 150 Night Rider even had what it called an "Expander" that switched on receive. It was a separate board that mounted inside.
I know it sounds stupid for me to say the above I am sure but we do stuff like this all the time to tx audio . I have never tried it but I am going to try it now soon. I have 3 kids one going off to college and 2 are Freshmen in High School so as my Great Grandfather used to say " I am as busy as a one legged man in an butt(self censored) kicking contest!". I do not get on here often. I hope some of these idea's even if not directly helpful spur some creative thought on the matter!
I just yanked out my handy dandy 1999 ARRLHandBook and have not found any gems inside of it yet that would relate to this idea.
Since most CB and Export radio audio starts to drop off at or before 2500hz it would be easy to filter anything above that. I think combining the enhanced crystal filtering and the audio idea's you could get to a point where the combination of selectivity and audio processing produce fantastic results.
I know none of those idea's keep the emissions from getting from your antenna to the radio or keep emissions from getting from your radio out to the antenna. I just thought they where cool.
