filter RX

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radium98
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filter RX

Post by radium98 » Sat Sep 26, 2020 2:46 pm

a question
Is there any Stripline filter on etched directly on pcb epoxy double side ,that can be used for reception .like the one used on rx for reception called cavity filter
like the one in this picture but in pcb mode?
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Albert H
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Re: filter RX

Post by Albert H » Mon Sep 28, 2020 12:07 am

Yes, but only at UHF and higher frequencies
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radium98
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Re: filter RX

Post by radium98 » Mon Sep 28, 2020 5:26 pm

Thanks.And why in VHF it can not be acheived ?

Albert H
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Re: filter RX

Post by Albert H » Wed Sep 30, 2020 2:27 am

Simply because the striplines are too large at lower frequencies. It's possible to do minor impedance conversions at VHF using board tracks, but the values of inductance available with even quite long tracks are far too small for useful filtering.
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

radium98
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Re: filter RX

Post by radium98 » Wed Sep 30, 2020 8:19 pm

thanks Albert.And what an easy diy filter will you suggest me to try for frequency 200-250

Albert H
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Re: filter RX

Post by Albert H » Thu Oct 01, 2020 1:32 am

The traditional pi filter - two coils that show 50Ω impedance at your frequency of interest, with 50Ω impedance capacitors at both ends and 25Ω impedance capacitor in the middle. Design for a frequency about 15% higher than the highest frequency you want to pass.

Get a copy of the ARRL Handbook. There's all the design notes you'll ever need for 225MHz (an amateur band in the USA)
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

radium98
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Re: filter RX

Post by radium98 » Thu Oct 01, 2020 6:25 am

thank you . ARRL Handbook what issue ?

Albert H
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Re: filter RX

Post by Albert H » Fri Oct 02, 2020 2:41 am

Get one of the ones from the 90s - you can get them cheap on Ebay. There's a wealth of useful info in there!
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

radium98
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Re: filter RX

Post by radium98 » Sat Oct 03, 2020 7:23 pm

if you can scan me some pages ,because i cant buye anything .:( sadly we have issues

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