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homebrew ubitx roofing filter #bitx20help #bitx40help #bitx40 #bitx20 #filters

circular.simetry@...
 

hello i have finished building the ubitx CM2KMK version and i have problems with the 45mhz crystal filter. the only filters i have in my inventory are the following--
22M03       45,1mhz     from a motorola GM300
49S10B     49,95 mhz   from a kenwood TK760
FL-210       21,8 mhz       from Icom M59
I have tested all of them by changing the frequency acording to each crystal in the source code.The best results so far i get with the 21.8mhz filter FL-210.
iI think the problem is matching the impedance with the two coils L5 and L7 i used 12 turns on T37-6 .
Please if someone have any documentation about the filters or knows what impedance they have i wil be very thankfull.
Thanks in advance ! 73de yo4huj

Ashhar Farhan
 

You could just make LC filters as well. A triple tuned filter should do the trick. While you are at it, change the 1st IF from 45 Mhz to 60 MHz or beyond.

- f


On Tue, Aug 20, 2019 at 1:54 AM <circular.simetry@...> wrote:
hello i have finished building the ubitx CM2KMK version and i have problems with the 45mhz crystal filter. the only filters i have in my inventory are the following--
22M03       45,1mhz     from a motorola GM300
49S10B     49,95 mhz   from a kenwood TK760
FL-210       21,8 mhz       from Icom M59
I have tested all of them by changing the frequency acording to each crystal in the source code.The best results so far i get with the 21.8mhz filter FL-210.
iI think the problem is matching the impedance with the two coils L5 and L7 i used 12 turns on T37-6 .
Please if someone have any documentation about the filters or knows what impedance they have i wil be very thankfull.
Thanks in advance ! 73de yo4huj

circular.simetry@...
 

thank you but if i change the frequency to 60 mhz or more i have to change the value of the capacitors and the number of turns?

kh6sky
 

You could use one of these inexpensive ($5 ebay) Texscan LC filters for a 70 MHz IF and it might go well. These are 25 kHz wide at the 1 dB points and I have not seen a curve but the data sheet says "sharp skirts".  http://www.alltronics.com/mas_assets/acrobat/92P053.pdf

circular.simetry@...
 

thanks

Lawrence Galea
 

Those filters are 25 MHz wide NOT 25kHz


On Tue, Aug 20, 2019 at 9:42 AM kh6sky <kh6sky@...> wrote:
You could use one of these inexpensive ($5 ebay) Texscan LC filters for a 70 MHz IF and it might go well. These are 25 kHz wide at the 1 dB points and I have not seen a curve but the data sheet says "sharp skirts".  http://www.alltronics.com/mas_assets/acrobat/92P053.pdf

kh6sky
 

Well that makes more sense.  How do you make a 25 kHz wide LC filter at VHF? You don't.  I optimistically misread. Thanks Lawrence.

As Roseanne Rosannadanna used to say..."nevermind."

Lawrence Galea
 

HI
Mistakes are made by those who never do anything, but then even those who never do anything make a mistake by not doing anything.
Enjoy.

On Wed, Aug 21, 2019 at 5:06 AM kh6sky <kh6sky@...> wrote:
Well that makes more sense.  How do you make a 25 kHz wide LC filter at VHF? You don't.  I optimistically misread. Thanks Lawrence.

As Roseanne Rosannadanna used to say..."nevermind."

kh6sky
 

I think you meant

Mistakes are made by those who do things, but then even those who never do anything make a mistake by not doing anything.

and it is so true. .






On Wed, Aug 21, 2019 at 5:06 AM kh6sky <kh6sky@...> wrote:
Well that makes more sense.  How do you make a 25 kHz wide LC filter at VHF? You don't.  I optimistically misread. Thanks Lawrence.

As Roseanne Rosannadanna used to say..."nevermind."

 

 

_._,_