I'm looking to learn CW. I have a old Heathkit SB102 which did not have the optional CW filter. And filters if you can find one go for $50 or more! Much more then I'd want to spend considering what I already put into it restoring it up. I'm at least 90% done so far! Just a few items left and its complete! Mostly cosmetic as it operates just fine wihout changing them.
So I was thinking it may be possible to just build a new filter using modern parts. The orginal filter has a center frequency of 3395.4MHz, bandwidth of 400Hz(600@6Db down, 2000@60Db down) and it has input/output impedances of 2kohm. So could a new filter be built to be close to the orginal specs? If yes how would one go about this? What parts are needed? When I looked online I wasn't finding what I needed to build one at a RF frequency. Only audio frequencys and nothing regarding impedances and such. Possibly a active filter? from what I found but I'm not sure since as that has gain and the orginal filter didn't since it's a passive network of crystals and caps. So maybe a resistive network at the output to attenuate the signal to then take the signal out of it?
If someone could help me with this by giving some insight on how to design this that would be awesome! Would be cool to build my own filter which I wouldn't have to worry about drifting over time. Some orginal filters have drifted! Then I could always build a SSB filter in the future should mine drift. If you want to design a full thing I'd love that but at least a little help figuring out how to design one for use at RF with a narrow bandwidth. Including the parts and math needed wi a little decription of how to proceed.
Thanks
So I was thinking it may be possible to just build a new filter using modern parts. The orginal filter has a center frequency of 3395.4MHz, bandwidth of 400Hz(600@6Db down, 2000@60Db down) and it has input/output impedances of 2kohm. So could a new filter be built to be close to the orginal specs? If yes how would one go about this? What parts are needed? When I looked online I wasn't finding what I needed to build one at a RF frequency. Only audio frequencys and nothing regarding impedances and such. Possibly a active filter? from what I found but I'm not sure since as that has gain and the orginal filter didn't since it's a passive network of crystals and caps. So maybe a resistive network at the output to attenuate the signal to then take the signal out of it?
If someone could help me with this by giving some insight on how to design this that would be awesome! Would be cool to build my own filter which I wouldn't have to worry about drifting over time. Some orginal filters have drifted! Then I could always build a SSB filter in the future should mine drift. If you want to design a full thing I'd love that but at least a little help figuring out how to design one for use at RF with a narrow bandwidth. Including the parts and math needed wi a little decription of how to proceed.
Thanks