Re: Crystal CW filter with Version 4 uBITX boards? #ubitx

ajparent1/KB1GMX <kb1gmx@...>
 

When and if you get it to work please post your results and what it took to make it work.

Yes the ports are 50 ohms, that's never been secret but if you have two 50 ohm devices
(source and load) and then parallel a third 50 ohms device what is that, not 50 ohms.
Only the IF and the Balanced mod are 50 ohms, the filter is 50 ohms in the band pass and
whatever outside it.  

I never said the idea to switching IF frequency will not work. ONly paralleling filter will not work well
due to one more or less shorting out the other.  You have already written that part up.  I did expllain
those of us that can design would do it and it would work well.  Also every stinking cheap am/fm
radio has a dual frequency if both 455 and 10.7 and thats been done for over 50 years.
Been in engineering or over 50 years, my specialty is making the won't work things,  work.
But that unusually means some fancy design or understand how it works to start with.

Two things.   I told you how to do it and it will work if you do that.   I said your hack
of paralleling them relies on things that will be guaranteed to work poorly unless lucky.
Also Farhan said 1.842mhz filter and you didn't try that.  

Now your own words:
>>>The idea of switching the IF frequency to switch filters appears to be sound - just need to find the magic crystal/capacitor/transformer combination and for that I need someone with better knowledge of crystal filters and better test equipment that I have.<<<
I have both and your proceed to disagree.  
Until other post their work it is vaporware.  I have your posting it didn't work.

>>>>So far I've not been able to get a signal through filters at 4.6,  6.2 or 8 MHz.<<<<

You didn't try 1.8432, and you did get some signal but the attenuation is high.  
Silly question did you try the filter without the 12mhz filter shorting it?  That
would prove your filter works.  You could also do that using a bench jig.
You only need signal generator and a scope maybe a few resistors to simulate
a 50 ohm load.

Me I'd mod the 12mz and make it a jones filter (varicap tuned variable bandwidth)
as used in some older Tentec and the Elecraft K2.   I like that as it means the board
only needs parts added (varicap diodes and resistors to a control point) and no
hacking it up.  It is an old idea and discussed before.


Allison

Join BITX20@groups.io to automatically receive all group messages.