Re: uBITX narrow IF filter mod for CW, anyone tried this?


Frank PA7F
 

Hi Alex,

Thank you for your reply! I think you have a very nice set up there with 4 and 12 MHz IF's!

In order to narrow the 12 MHz IF for CW, Farhan suggested to add 220 pF capacitors across the existing 100 pF capacitors in the 12 MHz IF crystal filter. I had hoped somebody tried this. You described on this group how you narrowed down the 4 MHz IF bandpass in your uBITX by using 68 pF capacitors to achieve a 400 Hz bandwidth. So you reduced the value of those caps to narrow the IF.

I have integrated the NEQRP SCAF-filter (audio filter) in my uBITX, this works good, but not perfect as strong signals are leaking through the filter.

73, Frank
PA7F


QUOTE
12/21/17  
i have been using a straight key for sometime. i have found no glitches in the straight key. i used the iambic keyer just for a few quick QSOs. I am straight key guy, hence the keyer code will need some improvement.
the cw is NOT generated with a side tone injection. The CW is generated by the SI5351 by putting it directly on the tx frequency. For those wishing to have a narrower filter, all you hve to do is to add another 220pf capacitors in parallel to the 100pfs across the ladder filter.
UNQUOTE
 

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