Filter ssb


Somebody have tested this?
July/August 2004 QEX (
It's a  Crystal Filters with Variable Bandwidth and Constant Center Frequency

there is a draft idea here in the end page.  Filter – uBitx     

I’ve noticed that sometimes there are multiple overlapping conversations. The filter in its design may not be narrow enough?




I am familiar with type of crystal filter. Several transceivers have used it with varactors in the shunt positions to make a variable bandwidth filter. Elecraft K2, 2n2 series rigs, and some by TenTec. These filters move some with bandwidth,  so sometimes the bfo is adjusted, or the operator must retune the signal.

The new idea here is the series varactors that keep the filter centered at the same frequency while changing bandwidth.

Note the existing ubitx filter has more ideal passband and skirt rejection. Only when another ssb signal gets very close would the adjustable xtal filter be useful. The benefit is mostly for narrowband signals like cw morse and rtty.

The K2 uses a wide fixed xtal filter like the one in ubitx, and an adjustable xtal filter for narrower bandwidth.  A key point is for narrow cw filtering a much lower frequency like 5 MHz works better, as has been discussed here. The existing IF is better for ssb.

I suggest keeping the existing ubitx xtal filter unless one does only cw and rtty.