Thanks to GW0OAJ for this article

A wider filter would be desirable, of course, and was calculated for.  A choice of 6th order would ensure a flatter response, hence was a design target.  A number of bread board layouts were tried, some for robustness, and also to include screening.  Later boards to try and eliminate the horrors in the results department.

These are only some of iterations and their reject results....  I save your bandwidth by only sending you some of the duds. Several were the design recalculations done, impedance matching LC circuit changes, xtal shunt capacitors changes, board layout adjustments.  Crystals re-matched.… mutterings about maybe a duff xtal.... etc and etc.

Finally a board worked!  Then variable shunt capacitors replaced the fixed ones for tweaking:

But before that, not too bad a shape and tad over 1 dB ripple on the top.  Width at just over 2K at -3 dB.  Stop band about -80 dB:


Results are easier to achieve with a low order, narrow band ladder than a wider band, higher order job.  However, the effort is worth it, particularly if it can be got right first time.

Xtal Ladder Filter part3

Copyright 2015  ©  Cwmbran and District Amateur Radio Society

Back CADARS Logo
Home About Us GB3RT Repeater News and Events Education Local Information  Local Conditions Useful Info

Cwmbrân & District Amateur Radio Society

For access to this area email webmaster

Members Only