Crystal Filter

Worked on the crystal filter today and  put the sna to the test.  Needed to play around with the settings for frequency span and frequency steps more than I though I would have to.  I didn't really think about how sharp the filter was and in order to really see the passband, the frequency span and step is very critical. I also noted, and it now makes sense, that the broader the parameters the less accurate the details are.  For example, the bandwidth and freq. max min at the -3dbm points.

Also setting the xtall input resistance does not change the characteristics of the waveform or the -3db points or bw.  It does however an effect on the data for Q, R, C, and L.

This is my first go at using the sna for the crystal filter function and I pretty sure I have set everything correctly.  There is one other parameter that I need to dig into further, but I'm sure its only needed when matching crystals.

So here's what I found out for the xtal filter for the LBS project.

These are the parameters that were set in the sna and shown in the pictures: Lo Freq. 4,913 and the Hi at 4,916. Step freq at 4hz.  I did at first span the hf band and then focused in on the crystal frequency.

1st picture shows the response when the probes were connected to the input side of the coupling transformers. The crystal input resistance was set at 50 ohms.  You can easily see the response data from the screen. 

2nd picture shows the response when the probes were connected to the input and output caps leading directly to the xtal filter and bypassing the coupling transformers. The crystal input resistance was set at 200 ohms.  Again the data is clear in the picture.  Note the bandwidth differences and the increase in the ripple. Quite a difference when bypassing the matching transformers.  It looks like in picture 1, that the ripple comes in at around 5-7dbm.  I'll need to do some reading to see how that matches up.

This is board is almost completed.  Still need to add power points and a capacitor between the amplifier circuit and coupling transformer.

So we are getting closer now to putting some of these boards together. Look for a suitable plank of wood to start with.  Its a little cumbersome with loose boards everywhere.  Likely something that will facilitate the "I let the smoke out" again. hihi.

73, Peter