Dave, I am wondering if you have some problem with the crystals in the variable IF filter. The variable filter design point is near 500 Hz. It will normally have attenuation below 200 Hz width and the passband will bet more 'ragged' above 1 kHz. What I am saying is that you should have a constant filter response at 700 Hz, 400 Hz with perhaps a small bit of attenuation at 200 Hz. Below that width, attenuation will increase rapidly.
If your K2 is below SN 2560, and it has not been upgraded, you have the older crystals in it and I highly recommend that they be changed with the matched set of 7 crystals available from Elecraft. That will change the attenuation. Of course, if your filters are not aligned to properly center on your sidetone pitch, that alone could be the reason for your observations - that would be more apparent as the width is narrowed (the signal falls on the slope of the passband rather than at the peak). See the filter alignment information on my website www.w3fpr.com - look at part 3 of the article dealing with K2 Dial Calibration. Use Spectrogram or Spectrum Lab or similar to give you a visual picture of the filter passband placement and the relative amplitude of the filters. One of the aspects (limitations) of the K2 is that your listening sidetone pitch cannot be changed at will without peaking the narrow IF filters at that new sidetone frequency. You may be able to change the sidetone pitch by 50 Hz each side of the filter center, but much beyond that will require that the filter centers be repositioned. 73, Don W3FPR On 11/4/2010 2:12 PM, dave wrote: > I dunno about the loss you are seeing but I've measured about 8 dB of > loss in my K2 at 200 Hz vs 1 kHz BW. That does strike me a quite a bit > of loss. I just don't use the narrow filters often. I know of at least > one other K2 that has similar loss. Anyone else? > > > 73 de dave > ab9ca/4 > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
