One of the activities we pursued was looking at the output spectrum of noise sources on some test gear Jack owns. Jack demonstrated his noise source and it works very well for testing 23cm filters. We then had a look at my noise source on the spectrum analyser. It had peaks and looked horrible. It occurred to me this morning that the reason for that was most likely stray RF being coupled into the noise source and being amplified by the mmic chain. I still haven't put my noise source into a metal box and the power supply decoupling could be greatly improved.
Despite the shortcomings of the test set-up it did allow me to see the 2m Band Pass Filter in action. A small shoulder on the left of the response curve could be either stray RF coupling or a result of this being a no-tune filter. But I'm really happy with both the noise source and the filter. Especially the filter. It's always pleasing when you build something that confirms your measurement technique for the inductors is really good. No trim-caps, no squeezing or expanding coils. Measure, design and build. Worked first time with no tweaking.
The spectrum analyser was set to 146MHz, 20Mhz per division. We didn't check or adjust for any drift in the spectrum analyser itself. As expected the response falls off faster on the high side. If you haven't read how I measure nH inductors then check out the post http://vk6tt.blogspot.com/2017/01/measuring-small-inductors.html.
Regards
Richard VK6TT
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