Cheap Chinese 70cm 100W Linear Amplifier - Part 2

I finally got my VNWA back from sdr-kits after receiving a DOA unit and then I found I had a faulty calibration cable as well, all of which was resolved quickly with no aggravations, so I had another look at the 70cm PA's LPF.

Though the original filter looked good on the old VNWA but I thought I'd better check with the new one just to be certain of the results.

Though the filter still looked fairly good I decided to adjust the inductor size slightly.  The original designed called for each coil to be wound on a 3mm mandrel for two turns so I increased the mandrel size to 3.2mm which yielded worse results but gave me some adjustment in the coils unlike the original.

The insertion loss stayed almost the same at 0.43dB but the return loss was improved by almost 10dB and the second harmonic was also improved by almost 10dB.    So the VSWR is now around 1.07:1 down from 1.2:1 originally.

LPF with increased coil diameters.

Now I just need to arrange to take the unit over to my friends with the spectrum analyser and see how the modifications have worked. 

Part Three coming soon.