Hi guys,
The notch filter most likely has nothing to do with this problem. In fact, yes, I recommended that Jain remove the notch filter (and also perform about a half dozen other changes). Sadly (amazingly?) he did not take my advice on anything I recommended... I know this because another PL member recently had Jian send me a set of DT-40 directly to Pangolin, to be modified and paired with a FB3 system we will soon be shipping.
I have done the mod to a number of PL members' DT-40 scanners. For those interested, you can see a brief report I made here:
http://www.pangolin.com/_Files/DT40.pdf
I have kept that report private, and sent it to Jian on September 25, 2007, so that he can improve his scanners (not only for himself, but also for all of his users and people purchasing scanners from him). Clearly this is no financial benefit to Pangolin. We just like to have equipment out there that is as good as possible...
As you can see, my mod actually makes the DT-40 easier to tune. Without the proper equipment (which almost nobody has), it is impossible to tune a notch filter. So... get rid of it! Also, Jian has unfortunately proven time and time again that he is unable to properly tune high frequency damping so... get rid of it!! By removing components, reliability is actually increased. So these changes not only improve performance but also reliability too...
Anyway, andy_con, if you want to send your scanners to me, we'll crank them up on the DSA and get them tuned up like clockwork.
Best regards,
William Benner