Dear Mat, sorry I was very busy and weren't able to reply to you soon.
I wasn't able to find the data sheet of the TDK Caps, but your proposal seems better than mine (tantalum caps)! Please note that, according to simulations, the ultimate out of band attenuation is achievable when ESR is less than 20 mohms or so.? Also, using a single 22 uF will preserve the response time during band switching that, in case of 2*47 uF, will become four times larger.
About other "time bombs": I had no time to think about it, I'll try do do so... It is possible, you know aged electrolytic caps may change their characteristics, I found one of them in tx audio path responsibe of tx spurs...
I also tried the new bandpass 28-30 MHz alternative filter but results were not good. Even though the filter was simulated and pre-tested with very good results (my previous picture on stand alone 28-30 MHz filter), once fitted into the equipment the overall response were bad (also modifications of polarization paths were performed and checked before). So I paid better attention to the schematic and I understood that the output impedance termination of the filter (the input impedance of the RF Jfet preamplifier) is NOT 50 ohm!
So, in order to synthetize the correct filter,?I got a Nanovna to measure the real terminating impedance, but I wasn't not able to get good results from it. After calibration the Nanovna reports an impedance of 120 ohm with open circuits, denying any reasonable measure different from 50 ohm. I subscribed to a Nanovna group to understand wether a solution is possible. I'll keep you informed.?
Also, once the full RX performances will be verified, I plan to check in depth the TX modulation paths because I suspect that some AGC behaviour will need attention.
And what about your new IF buffer??
Enrico IK2XEI
