LDMOS Amplifiers and The Control System
The control System
My initial thoughts on the switching of the low pass filters reflected on my past experience with filter switching harkening back to my KWM-4 SSB/CW transceiver built in 2013. When I built the KWM-4, this was a real challenge as my goal was to have no band switch as such; but rather to take advantage of a three digit code that could be associated with band memories that was generated in the K5BCQ kit. By using the encoder to menu change bands the three digit code associated with the bands could provide the signals to control the band pass and low pass filter banks. So why not the same here with the LDMOS amplifier?
Shown below are the BPF and LPF boards in the KWM-4.
Below is the KWM-4 schematic that was initially used with the project which was later changed to the second circuit which was finally used in the project. The second circuit uses P Type MOSFET’s and in effect used less parts. For test purposes I included the ability to manually switch band using three toggle switches. This proved beneficial as I could bench test the LPF or BPF boards without the need to have the frequency controller.
Interesting side note — the concept/circuit of taking the three digit code and coming up with the band switching signal was done on my own. Finally I designed something where it worked and it was done with my own hands. I shared this with K5BCQ and he said –why didn’t you use a CD4028 as you can decode and drive the relays directly. The case of the better mousetrap has once again arisen to the top. Well it was my design and it did work!!!!