Yesterday's blog entry had about as much appeal as passing gas in a church service. Today's posting likely would be a "double dose" that includes not only refried beans but cabbage as a starter mechanism. I go forth well knowing the disdain for today's post.
Yesterday's post suggested the 2N3904 as fulfilling the FOAM template for home built SSB Radios. FOAM of course is Filter, Oscillator, Amplifier and Mixer.
One area "illuminated for development" was the Driver and Final Stages and how to get more juice out of a combination 2N3904's. One faithful blog reader turned to AI and furnished me a design for a Push Pull Driver stage capable of delivering 250 Milliwatts of RF (10 Volts PTP). It was a pretty simple circuit using FT-37-43 cores on the in and out ports. Thanks Bruce!
In my own thoughts about how to do it I thought of Hybrid Combiners, and this is sort of cool where you could have two or four individual amps and sum their outputs using a bit of Ferrite magic. That search turned up two references (likely out of hundreds) and the 1st is a book by Doug DeMaw, W1FB (SK).
Doug was a co-author with Wes, W7ZOI of Solid State Design for the Radio Amateur, which I consider as better than EMRFD. Just my opinion. The book in the link reads much like SSDRA and you can download it from the link.
One subject I covered long ago in this blog was Capacitive Matching in tank circuits. Doug covers this subject with some great lead by example information. There are even some practical circuits using BJT's and FET's with the detail to build them. I had never heard of this book before and undoubtedly, I will get emails to the effect how did you not know.
The second reference is from Helge Granberg, the RF Amp expert from Motorola and his Application Note #749. In a separate App Note Granberg presented a design for a 1KW output ham amplifier using four separate 250-watt amps and using a Hybrid Combiner summed the outputs to yield a 1KW Broad Band amp. He is the man.
Below are two examples of simple Hybrid Combiners from the #749 for two amps and you need to read the note about the 25 Ohm transformation. Another ferrite core on the output can make 25 Ohms look like 50 ohms. A Ferrite core with 10 Turns and 7 Turns will do it as 10^2 = 100 and 7^2 = 49 which giveth 100/49 = 2.04 which is close enough for government work.
BTW I have used circuit 7B in one of my homebrewed SDR transceivers to take the on the air signal from the Band Pass Filter to provide an I and Q input to the pair of ADE-1's. It is this same circuit that works when transmitting to combine the I and Q summed output to the BPF.
Them that know can make things go!
73's
Pete N6QW