Re: RF power chain mods and improvements..


Howard Fidel
 

Attached is my driver it goes between VR1 and the outputs of T10 you need to remove C84 and T10 and insert this circuit. I am using the AMP signal to reduce the overall power output when driving a linear amp which needs 5W not 10W. U7 is a current driver, I chose it because I have a number of them, I probably could select something better, or use an emitter follower but it should do the job at 0 cost for me. The same with the T13-1 transformer, I have them. The opamp was selected for its speed slew rate voltage and current drive capability. C45 is there because U7 needs a minimum load capacitance for stability. I will see if I need to add something there later. TX is the switched 12 volts that is there in transmit only.
I am working on a PCB with this being one part of a daughter board for the uBitx. I would be interested in any feedback. I am not suggesting that this is a cost effective way of improving the uBitx for production. I will post the entire schematic in a few days.

Howard

On 6/8/2018 11:50 PM, Jerry Gaffke via Groups.Io wrote:
And if you really wanted an MMIC for the pre-driver,
here's a cheap one capable of 18dBm.  $0.55 each if you get a reel.
    https://www.mouser.com/ProductDetail/Infineon-Technologies/BGA-616-H6327?qs=sGAEpiMZZMsHFhLSzabyWc6yBY9ZVzZQAmz94oaQAYo%3d


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