Today I decided to be brave and make up the PIN diode attenuator for the TX driver chain. The output from the PPLL VFO is too high for the PA stage and I want to add a keyed stage between the VFO and the PA so decided to use a PIN Diode attenuator followed by a low gain amplifier.
Looking around for PIN diode I found the HSMP-3814 which is a dual diode SO-23 package. A useful reference is the Avago application note 1048 which details a circuit and layout which is good to 3 GHz. Not wanting to get into making a PCB,and only wanting to go to 30 MHz,I used some DarTec RF matrix board which has a copper backplane.
I also had a drawer full of salvaged SMDs and found enough for a trial except a 680R resistor so used a half watt leaded specimen!
The circuit worked first time and looks to be just fine for what I want. Next will be the wideband driver amp and a splitter for the VFO output.
That is enough for today as a couple of hours working with SMDs gives me an aching neck!
I know there is too much solder,I have cleaned up the board a bit since the photo was taken.
(Click image to enlarge)
