Hi,
I suspect a few of us are running these TXers off a 12/13.8 V PSU and regulating the PCB down to 5v.
A week or so back I considered running just the PA off 12V. I think some have already tried running them off 9v. I dont know much of their success.
These are just some notes from my work on a 40m version
(1) Cut a track to seperate the 2N7000 supply leaving the 47nF joined
(2) The FET output would match better via a 200 ohm transformer rather than a choke when running a 12.5v supply. I used a 6 turn bifilar choke using the existing FT37-43 on the drain of the 2N7000. (A 9 turn choke for 80m should be ok) The tap goes to the 1nF capacitor feeding the LPF.
6 turns is adequate as the inductive reactance,since it is about 10x the load value
(3)An additional 47nF or 100nF needed for bypass on the 5v supply on the PCB as there was only one bypass capacitor fitted.
My previous measurements on my 30m unit gave about 23mA for the other stages with ~ 60mA for the final FET stage for about 100mW output.
With the mod's the unit gave
(1) ~ 350 mW for 60 mA PA current (pushing the boundary a little)
(2) ~ 280 mW for 50 mA PA current
(3) ~ 100 mW for 23 mA PA current
Total transmitter currents are about 23mA higher
With the improved match and 12.5v, the PA efficiency is around 50% vs 33% for the 5v setup. So 350 mW o/p is possible but rather caning the 2N7000 since there is no heatsink (2N7000 device disappation max is 400 mW. At ~ 50mA final current it should be reliable
I checked the CW keying, by disconnecting the bias pot from the 5V and got in excess of 35 dB backwave
A little PCB/Vero/ratsnest for a 78L05 regulator and bypass capacitors is required for feeding the other stages from the 12v
Very pleased with the improvement in power (about 5 dB or 3X).This should improve the QRSS signals from this part of the world.
Another station is looking at using the changes in his 80m Hans Summers kit just received
Kevin
ZL1UJG
