Sometimes ago i bougth on a flea market a D1029 LDMOS pushpull FET, which i thought might be usefull in a 2m or 4m PA.
I decided to build the 4m PA to boost the low power of my IC7300. Now we just need permission to use more power on 4m.
From the datasheet it can bee seen that it should be possible to get arround 300W output with <6w drive in linear operation . First i planned to make my own PCB, but i found on ebay several offers for a 100W FM-VHF RF poweramplifier DIY -kit, which comes with a PCB and all the components, some can be difficult to find , like 25ohm coax cable for the impedance tranformation:
I replaced the supplied MRF186 transistor with my D1029 but used all the other components. For my transistor the optimun 70MHz Load impedance Zl can be calculated to 1.5-j0.2 Ohm, and the optimum source impedance Zs to 1.5+j5.9 ohm, the calculated gain is then 24.8db .
Before mounting the transistor i measured the load and source impedances seen by the transistor. i measured:
Zl=5.1+j1.2 and Zs=4.8 +j3.0 which is a bit off from optimal, but there were plenty of gain so i could afford somme mismatch loss.
Before testing the PA must be mounted on a big cooling fin. I mounted the PCB on copperplate first and then on a bigger cooling fin. I made a small external PCB with a small realy to swicth the coaxrealys and swich biasvoltage. Bias is adjusted to IQ=2A, here are some results:
|Pin [W]||Pout [W]||I@28V [A]||gain [dB]|