Archives

All posts for the month February, 2017

This is a drawing of the voltage & current sensing board. If you look further down on my site, this is the board on top of the rf-deck with red wires going through blue hall-effects elements. There is some more stuff on this board, and this is the VDD FET switches, but these are not in detail in the drawing.

Last night, during light burn-in tests, the amplifier suddenly dropped gain.
No alarms, no nothing, but one of the MOSFETS was drawing a lot less current compared to the other, it was also operating in class C. It turns out that for some reason the gate2 on the failing MOSFET has broken down. DAMN!!!!!!!!

Digging in to the RF-deck

 

Failed MOSFET

 

Gate2 to source breakdown. 70 ohm  dc-path between source and gate2 do not make any sense.

Have been working on my 144 MHz SSPA project since 04:00z this morning.
Now the time is 22:30z and I am tired. Continue tomorrow morning.
Here are some pictures of project status.

Starting point this moring

 

PT-100 Temperature sensor

 

Left/Front

 

Rear/Left

 

Rear/Left

 

Inside

 

More inside

 

73 All

Temporary Yaesu Elevation Rotor Fix

Earlier I fried my elevation motor, and I was in need of a quick fix.
The plan is to eventually rewind the original 24VAC motor but this will take some time and materials I do not have for the time being.

The quick, non-destructive solution was to get a $7 worth 24VDC motor, and put that in to service.
All I had to do, besides the rectifier system, was to drill two new holes in the motor bracket and move the cogwheel over to the DC motor shaft.

The ZHENGKE ZGA25RP DC 24V 500RPM Micro Gear Box Motor have an unload speed at about 500 rpm, so the elevation is moving at about 1/5 of the original speed. However, this is more than sufficient when tracking the moon. The stall torque is also sufficient due to the low gearing.

I am considering to get a larger, faster and more powerful DC motor, but then I will have to ether do a non-reversal cogwheel modification or get hold of an another cogwheel that will fit.

 

Left: Original 24VAC motor.
Right: very small 24VDC motor fixed to the original bracket .

 

DC motor, rectifiers and relay in place.

 

 

schematics