Hi guys, I have an update regarding my mosfet troubles. To keep the story short……….:

Last weekend I got the replacement mosfet, I installed it, SUCCESS!!! According to its markings, it was a couple of years older than the other one, and it needed abt. 0.5 volt higher bias voltage, but this is fine once adjusted.

Then I started testing again, this time with a more mature swr protection system, this system tripped immediately. Hmmmmm. What could be wrong???

OK, fast forward, back to the time of breakdown event: It was a late weekend evening. The operator may have been a bit tired, eager to produce some results. There may have been a couple of beer cans in the way.  🙂 And the shack do not look good in daylight… this does not help at midnight, but it may appear better, visually.

I am now, pretty sure that the cause of the mosfet breakdown was a missing load, not spikes or over drive from the driver. Looking for the cause for the high swr situation mentions above, I found that the TX relay (narda 023 series) had a short due to internal welding!!!! Also, the coax connected to the transmitter port had a short. The RG-142 Teflon center insulator had developed a puncture, shorting it out!!!!! There have been some serious voltage on the loose here.

Well. I repaired the relay and exchanged the damaged coax. Up and running again, but not for long. A piece of advice; knowing about their internals, relays like the narda 023s, do not abuse them. They are high cost, wide band, low insertion loss, high power relays, but keep them below the rated power limit. I think these are rated to at abt. 1Kw @ 100 MHZ @ low vswrs conditions. Well, I tested it for key down, 2Kw at 3 minutes and it would not operate any more. Wye?? Because the internal plastic bits has melted and permanently deformed.

Looking for a better replacement I discovered that an electromechanically solution does not in practice exist at these power levels. Not what my wallet is going to accept any way.

Then I come to think of SM5BSZ Leifs page, about High Power PIN Diode Switch. Well, I do not have suitable PIN diodes, but I have many different relays. Let’s try that instead. …….And  it works. Only trouble is that my Q is to high. RF-current melt the solder and things broke down……again. But this can easily be rectified.

…… be continued……….

……here are some pix.

Narda 023 series


New switch


still more new switch


Rear of new switch

Broken new switch 🙂 But this is going to be fixed.




Video above show the first run with the new switch. It broke down, but this time the mosfet protection works.



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




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










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.




Probing around for a powerful 48vdc supply solution I landed on a fair priced Eltek Flatpack2 rack unit. I know, it is an overkill for HAM shack use with its 8kw of DC output power. But as Jeremy Clarkson says; quote “Power and speed solves many things”  🙂
Anyways, this really is a part of a telecom UPS system, and telecom 48vdc system has negative distribution with positive common return rail. This is the opposite of what we HAM usual needs, so it has to be rewired, or re-bared rather.
This is a 2U rack module with a smartpack2 controller and 4 x Flatpack2 2000w HE rectifier units. You can run a single rectifier without the controller but it will default to about 53,5 volts. In order to change the operating output voltage, you need the smartpack2 controller.
With the factory access password, you can with the controller permanently write new settings down to the rectifier, and it will default to any valid voltage value. Of course it is possible to hack and reverse engineer the eltek CAN-bus protocol with other tools. I know the e-bike community has done it.

Here are some pix:

Smartpack2 rack without load fuses cover panel.

Smartpack2 rack without load fuses cover panel.

Smartpack2 rack unit

Smartpack2 rack unit

Original common positive (+) return bar.

Original common positive (+) return bar.

Rewired to common (-) negative return bar.

Rewired to common (-) negative return bar.


Load fuses

Complete unit

Complete unit

PowerSuite for M$ windows config and monitoring tool.

PowerSuite for M$ windows config and monitoring tool.

Want one of these; search for “SGVU-L” @ ebay.
I am planning to use this in displaying RF-power measurement, but it needs some modifications. So stay tuned……………

Here is some more info:
I got this of ebay as a kit. PCB’s are very nicely build. Kit comes with LM3916 chips, which is a semi logarithmic VU meter LED driver.
Cascading six of these don’t really make any sense if you want to use it as a meter for readings.
So, I have replaced the LM3916 with one LM3915 logarithmic 3 dB/step driver chip for the ten first LED segments, then five LM3914 linear LED driver follows for the rest of LED segments.
Of course this is for one channel only, so you need 2 x LM3915, and 10 x LM3914 for doing both channels.