Guidance?

[Dave Cheitel]

Hello all,

I am looking to embark on the 100w amp project. I am going to purchase the 3 circuit board pack but am missing info. there is the amp, t/r/swr bridge, and filter boards. aside from power supply, do I also need Arduino as a controller? is there any built in power transistor protection? 

Has anyone drawn up any diagrams on how the 3 boards interconnect. Im good at building but probably lacking in the area of figuring out the unstated parts of the project.

Any help from those that came before me would be appreciated.

73

Dave AB6KX

[jcve...@gmail.com]

Hi Dave,

The T/R Switch board has ports labeled XCVR, AMP_I, AMP_O and ANT. Connect the XCVR to you transceiver, the ANT to the antenna or tuner. AMP_I goes to the input of the power amp. Amp_O should be connected to the output of the power amp but this is generally where we put the low-pass filter band. So connect the output of the amp to the input of the LPF and the output of the LPF to the AMP_O on the T/R Switch.

None of the boards have any control systems, that's up to you. Could be an Arduino, PIC, analog control system and what it does is again up to you.

You will need to select the correct band on the LPF board and you need a PTT signal to switch between RX and TX. It's best to monitor the reflected power and limit it to 10W max. You might also monitor the drain current and limit it to 4A. The heatsink temperature should be less than 70C. The drive power should be less than 2W.

The easiest way to do this is simply remove the PTT signal if any of these conditions are not correct but you could also provide limiting circuitry to reduce the drive or increase the fan speed  to mitigate the fault condition.

73,

Jim WA2EUJ

[Nick Kennedy]

It does cause a little head scratching and is good to diagram out how you're going to connect things to get a good feeling about having it right.  

The relay/SWR board does a switch-around function for a transceiver driver. I'm using a separate RX and TX and have an extra port. I use it to short the receiver input when in transmit.  I'd eventually want to go to a PIN diode T/R switch but want to start out using the circuit as designed.

I'm doing most of the stuff Jim described with my Arduino control program. I bought a high side current transducer to measure the drain current. I see that 10 W reflected is 2:1 SWR at 100 W output.  I may allow a little higher but not too much. I have a feeling that this power device is fairly rugged. I'd also like to use a digital attenuator to run back the power rather than trip completely, if I can make it work. The driver chain needs to be linear enough to give the expected reduction. But for extreme faults, I'll "lock out" transmitting. Maybe there should/will be a reset button so the user can get back on the air after evaluating the condition.

73

Nick, WA5BDU

[Dave Cheitel]

time for another small round of questions. I will be starting to build the AMP portion once all parts arrive. Looking for advise regarding the standoffs. what types are you using? are they male male? what are you using to make the 2.5mm threaded holes. im newer to the home brew circuit so this is info outside of my wheelhouse. lastly (for now) what type of heatsink/fan combo is used in this design? 

If anyone has pics and/or build notes they would like to share to help out with all the unasked questions, I would love to see what you did.

Thanks so much for your support and patience. 

Dave

AB6KX

[Nick Kennedy]

I get heat sinks from hamfests so their size and appearance varies. For this project, I have one that I like which was probably a CPU cooler. There's a flat copper piece 1/4 inch thick and 2.5" by 3" square. One one side, lots of fins, 1 & 3/4 inch tall. The side without the fins is just that flat piece of copper where I attach my MOSFET. 

I've put my transmitter inside an aluminum chassis. On the outside (top) I cut a hole a bit smaller than the copper heat sink and attached the sink to the chassis with screws through the aluminum chassis and into tapped holes in the copper plate. So the heat sink is outside the chassis, but the flat copper surface is accessible from the inside and I mounted my amplifier board to it with standoffs and screws into tapped holes.

Tapping those holes was a challenge for me as I have little experience with that, plus that thick piece of copper is a challenge to tap. I'd broken off a few taps with this thing on earlier projects, but finally settled on M3 screws and bought some taps made for that size. Those screws were for mounting the board. A larger one is needed for the MOSFET's tab and a #6 is the largest ASTM size that will fit so that's what I used.

As for standoffs for the board, I typically go with what's in my junkbox but in this case the height can't be arbitrary since the MOSFET must just reach the heat sink. My measurements said 0.25" and I had some sleeve type (little cylinders) metal standoffs that worked OK. An M3 screw goes through the board and stand-off and into the tapped hole in the heat sink.

I'd forgotten a bunch of this stuff. Had to go back and check my notes.

73

Nick, WA5BDU