Do It Yourself Plans for the KJ6KO 15W in 130W out 902Mhz Amplifier.
Updates for the "NEW BOARDS" are in GREEN.
These are the instructions for putting together the board and case for the 15W drive 902 amp if you purchased one of my surplus boards.
The finished product!
This will guide you in the construction of the above amplifier from a basic "board" and optional case/heatsink.
NOTE: If you use your own heatsink, you CANNOT MOUNT THIS BOARD FLAT AGAINST A FLAT SURFACE! The original heatsink shown above has large cavities under the combining networks and there are several traces on the bottom of the board that are not insulated. You would have to space the board approx ¼" off the heatsink or "rout" out a space under the combining networks. It's easier to spend the $10 for the original case!
It takes me about 3 hours to put one together from start to finish. Here is a list of what you need and what you get if you purchase both the board and the case from me.
What You Get...(if you purchase both)
1) The complete board
2) Enough of the strange little hollow, soft, 1/16" hex self-threading screws to attach the board to the case.
What You Need...
1) Aprox 20 X 4-40 3/8" screws to attach transistors, regulators and case lid.
2) 2 X TO-220 Transistor Insulator Kits.
3) 1 X TIP-30 PNP Transistor (or equivelant for bias switch).
4) 1 X 2.4K ohm 1/4w resistor (for LED).
5) 1 X 4K ohm 1/4w resistor (± 200 ohm).
6) 2 X rf connectors of your choice.
7) Three Terminal Power connection of your choice...+V, -V and Bias Activation.
For the NEW BOARDS, you will receive the board and heatsink still together as they came from the factory minus one driver device.
Preparing The Board.
!!Ignore this step with the "NEW" boards!!
The first thing that needs to be done is to clean the cut edges "D" to remove any burrs and make sure that none of the traces "A & B" have any loose ends shorting to the ground plane. Points "A & C" are the bias input to the devices. Note that the trace between points "B & A" has been cut. This will have to be reconnected on the top of the board so that points "A, B & C" ar all connected together. You can remove the isolator on the output, as it is not used, but leave the large, blue load next to it as it is part of the output combiner.
After you are sure there are no shorts, mount the board in the case using the hollow 1/16" hex screws. NOTE: These are tricky! Use a 1/16" allen wrench pushed all the way thru the screw! They strip very easily and are quite "stiff" to install into the case. I would recommend practicing on a couple first just to get the feel of how they thread into the case. When they contact the board and "feel snug", stop tightening! After you do a few, you will get the hang of these things. Unless you want to tap all 20 of these holes with something more usable like a 6-32 screw, you are stuck with these little things!
Once the board is mounted, several connections need to be made.
FOR THE NEW BOARDS...jump to step 6) as the only connection for the bias will be at the plug shown in the picture below.
1) Attach the LM-317T regulator to the case using a 4-40 screw and Insulating Kit. The tab/pin2 MUST NOT contact the case! This regulator has been bent back and fourth a couple of times and the leads may be weak, so it would be a good idea to re solder them just to assure their strength once it is mounted in place. The components to the left of point 1 are not used.
2) Cut off the pin closest to the LM-317T on JP1 (Point 1) and solder a wire from the other uncut pin on JP1 to the trace on the outer edge of the board at point 4. This is the switched 28V to turn on the bias. Point 1 is electrically connected directly to pin 3 on the 317T. The blue wire soldered to pin 3 on the 317T is running to the TX LED.
3) Solder the chip cap at point 5 so that one end is soldered to one end of L5 and the other is soldered to a small ground connection at the very edge of the board as shown. Be sure it is NOT connected to the small plate-thru hole (Point 2) just above L5!
4) Solder the two 2.7 ohm resistors at point 6 on top of each other in their current position which is electrically parallel to L5 as shown.
5) Solder a wire between one end of L8 (point 3) and the small plate-thru hole above L5 (point 2)(this trace is connected to C41). This will complete the missing trace between point A and B on the bottom of the board shown in the picture above.
6) Test the circuit. Apply anything between 10-28V to point 1 or point 4 (Point "Y" on the NEW BOARDS) and you should get 5V on point 3 and around 0.6V on the base of both transistors.
7) Now connect the LED to either point 1, point 4 or pin 3 of the LM317T to monitor the 28V side of the bias regulator. Use a 2.4K resistor. You can also attach the LED to the 5V side of the regulator if you wish to monitor the output side. If so, use a 500 ohm resistor to the LED in stead.
Now take the power connector, unplug it and carefully cut it in half. (New boards will already have a "half" connector) Scrape any burrs off the cut edge as this is a three layer board and you don't want any shorts. Solder your two power leads, from whatever power connector you are using, to the two outer pads (X). These are the two VCC inputs to each separate device.
Connect your SWITCHED 28V "BIAS ON" to the inside pad (Y). This will supply 28V to the LM-317T regulator for bias.
Now you need to connect whatever you are going to use to switch the 28V "bias on". I use a TIP-30 PNP transistor as shown. I simply drill and tap a 4-40 thread and mount the transistor, using an insulating kit, to the case in the "rear" section near the power and RF connections. Connect using the schematic shown below. I do not recommend using a relay, as the inrush current charging the caps near the LM317T is very high and can burn the relay.
Now connect the RF in and out cables as shown below. If you wish, you can retain use of the circulator, but I have never tried this and can only assume it will work. Expect about 0.7db loss thru the circulator. There are also power out detection pickups on this strip that can be used if you feel so inclined. (The "sawtooth" strip.) There also appears to be some sort of "reflected power" detection on the return port of the circulator (marked "output") that can be used if desired.
NOTE: Keep the cables clear of the combiners! The field around them is very pickey. If you lay even an insulated cable or wire over one of these, the output will NOT be what you expect...if at all!
NEW BOARD............................................................................................................INPUT...................................................OUTPUT..Note the cut trace.
On the new boards, it is better to route the coax from a different direction over the unused portion of the board (left picture in orange) so you are not so close to the input combiner. C30 will not be present and C34 will be moved. Note the small trace between the pads where C30 used to be and be careful not to cut it. If you accidently do, simply run a jumper around the cut. This supplies bias to the device on that side of the board from the regulator.
You will have to scrape the coating off of the ground plane and traces on the board (area in yellow on new boards) and "tin" it with solder so you can solder the coax shield and center conductor to it.
Be sure to leave enough "pad" to solder to on the output as this is a plate-thru trace to the bottom of the board.
Now a few basic tests. With a 50 ohm load on the input and output, apply power and turn on the bias, There should be about 0.6V on the base of each device and each one should be pulling around 200ma of bias current. Apply a small amount of RF...around 1W, and you should have close to 10W of output! Check the SWR looking in to the amp, it should be better than 1.3:1. If not, adjust C54 & C55. Slowly increase to 15W in and you should be around 130W out! This amplifier will easily handle 20W of input.
Now you should be ready to go! There is usually no tuning involved. The only available tuning is input tuning via C54 & C55 on the input, but I have never had to adjust them. If you want to get brave, you could probably replace C48 & C53 on the output with high quality adjustable caps and get more output as these devices are rated at a minimum of 75W each and they are tuned for 869-896 Mhz! I have never tried it. Another trick is to add about a 10pf variable to the input and output combiners to ground, parallel to the 50 ohm load on each. Be careful not to remove the small square inductor near the unput 50 ohm load. There is usually a chip cap already in place on the output side. You can replace this with a variable and tune both for best output.
Any questions or comments....email me.
73 de Greg