In the area where I live, they're used as transmitters for atv, 76K8 packet radio en wideband hi-fi audio.

I realize it's not a new technique: Several times it has been described how to convert this lnb into a transmitter. Yet it appears to be difficult to complete this conversion successfully. Many people with two left hands, like myself, need additional hints from those who've done it before.

Marco doesn't like writing stories. That's why I'm doing it, to increase activities on 10 GHz.
 

Click here for the functional diagrams in PDF.

It's not difficult to convert this lnb into a 10 GHz atv transmitter. Usually amateurs use horizontal polarization in the 10 GHz band. Therefore the vertical part is not used. Transistor T1V is spare. The amplifier stages are rotated 180 degrees. T3 is swapped with T1H. Band pass and notch are shortened, the mixer is replaced by a capacitor. Where the if-amplifier used to be, a new simple modulator is built. Via this new modulator both supply voltage and base band signal are applied. So only one cable is needed.

The modifications are described step by step. After each step, there's a check. If the result isn't satisfying, it's clear which step is causing the problem.

Remove the four blind rivets with a 3 mm drill.

Remove the outside cover, it can be luted as well.
 

Mark the gate on every transistor housing, using a pencil.

Now take the large soldering-iron. Coat the bottom side of the pcb with tin-solder, exactly UNDER the four transistors. Place the soldering-iron back in its holder so you have both hands free. Now heat the pcb from below by pressing it against the soldering-iron, exactly on those spots you've coated with tin-solder before.
 

The corner of the pcb with the if amplifier stages must be made empty. This is done the same way: Heat the pcb from below and just sweep the parts of.

The empty space is used for some new parts. They make it possible to apply voltage as well as modulating signal via the same F connector, so you only need one cable between shack and transmitter. Schematics available in PDF.

Remove the three-pin mixer. Place a 4.7 pF smd capacitor at the empty spot.

Remove the 10 GHz notch with a scalpel.

Remove the band pass filter with a scalpel and replace it with a brass foil strip, 1.2 mm width and 0.05 mm thick. Use some glue to position it correctly and coat it with solder-tin afterwards.

Solder 4.7 pF smd capacitors at the positions where T3, T2 and T1H where placed before. Now the output of the oscillator can reach the horizontal antenna in the feed horn. The signal travels via the brass foil and the 4.7 pF smd capacitors.

Place the pcb back in its housing. Connect the F connector and place back the inside cover.

Apply voltage to the F connector: Between 12 and 15 V. Use your 10 GHz rx equipment to see where the oscillator is transmitting. Adjust the screw above the puck to change the frequency. Turning it clockwise results in the frequency going up. It appears you have maximum output power between 10.4 and 10.5 GHz, so make sure it's in this frequency range.

Connect your 10 GHz diode detector to a voltmeter. Place it against the blue cap of the lnb in such a way that the polarization matches. Although the amplifier stages aren't placed yet, you already measure a little output power. Not much, but you see the needle moving. Find the position where the meter shows the highest voltage.
Write down what the meter shows. You need this information later!

Now take the pcb out again and concentrate on the position where T3 used to be, so the first stage after the oscillator in the 10 GHz transmitter. Remove the 4.7 pF smd capacitor and place T1H or T1V at this position. Notice that the gate of the transistor points towards the oscillator, so exactly the opposite of the original situation: Gate and drain are switched. Via a track the drain is connected to an smd capacitor and an smd resistor. The same goes for the gate. Swap both resistors and swap both capacitors. Cut the track that goes to the drain, cut the track to the gate. Now make a cross connection. Study the following pictures.
 

Place the pcb back in its housing and check the output power. It must be more this time. Write down what you measure” this time.

Remove the pcb and concentrate on the next amplifier stage. T2 used to be there, now replaced by an smd capacitor. Remove the smd capacitor you've placed there before and place back T2. Notice that the gate points towards the oscillator this time, so exactly opposite to the original situation. Swap the smd resistors on gate and drain, the same for the smd capacitors on gate and drain. Make the drain stub 2 mm longer using brass foil. Make a cross connection like you've done before.

Place the pcb back in its housing and check the output power. Again it must be more than before. Write down what you measure.

I'm sure you've read this before: Remove the pcb and concentrate on the position where T1H used to be. Now there's a 4.7 pF smd capacitor, placed by you. Remove this capacitor and place back T3, with its gate towards the oscillator. Attention: Don't swap the smd capacitors of gate and drain this time. Remove both smd resistors. The one that used to be at the drain is placed back at the gate. The drain gets a new 10 Ohm smd resistor. Make the cross connection for this stage.

To make sure the final stage always has a negative voltage on its gate, two smd resistors have to be removed: Rh in the photo. Both resistors are 160 k Ohm. There's "164" printed on top of them.

It's possible you can't make enough deviation, in spite of the fact you're applying a lot of base band signal. In that case you can experiment with the position of the oscillator puck.

If you have a simple spectrum analyser up to 500 MHz, use an original Blue cap as an extra converter. This way you get the range 10.0-10.5 GHz and you can see your own transmitter.

Several Bluecaps have been converted yet. Output power is about 35 mW. More output power is possible: See PE1MMI's high power Bluecaps.

In my area Bluecaps are used to transmit 76K8 G3RUH compatible packet radio on a sub carrier that can be modulated from a few Hz up. It's also possible to apply the packet signal directly by connecting the lf output of the modem to the transmitter. Problems may occur because modulating signal and voltage travel over the same cable. In that case you should use separate cables for lf and voltage.

The pictures show that the track to the not used horizontal antenna is cut. This is not necessary. It doesn't result in extra output power via the horizontal antenna. You can only find this out by trying, that's why the track is cut in the picture!

The transmitter can be positioned in every commercial 10 GHz dish. Without dish is also possible, which can be seen in the first picture of this document. Those transmitters carry a 76K8 packet radio link over 20 km distance. The receiving side uses a 30 cm dish. The transmitters are 35 m above ground level on top of a 9 story building. The receiving site, 20 km away, has its 30 cm dish 24 m above the ground.

With a Blue cap transmitter also in a 30 cm dish we make qso's over 40 km distance, from home to home. Both TX and rx dish 15 m above the ground. Nice to live in a country that's so flat!

Many thanks to Twan van der Meer, PE1NHL, for making several of the pictures. Also thanks to Elmar Leinen, DL5OBW, for sending improved pictures.
 

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