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Build a 10 GHz upconverter from a downconverter

  • Schematic

  • * No computer drawings made yet *

  • What are we going to do?

  • First, find yourself an old (working) LNB.
    LNB's without a build-in feedhorn are generally the oldest and easiest to rebuild. These old LNB's are only capable of receiving the lower band. The local oscilator works on 9.75 GHz. If you change the LO frequency to 9 GHz, the entire 3cm band will range from 1000 to 1500 MHz.
    After changing the LO frequency, we are going to turn the functionality of the LNB around, constructing a transmitter from a receiver.

  • Changing the LO frequency

  • The oscillator uses a DRO (Dielectric Resonant Oscillator). This is the white disk in the picture below:

     (click to enlarge)

    The size and the material the DRO is made off, determine the frequency of the oscillator. The bigger the DRO, the lower the frequency.
    To lower the frequency from 9.75 GHz to 9.00 GHz I took another 9.75 GHz DRO and tried stacking them on top of each other.
    The LO frequency was far too low. So if I remove the DRO, the frequency is too high and if I place it on top of the other, the frequency is too low.
    Then there must be some place in between where the frequency is 9 GHz.
    I moved the second DRO around for a long time, but I finally found a place where the frequency indeed got down to 9 GHz. This place is shown in the picture above. (The second DRO sits at the end of the oscillator trace).
    Strange enough, the frequency is VERY stable at that point, and moving the DRO a little bit around only causes the output power of the oscillator to variate.
    To determine the DRO frequency, you need a universal LNB (or at least an LNB with a 10.6 GHz LO) and two satellite receivers.
    A receiver with AFC and signal strength meter is the perfect tool for this job. The second receiver is only used to create the LNB supply and 22 KHz signal for our universal LNB.
    Remove the screws and open the housing of the universal LNB and lay it down on the table. Connect it to the second receiver and make sure the receiver is configured for high-band reception (so the 10.6 GHz LO will be used). Now point the LNB you want to adjust towards the open LNB.
    You should receive a signal at 1600 MHz (10.6 GHz - 9.0 GHz) when the LO is at the right frequency. The signal will show on your TV as a gray or black image, since it's only a steady carrier we're looking at. (So don't use one of those receivers with video-squelch... :)
    If your receiver happens to have a signal strength meter, you can move the DRO little bits around to get the best signal.
    When you have found the right spot, glue the DRO onto the PCB with a little droplet of quick hardening glue. Mind that the signal strength might slightly change due to the glue. If the signal gets worse, twiddle around a bit with the DRO again quickly before the glue hardens.
    Now you can do one of two things: leave the LNB as it is and use it for reception, or go on and build yourself a 3cm TX.

  • Reroute the output circuit

  • The signal that's coming out of the mixer, is fed from one side of the LNB to the other. On the other side, where signals range from 950 to 1800 MHz, the signal is amplified and fed into the output connector of the LNB.
    Since we want our signals to travel the other way, we'll have to change some things here.
    I just cut the input trace of the first amplifier and the output of the last loose and made a little coax bridge from the input connector to the mixer input as show in the two pictures down here:

     (click to enlarge)

    If the 23cm transmitter you are going to use with the upconverter isn't capable of pushing some mili Watts into the upconverter, you can also turn the amplifiers around by twisting the first input with the last output through two pieces of coax. Although I don't this is neccesarily, since I use the upconverter with only a few mili Watts of driving power and still it creates a fair amount of output power.

  • Reverse the (former) input FET's

  • Now back to the upside of the LNB.
    As show in the following picture, this LNB uses three input FET's to amplify the received signal.

     (click to enlarge)

    The easiest way of reversing these FET's is by removing the entire PCB from it's housing. Then take a soldering iron and push it to the bottom side of the PCB underneath the first FET. Take a pincet and gently lift the FET off the board. The FET's are all marked, but please don't forget what mark was on what side.
    Put the FET down on a anti-static surface. When moving/removing the FET's, make sure you took the proper precautions to avoid ESD. These FET's are extremely static sensitive.
    Now remove the other FET's as well. After that, start placing them back 180 degrees rotated and in reverse order. So the little dot will be on the other side and where FET 1 used to be, FET 3 will be replaced.
    Put the board back inside the housing when all FET's are soldered in.

  • Change gate & drain supply

  • Since we rotated and reversed all FET's, we also have to reconnect the gate and drain power supply on the other board so all gates and drains are connected the same way as before we reversed them.
    This can be done using normal wires since this is just plain DC.
    I just cut through the six traces and reconnected them with some wires as shown in this picture:

     (click to enlarge)

  • Test the transmitter

  • Now we should have a upconverter. To test the thing, we need a 23cm transmitter and a LNB with a 9.0 GHz LO. Connect the 23cm transmitter to the upconverter and make it transmit a test pattern. Connect the LNB to a receiver and set the receiver to receive at the same frequecy the transmitter is transmitting. When you point the LNB towards the upconverter, you should see the test pattern.
    The original mixer that was in my upconverter-LNB, was a very old one that didn't work too well. This resulted in a poor signal. I replaced the thing with a mixer from a newer (defect) LNB as shown in this picutre: (it's the little black SMD thing with '2R' written on it)

     (click to enlarge)

    This mixer is the HSMS-8102 from HP.
    The output power is now much greater. I don't have the proper equipment to measure how much power is really coming out of the upconverter, but getting the thing to create as much as possible is not that hard if your satellite receiver has a signal strength meter.

  • Some pictures

  • (click on the images to enlarge them.)


    Inside 1 - Supply & output circuit:

    Inside 2 - 10 GHz part: DRO, mixer & FET's

    - Created by Daan Vreeken - PA4DAN -

    Email me with questions/comments : Daan <Daan @ pa4dan . nl>