A 10 GHz Dual Conversion High Side LO Transverter from Surplus Qualcomm

OmniTracks Units -- Part TWO -- Modification Procedures.

K. Banke - N6IZW - San Diego Microwave Group

1. Mark the location of RF connectors and board cuts for coupling capacitors.

Before removing the boards from the baseplate, Carefully drill through the board in the two places shown using a .050 diameter drill just deep enough to mark the baseplate. These are the locations for the Rx & Tx RF SMA connectors. The upper connector hole (Tx) is located 0.5 inches to the left of the transistor case edge. The lower hole (Rx) is located 0.4 inches to the left of the transistor case edge. Make the cuts as shown in Figure 1 using a sharp Exacto knife.

2. Baseplate removal, modification, and connector installation.

After making the holes and cuts, remove all screws and lift the boards off of the baseplate. (Note: the original antenna connector pin must be desoldered to remove the board. Once the boards are removed, drill through the plate in the 2 locations marked using a 0.161 drill to clear the teflon insulator of the SMA connectors. Use a milling tool to remove enough material on the back side of the baseplate (see Figure 3) to clear the two SMA connector locations, taking the thickness down to about .125 inches (may vary depending on available SMA connector pin length. Locate, drill and tap the baseplate for two 2-56 mounting screws at each connector. Mount the SMA connectors on the baseplate and cut the Teflon insulator flush with the top side of the baseplate (circuit board side). Carefully clear the ground plane around the two connector holes on the bottom side of the circuit board to prevent the SMA probe from being shorted (using about a .125 drill rotated between your fingers). Reinstall the circuit boards onto the baseplate.

3. Add coupling capacitors

Add the 3 capacitors along with the additional microstrip pieces to modify as shown in Figure 2 .

4. Extend the Tx LO filter elements to the total length shown in Figure 4. Filter extensions are made by cutting .003-.005" copper shim stock into strips about .07" wide and tinning both sides of the strip shaking off excess solder. No additional solder is normally needed when attaching the extensions as the tinning reflows when touched by the soldering iron. The length of the top element (0.21) is measured between the marks as shown.

5. Extend the LO filter elements as shown in Figure 5. Again, total element lengths are shown except for the right-most element which has additional dimensions.

6. Extend the Rx filter elements as shown in Figure 6. Dimensions shown are total element length.

7. Extend the Tx filter elements as shown in Figure 7. Dimensions shown are total element length.

7a. Add the tuning stubs to the X5 Multiplier stage as shown in Part Three of this web page article. This step was inadvertently omitted from the original article in the Microwave Update '99 Proceedings.

8. Modify the 2nd LO amp board, mount onto Xverter and connect 1136 MHz LO input through 1 pF coupling capacitor as shown in Figures 8-10. Figure 8 shows the overall second IF converter which is mounted using 2 grounding lugs soldered to the top edge of the LO amp board and secured by two of the screws which mount the main xverter board. Figure 9 shows the coax connected to the 1136 MHz point on the synthesizer through a series 1 pF capacitor. Figure 10 shows the mounting and wiring of the SRA-11 mixer onto the LO amp board. Note the cut on the original amplifier output trace after the connecting point to the mixer. The mixer case is carefully soldered directly to the LO amp board ground plane. The IF SMA connectors are mounted by carefully soldering them directly to the top of the mixer case.

9. Program the synthesizer as shown in Figure 11 by carefully lifting the pins shown with an Exacto knife. Ground pin 10 connecting it to pin 6 which is ground. Add the two 3000 pF and 1000 pF in parallel with the existing reference filter capacitors as shown in Figure 12.

10. Add a 1 pF capacitor as shown in Figure 13 to lower the VCO frequency

11. Add three Tx mixer tuning stubs as shown in Figure 14.

12. The Tx/Rx control is connected as shown in Figure 15. Grounding the control line places the transverter in the Tx mode. The control can be open or taken to +5v to place the transverter in the Rx mode.

13. The +12VDC power input is connected to the point as shown in Figure 16. The original air core coil with one end connected to that point has been removed from the board. (This choke was originally used to supply +12V to the transverter through the 1st IF port)

14. Powering up the Transverter.

Apply +12V to the power connector and verify that the current draw in Rx mode is about 0.5 amp. Connect the 10 Mhz reference to the transverter board. Pin 43 of the synthesizer IC should be high when locked., If available, use a spectrum analyzer to check (sniff using a short probe connected by coax) the synthesizer output frequency and spectrum. The synthesizer should be operating on 2272 MHz and no 2 MHz or other spurs should be visible. Carefully probe the drain of each FET in the LO multiplier, LO amp, and LNA to verify biases are approximately +2 to +3VDC. A drain voltage of near 0V or 5V probably indicates a problem with that stage. Place the transverter in the Tx mode and verify the biasing on the Tx LO amp and Tx output amp stages.

Tune the 992 MHz 1st IF filter (not part of the transverter board) and connect it between the 1st IF ports on the transverter board and second IF converter. The Rx noise level at the 2nd IF port on the 2nd converter should be very noticeable on a 2 meter SSB receiver.

A weak 10368 MHz signal can then be connected to the Rx RF input connector and monitored on the 2 meter SSB receiver. The overall gain from Rx RF input to 2nd IF output should be roughly 35 to 45 dB.

Place the transverter into Tx mode and connect about 10 dBm at 144 MHz to the 2nd IF port. Monitor the power level at the Tx RF output port and add/move the Tx amp tuning stubs shown in Figure as required for maximum output. Typical Tx output will be about + 8dBm. This is considerably more than required to drive the 1 watt amp to full power.

For further conversion and materials availability information contact Chuck Houghton, WB6IGP (clhough@pacbell.net) or Kerry Banke N6IZW (kbanke@qualcomm.com) of the San Diego Microwave Group.

Additional conversion information articles and sources:

C. Houghton,WB6IGP & Kerry Banke, N6IZW, "Microwave GAAS FET Amps for Modification to 10 GHz", NTS FEEDPOINT Newsletter, December, 1993.

Ken Shofield, W1RIL, "Suggestions for Modifications of Qualcomm LNA Board for 10 GHz", Proceedings of the 21st Eastern VHF/UHF Conference, August, 1995, pg 63 and "Modification Update of Omitrack PA Board for 10 GHz". Pg 65. Also at http:/www.uhavax.hartford.edu/disk$userdata/faculty/newsvhf/www/w1ril.html.

Bruce Wood, N2LIV, "UP, UP & Away to 10 GHz Semi-Commercial Style", Proceedings of the 20th Eastern VHF/UHF Conference, August, 1994, pg 133

10 GHz Qualcomm Modification Notes by Dale Clement, AF1T