This page presents article "A 1269MHz Transmit Converter with 70cm IF Input" published in the May/June 2003 issue of the Amsat Journal.  This page also provides updates from the original article.

Here is the original article as I submitted it to Amsat. It is made available to you with the permission of Amsat-NA:  

A 1269MHz Transmit Converter with 70cm IF input By Bertrand Zauhar, VE2ZAZ, April 2003

Please visit this page frequently, and right before assembling the boards, as new information will get added regularly.

I would apreciate [ reading back ] from the ham experimenters who build this project. This will allow me to improve this page by providing additional clarification if necessary. Thanks!

Bert, VE2ZAZ
 

In summary: Replace U2 with an ERA-5 amplifier Replace R4 with a 43 Ohm 1/2W axial resistor Replace U1 with a 7808, 1-Amp voltage regulator The shematic and parts table below were updated to reflect the changes. Be careful when mounting the 7808 on the Mixer board. Notice that pin 1, the input pin, is located on the left side when reading the marking on the 7808 regulator. This is reversed compared to the 78L08. The drawing on the left side illustrates the difference.

An easy workaround to this effect is to solder a wire between the two resonating elements of the 1269MHz bandpass filters, as shown in red on the figure to the right. The wire increases coupling between the resonating elements, thus decreasing insertion loss of the filter. This wire has little effect on filter performence for out-of-band rejection. Use AWG-30 gauge (0.010 inch) wire such as of the "wire-wrap" type. Run the wire against the PCB surface and fit both ends inside the ground vias. Solder to the inside of  vias. A slight touch up on the variable capacitors adjustment may be required to peak the output. Thanks to Jacques VE2AZX for the great idea.

Mike K9QHO reported to me a mistake in the Digikey part number I had provided in the parts list below. The temporary tespoint capacitor on the Mixer board is indeed a 10nF (.01uF) one. The Digikey number now stands corrected in the table.

Fred Reimers from FAR Circuits is kind enough to provide some of the parts required to assemble this project. This is done at no additional cost when ordering the PCB set. All chip capacitors and chip resistors required to assemble this project are supplied. As well, the 7808 regulators, the 78L08 regulator and the 470nH inductor are provided. This will save you time and money when assembling the PCBs. Refer to the [ Detailed Parts List ]  below for a detailed list of the components supplied.

Please visit FAR Circuits at http://www.farcircuits.net  for more details.

The circuit schematics were printed in a reduced size in the article. Here they are in full size.

The Mixer board's schematic diagram Version 3 (27/10/2003).	Click on the figure to enlarge it.
The LO board's schematic diagram.	Click on the figure to enlarge it.
The LO Tripler board's schematic diagram.	Click on the figure to enlarge it.

Similarly, the PCB layout drawings are provided here for improved readability.

The Mixer board's layout	Click on the figure to enlarge it.
The LO board's layout	Click on the figure to enlarge it.
The LO Tripler board's layout Version 2 (25/10/2003)	Click on the figure to enlarge it

Trimcaps on the Mixer Board On the Mixer board, trimcaps should be mounted as shown in the drawing at right.
Trimcaps on the LO board On the 572MHz Lo board, the three trimcaps should be mounted as shown in the drawing at right.
ERA Amplifier Biasing Detail This is a drawing that shows the approach for biasing RF MMIC amplifiers on the LO and Mixer boards. The LO Tripler board does not require the four ferrite beads, but the feedpoint principle remains the same.
7808 Voltage regulator on LO Board This drawing shows how the 7808 voltage regulator should be installed and soldered.

Additional Recommendations

 LO board

• The builder should solder the external + supply wire before installing U1, the 7808 regulator, as the supply pad is located right under the regulator.
• Y1, the crystal should have its lead ends shaped in a "L" to allow for better contact with the PCB pads.

LO tripler board

• If the required +7dBm output cannot be achieved, the user can reduce the value of the pi attenuator located between the two inter-digital filters.

• 75 Ohm chip resistors are provided by FAR Circuits for R1 and R3 instead of the specified 78 ohm value. This is an acceptable substitute.
• Diodes D1 and D2 are optional. They help protect the mixer from an overload at the IF IN port.

• Inspect the ERA amplifier areas for any residual copper. The holes should have no conductive material on their inner wall. As well the triangular ground pads should not come in contact with the signal traces on either side.
• The input and output traces should end flush with the PCB edges. There should not be any gap without copper between the end of the traces and the PCB edge, as this would cause an impedance bump. The user can file the PCB edges until such gap disappears.
• If the builder wishes to drill holes for mounting the PCB in an enclosure, these holes should be drilled either in the ground pads or where there are no pads at all. These holes should be drilled away from coupling elements such as microstrip filters and wire filters.
• The 4.7uF tantalum chip capacitors have a line marking that indicates the positive electrode

The following tables are lists of parts with associated Digikey part numbers for reference. Changes from the original Amsat Journal article are marked in red. Parts marked with an asterisk (*) are provided as part of the PCB set.