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The Oct 2006 Project to Build a S Band Downcoverter
02/07/10 - Andy Flowers, K0SM

An Easy Way to Receive S-Band Using the Cal-Amp 130016

Andy Flowers, K0SM

This is a project that has evolved over the last year. So far I have managed to use these surplus MMDS converters as RX-converters to receive both 2304 and 2401 MHz. The modification is truly “no tune” and requires no test sophisticated test equipment—not even a VOMfor the basic modification! We’ll be doing this modification as a group at the October meeting, so please bring the following materials if you have them. If not, please come anyway as we will have extras and we’ll be able the share the test equipment.

Required Materials:

  1. Hobby knife to cut traces
  2. Philips screwdriver to remove case and filter
  3. Packing tape
  4. Small wire cutters
  5. Tweezers
  6. Scissors

Other useful equipment:

  1. Fine-tip soldering iron and solder (.015 or .022) for optional modifications
  2. Radio that will receive 123MHz (in FM for AO-51 satellite)
  3. Coaxial cable with F-connector on one end and connector for radio on other.
  4. Coaxial cable with F-connector and stripped wire/allegator clips on other
  5. DC-power inserter/block with F-connectors (eg, for satelite TV)
  6. DC supply capable of 15-30VDC at 250ma

Instructions

1. Open the case by removing all the screws. You may need a flat screwdriver to pry the case apart. You can slip the scredriver between the plates underneath the N connector and the area directly opposite of it. The following picture can be used as a reference for what all of these parts are. If this stuff looks unfamiliar to you, fear not! At the meeting we’ll have an opportunity to discuss how this all works!

 

2) Remove the filter cover by taking the five screws that hold it in place:


 

3) Take out the two stainless screws holding down the copper filter element.


4) Remove the filter element. It should pull up easily with a small screwdriver as leverage. Be careful not to lift the boad traces to which it is attached.

 

5) Bypass the ceramic filter with a short piece of wire about 1⁄2” long. You may find it helpful to scrape away some of the green silk-screen on the traces to give you more room. Also, you will want to tin the wire first. Tweezers will come in handy here.


6) Using a hobby knife, cut the 2.15 GHz filter traces as shown below:

 

7) Place 4 layers of packing tape over the 2.5 GHz filter as indicated in white above. Be sure to press the layers down firmly.

 


That’s it! We’ll be testing each one at the meeting with a signal source and a radio. We can also do further modifications for 12VDC operation, and separate DC/RF, and 2304 MHz RX, but we can cover those at the meeting. We’ll also talk about some cheap antennas that we can use for AO-51’s S-band downlink.