Channel element substitute for the Mitrek

by AK2O

 


No channel element on hand ?

If you want to check the front end's bandwidth and didn't have several crystals (CEs) to experiment with here's an interesting alternative for both VHF and the UHF Mitrek radio. By using a high-level signal generator you can "replace" or simulate the crystal output. It needs to output in the +5 ~ +15 dbm range. The second generator will used for only the receiver, into the front end, obviously, lower level in the -100 area, however, should have plenty of level (-20 dbm) when the receiver is out of tune. Each radio band has a difference "crystal" formula, therefore, the high level generator will follow:

  • For the VHF radio, it will need to operate in the 11 ~ 15 MHz area for the transmitter and 41 ~ 55 MHz for the receiver.

  • For the UHF radio, it will need to operate in the 11 ~ 13 MHz area for the transmitter and 45 ~ 51 MHz for the receiver.

    First, find an old channel element and remove the crystal inside. Then install a 1 Meg. resistor across the crystal tabs. Then install a .01 uf cap on each end of the resistor. Install the center of small coax to the end in the center of the PCB and the shield on the other end. This is the same procedure for the transmit and receive elements. A piece of tape is good to prevent the center conductor touching the element (metal) housing. Glue the coax in place, drill a hole on the Rx housing. For the Tx remove the IDC pot; and use that hole. reassemble the elements and glue the coax in place.

     

     

     

     

     

     

     

     

     

     

     

    Terminate the far end of the coax with a chassis type such as shown a BNC. For the receiver you'll also need to install a alligator clip on the shield side while in use. The pictures are self explanatory.

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    The transmitter will be fairly "dirty" with noise, however is adequate to find out if it tunes properly. For the receiver, this method is not guaranteed to produce spec sensitivity but will get you in the ball park. Using the manual's schematic, remember to align both the transmitter and receiver properly once you obtain the proper (compensated) re-crystaled channel element for the operating frequencies you plan to use. SRG used International Crystal Company since 1975. They accept credit cards and possibly even personal checks. MO's of course.

    This document may be used for Amateur purposes with the Author given credit for it's content. This document may be printed and passed on to other Amateurs, with the understanding not to modify or change the content of the document without the Author's permission. Notifications of typos or errors are welcome.

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