Wednesday, January 27, 2016

Microwave Transceiver Teardown

I was recently gifted a microwave transceiver with essentially no info about it other than a vague comment about "it might have fallen off a pole somewhere." Having no immediate use for it, and with a premium on storage space in my life these days, I figured I'd tear it apart and see how it works.


I took apart the down-converter section that's fed by the Rx Gunn diode, but I'm afraid the exact mechanism of the ring hybrid in it has left me a bit flummoxed.
The Rx signal comes in through the feedline on the top left. The top and left holes were grounding screws, the Gunn cavity is the top right feedline, and the bottom right goes through the block to an amplifier on the other side before leaving via an MCX connector. My lack of training in RF systems is starting to show...

Monday, January 4, 2016

Building a Simplex Repeater


In this installment of the "How to Build a Repeater" series, I explain the concept of a simplex repeater and how to assemble one out of an Argent Data ADS-SR1 and a Motorola Maxtrac. Thanks again to Argent Data for providing me with an ADS-SR1 to play with; it's a fun little controller.

Pinout diagram for the interface cable, including the color code assuming that you crimp the ADS-SR1 side as if it were a standard T568B Ethernet cable (or started with an Ethernet cable and cut it up). This pinout depends on you correctly programming the MaxTrac to output SQL + PL/DPL decode on pin 14. Pin 8 is another popular option, in which case you should modify your cable accordingly.

The same cable should work with any other Motorola radio which has the same 16 pin (or 20 pin in newer radios) accessory connector, which is why I love working with Motorola radios so much.

A couple mistakes in the video:

  • I forgot to account for the addition 800Hz deviation caused by the transmitter's PL encoder. I should have set the repeater gain looking for 3.8kHz output deviation, not 3.0kHz
  • I said the station was part 97 legal, but that's without me checking that the default morse code speed from the controller isn't greater than 20 words per minute, which is an ID requirement for part 97. A bit unfortunate that the setting in the ADS-SR1 is on a unitless 0-99 scale and not just in words per minute.