As a matter of fact, I'm playing with one right now. If anyone has schematics or a service manual with schematics it would be greatly appreciated and would aid my efforts tremendously. Or any information on the mobile radio that was used with these would help as the repeaters seem to share the RF and SPU boards minus a few components here and there. It seems to be technology that has been allowed to die.
The company that designed this stuff was called Linear Modulation Technology out of England, a subsidiary of Intek Global. These were later produced by EF Johnson as the Viking LX series. It is unknown if Midland while under the Securicor name actually produced them or not. Mine has a EF Johnson klingon added with the wrong shade of white paint and a Securicor sticker slapped on top of that. The system used is called Linear Modulation. Similar to SEA's ACSSB system, but different enough that the two companies products are incompatible. Apparently the FCC didn't care what people used on 220-222 MHz, as long as it fit into a single channel. Both are Upper side band designed to fit in a 5kHz wide channel. DSPs spilt the audio passband in the middle for insertion of a pilot tone while the upper portion of the original audio is transposed above the pilot tone, you get about 3300 Hz of audio bandwidth, about 400-500Hz of split for the pilot and the rest is channel guard. In LM, the pilot tone that is used for AFC and AGC. In ACSSB the pilot tone also serves to send trunking data, while the audio is compressed and expanded for noise reduction. In the Securicor the receiver brings the RF down to a 12.5kHz second IF and the DSP goes to work on it as a software defined radio. As a matter of fact this is considered the first SDR made, with patents back to 1991. The transmitter is basicly a phase method SSB generator that uses the DSP and 2 DACs to generate the 90 degree phase shift. there are like 5 mixers on the RF board. On Mon, Nov 9, 2009 at 9:39 AM, ag4uw <[email protected]> wrote: > Anyone have any info on the Securicor 220 mhz repeaters??? Can they be put > in the ham band?? Thanks Freddy N4XW > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > >
