As I recall the Control channel was FM for some
reason.. and voice was LM.... They made a mess of
the spectrum around them when they occupied sites
with other 220 systems.. including themselves..
We had a site with (2) 5 channel Securicor
trunks. They could never run both at once as the
control channels blocked each other even on
separate systems on separate freq blocks..
If some Securicor folks are around they might
still be able to comment on that... They had 100w PA's too as I recall...
I helped install them at the site, but they told
us little of what was under the hood...
Doug
KD8B
At 12:58 PM 11/9/2009, you wrote:
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
<<mailto:ag4uw%40yahoo.com>ag...@yahoo.com> wrote:
> Anyone have any info on the Securicor 220 mhz
repeaters??? Can they be put in the ham band?? Thanks Freddy N4XW
>
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> Yahoo! Groups Links
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