[Motorola] public safety using DCS

[Eric Lemmon]

Jeffrey,

Digital Coded Squelch (DCS) has been around long enough that most radios that
are retired from commercial  and public safety service have that capability.

The most common reasons for using DCS instead of PL are that  it is universal
across radio brands (unlike PL) and it is much more difficult to hack.  DCS
usually requires direct coupling to the modulator, and this is perhaps too
difficult for inexperienced techs.

The downside to using DCS is that the turn-off tone, about 134 Hz, is the
same for all codes and thus prevents- or seriously impairs- the creation of
talk groups on one RF channel.  Also, if another user on the same RF channel
is using PL of 131.8 or 136.5 Hz, it might mute your radio.  Some low-end
radios from Standard, Uniden, Maxon, and others use a rather crude means to
generate the DCS codes, and I have almost always had to tweak even brand-new
radios in order to make them code and decode the DCS signal properly.  That
is one reason why cheap radios are much more costly over time than good
radios!

Because Kenwood and Motorola use different phase shifts and timing for their
respective reverse-burst squelch-tail elimination schemes, these two brands
do not mix well in systems that both code and decode CTCSS- public safety
services, for example.  That is why most police and fire departments (at
least, those that I know about) will use one brand of radio throughout the
system.  In the system I maintain, I converted the entire fleet to DCS just
to avoid the annoying squelch tails that almost always occurred during
contacts between brands.  It's one of the dirty little secrets that both
Kenwood and Motorola publicly deny exists, but for which they both have flash
upgrades to correct.

73, Eric Lemmon WB6FLY

JEFFREY MICHAEL KENYON wrote:

> Hi everyoen. Last weekend while on vacation in Sanilak County, Michigan I
> noticed something odd.  The County Law Enforcement frequency is currently
> using a repeater with a DCS on it rather then a PL tone.  This county
> doesn't have much in it other then summer homes, and I would not have
> guessed that the county would have much money to upgrade to anything
> special, but I don't know how long they have been on VHF and what they
> switched from, but has anyonworked with this county, and what would a
> county like this use radio wise if many of the older radios won't support
> DCS?  Any information would be appreciated, and thanks in advance.
>
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