Service manual

Page 4
SVR-250 Service Manual
Functional Description
Generally, vehicular repeaters are used as mobile extenders in cross-band operation: the link is VHF/UHF/800
MHz simplex and the mobile is Lo-band, VHF, UHF or trunking. In-band operation is possible, but care must be
taken to prevent interference between the mobile's higher power transmitter and the repeater receiver. Proper
frequency selection and antenna placement are important even in cross-band operation, but especially for inband
use. Low power pre-selector cavities may be placed in line with the repeater antenna cable since it is simplex and
low power.
Important Note
The SVR-250 is designed to operate on simplex frequencies; part of the multi-vehicle format dictates that
all of the SVR-250s must be able to monitor all link traffic on site and be able to determine if a handheld is
transmitting, or if other repeaters are transmitting. The handhelds must transmit CTCSS, but should be carrier
squelch receive. The handhelds should not use CTCSS decode if the repeater is utilizing the multi-vehicle
format, as this will interfere with the priority sampling which is essential for multi-vehicle operation. Also, the
handhelds would have to have different encode and decode tones in order for the repeater to be able to tell the
difference between handhelds and other repeaters, so the handhelds would not be able to hear each other. The
repeaters should not transmit CTCSS unless used only in a single vehicle environment.
When the user leaves the vehicle, they activate the SVR-250 via their mobile radio front panel or a separate
switch. When the mobile radio is receiving carrier and proper tone, the SVR-250 will begin transmitting on the
handheld’s receive frequency. The user is able to hear and respond to all radio traffic, including other handhelds
at the site. The SVR-250 can be programmed to give the handhelds priority in a conversation by periodically
sampling for handheld activity (carrier and proper tone) during base-to-portable transmissions. During sampling,
if the SVR-250 detects a handheld transmission, it will cease transmissions, key the mobile radio and repeat
portable-to-base. This allows the handheld to respond during repeater hang time or during full duplex interconnect
calls. Priority sampling can be enabled/disabled through PC programming and the interval can be programmed
between .25 seconds and 2.5 seconds in .25 second increments.
The SVR-250 has a programmable time out timer for base-to-portable transmissions. If the mobile COR is
active for more than the programmed time (and the SVR-250 is the priority unit) it will send a double blip and cease
transmission until the mobile COR is inactive. The time-out is in affect regardless of whether the SVR-250 is
programmed for priority sampling or not.
Multi-vehicle operation
The SVR-250 has 2 different multi-vehicle priority formats; both are compatible with the existing SVR-200
and Motorola PAC/RT formats. The new SVR-250 with ESP
TM
logic has enhanced features that ensures a priority
vehicle is selected and ready to transmit during the idle time rather than during voice transmissions. The 2 formats
are explained below:
SVR-200 Legacy format
When the SVR-250 is first activated, it will transmit a short “lock tone” that alerts the user that the system
is functioning. It will then assume the priority status and be ready to repeat any base-to-portable or portable-to-
base transmissions. If another unit arrives on scene and is activated, it too will transmit the “lock tone”; when
the first SVR-250 detects the lock tone from the second unit, it will increment a “priority counter” and will no
longer repeat any transmissions. The recently arrived unit will be the priority repeater, and the first unit will be
1 count away from priority. This process will continue for each unit that arrives at the site, creating a priority
hierarchy for up to 256 vehicles, each with a unique count and only one unit at priority status. The SVR-250 will
not transmit its lock tone if the radio channel is busy when first enabled. It will wait in non-priority status until
all transmissions cease, then send its lock tone and become the priority unit.
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