Service manual

Page 6
SVR-250 Service Manual
When the SVR-250 detects that the mobile is transmitting, it will continue to monitor the on-air line until the
transmitter remains keyed for at least 250mS to ensure that the radio is not handshaking or retrying. After
successful acquisition of a voice channel, it will continue to hold the mobile PTT active for 2 seconds and transmit
a go-ahead blip to the handheld operator. The user then keys their handheld to speak on the voice channel. If the
user does not key up within the 2 second period, the SVR-250 will unkey the mobile and send intercept tone as
before.
If the user keys their handheld only once, or they key the first time for more than 1 second, the SVR-250 will
cancel the call attempt and send intercept tone to the handheld operator. All of the queuing and error tones will
only be sent if the handheld is not transmitting to ensure that the user hears the proper tones.
The SVR-250 can also be programmed to work in a similar way for use with the MSV mobile satellite phones,
except the time delays are extended to work properly within the network.
Emergency Operation
The SVR-250 can be programmed for Emergency operation on a per channel basis. If enabled, the SVR-250
will scan for 2 different CTCSS tones or DCS codes. The secondary tone/code is used to indicate an Emergency
condition from the portable and will assert an output pin when decoded. There are 2 different Emergency formats:
Emg output only or Emg output with voice repeat. Emg output only will assert pin 10 on the main cable for as
long as the secondary tone/code is being received; it is used as a momentary output to the mobile to initiate an
Emergency sequence. This is the most common configuration with Motorola or MA/Com radios. Emg output
with voice repeat will assert pin 10 as before, but will also key the mobile and repeat portable-to-base as long as
the secondary tone/code is being received. This format is used with the Tait mobiles. Additionally, there is a solder
jumper on the main logic PCB that determines if the Emg output signal pulls to ground (NO) or breaks ground
(NC).
Dual Tone Operation
The SVR-250 normally requires its own frequency and earlier technology suffered when there was strong
co-channel interference present. The SVR-250 can be programmed for dual CTCSS/DCS receive that will
eliminate interference from co-channel users. The portable radios will still be carrier squelch receive, but the
SVR-250s will be programmed with a CTCSS/DCS encode that is different from the primary tone/code decode.
The secondary tone/code must be the same as the encode tone/code. During base-to-portable transmissions, the
SVR-250 will sample as before. If it sees carrier and primary tone, it will reverse direction and repeat portable-
to-base. If it sees secondary tone (another SVR-250 transmitting) it will cease transmission and become non-
priority. If it sees carrier with no tone (or neither programmed tone) it will ignore the co-channel interference.
If three consecutive samples have co-channel interference, the SVR-250 will change the sampling rate to 2.5S
(maximum) to reduce the effects of the extended sample time, until the co-channel signal is no longer present.
Dual Tone receive and Emergency operation are mutually exclusive.
Auxiliary Receiver Operation
In operations where the vehicles do not transmit mobile-to-mobile (half duplex), the non-priority vehicular
repeaters will not see mobile COR when a priority vehicular repeater keys its mobile during portable-to-base
transmissions. This can cause the non-priority repeaters to incorrectly assume priority. The SVR-250 can be fitted
with an additional 16 channel scanning receiver that is programmed for the mobile transmit frequency. This
Auxiliary receiver can have up to 16 mobile transmit frequencies programmed into it and will provide the mobile
COR indication needed for the non-priority repeaters to remain at non-priority. The Auxiliary receiver option can
be programmed to operate on a per channel basis.