Rev B
5
SRX_400 receivers produced after April 1994 (look for an “A” in the serial number) are
equipped with a new power management system which provides true "fast-charging” of
batteries, independence of charge and external power functions and a bicolor charge status
indicator. The new supply is designed to charge the receiver's battery at or near the
manufacturer's recommended maximum rate until full charge is achieved or until a preset
timeout expires, at which time the charge current is reduced to 1/8 of the fast charge rate
("trickle" charge). For a C pack, a charge current of 500mA will provide a full charge in about 4
hours. In cold weather it is also important to
allow the receiver to warm up to at least 10°C
before fast charging
. Fast charging will be suppressed if the internal battery voltage falls below
4 volts, so allowing very deep discharge (e.g., leaving the receiver running unattended for long
periods) is not recommended. If this condition does occur, the charge controller will switch to
trickle charge mode (green light goes on) immediately on connecting the charger. When the
battery voltage rises to a safe level, fast charging will commence automatically.
If a charger of lower capacity is used, the fast charge controller will supply current at the
charger's maximum rate for 4.5 hours (preset timeout) but will then either have to be manually
reset for additional charge cycles, or be allowed to trickle charge up to the rest of the battery
capacity. Note also that the chargers supplied with the SRX_400 ‘A’ models will charge older
receivers very efficiently (6 hours for a fully discharged “D” pack), but must be manually
disconnected to avoid overcharging (overheating) when the cells are full. For safety reasons,
therefore, Lotek does not recommend the use of new chargers with older receivers.
Battery service life is specified by the manufacturer to be more than 500 charge-discharge
cycles. NiCad batteries will lose their charge over time even if they are not used, and they
typically exhibit some form of “memory” effect if operated under repeated partial charge or
discharge conditions. If you are going to store the receiver for extended periods (e.g., over
winter) it is recommended that you charge the battery once a month to conserve memory backup
power (see below) and to avoid possible impairment of the battery’s energy capacity and overall
life. To minimize memory effects, the best procedure is to run the receiver until the low battery
symbol appears (when the
SHIFT
key is pressed), and then charge until the trickle mode engages
(LED switches from red to green). If the receiver is inadvertently stored for an extended period of
time without charging, performing a few (1-3) charge-discharge cycles will often restore the main
battery to a usable condition, but will not recharge the memory backup battery. All batteries are
protected by a resettable fuse. Batteries are replaceable by Lotek Engineering.
The SRX_400 can also operate from an external 11-16V DC power source via a rear panel jack.
An external power cable is supplied. In SRX_400 ‘A’ models, application of external power will
disable the internal battery as long as the external voltage is above ~10 volts. Internal batteries
cannot be charged from the rear panel power jack.
If the SRX is powered via the rear panel jack
the applied voltage should not exceed 16V DC.
In order to satisfy electromagnetic compatibility (EMC) and electromagnetic immunity (EMI)
of SRX systems, the wall charger used with the system must comply with corresponding national
regulations. Every wall charger supplied by Lotek Engineering Inc. complies with national
standards of the country of final destination.
The RF signal input jack labeled 'ANT' on the front panel is a standard BNC type which will
accept any appropriate (50 ohm) antenna or mating cable. When using a signal generator be
careful that the signal power does not exceed 0dBm. Other front panel connectors include the
battery charger jack labeled 'CHG' (see above for charger description) and the headphone jack
labeled 'EAR'. Lotek recommends the use of isolating headphones model H10-00 manufactured
by David Clark. The knob labeled 'OFF/VOL' is used to turn the receiver on and off as well as
for volume control. The front panel speaker is a Projects Unlimited AT-38008M.
A 9-pin (DE-9P) connector on the rear panel is used for RS232 serial communications. The
pinout for this connector is given in Appendix A. SRX_400 ‘A’ receivers have a second serial
