Midland Radio SP-300 User Manual
SP-300 Series
SERVICE
MANUAL
Maxon America, Inc. 10828 N.W. Airworld Dr. Kansas City, MO 64153 Tel: 816-891-6320 Fax: 816-891-8815
Part Number: 680-100-0155
April 2001
MAXON
SP-300 HAND HELD
TABLE OF CONTENTS
SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
DESCRIPTION OF CONTROLS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
THEORY OF OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
DIGITAL CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
RF CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
RF CIRCUITS PLL SYNTHESIZER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
RECEIVER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
MAINTENANCE AND REPAIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
REMOVING & REPLACING THE BELT CLIP . . . . . . . . . . . . . . . . . . . . . . . 13
REMOVING & REPLACING THE BATTERY . . . . . . . . . . . . . . . . . . . . . . . 14
REMOVING & REPLACING PTT ASSY. . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
REMOVING & REPLACING THE ACCESSORY CONNECTOR . . . . . . . . 15
REMOVING & REPLACING THE ANTENNA & CONTROL KNOBS . . . . 15
REMOVING & REPLACING THE BACK COVER . . . . . . . . . . . . . . . . . . . . 16
REMOVING & REPLACING THE MAIN BOARD . . . . . . . . . . . . . . . . . . . . 17
REMOVING & REPLACING THE DAUGHTER BOARDS . . . . . . . . . . . . . 19
REMOVING & REPLACING THE SPEAKER . . . . . . . . . . . . . . . . . . . . . . . . 19
COMPONENT REPLACEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
PROGRAMMING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
ALIGNMENT PROCEDURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
TEST EQUIPMENT SETUP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
ALIGNMENT POINTS DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
VOLTAGE CHARTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
SP-300 SERIES UHF & VHF DIGITAL SECTION PARTS LIST . . . . . . . . . 29
SP-300 SERIES VHF RF SECTION PARTS LIST . . . . . . . . . . . . . . . . . . . . . . 31
SP-300 SERIES UHF RF SECTION PARTS LIST . . . . . . . . . . . . . . . . . . . . . . 34
COMPONENT PINOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
SCHEMATICS & BLOCK DIAGRAM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
VHF FRONT-END . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
VHF POWER AMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
UHF POWER AMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
UHF FRONT-END . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
VHF V.C.O. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
UHF V.C.O. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
TCXO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
ACC-200 BATTERY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
FUSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
P.T.T. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Digital Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
VHF RF Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
UHF RF Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
PCB LAYOUTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Page -i-
May 2001
MAXON
SP-300 HAND HELD
Board Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Exploded View. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
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May 2001
MAXON
SP-300 HAND HELD
SPECIFICATIONS
GENERAL
Equipment Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hand portable
Band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . UHF/ VHF
Channel Spacings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.5 kHz, 25 kHz programmable
RF Output Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5/ 1 watt
Modulation Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F3E
Audio Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 mW (Ext with 8 ohm)
400 mW (Int with 2 ohm)
Intermediate Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45.1 MHz & 455 kHz
Number of Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16/ 4
Frequency Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Synthesizer
Operation Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Intermittent
90 : 5 : 5 (Standby: RX: TX)
Power Supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rechargeable Nickel-metal Hydride
Battery, 7.5 VDC +/- 10 %
TEMPERATURE RANGE
Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . From - 40° C to + 80° C
Operating. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . From - 30° C to + 60° C
CURRENT CONSUMPTION
Off. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . < 1 mA
Standby (Muted) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . < 30 mA (Battery Save On)
< 60 mA (Battery Save Off)
Unmuted, 100 % Max AF Power . . . . . . . . . . . . . . . . . . . . . . . . . < 500 mA
Transmit 5 Watt RF Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . < 2.4 A
BATTERY LIFE (5-5-90% Duty Cycle)
1350 mAh. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Hrs @ 5 W
Page -1-
May 2001
MAXON
SP-300 HAND HELD
FREQUENCY BANDS
RX TX
VHF: V2 148.000 - 174.000 MHz 148.000 - 174.000 MHz
UHF: U2 440.000 - 470.000 MHz 440.000 - 470.000 MHz
DIMENSIONS
Radio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (141mm)H x (58 mm)W x (37 mm)D
WEIGHT
Radio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 grams
With 1350 mAh Battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425 grams
TRANSMITTER
Carrier Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . High: 5.0W
Low: 1.0W
AUDIO FREQUENCY DEVIATION
Without Subaudio Tone Modulation:
25 kHz Channel Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Max. ±5.0 kHz
12.5 kHz Channel Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Max. ±2.5 kHz
With Subaudio Tone Modulation @ 10 % Peak Deviation
25 kHz Channel Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Max. ±5.0 kHz
12.5 kHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Max. ±2.5 kHz
Audio Frequency Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Within +1/-3dB of 6dB octave
ADJACENT CHANNEL POWER
25 kHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . < 70 dBc
12.5 kHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . < 60 dBc
Conducted Spurious Emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . < -60 dBc
Page -2-
May 2001
MAXON
SP-300 HAND HELD
Transmitter Audio Distortion (Without CTCSS) . . . . . . . . . . . . < 5% @ 1 kHz
Hum & Noise:
12.5 kHz Channel Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . > 40 dB (with PSOPH)
25 kHz Channel Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . > 40 dB (with no PSOPH)
Load Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . No osc at ³ 10:1 VSWR all phase angles
a n d s ui t a b l e a n te n n a
Peak Deviation @ 1 kHz (Nom. Dev +20dB)
25 kHz Channel Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Max. 5.0 kHz
12.5 kHz Channel Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Max. 2.5 kHz
RECEIVER
Sensitivity (12dB Sinad) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . UHF: < -117 dBm(.31µV)
VHF: < -118 dBm(.28µV)
Amplitude Characteristic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . < ±3 dB
Adjacent Channel Selectivity:
25 kHz Channel Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . >60 dB
12.5 kHz Channel Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . >50 dB
Spurious Response Rejection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 dB
Intermodulation Response Rejection . . . . . . . . . . . . . . . . . . . . . . 65 dB
Temperature Stability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.0005% (-30°C to +60°C)
Conducted and Radiated Spurious Emission . . . . . . . . . . . . . . . . Per FCC and IC Rules and Regulations
AF Distortion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . < 5%
Frequency Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 dB/octave de-emphasized response in
the range 300 Hz - 3000 Hz
RX Hum & Noise:
25 kHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . < 40 dB
12.5 kHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . < 40 dB
Page -3-
May 2001
MAXON
SP-300 HAND HELD
RX TONE DEMODULATION CHARACTERISTICS
SUBAUDIO TONES - CTCSS
Tone Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Hz to 250.3 Hz
Non-Standard Tones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Hz to 260 Hz
Due to continuing research and development the company reserves the right to alter these
specifications without prior notice.
Page -4-
May 2001
MAXON
SP-300 Series HAND HELD
SP-300
The SP-300 Series of portable radios from Maxon, utilizes
the latest technology in its design and manufacturing. Both
the VHF and UHF models are PLL (Phase Lock Loop Synthesizer) / microprocessor controlled, and offer 1 or 5 watts
of power with 4 & 16 channel capability. Multiple functions
including Scan, CTCSS / DCS signaling and 12.5 & 25 kHz
channel spacing are standard in these fully programmable
wide bandwidth handheld units.
INTRODUCTION FEATURES
Main Features
• Wideband
•Scan Mode
• Busy Channel Lockout/Marked Idle Enable
• Standard/Non-Standard CTCSS/DCS Signaling
• Transmit Time-Out Timer/Tx Inhibit
• Beep Tone Enable/Disable
• Low Battery Indication
• Memory Protect
• External Option Detect
• 5/1 Watts Programmable RF Power
• Battery Save Circuitry
• Locking Accessory Connector
Wideband
This software is made to work and control the wide band
receiver/transmitter boards.
Scan Mode
During programming of the radio, any channel can be
selected as a scanned channel. When a channel is selected as
a scanned channel, it becomes part of the scan list. The scan
list will be activated by switching to the channel that was
selected as the scan channel during programming of the sys-
tem parameters.
The channel that was selected as the scan channel can still be
used as a receive only channel when in scan mode or receive
and transmit channel if the channel has been programmed for
“Priority Scan TX”.
Scan Channel Delete
When the unit is in scan mode the monitor button can be
pushed to delete a channel from the scan list. If the monitor
button is pushed while scanning has stopped to monitor an
active channel, that channel will be deleted from the scan
list. The channel will remain inactive in the scan list until
the scan mode is re-initiated by switching off the scan list
channel and switching back to the scan list channel. Any
number of channels can be deleted from the scan list in this
way. The scan list is always initiated with all the scan list
channels active.
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May 2001
MAXON
SP-300 HAND HELD
A priority channel can be selected while programming the
radio. A priority channel is a channel that can be period
cally checked or looked back to while receiving on any chan-
nel in the scan list, or in normal operation. It can also be
selected for all transmissions during scan mode.
To transmit on a channel in the scan list, the channel selector
must be placed on the channel that the transmission is to be
made on. As a system programmable option, it is possible to
transmit on a scanned channel while the channel selector is
on the scan list channel. This is the “Normal Scan TX”
option. If this option is enabled the PTT can be pushed during the scan wait time and the transmission will be on the
channel that was just activated. If this option is disabled, the
transmission will be on the priority channel (if there is no
priority channel programmed the transmission will be inhibited and out-of-lock indicator will be issued).
Any channel, whether it is in the scan list or not, can be designated as a look back channel. When a channel is designated as a look back channel, and the channel is selected, the
radio will periodically look back to the priority channel during reception on the selected channel. The radio does not
require a scan list to be entered in order to use this function,
however, the radio MUST
for the function to work.
have a priority channel selected
Busy Channel Lockout
i-
If this feature is enabled, the unit will not transmit when a
carrier is present. A beep tone will sound when the PTT is
depressed.
Marked Idle Enable
If this function is enabled, the unit will transmit provided
that the correct programmed CTCSS tone or DCS code has
been decoded. This function is essential for repeater operation.
Normal/Inverted DCS
This function is selected by channel during programming of
the radio. During programming of each channel of the radio,
a selective signaling option for TX and RX is selected.
When the DCS signaling option is elected, it can be selected
as either normal or inverted. The selection can be made differently for TX and RX.
Standard/Non-Standard CTCSS
When programming a channel with CTCSS, any frequency
from 55 to 250 Hz can be selected in 0.1 Hz increments. The
radio is capable of encoding and decoding two non-standard
CTCSS tones.
• NOTE: The programmer must disallow the programming of a channel as a look back channel if no priority
channel was selected.
The channel scan speed is system programmable in a range
of 50 milliseconds to 2 seconds in 10 millisecond increments. The default value is 100 milliseconds.
Scan Delay Time
Scan delay time is system programmable. The scan delay is
the time the unit remains on a scanned channel, after receiving or transmitting on that channel. The time is programmable from 1 to 10 in 1 second increments. The default value is
4 seconds.
The scan delay time will be reset each time the receive channel is active and each time the PTT is pushed on that channel. As long as the conversation continues on the channel,
the receiver or the transmitter is active before the scan delay
time expires, the unit will not resume scanning.
As a programmable option, the LED on the top panel of the
unit will flash at the scan rate while in the scan mode. If the
“LED scan indication” is programmed to enable the LED
will flash. If it is programmed to disable, the LED will not
flash.
Transmit Time-Out-Timer (TOT)/TX Inhibit
The time-out-timer is system programmable for 10 seconds
to 990 seconds, in 10 second increments and can also be
selected as disabled. The addition to this feature is a programmable lock-out-timer that inhibits the radio transmitter
for a specified time after the time-out time expires.
When the time-out-timer function is enabled, and the TX
inhibit function is disabled, the radio will transmit after the
time-out-timer has expired and the PTT button is released
and depressed again. With the TOT and TX inhibit, the
radio will not transmit after the time-out has expired, even if
the PTT is released and depressed again. Transmission will
not be allowed until the TX inhibit time has expired. TX
inhibit time is system programmable from 5 to 60 seconds in
5 second increments. The radio will beep one time, 5 seconds before the TOT time expires. This will indicate to the
user that the transmitter is about to be locked out. If the PTT
is released and depressed again anytime before the TOT has
expired, the TOT time will be reset. If the beep tone enable/
disable is set to disable, the one beep will not be issued. The
radio will beep 4 times when the TOT time expires. After
the TX inhibit time passes, the radio will beep one final time.
Page -6-
May 2001
VCO Lock Time
The micro will allow more lock time for the VCO before the
out-of-lock beep indication.
Low Battery Indication
Low Battery Indication will be changed so that it does not
inhibit RX and will allow one transmission after low cell is
indicated. Low cell will not be indicated during transmit
mode. If the battery goes below specified limits during the
TX mode, low cell will be indicated immediately after
releasing the PTT button.
After the low cell indication is issued, the transmitter can
only be used one time. When the PTT is pushed again and
then released, the transmitter is locked out until the unit is
powered down and then powered back up.
Memory Protect
The software is such that if the radio is inadvertently put
into program mode it will not lose the contents of the
EEPROM memory. Data will only move in and out of the
memory when the programmer is attached.
MAXON
SP-300 Series HAND HELD
External Option Detect
An input to the microprocessor will be available that will
indicate to the microprocessor that the external option has
been selected. This input should be connected to the external option connector. External option should be selected for
each channel. If a channel is selected during programming
for external option, this input should be active when the
channel is selected during operation of the unit.
Page -7-
May 2001
MAXON
SP-300 HAND HELD
DESCRIPTION OF CONTROLS
The controls, indicators and antenna connections on the VHF and UHF Scanning Handheld Series radios are all located on the
top panel. The accessories socket is located on the radio chassis right hand side. The monitor and PTT buttons are located on
the radio chassis left hand side.
ITEM DESCRIPTION
1. Antenna Connector 1/4" UNEF socket
2. 4 Channel Select Switch Rotary switch, used to select one of four and to engage in scanning function
3. 16 Channel Select Switch Rotary switch, used to select one of sixteen and to engage in scanning function
4. Status Indicator (busy TX/BT) Tri-colored LED indicator
5. ON/OFF Volume Control Main power switch and volume control. Fully counter-clockwise is OFF position
6. Battery Lock Used to lock the battery in place
7. Push-To-Talk Button Push to talk, release to listen
8. Monitor Button When pressed, monitors the chosen channel
9. Option
10. Speaker Sound reception
11. Microphone Sound transmission
12. External Speaker Socket used for external microphone with speaker
13. Belt Clip
14. Battery
15. Battery Charger Contacts
16. VHF Antenna
17. UHF Antenna
Used for controlling installed external option
Belt Clip
Power Supply
Contacts used for charging battery
Antenna
Antenna
ANT CH
4
3
2
1
1
CON701 Pinouts
CON701 - Pin 1
Pin Function
Data
1
Clock
2
N/C
VOL
2
ANT CH
7
8
9
7
4
1
16
3 4 5
VOL
11
13
3
+7.5V
4
N/C
5
N/C
6
Gnd
7
Mic+
8
N/C
9
Int_Spkr_Mic_Dsbl
10
Spkr+
11
N/C
12
12
10
11
13
16 17
6
maxon
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May 2001
14
15
MAXON
SP-300 HAND HELD
THEORY OF OPERATION
The VHF and UHF scanning handheld series radios are comprised of one main PCB. The main PCB contains the transmitter, receiver and control circuits. The control circuits
contain the micro controller and associated digital circuits.
DIGITAL CIRCUITS
IC 411 is a digitally-controlled analog switch which internally consists of three single pole, double throw switches.
By placing a high (5V) or low (0V) on the control lines
which consists of A, B and C. A controls the X ports, B controls the Y ports and C controls the Z ports. Example: A high
on control A would connect X to X1. A low on control A
would connect X to X0.
CTCSS/DCS Decode Circuits
Discriminator audio from Pin 9 IC5 is fed into and associated parts, which are the first 2 poles of a 6th order 250 Hz
Chebeyshev low pass filter. The output from pin 1 (IC406A)
is fed into IC411 (Pin 2) and output to pin 15 (IC411). The
signal is then fed to Pin 8 (IC407) which is a 6th order low
pass Butterworth switched capacitor filter. The output from
the Butterworth filter (Pin 3 IC407) is then fed to the remaining 4 poles of the 6th order Chebeyshev, which consist of
IC406C and one of the two operational amplifiers internal to
IC407 (MF6-100) along with associated components. Both
the Chebeyshev and the Butterworth combines for a 4dB ripple low pass filter when programmed for 250 Hz. The output
of IC406C (Pin 8) is fed into the remaining operational
amplifier internal to IC407 (MF6-100) which forms the
squaring circuit for the Decode signal. The signal is output
from Pin 2 IC407 (MF6-100) and fed into IC409 (micro)
where it is matched with a preprogrammed frequency. If successful, a Decode occurs, which is shown by a green L.E.D.
on the top panel of the VHF and UHF Scanning Handheld
and audio is heard. If valid Decode was not seen, the busy
L.E.D. (Yellow) would be shown.
CTCSS/DCS Encoder Circuit
During TX encode the tone squelch digital signal is produced as a 3-bit parallel word at Pins 15, 16, and 18 of the
micro controller (IC409). The 3-bit digital signal is converted to an analog signal by resistors R478, 479 and 480.
The analog signal is fed into IC411 Pin 1. The signal is output on Pin 15 (IC411) and fed into Pin 8 of IC407 (6th order
Butterworth clock tuned low pass filter). The filtered encode
output from Pin 3 (IC407) is fed into Pin 13 (IC411) and output on Pin 14 (IC411). The filtered encode signal is fed to
IC406B and RV403 (sub-audible gain control), the output of
IC406B is then fed to the audio mixer circuit.
External Mic/PTT Control Circuit
The external microphone is connected via the CON701 connector on the right side of the handheld. The internal mic and
speaker are disabled by grounding of pin 10 of CON701.
Pulling pin 10 of CON701 low will bring the base of Q702
low, switching the transistor off. This removes the ground
from the internal microphone, shutting it off. Pulling pin 10
of CON701 low will also pull the Gate of Q701 low, turning
it off. This will disconnect the speaker from the rest of the
circuit, shutting it off. To enable transmit the Q406 base
impedance is low (below 20k ohm), Q406 and Q407 turn on
and Q407 collector is low, which is connected to IC409
(micro) Pin-24.
Channel Select Circuit
One of 16 channels(SP-330 & 340) or one of 4 channels(SP310 & SP-320) may be selected, using the channel switch on
the top panel. The channel switch encodes the channel number selected into a 4-bit binary code. The binary code plus
one is equal to the channel number. The binary code is
decoded by the micro controller enabling the appropriate RX
or TX frequency and associated data to be selected from the
EEPROM.
z
NOTE: Any of the channel locations may be a scan
ning position. Refer to Operators Manual for further instructions.
Low Battery Indicator Circuit
When the battery voltage drops below 5.4 VDC, D403 and
Q417 turn on. The micro controller disables the transmitter
and at the same time enables the red LED and sends an alert
tone to warn the user. The battery should be replaced or
recharged at this time (one tx allowed after low battery).
EEPROM
RX/TX channels, CTCSS/DCS as well as other data from
the programmer are stored in the EEPROM. The data stored
is retained without power supplied. This is a non-volatile
memory. The EEPROM may have information re-programmed or erased. IC408 is an EEPROM with 2048
(8x256) capacity and data is written and read serially.
High Pass Filter
The high pass filter is an 8-pole, 1 dB Chebeyshev active filter that comprises IC410 and associated components. The
de-emphasis is provided by resistor R451 and capacitor
C471. Receive audio is passed to IC410 by Pin 4 of IC411
where sub-audible tones below 300Hz are removed. Mic
audio is also fed into IC410 via IC 411 (Pin 4) where subaudible voice products below 300Hz are also removed.
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MAXON
SP-300 HAND HELD
Mute (squelch) Circuit
The mute circuit which is controlled by the output of IC409
(micro) Pin 77 (386EN) is connected to Q34 via R122 which
mutes the LM386IC on the RF circuits. Pin 77 also controls
IC402B which mutes the audio path to the RF circuits.
TX Audio And Filter Circuits
The TX audio from the internal mic or external mic is fed
into IC411 (Pin 3). The TX audio is output on Pin 4 (IC411)
and into the high pass filter (IC410), where sub-audible
voice products are removed. The TX audio output from
IC410 is fed into IC404D & C, with associated parts form a
mic amplifier and limiter. The output from Pin 8 IC404C is
fed to RV402 (TX Modulation Level Adjust) and fed into
IC404A & B to form a 3k low pass filter. The output of
IC404A (Pin 1) is then fed into the Audio Mixer Circuit.
Analog Ground Supply
IC406D supplies (2.0V) to operational amplifiers circuits.
Audio Mixer And Inverter
IC405A is an audio mixer where audio and sub-audible tones
are combined. RV401 is used as a balance control. IC405B is
an inverter.
Monitor
The unit will contain a switch mounted on the PTT assembly
for monitor function. This will be enabled or disabled by
programming software.
RF CIRCUITS
Transmitter
The transmitter is comprised of:
1. Buffer
2. P.A. Module
3. Low Pass Filter
4. Antenna Switch
5. A.P.C. Circuits
Buffer
VCO output level is -6 dBm and amplified to +10dBm
(UHF), +6dBm (VHF). The buffer consists of Q16 and Q17
for isolation and gain.
P.A. Module
The P.A. Module consists of Q501, Q502 and Q503. Three
stage amplifier Q501 amplifies the TX signal from +10 dBm
to 100 mW. Q502 is amplified to 1.0W. Q503 amplifies to
5W and then matched to 50 OHM using the L.C. network,
thereby reducing the harmonics by -30 dB.
Low Pass Filter
L7, L8, L11, C72, C73, C74 and C75 are the 7th order Chebyshev low pass filter. Unwanted harmonic are reduced by
-70 dBc.
Antenna Switch
When transmitting, the diodes D5 and D6 are forward biased
enabling the RF signal passage to the antenna. D6 is shorted
to ground inhibiting the RF signal to the front end. In receive
the diodes D5 and D6 are reversed biased passing the signal
from the antenna through L13 and C83 to the front end without signal loss.
Automatic Power Control (APC) Circuits
The APC circuit containing the variable resistors RV1, RV3,
IC3 and Transistors Q18,Q19,Q21 and Q22. The current
from the collector of Q503 is detected at R109, it is converted to voltage at IC3A and compared with the reference
voltage at IC3B. In transmit (+5V) is applied to the input of
IC3B via the potential divider R45 and R46. The differential
signal at the output of IC3B is passed to Q21 and Q22, This
voltage controls collector voltage of Q502 that produces a
constant power output. RV1 is used to adjust the high power
and RV3 is used to adjust the low power.
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SP-300 HAND HELD
RF CIRCUITS PLL SYNTHESIZER
12.8 MHz TCXO
The TCXO contains the 3-stage thermistor network compensation and crystal oscillator and modulation ports. Compensation is +/-5 PPM or less from -30c to +60c.
PLL IC Dual Modules Prescaler
Input frequency of 12.8 MHzto IC2 MC14519 pin 20 is
divided to 6.25 kHz or 5 kHz by the reference counter, and
then supplied to comparator. RF signal input from VCO is
divided to 1/64 at prescaler in IC2, Divided by A and N
counter in IC2 to determine frequency steps, and then supplied to the comparator. PLL comparison frequency is 6.25/5
kHz so that minimum programmable frequency step is 5/
6.25 kHz. A and N counter is programmed to obtain the
desired frequency by serial data in CPU. In comparator, the
phase difference between reference and VCO signals is compared. When the phase of reference frequency is leading, Fr
is output, but when VCO frequency is leading, Fv is the output. When Fv=Fr, phase detector out is very small 0v pulse.
64/65 modulus prescaler is comprised in IC2, and has two
output ports:
Port A pin 16: tx enable 2
Port B pin 15: prescaler power save control in PLL IC
pin 13 labeled test2 allows the technician to see the output of
the dual modules pre-scaler for trouble shooting purposes,
no connection should be made to this pin.
Level Shifter & Charge Pump
The charge pump is used for changing output signals Fr, Fv
at PLL IC from 0-5v to 0-12v necessary for controlling vco.
Reference Frequency LPF
The Loop Filter contains R12, C21 and C22. LPF settling
time is 12 mS with 1 kHz frequency. This also reduces the
residual side-band noise for the best signal-to-noise ratio.
DC to DC Converter
The DC to DC converter converts the 5v to 14-16v to supply
the necessary voltage for wide range of frequencies in the
VCO.
VCO
The VCO consist of an RX VCO and TX VCO. Is switched
TX/RX by power source. It is configured as a colpits oscillator and connected to buffer as cascade bias in order to save
power.
The varicap diode D201/D301 are low-resistance elements
and produce a change in frequency with a change in reverse
bias voltage (2-11v). L203/L303 are resonant coil, which
changes the control voltage by the tuning core. D202 modulation diode, modulates the audio signal. C204 compensate
for the non-linearity of the vco due to modulation diode, and
maintain a constant modulation regardless of frequency.
RECEIVER
Front End
The receive signal is routed backward through the low pass
filter, then onward to Pin 1 of the Hybrid Receiver Front End
Module to a bandpass filter consisting of (VHF C622
through C608, L607 through L604) and (UHF C601 through
C610, L601 through L603) is coupled to the base of Q601
which serves as an RF amplifier. Diode D601 serves as protection from static RF overload from nearby transmitters.
The output of Q601 is then coupled to a second bandpass filter consisting of (VHF C607 through C601, L603 through
L601) and (UHF C612 through C623 and L604 through
L607). The output of Pin 6 is then coupled to the doubly balanced mixer D9. The receiver front end module is factory
pre-tuned and requires no adjustment. Repair is effected by
replacement of the entire module of the proper banded module. These are VHF 148 MHz to 174 MHz and UHF 440
MHz to 470 MHz. The receiver front end module signal pins
are as follows:
1. RF Input
2. Input Ground
3. N/A
4. Receive +5V
5. Ground
6. Output
First Mixer
D9, T2 and T3 are double balanced mixers which provide
the 45.1 MHz intermediate frequency output. The filtered
frequency from the front end module is coupled to T2. The
45.1 MHz IF output is matched to the input of the 2-pole
monolithic filter by L14, L31, C69 and C97. The crystal filter provides a bandwidth of +/-7.2 kHz from the operating
frequency providing a high degree of spurious and intermodulation protection. Additionally, a 90 MHz trap (XF1) is also
placed at the filter output to provide additional attenuation of
the second order IMD. The output of the filter is impedance
matched by C97 and C69 to the base of the post of filter IF
amplifier Q25.
Second Oscillator Mixer Limiter And FM Detector
The output of the post filter amplifier, Q25, is coupled, via
C98 to the input of IC5 (MC3371). IC5 is a monolithic single conversion FM transceiver, containing a mixer, the second local oscillator, limiter and quadrature detector. Crystal
X1 44.645 MHz is used to provide resultant 455 kHz signal
from the output of the second mixer. The mixer output is
then routed to CF1 (455F) or CF2 (455HT). These ceramic
Page -11May 2001
MAXON
SP-300 HAND HELD
filters provide the adjacent channel selectivity of 25 kHz or
12.5 kHz bandwidth.
Squelch (mute) Circuit
The squelch circuit switches off the power amplifier when
no audio signal is present. The squelch circuit consists of a
16 kHz band pass filter and a noise detector circuit.
16 kHz Band Pass Filter
The audio signal from Pin 9 of IC5 (MC3371) is filtered by a
16 kHz band pass filter consisting of L16 and L17. The noise
in the IF passband is accepted and voice frequencies and
their products are rejected. Any noise present at the output of
the filter is applied to the noise detector circuit via RV2.
RV2 is used to adjust the squelch circuit sensitivity and is
normally adjusted to produce a noise squelch opening sensitivity of 10 dB to 12 dB SINAD.
Noise Detector
The noise detector in conjunction with IC5 consists of Q26,
Q27, D8, D11, TH1, and their associated biasing components. Noise fed from the output of RV2 is amplified by
Q27, then rectified by D11. This output is then buffered by
Q26 and fed to Diode D8, which controls Q24 providing
ground to the mute control Pin 14 of IC5.
Low Pass Filter
A low pass filter formed by C115, C116 and R91 removes
any extraneous 455 kHz energy from the AF output of the
FM receiver chip.
Speaker Audio Amplifier
After signal detection and audio filtering, the low level audio
is returned to the RF circuit via VR3. This is then routed to
Pin 3 of IC6, (LM386N-3), to provide speaker audio. IC6 is
enabled by a logic high applied to Q34 which in turn enables
Q33, applying power to Pin 7 of IC6.
Page -12May 2001
MAINTENANCE AND REPAIR
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MAXON
SP-300 HAND HELD
GENERAL
Any repair or adjustment should only be made by or under the
supervision of a qualified radio service technician.
When removing or fitting, use the Exploded View and Parts
List (Page 51) in conjunction with the following procedures:
REMOVING & REPLACING THE BELT CLIP
Removing the belt clip:
1. Depress the metal release tab located on the top of
the belt clip with one hand.
2. With the other hand push the belt clip out of the belt
clip rail.
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Figure 1-Belt Clip Removal
To replace the belt clip:
1. With the slides of the belt clip positioned in line with
the belt clip guide rails, slide the belt clip into position until a click is heard.
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Figure 2-Belt Clip Installation
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Page -13May 2001
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