AR8000 Bulletin Page

Installing the DS8000 Speech Inversion Decoder

The DS8000 may be fitted to the AR8000 (or AR5000) to provide analogue speech inversion descrambling. It is primarily intended for Japanese cordless phones and some UK PMR446 transmissions. The DS8000 fitting & operating instruction sheet is available as a 50kB Acrobat PDF. For operation with the AR5000, refer to the AR5000 operating manual.

AR8000 Discriminator Output

The discriminator output on the AR8000 is taken from pin 11 on U1 (a TK10489 on the middle IF board). To access the board, split the set by removing screws in the battery compartment and at the top. The set splits into two main pieces; the IF board is in the rear half. To remove the IF board, unscrew nuts off each encoder on top, remove two screws at the bottom (ensure battery terminals are straight), and gently ease the board away. U1 is on the rear of the removed board; the discriminator output is from pin 11 of the TK10489 and a suitable earth connection.

Opto Scout Modification

This modification adds a small jack to the radio for connecting the Scout™ via a flexible cable using 2.5mm phone jacks. This allows easy connection for reaction tune operation. This modification may void the manufacturer's warranty.

The addition of the jack is straightforward for a qualified electronics technician experienced with two-way radios and scanners. Careful soldering is necessary. If inexperienced, seek assistance.

Procedure:

1. Disassemble the radio and check the jack location against the provided diagram. Ensure batteries are removed and the power adapter is disconnected.
2. The jack is a 2.5mm (3/32") phone jack. The centre or tip connection from the Scout carries data. Use number 24 stranded wire. Wire lengths are short, just over an inch.
3. A hole is not strictly necessary; locate the position relative to the power jack. Ensure the jack will not interfere with PC boards upon re-assembly. Use an X-acto knife to create a hole in the soft plastic, checking the size against the jack. Bevel the edge for the nut if needed. A drill can be used if a small bit is available, but protect internal components.
4. Ground connections can be made conveniently. The diagram shows suitable positions. The data connection in the AR8000 is taken from a chip resistor. Solder carefully. Check continuity between the jack nut and the radio's PC Board ground connection. Re-assemble if polarity is correct.

Power up (Scout related)

When the Scout is powered on, a display self-test occurs: all front panel segments illuminate for two seconds, followed by 'SCOUT' for two seconds, then the communications LANGUAGE for two seconds. The Scout then operates in the mode selected by the FILTER and CAPTURE switches (AOR AR8000 or CI-V ICOM).

Changing the CAPTURE switch during the self-test toggles the serial communications language between CI-V and AR8000. The default is 9600bps; experiment with CR/LF or NEW_USER_MODE for correct parameters. In 2VFO mode, reaction-tune occurs when new frequencies are clocked by the Scout. The AR8000 will react and follow the Scout's display; recall SCOUT MEMORIES to select frequencies for storage.

AR8000 Keypad Replacement

The AR8000 keypad is a membrane with carbon printed contacts that can deplete with use. Two types of replacement keypads were available: standard (original) and 'hard shell' (with a protective cover over printed letters). A new keypad, introduced in 2003, replaces both types.

Some users find fitting later keypads slightly difficult, as they may be marginally larger, requiring slight enlargement of front case holes with glass-paper. Before starting, place the set on a duster to prevent scratching.

Procedure:

1. Remove 2 silver screws in the battery compartment.
2. Remove 2 side screws (small black screws next to rubber side pieces, only the one nearest the rear panel on each side).
3. The front panel, with rubber side pieces, can now be removed. Apply slight force to pull the two case halves apart; do not lever or twist them to avoid bending internal connector pins.
4. With the front case half removed, the main circuit board must be removed to expose the keypad. Remove 5 silver screws holding the board and unclip the speaker connector.
5. Carefully lift the board away from the case; the side switch panel will lift with it.
6. The keypad can now be lifted out. Board contacts with contamination can be cleaned with a non-residue solvent and cloth.

Refitting is the reverse. Ensure the new keypad is correctly oriented and its keys align with the case slots before refitting the board. Mate the case halves carefully, ensuring all connector pins locate correctly. Press halves together parallelly. Do not overtighten screws. Power up and test all keys.

Wandering "Birdies"

Floating birdies may result from interaction between the two DC-DC inverters on the IF PCB and the ceramic crystal on the CPU PCB, especially when boards are close together in the fully assembled set.

The CPU crystal frequency is 4.91MHz. To access it, remove battery compartment screws and rear half case screws. The receiver separates into two; the crystal is on the CPU half, soldered directly, resembling a miniature fuse.

A *metal cased* crystal package style HC49/4H (half height) is recommended, or a watch style crystal. Legs may need soldering to PCB crystal pads. Frequencies above 4.2 MHz are generally acceptable (though beep pitch may change). For REMOTE CONTROL/CLONE capability, a frequency close to 4.91 MHz, such as 4.9152 MHz, is recommended.

Tightening BNC socket and replacement of wire link

Before starting, place the set on a duster to prevent scratching.

1. Remove 2 screws (silver coloured) in battery compartment.
2. Remove 2 side screws (small black screws next to rubber side pieces, nearest rear panel).
3. Remove front panel (slight force, pull halves apart). This leaves RF and IF boards connected.
4. Remove the three rubber knobs on the top panel (pull and twist). Replace if soft or damaged.
5. Remove nuts holding volume, squelch, and encoder controls (use pointed pliers).
6. Withdraw the two battery terminals from the IF board sockets (straighten ends if bent).
7. Undo two screws holding the PCB and withdraw the board by lifting the bottom (separating IF/RF connectors).
8. The rear of the BNC socket is now visible. Some sets have an earth strap that needs desoldering.
9. To tighten the BNC socket: it's easier if the RF board is removed (three screws) and the top panel removed from the RF board (desolder BNC centre/earth points). Tighten the BNC using pointed pliers. A trick is to use an old BNC plug on the socket, hold it with large pliers, and tighten the nut with pointed pliers. Be aware that excessive force can shear lugs. A sealant can be used on the nut to secure it; super-glue is an option but makes future removal difficult. Do not use screw-lock, as it can make the plastic brittle.
10. If the antenna wire link was broken, it can be replaced. The original is a solid wire through a small bead. Replace with soldered wire or flexible wire. The bead can be transferred.
11. Rebuild the unit in reverse order. Re-solder the BNC earth. Fit control pots through the top panel before connecting IF/RF boards. Ensure front section and IF boards are positioned correctly. Re-fit battery terminals before the front panel, bending protruding wire to prevent them coming loose. Do not overtighten control pot nuts; ensure they are central. Rubber knobs push on.
12. Test your work.

EARLY AR8000 (first 500 units) CPU tolerance - won't always switch on

Some AR8000 units may not switch back on after being switched off, particularly with NiCads. The LCD lamps might illuminate, or nothing may happen. This is a minor tolerance issue due to a high-value resistor (1M OHM) in the reset circuit, causing one inverter not to switch off.

The remedy involves fitting a diode (e.g., 1SS268 or 1N4048). This has been standard on production units from serial 10500 upwards.

Procedure:

1. Remove the battery cover and NiCads.
2. Remove the two screws in the battery compartment.
3. Remove the two side screws nearest the rear case (not all four).
4. Carefully separate the two case halves.
5. Locate the 1M OHM surface mount resistor (R6) on the microprocessor PCB. Fit a diode across R6, anchoring it between the regulator S-8054 and C8. A 1SS268 diode (double diode SMD package) is used, with one leg unused.
6. Reassemble and test.

AR8000 BANDSCOPE bandwidths

Bandwidth is defined as centre frequency plus/minus five divisions. The response levels are as follows:

AR8000 'PLL ERR' display

If the 'PLL ERR' message appears when batteries are slightly discharged but the receiver functions from an external supply, add a 10pF capacitor to the IF PCB in parallel with R33 to prevent PLL unlock.

AR8000 low battery indication

Occasionally, the 'LOW BATTERY' message may appear prematurely on the LCD. The 'low battery' message should typically appear when voltage drops to 4.2V, and 'battery error' when it drops to 3.5V (at which point the receiver stops functioning).

The low battery display is monitored by the CPU via a potential divider (resistors R25 (33k OHM) and R26 (100k OHM)) on the CPU PCB. If incorrect results are displayed, adjust the values of R25 & R26.

AR8000 squelch splutter (audio mute)

Squelch operation is controlled by the squelch line to microprocessor pin 63, and audio mute by pin 11. There is minimal delay between these lines. The squelch signal is fast relative to RF input, meaning signals near the threshold can produce broken recovered audio (audio mute).

Early production sets had a squelch threshold of 0.2uV to 50uV. Later sets have a narrower range of 0.15uV to 1.5uV.

The mute delay time constant is controlled by R81 (100k OHM) and C96 (0.1uF) on the IF board. Increasing this constant provides a 'nicer' audio mute response (reducing squelch chopping) but may cause a brief 'shhhh' noise at the end of transmissions. Altering C96 to 2.2uF or 4.7uF (or paralleling 1.0uF) adds about a second of delay, which helps remove squelch chattering on smaller signals. RF performance is unaffected.

AR8000 squelch 'blindness'

It is possible for the AR8000 squelch to remain open regardless of control position (even fully clockwise) when no signal is present.

Procedure to observe:

1. Place the receiver in [2VFO] mode.
2. Enter a VHF frequency into VFO 'A' (e.g., 145.400MHz NFM) with no transmission.
3. Switch to VFO 'B' by pressing [2VFO].
4. Enter a frequency into VFO 'B' (e.g., 5.505MHz USB), ensuring a signal is received and AGC is produced.
5. Press [2VFO] to swap back to VFO 'A'. White noise will be audible and cannot be muted even with the squelch control fully clockwise.

The squelch will then close if:

• A good strong signal appears and then departs.
• The [MONI] key is pressed.
• The tuning [DIAL] is rotated.
• The wanted frequency is re-entered via the keypad.

This behaviour has been observed on all sets and is considered a 'characteristic'.

AR8000 locked out memory - VFO transfer CPU reset

A situation exists where the AR8000 can be made to reset. This occurs if you press [A=B] to transfer a locked out memory channel to VFO. The receiver will appear to function correctly but will reset upon the next power cycle.

To transfer a PASS CHANNEL to VFO, use the [ENT] key to transfer the frequency to the temporary VFO (rather than 2VFO), as described in the operating manual, or unlock the memory channel first.

AR8000 supplied aerial frequency response (RA8000)

A test on the AR8000 antenna showed a significant dip in response around the VHF marine band. This was measured by injecting a 0dBm signal into an uncalibrated VHF antenna approximately 2 metres away from the AR8000 antenna, connected to a spectrum analyser's 50OHM input. Telescopic aerials provide better results, especially for marine monitoring, but are less concealable and more prone to mechanical damage.

A graph illustrates the frequency response, showing signal strength (dB) versus frequency (MHz), with a notable dip in the VHF marine band.

AR8000 stuck on lower case memory banks

Some AR8000 operators have found their sets automatically revert to LOWER CASE memory channels when manually selecting memory locations. This is caused by enabling the 'select scan' mode. With one or more memory locations tagged for 'select scan', the AR8000 automatically selects the CASE of the first tagged location. Other CASE memories are selectable but require manual selection each time a location is entered.

For example:

• If memories a01 & A02 are tagged for 'select scan', the set will automatically go to lower case memories unless specifically requested otherwise.
• If memories a03 & A02 are tagged, the set will default to upper case locations in manual select.
• If the first tagged memory location in upper and lower CASE memories is the same (e.g., a04 & A04), the set will not automatically default to either case; memory retrieval will behave as if 'select scan' is not enabled.

EARLY AR8000 audio scan component change

On early production units (above serial 10500 but below 12000), the audio scan/search facility may fail to stop on low-modulated signals like 12.5kHz NFM transmissions. This is likely due to a reduction in AF gain in NFM to minimize microphonic behaviour, which also lowered the signal path to the CPU monitoring modulation.

To compensate, component values around U5(B) were changed:

These changes were applied to all later production units. A possible side effect is distortion when receiving a strong high-level AM signal with a tape recorder adapter (CR8000) connected.

AR8000 narrow AM filter

Lowe in the UK developed a modification for the AR8000 to switch the SSB filter for narrow-band AM reception (short wave), using the DS8000 for filter selection. This modification was dropped due to 'CE' emission standards. The modified AR8000 was marketed as AR8000DX. More recently, narrow AM switching has been offered, believed to be from the same design, though AOR has no specific information.

Other designs for switching the SSB filter for AM listening have been posted online. The following is an example, not intended as a modification text, nor endorsed or tested:

No cuts to pins or sockets are required. Make etch cuts near F3 and F4, using existing feed-through holes to solder 'wire-wrap' wire. Break the lines feeding the 12kHz (NFM) and 4.0kHz (SSB) filters. Use a DPDT switch: one position is normal, the other breaks the etches and routes the voltage for the 12kHz filter to the 4.0kHz filter, connecting to resistors feeding diodes that direct the path through both filters.

AR8000 RS232 signal level response

Using the LM command via RS232, a theoretical signal level response with up to 64 steps can be obtained, though in practice, it is little over 40 steps. Response levels may vary slightly between sets but are consistent for each individual set.

Levels from a later production unit are as follows:

AR8000 top panel knobs

Top panel knobs may loosen over time, particularly on earlier units. The on/off switch might not function due to the knob slipping. This is caused by the rubber composition reacting with the metallic control shafts. Later AR8000 knobs have a harder composition and thicker walls, making them difficult to remove.

When replacing knobs, clean the shaft with a cloth or tissue to remove residue, as a green fluid is often present. Replacement knobs are available from the AOR UK Service section. Vol/On/Off and Squelch knobs have 'dots', while the encoder knob is blank.

AR8000 Battery contact springs

The battery contacts provide the battery feed to the main PCBs. They pass through small holes in the case and into sprung sockets on the PCB. This design allows for contact replacement without removing case parts, but has drawbacks: contacts may come out with batteries, and sockets can be pushed away.

Later sets addressed this by bending the end of the battery contacts over slightly after the wire passed through the socket.

To replace or re-fit the battery contacts:

1. Remove the battery cover and batteries.
2. Remove the two screws in the battery compartment.
3. Remove one screw from each side panel (preferably the ones nearest the rear panel).
4. Pull the two case halves apart; slight resistance will be felt from the inter-board sockets.
5. The battery contacts and their sockets are now exposed on the middle PCB.
6. If contacts are bent, straighten them with pliers before pulling them out.
7. If contacts are out, check that sockets are straight and upright on the PCB.
8. Check socket springiness: the metal section should be springy and the gap should close after contact removal.

Briefly how to do this:

1. Remove the three control knobs.
2. Remove the three lock nuts (use fine pliers).
3. Unscrew the two board screws.
4. Remove the board.
5. Unsolder the offending socket.
6. If removing both sockets, refit each in the other's position. If only one is removed, spring contacts can be exchanged.
7. Re-assemble in reverse order (new control knobs may be needed).
8. Re-fit battery contacts through the battery compartment holes into the sockets. Bend the protruding wire end slightly to prevent them from coming out again (or use super-glue on the contact/slots if they are short).
9. Re-assembly is the reverse procedure. Ensure inter-board contacts fit correctly and side panels align.
10. Refit batteries and test your work.

Additional note:

Three 'double' battery contacts are fitted, located by slots and plastic lugs. These rarely cause problems, but later sets have glue in the slots and on lugs for robustness. Apply glue carefully, avoiding the spiral contact section.

AR8000 DC socket replacement

The AR8000 is fitted with a 1.3mm concentric power socket. While robust, it can fail after years of use or if solder connections break due to rough handling. These issues can be rectified by soldering. A new socket and control knobs are relatively inexpensive.

To carry out the work:

1. Remove the battery cover and batteries.
2. Remove the two screws in the battery compartment.
3. Remove one screw from each side panel (preferably nearest the rear panel).
4. Pull the two case halves apart; expect slight resistance from inter-board sockets. The CPU/display board remains attached to the front/top panel; rear (RF/VCO) and centre (IF) boards remain attached to the rear panel.
5. The power socket is visible on the centre PCB. Battery contacts and sockets are also exposed.
6. Remove the three control knobs (they may be stiff; replace if worn/soft). Clean shafts of oil or sealant. Leave knob refitting until after testing.
7. Remove the three lock nuts (use fine pointed pliers).
8. Remove the two board screws.
9. Lift the centre PCB straight away from the rear panel, withdrawing control pots from the top panel. Resistance will be felt due to a centre connector.

With the underside of the board exposed, the power socket can be desoldered and removed, or re-soldered if joints are fractured. For added robustness, apply a small amount of solder to the two exposed parts on the upper side of the socket. If PCB solder pads have fractured, bridge the broken section with wire. A spot of glue on the underside of the power socket can add robustness and hold it during soldering.

Re-assembly is the reverse procedure. Ensure inter-board sockets are mated correctly. Refit battery contacts and bend the protruding wire end to prevent accidental removal. When fully assembled, connect the power supply and test work, including battery operation, before fitting the control knobs.

Many thanks for the Infos to www.aoruk.com.