AEG ASG 6861 (01) PDF Document

The AEG ASG 6861 is an assembly which is part of the field radiotelephone, Model SE 6861/12, a portable HF transceiver unit with an RF output power of 20 W. In the transmitting mode, it automatically matches the 50 Ω output of the 20-watts amplifier to an antenna impedance other than 50 Ω. It is also used to match the input impedance of the RF assembly to a different antenna impedance. Using the AEG ASG 6861, a VSWR (voltage standing wave ratio) of equal to 1.5 can be obtained when using different antenna types and operating at different frequencies.

The AEG ASG 6861 can be used with all types of antennas such as:

– whip antennas

– long-wire antennas

– wide-band antennas

The electrical specifications for the AEG ASG 6861 apply for an ambient temperature of +25 °C ± 15 °C.

On the AEG ASG 6861, tuning is always required when a VSWR exceeding 1.9 is being measured. Variations of the VSWR may result from frequency changes, antenna replacement, or from a defective antenna. The decision whether or not a new tuning procedure should be initiated is made approx. 75 ms after transmitter keying by depressing the PTT (push-to-talk) button. Whenever the PTT button is depressed, the antenna tuning unit is turned on for at least 100 ms to check for sufficient matching. If a new tuning sequence is required, it will be initiated.

Since the AEG ASG 6861 antenna tuning unit is always used as an integral part of the field radiotelephone, Model SE 6861, refer to Section 2 of the SE 6861 instruction manual for operating instructions.

No special measures are required for conservation of the AEG ASG 6861 during extended storage periods. The assembly does not contain components that might alter their properties or self-consuming components. However, the assembly should be stored in a dry and dust-free room where risks of contamination are excluded. If this is not possible, the assembly should be protected by special packing material (e.g., by welding in packing foil).

Whenever the PTT of the portable radio-telephone, SE 6861, is depressed, its organizer provides the “13.5 VDC tuning” control signal and the constant tuning level of 10 mW to the antenna tuning unit for at least 100 ms. Subsequently, the following program is run in the AEG ASG 6861:

– The reset pulse generated by the microprocessor initializes the latter and the input/output device.

– The “13.5 VDC tuning” control signal causes the tuning level to be switched to the current tuning network configuration through the directional coupler.

– The logic level of the D-bit control line is read. If the transmitting frequency is equal to or greater than 8.3 MHz, the high-value inductors are inhibited from being switched into the tuning network to avoid self-resonance.

– At the same time, the “13.5 VDC tuning” control signal is recognized by the CPU as the tuning command. This results in the “ASG back indication” control line to be pulled up to 13.5 VDC. In addition, the timer is triggered to generate a delay time of 3.3 s while the DC voltage is read from the temperature transducer.

– Subsequently, the DC voltages from the directional coupler’s output are read and corrected depending on the ambient temperature.

– From the measured values, the CPU determines whether or not the VSWR is equal to or less than 1.9 (threshold for retuning operations). If it is, retuning is not required, and the “ASG back indication” line is set to 0 V.

To remove the PCB assemblies from the AEG ASG 6861, follow these steps:

1. Loosen the four screws from the cover of the antenna tuning unit and remove the cover.

2. To remove the coil PCB assembly and the relay PCB assembly (which together make up the tuning network), you must first:

– Loosen the four screws at the sides of the antenna tuning unit.

– Disconnect the RF line to the RF output of the antenna tuning unit from the relay PCB assembly.

3. The remaining PCB assemblies (sensors 1 and 2, and the CPU) can be pulled out of the enclosure using the corresponding pull-out openings.

4. The motherboard can be removed after loosening four screws.

To reinstall, follow these steps in reverse order.

Remove dust from the AEG ASG 6861 assembly enclosure using a soft, clean and lint-free cloth or a soft, clean brush. Remove heavy contaminations by cleaning the enclosure using a spirit-damped cloth. Clean contacts with a non-aggressive agent.

The following special tools, measuring, and test equipment are required:

(1) Power attenuator, 30 W, 30 ≥ 0.2 dB, 50 Ω, 0 to 100 MHz

(2) Thermal power meter with measuring head, 0.1 MHz to 100 MHz, 100 mW

(3) Rod dummy antenna, part no. 52.6866.040.00

(4) RF millivoltmeter with 50 Ω feed-through measuring head, 10 kHz to 100 MHz, 10 V rms

To test the RF output voltage, first ensure the AEG ASG 6861 is installed in the SE 6861 field radio-telephone with a hand-set connected.

1. Connect the rod dummy antenna (3) to the rod-antenna connector of the SE 6861 transceiver.

2. Connect the feed-through measuring head of the RF millivoltmeter (4) directly to the test output of the rod dummy antenna and terminate the remaining connector of the measuring head with 50 Ω.

3. Set the SE 6861 transceiver for A1A transmissions and for an RF output power of 20 W. A tuning sequence will be performed whenever the PTT button at the hand-set is depressed.

4. The minimum RF output voltages to be measured are listed in the table below:

To test the RF output power and tuning time, first ensure the AEG ASG 6861 is installed in the SE 6861 field radio-telephone with a hand-set connected.

1. Disconnect the rod dummy antenna. Connect the power attenuator (1) to the BNC-type antenna connector using an RF cable with a maximum length of 0.5 m (1.6 ft).

2. Connect the measuring head of the thermal power meter (2) to the output of the power attenuator (1).

3. Set the SE 6861 transceiver for A1A transmissions at an RF output power of 20 W. A tuning sequence will be performed whenever the PTT button at the hand-set is depressed.

4. The table below lists the frequency settings and the minimum RF power levels that should be measured. The RF power levels read from the power meter must be multiplied by the attenuation factor of the power attenuator to obtain the actual power levels.

The time required for a tuning sequence must not exceed 3 seconds.

Perform troubleshooting of the AEG ASG 6861 following the general rules for assemblies containing digital and analog circuitry. Due to the complexity of the circuitry, a strictly defined troubleshooting method cannot be recommended.

Faults can be located relatively quickly by successively replacing the PCB assemblies with assemblies from a functioning AEG ASG 6861 unit. PCB assemblies of the same type can be interchanged between different ASG 6861 assemblies.

The information in Section 4.2, “Mode of Operation”, along with circuit diagrams, component layouts, and connector pin assignment tables, should be sufficient for tracing faults to the component level.

No soldering should be attempted on PCB assemblies except on solder terminals or solder straps, as the protection varnish can be damaged by overheating, which might affect reliable operation.