ICOM A2Z-201 Radio Accessory Connector Breakout Board User Guide

Icom Radio Accessory Connector
Breakout Board
A2Z Tech LLC 2024
A2Z-201https://store.a-2-z.tech/

Overview

The Icom Accessory Connector Breakout Board (IACBB) breaks out all of the documented signals for Icom radios that have either a single 13 pin Accessory Connector or dual 7 pin and 8 pin accessory connectors.
A list of known compatible radios is shown in Table 1. There may be other compatible models.
Appropriate male-to-male 7, 8, or 13 pin DIN cables are required to connect the breakout board to a radio.
The basic circuit is very simple. Each signal is just routed from the appropriate Din connector pins to an RCA jack. Some additional DC isolation provisions are provided for the audio signals and some protection is added to signals that might have relays connected.
The 7 pin and 8 pin connectors carry the same signals as the 13 pin connector. The 7 and 8 pin connectors are typically found on larger format radios with more rear panel space. The single 13 pin connector is used on more compact radios with limited rear panel space.
The IACBB includes provisions for adding 600 ohm isolation transformers to completely ground isolate that MOD-IN and AF OUT audio signals.
Some Icom models do not apply squelch to the audio coming out of the Accessory connector. The IACBB includes a circuit to mute the audio output based on squelch status. This is useful when using a mixer and external speakers for long term monitoring of a channel for activity.
The HSEND, VSEND and 13.8 volt signals include 100V 1A Schottky diodes to protect the radio if relays are connected directly to these outputs.

OPC-599 Functionality
All signals are connected between the 13 pin, 7 pin and 8 pin connectors on the circuit board. This means that the IACBB replaces the functionality of the Icom OPC-599 adapter cable when it is connected to a radio with a 13 pin Accessory Connector. This allows you to use accessories compatible with Icom 7 and 8 pin connectors through the IACBB. All the signals will still remain available at the RCA jacks. However, when using the 7 or 8-pin Din connectors for Icom-compatible accessories, you must be sure that any additional use of signals at the RCA jacks doesn’t interfere with the other accessory.

CAUTION:
Never connect more than 1 radio to the DIN connectors on the IACBB. You may damage one or both radios.

Output Connectors

Table 1 Known Compatible Icom Radios

NOTE on DIN cables:
Several commonly available 13 pin male-to-male DIN cables have been found to have pin 13 connected to the connector shield. This will pull the SQL-S signal to ground and will defeat the squelch audio mute circuit. All other signals are unaffected and the cables do not cause any damage.
Cables identified as Icom AT-180 Data Cables have all 13 pins wired through. The squelch function will operate as designed with these cables.
Commonly available 7 and 8 pin DIN cables that have been tested all pins wired through and operate as desired.

Signal Descriptions

13.8 V
Power is provided to this pin when the radio is powered on. Current is limited to approximately 1 amp.
Using more current will result in blowing an internal fuse in the radio and/or possibly damaging the radio.
This signal can be used directly for low-power accessories, such as meter backlights in external RF wattmeters or SWR meters.
It can be used with external relays to have any number of DC or AC-powered accessories automatically power on and off with the radio. Some examples include linear amplifiers, rotator controllers or automatic antenna switches that connect antennas when the radio is powered on.
Although not strictly necessary, a 100V, 1A, reverse Schottky diode is included on the interface to provide additional protection to the radio if an external relay is connected directly to the phono jack.

8V
This is a bias voltage supplied by the radio. It is current limited to approximately 10ma.

ALC
This is the Automatic Limiter Control input from an external amplifier. This signal is expected to be between (-)4 and zero volts. This is a duplicate of the signal on the ALC jack for radios equipped with a separate ALC connector.

BAND
This is a variable output voltage from the radio that changes based on the current operating band. It can be used to control the band setting on an external amplifier or to control an automatic antenna switch.

VSEND
This signal only exists on radio models that include HF and VHF/UHF capabilities. See (H)SEND signal description for operation details.
NOTE: The default is for this signal to operate only when the radio is on a VHF/UHF band, typically 2 meters or 70 cm. Some Icom models include Menu setting options to select which band(s) this signal is active on. Refer to the radio instruction manual for more details.

(H)SEND
On HF only or HF and 6-meter radios, this signal is labeled SEND. On radios with both HF and VHF/UHF capability, this signal is labeled HSEND.
This signal can be used as both an Input and Output. When the radio is put into transmit (by microphone PTT, for example), this signal is pulled to ground by the radio. In this mode, the signal can key an external amplifier or an automatic antenna switch for separate receive and transmit antennas. The interface board includes a reverse, Schottky diode. So the signal at the phono jack can be used to drive an external relay directly. Use caution when selecting a relay as this signal can typically only sink approximately 200ma, maximum.

NOTE: This signal does not include any high voltage protection. So an external relay must be used when keying a tube-type amplifier with a high- voltage keying circuit.
This signal can also be used as an input to key the radio. If an external source pulls this signal to ground, it will key the radio transmitter. This feature can be used with an external PTT footswitch, an external digital mode encoder/decoder device, or other appropriate accessories.
NOTE: On HF + VHF/UHF radios only one of the HSEND or VSEND signals will be active for both input and output at any one time. This is based on the current operating band and associated menu setting options.

Why do you need both HSEND and VSEND Signals?
One reason would be in a setup that included separate, external high-power amplifiers for HF and VHF/UHF. In this case, the HF amplifier must be keyed only when the radio operates on an HF band. The VHF/UHF amplifier must be keyed only when the radio operates on a VHF/UHF band. Having both the HSEND and VSEND signals available allows this to be accomplished with a minimum of external logic and circuitry.

SQL_S
This is the squelch output from the radio. The signal is grounded when the squelch is open (signal present). This signal is used by the on-board audio mute circuit. It can also be used by external equipment to detect the presence of a received signal, typically in FM applications.

FSKK
This is the Frequency Shift Keying – Key input. It operates when the radio is operating in the RTTY mode.
In this mode, the radio transmits a steady carrier on the MARK frequency when this input is open. The radio shifts the carrier to the SPACE frequency when this input is grounded. This signal is typically used when operating the radio with a legacy RTTY interface and/or with legacy mechanical RTTY equipment.
NOTE: Vintage RTTY equipment often operates with high-voltage current loops. This input does not provide any high-voltage protection for the radio. When operating with any high-voltage current loop or similar signal, an appropriate isolation interface must be provided.

AF Out
This is a fixed, line-level (100-300mV) audio output from the radio. The signal brought out to the phono connector is DC isolated from the radio by 1.1uf of capacitance. The capacitance is large enough that it does not have an appreciable effect on the audio frequency response.

Ground Isolation
The capacitive isolation does not provide full ground isolation of the audio signal. If full ground isolation is desired/required, the circuit board has provisions for 600 ohm audio transformers (T1 & T2). T1 isolates the AF Out audio. T2 Isolates the Mod In audio.
To implement ground isolation, both audio transformers must be installed. Cut Net Tie traces A, B, C, and D on the PC board and install transformers T1 and T2. The board layout supports Tamura MET-46 (DigiKey p/n MT4110-ND) or equivalent audio transformers.

The signal is routed through a mute circuit that mutes the audio whenever the radio squelch (SQL_S) is closed. The mute function can be bypassed by installing a jumper between pins 1 and 2 of J4.
Some examples of how this audio may be used:

• Input to a mixer to combine audio from multiple radios into a common ham shack speaker system.
• Input to external digital mode or other decoders.

NOTE: On more recent Icom radios, this signal can be changed to a 12kHz IF output through a settings menu. If the IF output option is being used, the on-board mute circuit should be bypassed.

Mod_In
This is a line-level (100mV) Modulation Input to the radio. The audio input at the phono jack is DC isolated from the radio by a 2.2uF capacitor.

NOTE: Some Icom radio models may require the radio to be in a specific mode and/or have the appropriate Menu settings in order for this audio to feed into the transmitter.

Ground Isolation
See notes on ground isolation under AF Out

Schematic

Circuit Board

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A2Z-201

References

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