ICOM IC-9700 PTT Expander

WARNING:
THE WARRANTY OF YOUR RADIO WILL BE VOID!

DO ONLY ATTEMPT THIS MODIFICATION TO YOUR RADIO IF YOU ARE ABSOLUTELY SURE YOU CAN DO IT AND YOU HAVE WORKED WITH SUPER SMALL SMD DEVICES BEFORE!

YOU NEED TO BE ABLE TO HANDLE A SOLDERING IRON AND HANDLE DELICATE ELECTRONIC CIRCUITS!

USE AT YOUR OWN RISK!

DO NOT BLAME ME IF YOUR RADIO STOPS WORKING AFTER ADDING THIS!

I am able to deliver finished boards for €12,- each plus shipping. Send me an email if interested, contact info on the CV/Contact page.

The IC-9700 radio manufactured by ICOM is a highly regarded 2M/70CM/23CM radio known for its impressive features and specifications. It is a popular choice among satellite, EME (Earth-Moon-Earth), and tropospheric propagation users worldwide.

This radio comes in a compact form factor with a multitude of features. However, due to its size, there are some inherent limitations. One notable limitation is the absence of separate PTT (Push-To-Talk) outputs for each operating band.

For instance, in scenarios where you are using the radio for 70cm and 23cm EME operations and have distinct power amplifiers for each band, having separate PTT outputs that become active only when transmitting on a particular band would be beneficial. Ideally, this would entail having three separate PTT outputs for the IC-9700.

While there are aftermarket solutions available that utilize the radio's CI-V connector to monitor the transmitting band and activate the corresponding PTT output, there have been reported instances of failures associated with these solutions. Some users have experienced damage to their preamps due to malfunctions or lack of security when using the CI-V interface for this purpose.

As a precautionary measure, prioritizing security in such setups is crucial. If feasible, opting for hardware-based solutions can mitigate risks associated with interface vulnerabilities. In the case of the IC-9700, achieving separate PTT outputs can be elegantly and securely accomplished using hardware methods.

Upon examining the schematics provided in ICOM's service manual for the IC-9700, it was discovered that there are three signals that become active (go high) for each selected transmitting band, in addition to a common PTT signal. By logically AND'ing these individual band signals with the common PTT signal, three distinct PTT outputs can be generated.

Below are snippets from the IC-9700 schematics, details of the PCB board design, and instructions on connecting the board to relevant points within the radio for implementing this hardware-based solution.

It is important to note that any modifications made to the radio, including the addition of external hardware like the one described, are done at your own risk. Such actions may void the warranty of the radio, and the user assumes all responsibility for any potential issues that may arise from such modifications.

Schematic of IC-9700

First some theory behind the PTT Expander. In order to create a separate PTT output for each band, we need to access four signals on the mainboard. We also need to tap into a +5VDC supply to power the PTT Expander board The board only consumes around 0.2 mA).

The service manual for the IC-9700 can be downloaded from this link.

If the theory does not interest you, you can just skip this chapter and go directly to the "installation" section below :)

The schematic above shows the three "TX active band signals", 12TXS, VTXS and UTXS. These are the 23, 2 and 70 CM TX active signals. The IC-9700 can transmit on one band and receive on another band (or transmit/receive on the same band). The "xxTXS" signals tells us which of the three bands are currently selected for transmission. The transmit band will have its "TXS" signal at a high level, the two other bands will have their "TXS" signal at a low level.

The "TXS" signals are used to control the IC3061 switch, this switch directs the generated HF signal to one of the three PA modules in the radio.

Luckily these three signals also ends up at the anodes of the three diodes: D3031, D3032 and D3033. These three diodes are conveniently located at the top of the baseboard, just beside each other (see below).

In addition to these three signals, we also need the common PTT signal.

PTT (active high level) can be found at the collector of the PNP transistor Q2933:

The PTT Expander board will also need +5VDC supply (only a couple of mA), we can steal that from the main board of the radio as well, there is a 5V voltage regulator:

Location on the mainboard of Q2933 (red arrow points to collector):

The PTT Expander board also needs 5VDC for the Quad AND gate. These 5V we can steal from the mainboard in the radio. There is a voltage regulator IC1221 ("7805") located just below the LAN RJ45 connector.

The Expander

The PTT Expander is a small PCB board, it measures only 40 x 19 mm. The board has only SMD components, leaving the back of the PCB as a solid groundplane. The board attaches to the mainboard of the radio using a double adhesive 3M tape. I use the 3M Pressure Sensitive Tape for this purpose (see below in "installation" section).

On the left side of the PCB you will find six rectangular solder pads:

+5V, connects to the IC1221 5V voltage regulator
GND, connects to ground at the C1223 capacitor (close to voltage regulator)
PTT, connects to the collector of PNP transistor Q2933
2M, connects to the anode of D3032
70CM, connects to the anode of D3033
23CM, connects to the anode of D3031

On the right side of the PCB, you will also find six rectangular solder pads:

2M, GND, this is the PTT signal for 2 meter band
70CM, GND, this is the PTT signal for 70 cm band
23CM, GND, this is the PTT signal for 23 cm band

These three PTT outputs are each driven by a NFET. The NFET is capable of withstanding 100VDC, and can maximum sink 1 Amp to ground.

Gerber files for the board (you can upload this ZIP file directly to JLCPCB or PCBWAY and get blank PCBs.

BOM file can be downloaded here

REMEMBER! If you need to control a relay (or another inductive load), you MUST connect a blocking diode across the coil of this load to prevent back EMF from destroying the NFET!

Schematic for the expander is shown below. It consists of U1 which is a CD4081 CMOS Quad AND gate, three NFET devices Q1..Q3 (IRLML0100), some 0 ohm resistors and some decoupling capacitors.

Installing the board in the IC-9700

WARNING: DO ONLY ATTEMPT THIS MODIFICATION TO YOUR RADIO IF YOU ARE ABSOLUTELY SURE YOU CAN DO IT! YOU NEED TO BE ABLE TO HANDLE A SOLDERING IRON AND HANDLE DELICATE ELECTRONIC CIRCUITS!
USE AT YOUR OWN RISK!

The section will show how to install the PTT Expander in the ICOM IC-9700 radio.
Again, ONLY do this if you are 100% sure you can handle this, you need to solder some small wires at places in the radio where there are not a lot of room!

IF you are confident this is for you, then proceed with the operation :)

First you need to remove the bottom cover of the radio. You need to remove 12 screws, 3 on both sides and 6 on the bottom.

On the picture above, you will find three red circles. One at the upper right corner (5V/Ground connection), middle/top (PTT connection) and lower mid (three diodes for the "TXS" signals.

Above you see the PTT Expander prepared with the wires that needs to be soldered at points in the radio.

I used a couple of pieces of double adhesive tape on the backside of the PTT Expander.

PTT Expander placed on the shielded box just behind the fan.

The three "TXS" signals soldered to the anodes of D3032, D3031 and D3033. Pay attention to the order of the signals!

PTT signal soldered to the collector of Q2933

5VDC and ground soldered to IC1221 and C1223.

All connections to the radio are now complete. Next up is the three PTT connectors.

The three PTT output connectors

I chose to get a "Video extender cable" with three RCA connectors (male and female), and cut that at a suitable length. You can do this with whatever you like. There are limited space to get the cable out of the radio (I did NOT want to make any holes in the backplate!).
With a small "modification" of the fan, there is just enough room to get the three PTT cables out of the radio.