IC-9700 PTT Expander

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!

The IC-9700 radio from ICOM is a very nice 2M/70CM/23CM radio. It has a lot of features, decent specs and is used by many satellite/EME/tropo users around the world.


The radio packs a lot of features in a pretty small box, and because of that, there will be some limitations. One of the more irritating limitations is the lack of separate PTT outputs for each band.

Imagine you are using the radio for 70cm and 23cm EME, you have two power amplifiers, one for each band (or maybe two sequencers etc.). In that case, it would be nice to have a separate PTT output, one that is only active when you transmit on that particular band. In the case of the IC-9700, that would mean three separate PTT outputs.


There are some solutions on the market, these all uses the CI-V connector of the radio where they monitor what band is being used for transmission. They then activate one of three PTT outputs based on that. This is a solution that will work as long as the CI-V communication works as planned....


I tend to wanna do stuff like that with as much security as possible, so if it is possible to do this using only hardware, I will stick to that.


In the case of IC-9700, it turns out it is elegantly simple to do just in hardware!

I looked at the schematics for the radio in ICOM's service manual, and it turns out there are 3 signals that will go active for each band, and a common PTT signal.

By AND'ing the individual band signals and the common PTT, it is possible to make three separate PTT outputs.


Below you will find some snippets from the IC-9700 schematics, the PCB board I have designed, and how to connect the board to the various points in the radio.


NOW, USE AT YOUR OWN RISK! I will NOT take responsibility for any problems that might arise in YOUR radio by using this, use at your own risk! And remember, the warranty will be void by adding stuff like this to your radio !



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 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 "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:

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.



REMEMBER! If you need to control a relay (or another inductive load), you MUST connect a blocking diode accross 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.

First unscrew the fan 

The remove the two plastic taps

Feed the PTT cable thru in the clearance next to the fan

Connect the wires from the three PTT cables to the PTT Expander. Remember to mount in correct order!

Finished result. Enjoy your three PTT outputs, the way it should have been from the start ;)