The ICOM IC-705 & Mods

There are some Groups one can join to keep up with possible changes, see what others are doing with it etc for example on Group.i0 "ic-705". A search should find the group easily.

What is it?

A new hybrid radio. Base station radio performance and functions are packaged in a compact and lightweight portable size. Whether you are taking your hobby to a SOTA, POTA, or some other "On the Air" location, the IC-705 will be your "GO TO" rig!

Output Power:		10W with 13.8VDC external power supply 5W with BP-272 Li-ion battery pack
Receiver Type:		Direct sampling
RX Frequencies:		0.030-470.000 MHz
Channels:		500
GPS:		Built-in

All Mode Radio

From HF to 50/144/430 MHz, enjoy a variety of bands in D-STAR DV, SSB, CW, AM and FM modes. The IC-705 receives continuously from the medium wave broadcast band to 144 MHz band. You can also enjoy FM broadcast and air band reception.

RF Direct Sampling System

The IC-705 uses the RF direct sampling method, which greatly reduces distortion. The high speed/high resolution real-time spectrum scope and waterfall display are incorporated in a compact design for the first time in this class.

Real-Time Spectrum Scope and Waterfall Display

Users familiar with the real-time spectrum scope and waterfall display as seen in the IC-7300 and IC-9700 can now use it in field operation. Utilize the base station feature without the price of one in a compact radio, quickly monitor band activity and find a clear frequency.

D-STAR Functions

Users can enjoy the latest G3 Gateway and DV mode features and have direct access to the D-STAR network with Terminal/Access point modes. The Photo Share feature as seen in the IC-9700 is available on the IC-705 to share photos with other IC-705 and IC-9700 radios without a computer.

GPS Functions

Enhance field operations with the built-in GPS receiver and antenna. Functions include location logging*, RX/TX locations via D-PRS, "Near Me" repeater search/scan, QSO recording with metadata*, and an internal clock synchronization.
*Micro SD required

What's inside the IC-705? Obviously there's a lot of 'stuff' packed into that small rig. Layers of printed circuit boards and shields. There's a nice Japanese you Tube video here, showing what's in there.

VK3FS has some excellent information on the IC-705. Well worth a read, pro's and cons are considered in buying this rig. Also has links to the Manuals and software.

The ICOM Manual is very detailed and it will be quite a job to set it up, although right now I have no interest in D-Star, which runs for many pages in the manual!

My plan is to use it mostly in the shack, possibly with a 50-100W linear and also to make a carry box for possible /P (portable) use. It will also contain one of the ATU boards "ATU-100" available on eBay. While this ATU is not ideal from a low current point of view, I have one available already. It uses standard relays rather than latching relays.

I have a plastic "ammo box" which should suit it perfectly for /P use. Plenty of room for a 7.2aH SLA (or Li-P) battery, plus the IC-705 and some accessories. And keep the rain out as the IC-705 is not waterproof or even splash proof it seems.

I also bought an additional ICOM power cable for more flexibility in using the rig. Icom Part number is OPC-2421 "DC POWER LEAD". It's pretty pricey though. One can easily build this yourself. Just ensure the connector is rated for the current that the IC-705 may draw.

My IC-705 arrived on 15th Sept 2020. Very impressed so far, in listening only, but a lot of reading of the Manuals required in order to understand some of the many features.

I decided to make a stand for mine to make it easier to use on the bench. It's just a simple bent piece of aluminium, with some rubber feet stuck on the bottom.

Click the drawing for a larger view. The dimensions for the hole locations are in the Basic Manual for the IC-705, page 2-2.

It's easy to modify this idea to suit your own requirements. eg add a socket for a vertical whip antenna.

PERSONALLY, I WOULD JUST MAKE MY OWN WITH SOME SUITABLY BENT UP ALUMINIUM SHEET.

Once I finalise my external amp and LPF, I need something to switch them, rather than change bands manually on the LPF. I contacted WB9IXS, who has made an auto band change Schematic using a PIC™ Microcomputer. I contacted Jim and he was kind enough to pass on his source code. I had though some PIC16F876 devices on hand, not the PIC16F886 devices he used. A friend (thanks Ric) assisted me to alter the PIC code to use my available PIC. It includes capability actually, to compile for either PIC type. (Jim has since added a frequency readout to his code but I don't have that code)

As presented here, it will decode for these Amateur bands: 160, 80, 40, 20, 17/15 & 12/10M bands. It should also be possible to decode other bands.

This is my test set-up. The LED's indicate which band has been detected. Showing 40M at present. These outputs will be buffered and fed to the LPF which in my case, requires a logic Low to change the LPF relays. The piece of PCB material is the RF input buffer stages.

There is an input RF buffer amplifier in the original design, but I found it to have some problems, so it was changed to use a high speed comparator chip and is in the actual PCB below.

RF enters the PCB at the bottom left of the PCB and is fed to the tiny comparator chip just above and to left of the crystal. The PIC Micro processes the squared up signal and outputs a Logic 'high' to the ULN2003 buffer on the right. 8 HF Amateur Bands can be detected with each band giving a LOW output to the header pin connector. In addition, if required the PCB can be fitted with 8 (0603 sized smd) LED's, not fitted, to indicate the band being decoded.

At the top of the PCB is an ISP connector for programming the PIC micro device. At the bottom of the PCB is another connector which can be used to provide a serial output if needed. While not coded as such, this output could possibly be used to switch an external Linear/LPF which uses serial input.

The project will detect a signal about -20dBm typically, and up to 10dB better, on the lower bands.

There has been a lot of discussion on the groups.io 'IC-705' group about interfacing to the PTT output of the IC-705, for connecting to various brands of Auto Tuners. There have been several cases of users having to return their IC-705 for repairs, after the PTT port transistor/s have died.

It's not helped by the fact that currently, ICOM have not released a Technical manual for the rig, so not much is known about the IC-705 ports.

Ron, VK3AFW, has designed an 'interface' schematic to avoid any potential conflicts with external equipment and the IC-705.

Since I plan to eventually add a 50-100W linear to my rig on occasion, I have followed Ron's suggestion. I added an optional relay output also.

This is Ron's Schematic for his buffer (plus my added relay). (pdf File updated 25th Jan 2022) and the draft PCB layout.

5th April, 2021 The V1 PTT Interface PCB arrived. The optional relay for a 'normally open contact' PTT out, is not fitted in the pictures. The PCB is ~41 x 26mm.

20th April 2021: A 'gremlin' (brain fade) got into this V1 PCB and the 3.5mm input connector has the 'TIP' & 'RING' reversed. Easily fixed by a single track cut and addition of a short wire on the bottom. However, I have updated the PCB to V2.0 as below . V1 mod Details are here.

21st April, 2021: V2.0 Bill of Material (BOM) pdf & Xcel (right click to save) is for a V2 pcb but notes on the BOM and V2 Sch, will show what's required for V1.

BLUETOOTH switching board is currently being worked on, which supercedes the one below. This one should be simpler and cheaper to build as it uses IC's to do what multiple transistors did in the version below. It also uses a larger (and cheaper) 2.8" ILI9341 TFT screen rather than the ESP32 version with integrated TFT display. The ESP32 Development Module is much cheaper also. It also provides outputs for the VHF and UHF bands. The extra screen space will allow for larger text etc and other information if required.

I am currently waiting for the draft PCB to arrive, to build and test it. Due in June.

Briefly, it uses 2 x MCP8574 devices plus 2 x ULN2803 parts in place of the smd transistors. There are 10 band (V1 was 6 bands) outputs, PTT out and two spares which can be programmed with other CIV commands.

NEW May 26th 2022 BLUETOOTH SWITCHING (V1 is current, will be replaced by V2 above when tested.)

Apart from the above methods for band switching and PTT buffer, a new project was to investigate using Bluetooth (BT) in the IC-705 to an external Micro using BT to do the switching. This is much nicer/neater, as no wiring is required to the IC-705. The idea is to use Bluetooth to switch and external Amplifier and Low Pass Filter. (Info on that project later.)

I take no credit for this software as the majority (99.99% !) was done by Wilfried (DK8RW). I acted as a 'tester' for the project with some minor sketch changes to suit this application. It uses an ESP32 "TTGO" board which is available from the usual on-line sources. This board has an in-built 240x135 pixel colour display which is used to display the current Band and Frequency plus Rx/Tx status. Some output buffering is needed as the ESP32 runs from 3v3.

Wilfried has a Github account here where the source code will be uploaded. See the Examples sub-directory.

Details of the Schematic for my build is below.. It includes buffers for the external LPF and PTT switching.

This is the TTGO board: It should be possible to use any ESP32 board with no display, and add an external display, although I haven't tried it.

Showing the interface in Receive and Transmit modes. (Actual TFT quality is much nice than the pictures here.)

Schematic includes details of buffers used to interface to IC-705 and in my case, a PA which requires a '+ve bias' supply to transmit.

It may look a little convoluted but the output of the 74HC42 switches from a high of 3.3v to a logic low level. This requires another inversion to produce a low going signal, suitable to operate the LPF and change over relays which are supplied with 12v.

I use the G6ALU PA and G4TZR Low Pass Filter, so the Sch is designed for that.. Both are detailed on Steve's G6ALU web page. SEE LEFT SIDE OF PAGE.

I designed a PCB for this project, which will cater for 6 bands. It should fit onto an ~63 x 63mm PCB which will contain the ESP32 TTGO board and allow it to be fitted to the front panel of the Amp for indication of state, as above.

Many LPF designs allow TWO Bands to be combined into one filter, eg 30/20M, 17/15M & 12/10M bands. This can be catered for, by allocating two bands to the one output, in the 'constexpr uint_t band2BCD' section, Line 145, in the "z_userprog.ino" file. I will give further details of this later.

NOTE: The PCB uses mostly smd components. If you follow my design, don't be frightened of smd, only simple tools are needed. Ones you probably already have,

I measured the PTT delay: from PTT out of the IC-705 to PTT out of the interface, at a max. of 24mS. There are three settings in the IC-705 menu available to delay RF output.

NEW VERSION Draft Sept 2025 I am currently working on a newer version of this board that also outputs discrete voltage steps for band changing, as used in the Xiegu XPA-125 linear amp. I don't actually have this amp but a ham contacted me recently to add this facility to my existing code, linked above.

I'm not quite ready to release the new version as I have a new PCB coming that incorporates a buffer for this mode also. This version will still have the separate outputs to drive a 'discrete' LPF design.

Lucien sent a picture of his version of the BT Interface. He modified the sketch (code) a little, to suit his application, see below. He added VHF and UHF for switching.

A component overlay drawing for V2 is here. If you wish to experiment on V1, you can add the three parts using the unused proto holes section in top left corner of the PCB. NOTE: check data sheet for the 2N7000 as it's possible there may be devices with pin-out reversed. So far though, mine have been as expected and shown below.

Assembly: I don't give any part by part assembly details, It's assumed you have some basic knowledge. But with smd parts, best to fit the low height parts first and work up to the larger (higher) parts. See the links above for Schematic and BOM.

Sept 28th 2021:- F1FCO has built one of my early V1.0 PCB's and reports "everything worked perfectly". Pierre didn't have the 2N7000 so used a BS170's instead. (note different pin out)

Brian, AB6UI, also built the interface but using the "V2.0" PCB and reports it works well.. Brian is not using the Jack, as the PCB is being incorporated into some equipment. And note the superb soldering by Brian!

Craig, N6CAV, kindly provided a 'corrected' overlay overlay drawing, showing the FET's and corrected text on right side,see below.

I have some of these V2.0 PCB's available. Gerber files for V2.2 are provided below if you want to spend a bit more..

Nov 2021: I built another V2 board below with new 2N7000's bought from a local source and assumed to be 'real'. Preferably from a known good source although I don't know if this is a general problem. I checked data sheets for several brands and the 2N7000's were orientated as mine is below.(the overlay for one device is reversed)

I don't really plan to 'fix' the PCB overlay as it's not a deal breaker, as long as you are aware of it.

TEXT ERROR:- (but see paragraph below also) As it happens, the overlay text on the output connector is also incorrect! (I must have been half asleep that day.) The pin marked 'FET' is actually the normally open relay contact. The pin marked "PTT" is the FET output if the relay is not used. Both are active LOW.

Aug 19th 2023:- The TEXT ERROR and FET orientation has been corrected. The new V2.2 Gerber files provided on an 'as-is' basis. You will get 6 PCB's on each panel ordered so if you order the minimum 5 panels (100x100mm) you will actually receive 6 * 5 = 30 PTT Interface boards. All care taken but it's up to you to check the files with a Gerber viewer. Share with friends or anything you wish. BOM is unchanged. Send me an email if you make the PCB from my Gerber files, on how you went.

I used 5v6 Zener diode (D3) as that's all I had in stock, but it's probably better to use a 4V7 400mW type. The Zener plus R5 & R6, keep the interface 'PTT out' inactive if the IC-705 is not plugged in. Otherwise you will have an active PTT output to your amplifier, when the IC-705 is not connected, which may or may not be an issue to you. Adding these parts is thus entirely OPTIONAL. Beware, if the Zener goes open circuit for example (highly unlikely) , then 12v will appear on the IC-705 PTT output. Albeit via over 10k ohms in series. It might damage the IC-705. Or it might not. Most likely not, but I take NO responsibility for this..

Version V2.2 overlay, by component values. See actual PCB for component ref. numbers.

Most of the "interfaces" I have seen or heard of, simply use the ATU's "TUNE" button to initiate tuning with the ATU-100. ICOM provide a "TUNER" button on the IC-705 itself which seems to me the more elegant way to do it.

The ATU-100 is available from a number of sources, from a kit to a fully built tuner in a case. Kits start about US$30 which is what I bought. Some kits don't have the smd parts pre-soldered, look for one that does if you don't like smd or just want to save time!

It actually turns out to be a little difficult to do, until one comes to understand the workings of the IC-705 "TUNER" function. Information on this is scant. I won't go into the details here for now, the Sketch will give you the details.

I decided to use an ATtiny85™ using the Arduino™ IDE to develop code for the function. Due to the lack of a meaningful way to monitor things while testing, I moved over to a Arduino NANO which allowed me to use Serial.print statements in the sketch to help debugging the sketch.

The result is that either the ATtiny or NANO could be used, as I have made the sketch able to compile for either device. The ATtiny85 requires a programming adapter to be made to program it, which is a nuisance if you don't have one already. Information for this is widely available on the Web. I used an Arduino UNO board with a home made adapter on top. See picture below. You could also use one of the 'prototype' boards that fit the UNO board for a nicer look.

Operation is simple, select the IC-705's Function...'2'... and the TUNER button should be not be grayed out when the interface is connected.

A short press of the button will RESET the ATU-100 if required. (All relays off etc)

A longer press will show the button as "ON" and the IC-705 will transmit and the ATU-100 will tune. There is a time out timer in the sketch to limit the tuner time if a match is not found. (The IC-705 also has a built-in timer of 60 seconds if no tune is found)

My programming adapter: pictured. I see that amongst others, SparkFun® Electronics have a ready made programmer available. (See Digikey.com "PGM-11801". Also the SparkFun web pages. I have not tried this programmer, but have no reason to believe it wouldn't work. I used what I had available.

Ideally, the ATU-100 needs some changes to allow lower power use with the IC-705. I altered the turns on the SWR transformer from 10 to 6 and also set mine up to tune with 1 Watt rather than the default value of 5 Watts. Location 05 in the EEMEM needs to be changed from 05 (5W) to 01 (1W). This requires the use of a PIC programmer to re-program that location. I used a PicKit3 to do the job. Clones of the PicKit3 are readily available on ebay etc. There are YouTube videos on how to do this, available.

For the NANO version, just the Arduino IDE is required, which you need anyway to compile the sketch, so maybe simpler for many to use.

Here's a screen grab of my draft Interface PCB. It can be fitted with EITHER an ATtiny85 or an Arduino NANO board.

The PCB is about 47 x 44mm in size. Size is limited by the stereo 3.5mm socket at bottom left and the NANO footprint. It could be smaller if just the ATtiny85 was used. I may make a version for that later. (See below !) It uses some smd parts. This one is just for testing, rather than using my breadboard setup.

The actual PCB (V1.0) assembled for the Arduino NANO and ATtiny versions. Feb. 11th 2021

The 3.5mm socket goes to the IC-705 via a patch cable. 4 pin connector on right hand side, to the ATU-100.

UPDATED June 2024 : Schematic of my dual interface version is HERE. (The schematic shows both the ATtiny85 and the NANO, only one is actually fitted.)

In the sketch, there is a directive to use either the NANO or ATtiny85 at about line 44. Make selection then compile in the Arduino IDE.

The ATtiny based PCB is smaller and now assembled also.The LED indicates 'tuning' is taking place. This is my preferred version..

NOTE: V1.0 board, The LM317L should be fitted as per the PCB above, NOT the overlay ! (V2.0T is OK)

Sept 2021, V2.0 PCB. Somehow the PCB in the 'R1' area is missing the pads. BUT see below for corrections. See the picture below, the left bottom PCB in a panel has R1 with pads but the PCB to the right, has no pads. Weird.

To correct this, scrape the solder resist off the tracks in the R1 area and fit a short across the pads, then mount R1 onto the pads/holes just above. Ignore R10 as it's not used. ** Click on the pictures for larger size. ** (Ignore the circle around R2)

My PCB was designed to fit behind a panel, so the stereo socket is easy to use, plus the LED can project through a hole to show the status also.

Both PCB's require a 12v connection, as for some reason, ICOM didn't make available a switched 12v output. Not normally a problem as the ATU-100 or other device will require 12v anyway.

Connection to the IC-705 & ATU100 requires a stereo 3.5mm plug to plug cable. These can be purchased on-line or it's simple to make one, preferably using twin core shielded cable. A cable needs to be made to connect the ATtiny PCB to the ATU-100. Since I assume that the ATtiny PCB will be housed inside the ATU-100, then just a short cable needs to be made. The 'A7' connection on the ATU-100 is a small pad on the bottom of the ATU-100 PCB. Ignore the 'A6' pad. A drawing might be uploaded, as soon as I can draw it up although should be fairly clear from notes on J1 of the Schematic or the overlay link above...

Updated 11th May 2021: The V2 version can take either smd or through hole parts, see pics below. Same layout and size though as V1. The LM317 orientation on V2 is corrected.

I may have a few spare V2 boards available. While "BC548" transistors are specified, most any NPN transistor should be fine. BUT, please check pin outs before fitting !

Sketch will be on request at the moment and subject to a disclaimer that it may not work for you.. Of course this involves connections to your IC-705 and I can take no responsibility for any damage that may occur if you do this incorrectly.

15th Feb.., 2021:- My sketch is working on both the Arduino NANO and the ATtiny85 versions. I did discover though that pin 'D5' on the ATtiny can't be used as a true I/O pin so moved some pin functions.

There are very few parts on either board, as you will see on the Schematic. ATtiny Link above.

When the interface is connected to the IC-705 via the 'TUNER' 3.5mm socket, it enables the TUNER button on the screen in Function...2

The TUNER button now becomes active and is no longer 'grayed' out. If you now 'long' press the TUNER button, a blue line will be visible around the button and the interface will become active and command the ATU-100 to auto tune. At the same time, the KEY line to the IC-705 is set low, telling the IC-705 to transmit a carrier. In the ATU-100, the A7 line will go HIGH signifying it's in TUNE mode.

Once the ATU has finished tuning, the A7 line underneath the ATU-100 PCB drops from a high level to a LOW level, and the interface pulls the KEY line high again and the IC-705 stops transmitting.

**While TUNER is active, pressing the PTT button will also cause the IC-705 to transmit a carrier and make ATU tune. If it had already done a tune then the ATU-100 does nothing as it retains the tune itself.

It's a bit inconvenient to activate the TUNER button using the 'Function 2' in the Menu structure so you can re-program the VOX button to directly turn on the TUNER function. To do this, press Menu/Set/Function..scroll to screen 9/10 (shown in top right corner) and press 'Front Key Customize'. Press [VOX/BK/IN] and select TUNER.

If you use VOX normally, then you can re-program some other key (button) to do 'TUNER' function. Refer to the manual for options..

Update 6th October 2021: N7DDC has released a QRP version of his ATU, the "ATU-10".

It has the IC-705 interface built in. You might like to consider that option. N7DDC has Gerber's available for the PCB but note some parts are very difficult to get right now. I have re-designed N7DDC's PCB to use some much easier to find (larger) parts. And much easier to solder also. See link below.

IC-705

All Mode Portable

What is it?

Output Power:

Receiver Type:

RX Frequencies:

Channels:

GPS:

All Mode Radio

RF Direct Sampling System

Real-Time Spectrum Scope and Waterfall Display

D-STAR Functions

GPS Functions