7100 Computer Interface

setting up USB audio levels on the Icom IC-7100

© 2018 by KV5R. All Rights Reserved. Rev. 9/10/2019.

Like most modern ham radios, the Icom IC-7100 comes with a built-in USB audio and serial ports, providing a one-cable connection to a PC without needing an external interface box, dongles, or audio cables. What this really means is that the radio contains a USB hub chip, two serial port chips, and a soundcard chip (just as you’d find in external interfaces) that presents a soundcard and two serial (COM) ports to the computer. To use them you just pick them from a list in your software’s audio and CAT setup, just as if they were external USB dongles.

Unfortunately the audio chip and the default settings that Icom uses are nowhere close to being matched with Windows. So we go on-line looking for good advice on settings, and as usual, we find a mess of conflicting information. But fortunately you landed here, and I’ll save you a bunch of trouble. So follow along by opening and adjusting your Windows Sound dialog box, and the radio’s Set → Connections menu.

Update: Windows 10 apparently identifies the radio’s sound chip properly and applies the normal line-level gain. The very low gain setting described below applies to Windows 7, and perhaps 8.


(Skip on down if you’ve already done this)

Do NOT plug in the USB cable before downloading and installing the Icom USB Driver! If you do, Windows will install a generic driver, and you’ll have to go into Device Manager and remove it, then install the Icom driver. Actually, it’s not an Icom driver (though you get it from them), it’s a Silicon Labs CP210x driver. Apparently, that’s the manufacturer of the serial UART chips used in the radio. The soundcard in the 7100 requires no special driver; Windows idetifies it as a “USB Soundcard Device” and uses a generic driver, just like if you plugged in any USB soundcard dongle.

Read the Icom USB Driver Installation Guide. Save the PDF for future reference. It has detailed instructions and screen-shots for Windows 7, 8, and 10.

Download the latest USB Driver (Version 1.30 {or latest} ), Driver Utility and manuals. Unzip it and click CP210xVCPInstaller_x64.exe (or _x86 for 32-bit Windows). AFTER installing the driver, reboot, then plug in the USB cable, and then turn on the radio.

In Device Manager, and programs that access COM ports, you’ll find two new (virtual) COM (RS-232 Serial) ports, named like COM3 and COM4 (or 5&6, or 7&8, if you already have some real or virtual COM ports). They will appear as “Silicon Labs CP210x USB to UART Bridge” in Device Manager, under the “Ports (COM & LPT)” branch of the device tree.

The first com port will be called USB1 in the radio’s docs and menus. This is the CAT (Computer Aided Transceiver, Icom CI-V commands) port you’ll use in all your radio software that provides and uses radio control. Yay! No more overpriced CI-V level converters, and no more overpriced interface boxes.

The second COM port is called USB2 in the radio. It can be set to output RTTY or DV data messages (to an ASCII terminal emulator software), or used for a NMEA GPS for D-Star.

The radio’s serial UART chips present RTS and DTR states, but the 7100 does not use them, so forget about PTT or CW keying via virtual hardware pins in your digi-mode software. You must use software that will PTT via CAT command, so older software that only sends PTT and CW keying via serial pins will not work.

Update 1: I found a little device for $10 that simply plugs into a USB port and the radio’s CW Key jack. It apparently contains (in the USB plug) a USB to UART bridge chip (it presents a virtual serial port to the computer), and uses RTS and a switching transistor to key (ground) the radio’s CW jack. It works fine. It’s called “LD-C103” and is a generic/unbranded part. Look on Amazon and Ebay.

Update 2 (12/02/20): FLDigi now supports CW keying via CAT! So no external keying interface needed. Thanks, Dave!

In your rig control software settings, pick the first COM port and set it to 19200, N, 8, 1, and CTS/RTS doesn’t matter; I set them to “Forced Off.” Note that if you have a 7300, you can use them and there are settings for their functions in the 7300’s Connectors menu. Note also that two programs cannot share the COM port. If for example you have OmniRig running in the background, then start HRD, you’ll get that good ol’ DOS-days error, “COM port already in use.”

Actually, there’s a way around that—a utility called VSPE (Virtual Serial Ports Emulator), whereby you map a real (or virtual) serial port to a new virtual port, then point as many programs as you like to the new port, and all can use it at the same time. Why? You might run HDSDR as a panadapter, with OmniRig providing CAT control to it, and you might also run your digi-mode software, and logging software, all of which need access to the radio’s CAT data on the same COM port. Strangely, the 32-bit version is free, but the 64-bit version costs about $20. VPSE has a nice graphical interface and is easy to set up, then forget. Note that once you’ve set it up, you need to save it’s setup, and tell it to start automatically with Windows. Then remember to set all your software to use VPSE’s port, not the radio’s port, for CAT.

Note (12/02/20): Apparently VSPE does not route or sequence CAT commands and replies. If you use two or more programs at the same time on VSPE, there will be CAT data collisions that will cause the radio and/or the software to do strange things. A partial solution is to reduce the polling times in the software to perhaps 2000 ms. Also, the JT code-based programs (WSJT-X, JS8Call, FSQCall) will not even start up if another program is on the VSPE port. One work-around that I've tried is using OmniRig for both programs. Set Rig1 and Rig2 to the same rigfile and port (the VSPE virtual port). Then set software 1 to use Rig1 and software 2 to use Rig2.

There’s also a free one called com0com, but its setup is a bit too confusing, so I didn’t mess with it.

The Icom USB connection also presents the USB soundcard chip in the radio, and it’s just like any USB Soundcard dongle—it shows “Speaker (USB Audio Codec)” and “Microphone (USB Audio Codec)” in the Sound dialog and anywhere you can select audio sources.

Audio Setup

Locate Windows’ “Sound” dialog in Control Panel, or right-click the little speaker in the Taskbar and pick “Recording Devices”.

In the Playback and Recording tabs of the Sound dialog, open Properties of both devices and rename them to something more meaningful:

Playback → Speaker (USB Audio Codec) → Properties → General, rename it to IC-7100 XMIT

Recording → Microphone (USB Audio Codec) → Properties → General, rename it to IC-7100 RECV

And in both of them, click the Change Icon button and set it to the 2-jack RCA cable icon. Showing a microphone that gets the radio’s output (like a speaker), and a speaker that modulates the radio (like a microphone), is pretty darn confusing, as are the generic device names… Yep, in good ol’ Windows, your radio transmits with a speaker and receives with a microphone. Why can’t they just say Input and Output? So don’t skip doing the above—it’ll make everything much easier.

Set Levels

Windows Sound Levels

First time plugging the radio into the computer, the USB audio levels will be set at 100% — EEK! Set them as shown below before starting any digi-mode software.

There is a known bug in the TI sound chip used in many modern amateur radios. This chip mis-identifies itself to Windows as a microphone device, causing Windows to add 30 dB gain to it. The solution is to lower the level slider, almost to the bottom, to -0.4dB.

In the Recording tab, open properties for the IC-7100 RECV (USB microphone) device, Levels tab, right-click the level slider and change it from percent to deciBels. To verify if your chip has the bug, lower the slider to minimum, then use the right-arrow key to raise it 3 clicks, til it shows -0.4 dB. But if your slider shows -96 to +30 dB, with 0dB in the middle, you don’t have the bug and/or Windows has properly identified the chip as a line-in device, and a medium level (0dB or 50%) is where you want it. Close the Properties box.

In the Playback tab, and open properties for the IC-7100 XMIT (USB Speaker) device. Set its level to -24 dB (20%). On my Windows 7 computer, I had to use 13%, but on the Windows 10 computer I use 20. YMMV. You will also set the radio’s USB MOD Level to 20. The trick is to balance them, not have one real high and one real low, lest you overdrive the audio chip and create distortion. And both must be set so the radio isn’t driven to any ALC indication, which is usually 25-30 watts on PSK-31, or 50-60 watts on a pure audio tone.

NOTE: YMMV, and the settings I gave above may be wrong for you, because Windows keeps changing the way it handles audio devices. Just be aware that your Recording (mic or line-in) may be normal, or may need to be set real low. You’ll soon know, when you send received audio from the radio to the computer, watching the green bar-graph in the Sound dialog. It should be bouncing around well under half-scale on band noise, and about three-quarters on a strong signal.

If you want to listen to the radio through the computer, you need to go to Sound → Recording → IC-7100 RECV → Properties → Listen, and check the “Listen to this device” box. It should pipe the audio to your default playback device, usually speakers or HDMI audio. And if your panadapter SDR isn’t muted, you can enjoy a nice echo from the differential latency… 🙂 I never listen to the radio on the computer, because of that latency.

As for monitoring your transmitted digi-mode audio, well, that’s not as easy, as there’s no Listen option for playback devices. Maybe turn on Set → Functions → Monitor in the radio. Yep, just tried it, that works even in SSB-DATA mode. I find it helpful to monitor the transmitted audio in digi-modes; it helps to know what you’re actually transmitting, when the tail stops, etc. Otherwise, you might not know you’re still transmitting, if your software macros didn’t go to receive as expected, and you’re not looking at the watt meter. I never want the computer transmitting anything I can’t hear.

Note: TURN OFF ALL WINDOWS SOUNDS! Transmitting chimes and other Windows’ noises is NOT LEGAL in the CW-Digi sub-bands. Sound (dialog) → Sounds (tab) → Sound Scheme, set to No Sounds.

Radio Levels

Next, in the 7100, press Set → Connectors:

  • USB AF Level: 50 (default)
  • USB MOD Level: 20 ← IMPORTANT! The input is WAAAY too hot at the default 50%!

Also, while in the Connectors menu, set:

  • ACC MOD Level and DATA MOD Level: set to 0%, if you’re not using those jacks. In this case, DATA MOD Level doesn’t mean SSB-DATA mode, it means the DATA jack on the back of the radio, where you’d connect something like a Pactor TNC.
  • DATA OFF MOD: set to MIC, ACC: disables mic and accessory jack inputs in SSB-DATA mode; enables them when NOT in DATA mode. (DATA OFF MOD means “MODulation source when DATA mode is OFF”, i.e., regular SSB voice operation.
  • DATA MOD: set to USB: ACC is the default, so it will not transmit USB audio until you set this! In this case, DATA MOD means “MODulation source when DATA mode is ON.” So, DATA MOD Level and DATA MOD are two entirely different things. Confused yet?

So, DATA MOD set to USB, level is controlled by USB MOD Level, and DATA MOD Level is only for the radio’s data jack. They could have done that a little better in the firmware…

On my Windows 7 system, with Playback at -30.9 dB (12%) and USB MOD Level at 21% produced the following results:

  • In DM780: 29 watts on PSK idle, 63 on PSK-off tone
  • In DM780: 50 watts on RTTY idle
  • In MixW3: 31 watts on PSK idle, 65 on menu Commands → Tune (it outputs a single tone but may also be set to two-tone)
  • In MixW3: 66 watts on RTTY idle

On my Windows 10 system, Playback at 20%, radio USB MOD Level at 20% produces the correct 30 watts on PSK-31.

So, if you’re on Windows 10, start with 50 and 50 for receive, and 20 and 20 for transmit. But in Windows 7, the receive (mic) will be near minimum, and the transmit (speaker) will be 12-13. YMMV.

Note that I have not tested this combination for distortion, I just set proper power levels. Also note that the USB MOD Level control is very sensitive — 20 produced 30 watts PSK and no ALC, while 25 produced 117 watts and full ALC (the default 50% would likely destroy something). You never want ANY ALC on digital modes, as it degrades the quality and readability of the signal, and splatters all over everybody else. See that LID on the waterfall that has 10 splatter images around his signal?


  1. The radio’s default USB MOD level of 50% is WAY TOO HIGH (sensitive), requiring setting computer level to 0-1% (no granularity). Reduce USB MOD to 20% then set computer level to 12-20% to set RF power to about 30 watts (no ALC indication) on PSK, or about 60 watts continuous tone.
  2. Do NOT limit RF power with the RF Power control, leave it at 100% and limit power with low audio drive. In Icoms, turning down RF Power just raises the ALC bias level, and we want no ALC action of any kind.
  3. Always decode and send digi-modes at 1500 Hz. Why? The 7100’s filters center on 1500 in SSB and DATA mode. So, if you tune somebody at 1000 on the waterfall, then dial the filter down to 100Hz, oops! Where’d he go? Outside the filter!

Regarding #3 above,

  • In DM780, set: Program Options → Waterfall → Center Frequency Marker → 1500. Clicking the C tag will tune the radio to put the selected signal at 1500.
  • In fldigi, set Configure → Miscellaneous → Sweet Spot, set CW to 600 (or your favorite offset), and RTTY and PSK to 1500. Then clicking the QSY button below the water fall tune the radio to put the selected signal at 1500.

Then you can click on a signal anywhere in the waterfall, then click the C tag (DM780) or QSY button (fldigi), and it will instantly tune the radio (via CAT) to move the signal to 1500. Then you can select narrow filter and start the QSO. Nifty! It’s like the CW Tune button on the radio, which tunes the signal to be at your selected CW offset.

Also, in fldigi, you can make macros that will QSY then set the filter with one click!

What’s Next?

Calibrating the IC-7100

73, — KV5R

16 thoughts on “7100 Computer Interface
  1. One thing I found in Win10 it wouldn’t let sound pass through to the speakers, even though it showed sound coming to the device, until I checked the “Listen to this device” checkbox under “Listen” tab in the device properties.

    • Yes, it’s a different “sound card” (USB Codec) than what the computer speakers use. The “Listen” checkbox basically Tees the radio’s sound device to the computer’s sound device.
      You can also turn on Set, Functions, Monitor in the radio and hear your digi modes that way.
      73, –kv5r

  2. Got the t420 and an Asus T-200 both operating TR4W properly on CW, thanks to your article. Am about to order some items from RAM Mounts for the mobile.
    72 Paul

  3. That cable did the trick, am able to key cw via TR4W program. I first tried jerking around (again) with the RigExpert Standard Interface box, with its multitude of wires, connectors, that I’ve had for more than 10 years and have yet to get it to do anything. I did something I’ve never tried before. Connected the confuser to the radio using a USB A-B cable. Eureka. Instant communication with TR4W. However, no CW xmit until I plugged in the LD-C103. Will start another post on related subject.

  4. “It’s called “LD-C103” and is a generic/unbranded part. Look on Amazon and Ebay.”

    I have ordered one that’s coming from China. Will take weeks. Do you know of any more local sources?

    I tried a RigExpert interface but didn’t do the trick.

    Also, your article is the first one I’ve read that makes any sense how to key cw on a 7100. My CW contesting program of choice is TRLog, https://www.trlog.com/, which is a DOS program and worked well. I then switched to their Windows version, https://www.tr4w.net/ and have spent years trying to key cw in the Windows environment. Am hoping the cable will allow me to key cw using TR4W. I do hf contesting these days via mobile.
    Am wondering if you would kindly try TR4W on your IC-7100 to see if it will key CW?
    Great article. Am grateful I stumbled upon your website. And that you are a VE2.

    73 Paul Hicks
    Wellington, ON

    • Howdy Paul,
      As stated, the LD-C103 uses RTS, so any software that sends CW using the (virtual) serial port’s RTS “pin” will cw-key the radio via the C103. Most software that sends CW can use RTS.
      I looked at TR4W User Manual, says it uses DTR for CW key, and RTS for PTT. But wait! In the TR4W Reference Manual p.72 says Radio one keyer RTS can be set to PTT or CW, in the ini file.
      I don’t know of any US or CA sources. Somebody should make one, it’s just a USB to serial chip and a transistor; one might even be able to add a transistor (and base resistor) to a common usb-serial pigtail, in the DB9.
      I looked at adding a transistor to the RTS pin of the serial chip in the radio, BUT it’s shorted to ground UNDER the surface mount chip, so no way to do it without removing the chip, and I don’t trust my hot-air rework skills (or my eyes) that far!
      73, –kv5r

      • Should be ve3zt/m
        Sorry I got you mixed up with ve2dx who makes breakout boxes etc. I’m 78 yrs so that’s my excuse and I’m sticking to it!

        I was rummaging through a box of cables looking for something, and I found that I have a LD-C103 cable! It’s about 4-feet long.

        Should I load the drivers before plugging in the cable to the 7100?

        Will be running TR4W on a Lenovo T420 and Win 10 Enterprise.
        72 ve3zt/m

        • Oh Goodie!
          Yes, install the drivers first. If you need them, see the link in the next comment, below.
          You’ll need to set TR4W’s settings file; see the Reference Manual PDF on the TR4W web site. Device Manager will show what COM port it selected after drivers and plug-in. I think you’ll need to put the port number in the settings file, and set Radio One RTS to CW. And set Radio One CAT to PTT. The 7100’s hex address is 88. That’s more than I know about it; I haven’t installed the program, so go by their 2 manuals.
          73, –kv5r

          • Appreciate your help with settings, etc. Have been clipping text from Forums, etc. for years and saving it in Evernote. An item I read somewhere says to make sure something is set to “straight key.” Am about to embark on the journey. Been trying to get TR4W to xmit CW for 10 years. Saw on QRX another poor slob had been too. 72 ve3zy/m

  5. Where did you get the driver for the LD-C103? I can’t seem to get mine to work. On a Windows 7 or Windows 10 machine.

    • Mine came with a mini-CD but didn’t have to use it. The LD-C103 uses the common CH340/CH341 USB-Serial chip.
      I have zipped the contents and uploaded it for you:
      LD-C103 Drivers (3.21MB zip).
      There’s a setup.exe file in \CH341-Drivers\CH341SER_WIN; also there’s a Setup_Readme.pdf that shows how to install it and find it in Device Manager. Install driver first, then plug it in.
      73, –KV5R

  6. Hello again Harold,

    This is Greg, We5gnf. Enjoyed your article about the 7100 as I NOW own one also. I have only had it for about 3 days. Still have my IC 706 mk2g also. I find the rig easy to navigate through the menu as I once had a IC 7300. The menu on this rig is almost identical to the 7300’s menu. I findd the rig to perform wonderful for my purposes. Anyway, good article, thanks for doing the article. 73 es stay healthy and safe.

  7. I am new to amatuer radio and appreciate the walkthrough.. I have a question about the rf power at 100%..

    I am using qrp at 5w for antenna purposes and do not understand the leave at 100%. Can you explain the low audio drive part in more detail.Please!!!

    • Yes. When operating computer HF digital soundcard modes, the radio is in SSB and the object is to lower the computer audio level to reduce drive to the radio (thus, transmit power) rather than reducing it with the RF Power control on the radio. The RF control asserts ALC bias to reduce RF power, but the action of the ALC imparts some distortion to the digital signal you are transmitting, so it’s better to leave the RF Power control up but reduce power by reducing the audio from the computer, so there is no ALC, and thus, you have a very clean signal.
      Most digital mode software has a “tune” function that will emit a steady tone, and while transmitting that tone you can reduce the computer’s output level until the radio’s transmit power is as desired.
      73, –KV5R

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