Fake CM108 USB Audio Devices

While working on some projects for APRS, I had the need for some more USB audio devices. LONG ago, I had purchased some “3D Sound” USB devices on eBay. These old devices used a chipset (Tenx TP6911) designed for “headsets” and have a fairly poor ADC, with a max of 24 KHz resolution (pretty low). The C-Media 108 chipset has long been considered a decent value chipset, so I went to eBay to find some CM108 based USB devices. I found a listing that was explicitly stating that it had this chipset.

eBay listing for CM108 USB Audio chipset devices
Clearly claims to be CM108 Chipset… but what is it really!?

I had heard about fake chips being out there, and knew that it was a strong chance of this being the case. But hey, these are plenty cheap and it was a low risk experiment!

I plugged one into my Raspberry Pi and ran dmesg

[  136.786975] usb 1-1.3: new full-speed USB device number 3 using xhci_hcd
[  136.933737] usb 1-1.3: New USB device found, idVendor=08bb, idProduct=2902, bcdDevice= 1.00
[  136.933757] usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[  136.933774] usb 1-1.3: Product: USB PnP Sound Device
[  136.933789] usb 1-1.3: Manufacturer: C-Media Electronics Inc.
[  136.956376] input: C-Media Electronics Inc.       USB PnP Sound Device as /devices/platform/scb/fd500000.pcie/pci0000:00/0000:00:00.0/0000:01:00.0/usb1/1-1/1-1.3/1-1.3:1.3/0003:08BB:2902.0001/input/input0
[  137.017913] hid-generic 0003:08BB:2902.0001: input,hidraw0: USB HID v1.00 Device [C-Media Electronics Inc.       USB PnP Sound Device] on usb-0000:01:00.0-1.3/input3
[  137.110053] usbcore: registered new interface driver snd-usb-audio

So far, it seems to be OK. dmesg is clearly saying this is a C-Media device that has been detected. Next I ran lsusb:

pi@raspberrypi:~ $ lsusb
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 003: ID 08bb:2902 Texas Instruments PCM2902 Audio Codec
Bus 001 Device 002: ID 2109:3431 VIA Labs, Inc. Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
pi@raspberrypi:~ $

Hmmm, that doesn’t look like C-Media! It clearly shows that it is a TI PCM2902 chipset! Well, let’s try another command, which is likely looking at similar datapoint:

pi@raspberrypi:~ $ inxi --audio
Audio:     Device-1: bcm2835-audio driver: bcm2835_audio
           Device-2: bcm2711-hdmi0 driver: N/A
           Device-3: bcm2711-hdmi1 driver: N/A
           Device-4: Texas Instruments PCM2902 Audio Codec type: USB driver: hid-generic,snd-usb-audio,usbhid
           Sound Server: ALSA v: k5.4.83-v7l+
pi@raspberrypi:~ $

If you look at the PID and VID from the dmesg and lsusb outputs, it shows “08bb:2902”. Doing some independent Google searches and you’ll see that it is indeed referencing the PCM2902 chipset.

So, we seem to have devices that are PCM2902 and NOT the CM108. Presumably, the eBay seller altered the firmware to display the C-Media in the labeling. If someone plugs these into a Windows machine, they would just see the C-Media labeling and be unaware of what is actually being used. Because most USB audio devices use a universal standard, there isn’t a driver confusion that would have made it obvious.

How do these chipsets compare?

C-Media CM108Texas Instruments PCM2902Tenx TP6911
DAC Sampling Rate48 / 44.1KHz48 / 44.1 / 32KHz48 KHz
ADC Sampling Rate48 / 44.1KHz48 / 44.1 / 32 / 22.05 / 16 / 11.025 / 8 KHz24 KHz
DAC SNR93 dB96 dB?
DAC Dynamic Range92 dB93 dB?
ADC SNR90 dB89 dB?
ADC Dynamic Range88.5 dB89 dB?
Resolution16 bit16 bit?
CM108 vs PCM2902 vs TP6911

Based on these specs, the PCM2902 isn’t a whole lot different than the CM108. There are certainly other things to consider when comparing. I included the TP6911, as that was what I was initially trying to replace and improve. Clearly either of the PCM2902 and CM108 are going to be better. I couldn’t even find more details or specs on the TP6911, even on the official datasheet!

For now, I plan to just use these PCM2902 and see how they perform. They may not be what I expected to receive, but they should get the job done.

APRSHOG Alert and Notification

During my lunch today, I was doing some testing with setting-up a receive-only APRS iGate. While I was watching the logs and troubleshooting a problem, I saw my callsign whiz by the screen. Oops! I had received a phone-call as I was getting out of the car, and forgotten to turn-off my HT! I quick went over to the NorCal APRSHOG site to see how “bad” I had been. Sure enough, I was already listed at #25 in the ranks at the time. I quickly ran-out to the car and powered off the HT.

This was all unintentional, and I am very conscious of the APRS traffic congestion, which is why I was working on setting-up a receive-ONLY APRS iGate. I decided I needed to find a way to try to monitor and make sure that I am alerted if this happens again. Next time this happens, I may not be watching APRS logs.

I wrote a little script that I called “aprshog-alert” to run on my Linux server. The script takes in my CALLSIGN and the threshold I want to be alerted on.

It will email me if my APRS callsign is ranked between 1 and 25 (considered a hog!):

[root@host ~]# ./aprshog-alert KI6ETL-9 25



RANK=`wget -q $SITE -O – | grep $CALLSIGN –before-context 1 | head -1 | sed -e :a -e 's/<[^>]*>//g;/

if [[ -z “$RANK” ]]; then
elif [[ “$RANK” -le “$LIMIT” ]]; then
echo You are on the APRSHOG list at a rank of $RANK . Check on $SITE | mail -s '# APRS HOG ALERT #' $EMAIL

I am confident that there are more elegant methods to accomplish this, but I wanted something usable immediately.

The final step is to add this as a cronjob on my Linux system, to run on an hourly basis. I don't want to abuse the APRSHOG site, so more frequent would be inappropriate.

73’s HAMigg, We’ll See You Another Day

This is old news now, but I felt compelled to post, since it has been a year since I have posted.

On June 18th, 2007, I posted about a new and exciting ham site called HAMigg.de. As of February 25th, 2008, HAMigg.de no longer exists. DL6KAC explains why the site was taken down, on his blog.

I personally am sad that the site closed, but understand his reasons. Really, I just think the ham community wasn’t quite ready for it. I had supported Christian by purchasing hamigg.com and having it forward to his site. I’ll hold onto the domains with the hope that someone can pick up the torch again and see if it will be more accepted.

CQ-CQ-CQ this is KI6ETL/AG

Last night I successfully passed the Element 3 exam for the General License. It has been just under a year since I got my Technician License. In this short period of time, I have learned a lot and met a lot of great people. I prepared for the exam by taking the FARS General License Class and we met one night a week, for 6 weeks. I'm sure we would have spread the class out longer, but there was a desire to get the tests taken before the July 1st question pool change. I'm not sure of the actual statistics, but it seemed like most people passed the exam. Now I need to decide what kind of HF rig I want/need.

Ham Radio + digg.com = HAMigg

It appears as if DL6KAC of ham-blog.de has come up with an interesting idea. He has created HAMigg, which is a social bookmarking site like digg.com but dedicated to ham radio! I think this could be very successful, as long as people get the word out. The name of the site doesn't exactly roll off the tongue, but gets the purpose across to those familiar with its inspiration. I'll be watching the site, and likely submitting to it as well.

Kenwood – Busy with RoHS

After writing “Kenwood Amateur Radio Division in Trouble?”, I decided to make a call.

I just spoke with Phil at Kenwood USA. I had called him, because I’ve been curious if a new 1.2Ghz HT would be coming out anytime soon. Unfortunately he said that their current task list is as such:

– Revampin current product lines to be RoHS compliant. One driving force to be RoHS compliant, is to be able to sell some of the equipment in Europe.
– Finish work on a new HF rig and release it (~1yr out).
– Start working on other new equipement.

Overall he said that I shouldn’t expect a 1.2Ghz radio for another 3 years. Phil’s suggestion was to use SkyCommand (or similar) from my HT, to connect to a TS-2000 at home (if line-of-sight was available).

An interesting side-note was that originally the Kenwood TH-F6A was going to be a quad-band with 1.2Ghz. Apparently the engineers were not able to get the radio to be quad-band with anything more than .5 watts on 1.2Ghz. The team decided to remove the quad and leave it as a tri-band, which ended up being one of their best selling HT’s ever.

I am confident that RoHS is important, and a good thing for Kenwood. Unfortunately this may cause them to slip behind the competition in the process. At the same time, it may provide them the excuse to skip a “generation” of technology.

Kenwood Amateur Radio Division in Trouble?

Michael S. Higgins (K6AER) wrote an interesting article on eham.net regarding the possible demise of Kenwood’s Amateur Radio Division. I am personally very happy with my Kenwood HT, and would be very sad if they closed the division. K6AER’s comments do seem valid, and he certainly has some very specific things to point to. I can only imagine that it is a difficult market to cater to, since development costs are likely high… small market… and high consumer expectations.

I doubt that this is really a problem just for Kenwood, but for all the manufacturers. The amateur radio is not exactly the booming hobby it has been in the past. I would imagine the best way to solve these issues is to get more people involved with the hobby, and for all ham’s to personally contact the manufacturers to show interest.

Read the article on eham.net
**UPDATE** Read “Kenwood Busy with RoHS”

Digipup: A Linux live CD for amateur radio

I'm not a huge fan of Puppy Linux, but it does have its place in the Linux world. In my opinion they have strayed too far from the standards of where config files and binaries are located on other distros.

Regardless of the above feelings, a new Puppy Linux distro has been created called Digipup. Digipup is designed for use by Ham Radio ethusiasts. The great advantage of this method of doing things, is it takes up very little space. A person could have the entire distribution installed on a cheap USB “thumb-drive”, which can be transported with extreme easy and durability.

Review / Read More

Ham Domain

Fred Atkinson (WB4AEJ) has posted an article regarding having “Ham Domain”, which is essentially what I have here at www.ki6etl.org. I obviously believe it can be a fun and interesting addition to the Ham Radio hobby. In his article he highlights QSL.net, which offers free web-hosting to “ham’s”. I obviously have done something a little more complicated, but this is a great option for people who do not care about making things fancy. I recommend checking out the article and make use of this great service.