Now for the part we all have been waiting for. How well does the DX-SR9 as an SDR transceiver? The answer in a nut shell is reasonably well with a few caveats. SDR reception is achieved by using the IQ jack on the back of the DX-SR9 and plugging in a 3.5mm stereo cable to the stereo mic / line jack of your PC’s sound card. The bandwidth of the IQ jack is approximately 48KHz. These means that you will see 24KHz of the band on either side of the center frequency. While not as large as some dedicated direct sampling SDR receivers, the 48KHz is adequate for Amateur radio use allowing you to see activity close to your operating frequency. Transmitting is achieved by routing audio from you PC’s speaker out via a 3.5mm cable to the DX-SR9’s rear MOD jack. Keying, Frequency settings, Mode, Power settings, etc can be controlled by your PC through the use of Alinco’s ERW-7 cable (Approx. $60) or equivalent. The ERW-7 cable is basically a USB to serial converter that terminates in a 3.5mm stereo jack.
Setting up the DX-SR9 for SDR
As mentioned above, you will need to use two 3.5 mm stereo cables to connect the DX-SR9 to your PC’s sound card plus the ERW-7 for computer control to a USB port. If they don’t automatically install, you may have to download and install the drivers for the ERW-7. Using Windows 8.1 the ERW-7 chipset drivers auto installed and worked fine. One thing you might need to be aware of that the IQ output needs to be connected to a STEREO input on your sound card. This is important for the SDR function to work correctly. If you have a desktop PC in the shack, this probably won’t be a problem. If you have an all-in-one desktop computer or a laptop, you maybe out of luck. A large majority of these systems on have a mono mic jack available for audio input and this is not going to work. However, the answer is to add an inexpensive USB sound card. This is a great idea anyway, since you can pretty much dedicate that device to using the DX-SR9 and you won’t have to recalibrate the sound settings for the DX-SR9 after changing your PCs audio settings for another application. The DX-SR9’s audio input requirements are not very demanding, since the most they require is a 48MHz sampling rate. Going any higher won’t gain any more bandwidth from the DX-SR9. Just be sure to check the soundcard’s input sample rate settings in your PC, since they are usually set less than 48MHz. Several USB audio adapters that were on hand were tested with the DX-SR9 and as expected they worked fine with a couple of exceptions. One USB audio adapter that was advertised in the specs to have a stereo mic in wound up to actually only have a mono input. Another adapter would not work correctly with the DXS-SR9 and the included KGTRX software. The problem turned out to be after some head scratching is that the DX-SR9’s IQ output is inverted. With SDR you can always tell when this is a problem because USB and LSB modes are reversed. KGTRX handles the IQ correction internally so there is generally no problems with the majority of sound cards. The problem with this particular USB sound adapter was that out of the box it’s left and right input channels were switched causing much confusion. It is important to realize that the DX-SR9’s IQ output is inverted when being used with 3rd party SDR software. Fortunately most SDR applications have a setting to let you switch Left and Right inputs via the software to compensate for an inverted IQ input. Of the inexpensive external soundcards tested, the best performance was achieved by the Creative Soundblaster X-Fi Surround 5.1 Pro USB Audio System with THX SB1095. The X-FI has a very low noise floor and provides very nice quality audio output making the DX-SR9 very pleasurable to listen to. You won’t use most of the features available on this card and you probably won’t to be sure that some of the DSP features are turned off. On the other hand, you might find some useful such as the equalizer function. The X-FI can also sample at 96MHz, but it won’t gain you much of an advantage since the DX-SR9’s IQ is pretty well locked in at 48KHz of bandwidth.
Connecting a microphone to the DX-SR9 can be as simple as plugging in an cheapo USB mic / headset (remember your soundcard mic input may be taken up by the DX-SR9’s IQ input) to a high quality USB microphone such as Blue Microphones Snowball USB Microphone (Gloss Black). One thing to realize, is that there will be a slight delay in the transmitted audio due to latency of processing the audio. This shouldn’t be a big problem for most modes except maybe for CW. If you prefer using studio microphones you might want to consider using one of the professional external sound cards that offer XLR inputs and Phantom power for condenser microphones. It’s pretty much up to you how you want to customize the output audio even with using 3rd party sound processing applications. However, it would be definitely handy to have a second HF radio around to allow you to tweak your audio settings and see what the DX-SR9 would potentially sound like over the air. As mentioned before, there will be some latency in the transmitted audio depending how fast your PC processor is. Usually the latency only involves a few milliseconds. On some of the higher end audio interfaces the latency can be reduced to 0 if your PC can handle it. You will know if it can’t by hearing crackling or stuttering in the audio.