The other day I had a request from Mike, VE3WDM to create a post on my setup running the KX3 as an SDR. Technically the KX3 is already an SDR (hardware components replaced by software through direct conversion receiver architecture)…so I think he meant to ask how use the KX3’s I/Q data in “SDR applications” (as the Elecraft Manual calls them). I will attempt to do this below.
Note: The setup below assumes that you are using a Window’s based computer (in my case I am using Windows 7) and that you have connected your KX3 to the computer using both the KXUSB (or KXSER) cable and the I/Q Output Cable (can be found in the KX3-PCKT Accessory Cable Set).
At a very basic level we will be using LP Bridge to connect radio to Na3P (panadapter) and to Log4OM (Logger). See image below. I have found this to be a very effective setup with the KX3. Those familiar with Larry Phipps’, N8LP, TelePost LP-Pan product will likely have already used LP-Bridge (I own Larry’s LP-100A…it is very good). My logger, Log4OM, is something new I found (also very good)…but you could substitute N1MM or any other logger here in the setup.
Step 1: Enable IQ output on Radio (see note below from Elecraft Owner’s manual…page 26).
Step 2: Confirm your COM setup on your KX3. Use the KX3 Utility to find your COM settings. From image below I can tell I am using COM8 with a speed of 38.4Kb.
Note: I use the KXUSB Cable to connect my KX3 to my computer.
Step 3: Setup KX3 Com Port using LP-Bridge. LP-Bridge was primarily designed to allow multiple applications to talk to the K3 at the same time. I suggest you start here first.
Using the image below you will note that under “K3 Com Port” options that I am selecting COM8 (the same port identified by the KX3 utility).
When you hit “Connect” after selecting your COM port you will notice that the “Rig Rcvd Text” field will begin receiving info from the radio. I find selecting the “Auto Connect” useful…once LP-Bridge is running it automatically connect to your KX3 (if your radio is powered on).
You will also see that I am using COM9 for “SDR Com Port” (we will use this for Na3P). You can set this up now or come back to it after you get into Na3P.
Notes: LP-Bridge creates these virtual COM ports when the software first opens (so it may take up to 30 seconds or so to get started).
Additional Notes: LP-Bridge provides “SDR Linking” (bi-directional Freq. and mode data), rig sharing (mirroring your KX3 so other software can talk to it), Hardware Output Ports (so your SteppIR beam has freq. info), and Auto Launch (to automatically launch your Na3P and other apps in sequence….I haven’t played with this feature yet).
Step 4: Setup of SDR Panadapter application. Below is my setup. It is pretty straightforward. For sound card setup please be sure to use Line In (microphone is generally not in stereo). I also use the MME driver (read about it somewhere as being the better driver for this application…but haven’t used the other drivers to confirm). Rig Type has a KX3 Option and you will again see the COM9 selected (I chose this value in LP-Bridge) with the other details like Baud found from the KX3 Utility.
Note: I prefer Na3P over HDSDR for various reasons (primarily because it reminds me of PowerSDR and has an interface that I am familiar with…but both have worked well).
*** At this point you could stop and test the setup by running LP-Bridge then starting NaP3 (in this order). Hit “Run”, in menu bar, of NaP3 to get it going. You will know if you are successful if you turn VFO A (big knob) on KX3 and see if Na3P tracks with you.
Step 5: Setup of Log4OM (or other software). By now you could likely guess how we set this up. In Log4OM I had an option to use Omni-Rig, which works quite well. Here is my current setup (see below).
In LP-Bridge I chose COM10 under “Virtual Com Port #1 (including Auto Create and Auto Launch options) and set modified the Progam or “Pgm” name to Log4OM. See below.
*** At this point you should stop and test the setup by running LP-Bridge then starting Log4OM (in this order).
Step 6: Run/Start Programs. Turn on your radio (KX3) then start LP-Bridge. Technically you could start LP-Bridge first, then the radio. Regardless, get LP-Bridge running before you start NaP3 (or logger). Once LP-Bridge is running (if you have selected “Auto Connect”) it will begin talking with the radio. At this point you could open and start NaP3 and Log4OM (or other logger).
When I first looked at a panadapter showing signals from my KX3 I immediately noticed two things: Noise and Mirroring. I also noticed another minor issue with NaP3 related to signal offset. I think the “noise” and “mirroring” issues are common problems in “SDR applications” so will cover them here.
Panadapter Noise: Being a Flexradio user I am not used to seeing a significant noise spike near (around) where my VFO indicator is. In my Flex 3000 with PowerSDR…any spike in the panadapter signifies a source of noise (birdies or other) and is a general nuisance if I happen to roll over to one and get it in the bandpass. I have come to find out that this spike is common to SDR radio architecture and can be reduced using a ground loop isolator (I found mine at Radio Shack). NI0Z has a great post talking about this and his setup with KX3 and HRD. I believe having an isolator in line really does help clean up the Panadapter. When I first connected the I/Q outputs to NaP3/HPSDR and other software the noise was quite bad (worse than shown below without). See below image of with/without ground loop isolator (I may not need it now). Also notice how the noise floor goes up slightly without it.
Mirroring (see image below). I can’t quite get my grasps on why this happens or how to correct it. In NaP3 I sometimes I can clear this up with a simple band or mode change. Sometimes is will correct itself (if I give it time). Or maybe its by doing both. If I come across something consistent I will update here.
Note: I have tried a few other SDR Panadapter programs with which I haven’t been able to remedy the mirroring at all. NaP3 seems to do a good job correcting itself after some time when I fiddle with changing bands, modes, etc.
NaP3 specific issue. Finally I do have a minor irritation with NaP3. Often, when I first start it up, I will notice that the signal is offset from where my bandpass is showing. See image below. In this case, I know the signal is in the band pass because I have tuned to it (and it sounds normal)…however when I view the station…he/she is showing up 1.5KCs.
I have also noticed, after a correction, that I can switch modes (CW to USB) and the issue will come back.
I have found in USB that I can simply move the IF Frequency Offset up by 10 and NaP3 will correct itself (even if I cancel out of the change). Below shows signal change immediately after I moved offset up by 10.
I have searched for ways to permanently correct this but have yet to figure this out (will post something here if I find out).