3dB Wireless Inc. and RF Designs SDR (Software Defined Radio)

Thank you for purchasing our version of the KB9YIG/WB5RVZ Software Defined Radio. Our design is based on the design by KB9YIG and WB5RVZ which is available in kit form, or assembled for you. We feel our design is suitable for many people in that it has the following benefits:

  • Our board is fully assembled and tested, possibly even demonstrated before you buy.

  • We use precision inductors, coils, and transformers for consistent high quality.

  • There is additional filtering on the antenna input against esd.

  • This board uses a Mini-USB connector.

  • Our board is powered off of the USB port to eliminate potential ground loops.

  • Our board has a crossover switch to swap left and right channels.

  • Our board has traces to cut to enable different grounding isolation schemes.

  • There are 2 LED’s on our board to show which band is in use.

Our version of the popular Softrock receiver is supported by popular software applications like HDSDR, WINRAD, FLDIGI, CWGET, and any software that works with the SIS-570 oscillator and the USB driver by PE0FKO. We would like to say we appreciate all Ham’s efforts in making an excellent kit and that we are proud to make our version, assemble and test it and answer any questions you have concerning our product.

For much more detail and links to trouble shoot or optimize your software environment and operation of this SDR you are referred to Google with the search terms “Softrock, KB9YIG, WB5RVZ and PE0FK0. These associated websites are full of helpful tips, information, and links to other software that will make you pleased to try out the exciting world of Software Defined Radios.


The SDR is a platform that uses a rf synthesizer to translate a piece of a desired radio spectrum down to the audio frequency range that can be sampled by a PC sound card. The Human ear can hear sounds from around 20 hz, to 20 khz. The soundcards in most PC’s record and reproduce these frequencies very easily. In fact, they can reproduce sound waveforms or electronic waveforms as high as 200 khz. By selecting the right target range of frequencies, the radio spectrum, as much as 200 khz of it, is reproduced in the computer. You can think of this as converting the range of 7.000 mhz to 7.200 mhz down to 0 to 200 khz. From this down converted spectrum, a modern computer can graph and process all this waveform, then apply DSP functions, to process parts of this spectrum into information our eyes can see and our ears can hear. This is what a radio receiver does, the new “trick” here is that the filters, amplifiers, codecs, and functions that used to be done in limited hardware are now done in Software. You no longer need to spend hundreds of dollars for fixed filter sizes, specific demodulators, and amplifiers. This is all done in software now.

How does a Softrock, or this SDR actually work?

The operator plugs the USB cable into the SDR, an antenna, and a stereo cable from the output of the SDR to an input of the PC Soundcard. The software for the PC to communicate with the SDR is loaded into the PC operating system, and the application used to process the waveform from the SDR is started. In other words, the USB driver is loaded into the operating system, the DLL is linked to the software application, and the software application is used to tune the SDR and process the waveform. The most simple way to say this is Plug it in, load the driver, start the radio software.

When everything is set up, the software application sends the primary center frequency of interest to the synthesizer chip on the SDR. The SDR samples the rf input by using what is called a Tayloe Detector. This detector samples 4 times per cycle of the RF and every other sample value is sent to the left or right channel of a sound card. This means that you are actually sampling the rf, storing it in a capacitor, then the PC digitizes this voltage in its soundcard (Left and Right channel audio). The PC takes this waveform and processes it using DSP functions to do whatever is desired. In a typical program the user would choose which part of this spectrum he wants to listen to, or process such as a fax, morse code, or voice. In fact, if you have the right software, you can decode any wave form you can receive. The added benefit of an SDR is that you have a Spectrum Display where you can see signal waveforms you are hearing, but just as important, you can see signals that are outside of the selected range of signals you are hearing. Most of the time this function is called a Pan Adapter or Spectrum Analyzer. They let you “See” the signal so you can select it. In addition to this, you now have a FREE RF Recorder. You can record a “Chunk” of spectrum and later play it back. Its like a DVR for your radio!

How do I make this SDR perform the best?

  1. You obviously need an antenna connected to the SDR. Any antenna matched to the band you are interested in will work. Some people use a multiband antenna such as a Windom. These work on multiple bands and are cheap. Some people use an antenna tuner to make their antenna perfectly matched to the frequency of interest.

  2. You need a STEREO sound card input. The MIC input is the best, but often it is MONO. The MIC input is usually more sensitive and has additional or better amplifiers. Sometimes the PC manufacturer uses the LINE inputs, attenuated and switched into the MIC circuit. Sometimes the manufacturer has multiple digitizer inputs instead of multiple connectors switched or multiplexed into the sound chip (digitizer). One of these selections, LINE or MIC will work the best. Some laptops do not have a external mic input on the chassis, it is on the docking station. Some laptops also only have mono mic inputs so if that is the case, an external USB sound card is in order. MONO will not work, 2 channel audio (STEREO) is required for a Tayloe detector to work.

  3. You need a fast sample rate in your sound card. The faster, the better. Cheap sound cards, or old cards will only sample at 40 khz. This means you can only display 40khz of spectrum. You can get sound cards that sample at 192khz. This means you can watch for (or record) all signals 100khz above and below the frequency you are interested in.

  4. You need high “Bit Precision”. If you sample at 40khz, and that sample is an 8 bit value, this means the value can be from 0 to 255. If you have a 16 bit value to work with, you increase the number of discrete voltage levels you can express to 0 to 65,535. This means you have very high fidelity. Hi fidelity is not useful for human voice, but it is very handy for digital signals, specifically PSK.

  5. You need a quiet rf environment, isolated from your antenna. Your computer generates RF noise, in the RF spectrum. In fact, this noise is even in the sound card circuits, the area around your SDR, your cell phone, your wireless mouse, cordless phones, etc etc. If you can put your SDR in a metal box, ground it, and shield the cables, or use a desktop computer – instead of a laptop, you will have much less noise being picked up by the SDR. One technique is to install the SDR in a metal box and mount the box away from the computer equipment. Then use a shielded USB cable to get to the SDR. You are still going to have RF in the sound system if your sound system is on a motherboard. You could use an external USB sound card, such as a Sound Blaster USB, in a metal box, grounded. You may still have noise inside an external sound card but not nearly as much as a laptop, because there is not so much going on in that external box compared to the computer.

  6. The last thing on this list you need to do is to calibrate the sound card. The SDR works by using the left and right channels to subtract one channel against the other and derive one signal and reject the other “image” of that signal. This is usually done with filters in a conventional radio, but is done with software in a SDR. In an ideal world, the left channel is exactly like the right. But remember, sound cards are made for sound, not rf. With a sound card, the human ear cant tell if one channel is 1 microvolt lower than the other (amplitude), or if the sound on one channel is slightly delayed from the other (phase). The ear can’t tell, but when you add an out of phase signal or incorrect amplitude signal, the result is distortion. This distortion in an SDR will show as duplicate and distorted images of the target signal in the display. If you calibrate the amplitude and phase of the sound card, you will get maximum image rejection. If you don’t, you will think your SDR is performing poorly. The frequency of the oscillator is actually a minor concern. It can be adjusted by tuning to WWV at 5, 10, or 15mhz and telling the SDR what the target frequency is versus what you had to tune to get it. The DLL will be adjusted to take the difference and apply it to what is displayed in the future so what you see is the actual frequency.

  7. Maybe there is one more thing… You need to specifically understand how the sound mixer and sound devices work on your computer, and how to operate your computer. You need to know how to turn off the unused inputs (reduces noise) and select sources to process. An example would be if your SDR is plugged into the MIC input of an external Soundblaster card, you would turn off the LINE inputs. You would also need to tell the SDR program to get its signal from the external device and not the internal PC sound card. You also need to keep other things from mixing into the SDR signal. It is also very helpful to know that the WAV channel is the sound you hear. This is frequently the same channel that goes to a program such as FLDIGI or CWGET. These programs usually process the sound coming out of the pc sound card before it goes to your speakers. The Windows error beeps and such also use WAV, so you might want to turn off those features in your “Sound Scheme”. The key thing here is that not understanding your computer is no excuse to blame the SDR, it only does what it is designed to do.

If your SDR and computer are ready to go, the process to install the software is detailed more specifically on the KB9YIG websites but a disk is included to get you started. Here are brief Instructions.

  1. Plug the Mini usb cable into the SDR and then plug the other end of the USB cable into your PC. If the driver loads automatically it will show as a device in the Windows Control Panel, System Icon, Hardware Tab, Device Manager Button, Libusb-win32 devices section as a device called “SoftRock40 – Si570 Control peofk0”. If it asks for the driver you need to install it. You do this by accessing the cdrom on your computer and copying the file PE0FK0-USB-Driver-Installer to your system and running it. This installs the driver required to talk over USB to the SDR. The program installs to c:\PEOFK0_Driver.

  2. Install CFGSR. It is on the cdrom and labeled setup.exe. After installation it will leave an Icon on your desktop labled CFGSR. Start CFGSR by double clicking on it. Check the USB tab, a device should show up in the bottom window, if it does; it means the driver and the SDR are working. Click the TUNE tab. Note that a little light labled FL1 is on and FL0 is off. This means Band 1 is selected. Select 1 MHZ in MOUSE WHEEL and roll the wheel until the frequency goes under 4 mhz. FL1 and FL0 will light. This means band 0 is selected. Above 8mhz, FL1 is off and FL0 is on. This is band 2. Above 16 mhz is band 3 and FL1 and FL0 are both off. What you have done here is verify that the USB interface and the atmel computer on the SDR are talking and band pass filters are being switched in and out. If you were to dial up a frequency on a nearby radio and you get an antenna closer to the SDR, you would be able to receive the RF oscillator. Or you could probe with a scope. Or rest assured the SDR was tested and delivered working. You could go to all the other tabs and write down what is set, before you go changing things. You can also read up on the PEOFK0 software. Close the application by clicking the usual close window button.

  3. Install the HDSDR software. When installed, a panel comes up asking you to make sure the Sound Card Selection is correct. Since this is a receiver and not a transceiver, you can only select the RX input signal source, and the RX output source. On some systems it will say “XYZ Brand Audio” in both windows. This means the Windows Default Audio IN and Windows Default Audio OUT. These are set in the Control Panel in Windows. You have to figure your particular options since it is different in all computers. You will usually have a clue and there will be listed multiple options if you have secondary sound cards in the mix. Click OK and the panel will go away.

  4. Click the ExtIO button in HDSDR. Its right next to the TUNE Frequency. If you get an error message saying “No Hardware Specific EXTIO-DLL found”, It means the HDSDR program doesn’t know how to talk to the USB driver. To enable this, copy the dll from c:\Program Files\CFGSR\ExtIO_Si570\ExtIO_Si570.dll to C:\Program Files\HDSDR\*.* (Copy and paste works for me). This will make the ExtIO button in HDSDR turn a different color. This technique would also be used with WINRAD or FlexRadio software to let the software communicate with various receiver dll’s so the SDR software developer can let various SDR manufacturers write their own software.

  5. Connect a 3 conductor shielded MIC cable from the SDR to the LINE in or MIC jack on your sound card. Some sound card manufacturers will put up messages to tell you something just got plugged in. The goal here is to assign the audio connector used by the output of the SDR to the audio connection used for sound input.

  6. Click the START button in HDSDR. You should notice the noise level increase and sound come out of your speakers, which should obviously be plugged in, turned on, and turned up, and not muted.

  7. Tune the LO to 7.200.00 and you should see the Hams talking. Play around with clicking on various signals in the middle window and try USB and LSB. Note how the frequency that you tune is close to the LO frequency. Also note that if you are looking for a specific frequency band, choose a frequency that is a little lower than what the target signal is on. Remember that the SDR LO sets the center frequency of the target spectrum. The radio works best if the LO is set to the bottom of the spectrum you are interested in. For example with a bandwidth of 48000, and a LO of 7.024.000, the displayed spectrum will be from 7.000.000 to 7.048.000 (48khz). If you have a quality soundcard you may be able to change the bandwidth to 192000 and see close to 200khz of spectrum, selecting anything that is active. Don’t forget that the more spectrum you watch, and the faster the screen draws, the more work your computer has to do. If your performance is lacking, close down unused programs, make the bandwidth smaller, and basically make less demands on the CPU. Or get a better CPU.

  8. When you use a mouse with a scroll wheel to make the entire spectrum move up or down, you may notice that some signals “Go the wrong way”. I.E. as you tune up, some signals,seem to follow you. These signals criss cross the genuine signals on the screen and are basically duplicates. These are “Images” and they are there because your audio inputs are not calibrated to perform well. This could be due to cable problems such as a little more resistance in one wire vs another, or the gain out of the amplifiers not being exactly the same. It could also be due to component value variations in your computer or the SDR. Either way, they are calibrated out by tuning the LO a strong, stable, unmodulated carrier, or if you cant find one tune the LO to 9.990.000 and TUNE the demodulator to the WWV signal at 10.000.000 in AM mode. If you use ECSS, the SDR will be tuned and lock on to the WWV signal (get close to the real frequency first). You will probably notice an “Image” at around 9.980.000. This is what we need to eliminate. Click the OPTIONS button and select RF Front End Calibration. Click Calculate and the software will decide how far off, actual is from desired, and display a correction amount. Click OK and the correction will be stored. You will notice that the TUNE frequency is now 10.000.000. The frequency is now calibrated and it is time to calibrate the levels. Click OPTIONS, then Input Channel Calibration for RX. While watching the Image, click on the + button next to the LEFT and RIGHT Samples delay. Go back and forth between settings and leave the setting selected that reduces the Image the most. Next slowly slide the RAW slider for Amplitude, up and down, to minimize the Image further. Then try the RAW Phase slider, slowly left and right to reduce it even further. By adjusting the RAW sliders and the FINE sliders alternately, you should be able to reduce the Image to where it is not noticeable or is barely noticeable. If after adjusting for a while you do not have success, switch the switch on the SDR from II to X. Then try again with the sliders. The switch swaps the Left and Right audio so you can try again. Some software lets you swap the audio lines (I and Q channel) from the options menu. When you get the Image reduced the most, you can click the OK button and the settings will be saved. The object is to remove the Image by adjusting its Amplitude and Phase relating one channel to the other. It helps if the signal you are adjusting with is not varying wildly due to ionospherics, or is not AM modulated by a broadcast. So once you can figure out how to identify an “Image” of a stable RF carrier, put it 10 khz below the center of the display (20 khz below the Source carrier). Static crashes don’t help, and neither does AM or fading band conditions so if you don’t succeed, try again when you find a good band opening and a stable unmodulated carrier. If all else fails, you can try an additional sound card, or an external sound card. It is not uncommon for an SDR program to be the first program to test the sound inputs in a never-before used configuration, thus revealing a weakness in the PC sound system. This inexpensive SDR relies on your computer resources to provide the hardware that is not included on much more expensive SDR’s.

With a properly installed SDR and good operating techniques, you should derive much enjoyment from your purchase. This SDR is the first version our company makes and a VHF/UHF version is planned. The SDR you received is also capable of being used for LF instead of HF but it must be reworked as the filters are all different, it is the same circuit board but with different filters.

Many people ask if the SDR can be used as a PAN adapter to monitor the IF of a typical receiver. Yes it can, the signal is typically at a frequency of 10.7 mhz and is available on the back of the receiver. By tunning the SDR to 10.6mhz and using a 200khz bandwidth, the spectrum will show 200khz of spectrum with 10.7khz in the middle. This may not be the best place because the center of the display is where the Image rejection is weakest due to deficiencies in the sound card and such. The spectrum can be offset another 10 khz and the tuner will present the signal of interest in the desired manner, in the center. There is something to be aware of though and that is to remember that the RF from the LO in the SDR is very close to 10.7 mhz, and this RF will go into the back of the radio and heterodyne with the oscillator in the radio and produce all sorts of havoc. If you want to use a SDR as a Panoramic display, it would be advised to install an Isolating amplifier and bandpass filter between the two radios. Another technique would be to move the 10.7 mhz IF to another range of the spectrum where interference will not result. This particular SDR is designed to stand alone on an antenna wire and tune from 1.8 mhz to 30 mhz and is optimized for 4 bands of 4 mhz, not 1 band of .2 mhz. It is certainly possible to do this with an SDR but the cost is kept low so this feature was not specifically designed into it.


Q: My spectrum comes in and out, is full of crackling sounds and my computer locks up or freezes.

A: Your sound card, or probably your input jack is damaged causing a loose connection like a cable broke. Test again on another computer or another sound card.

Q: I can’t get my Images to go away.

A: You should be able to get about 70 db of difference. If not, there is probably crosstalk between the left and right channels in your sound card. Try a better audio cable, a different sound card, a lower gain setting in the sound mixer, or a different computer.

Q: I can get an Image to be attenuated 70 db, right next to it is a signal that wont go away.

A: Maybe that signal is supposed to be there. Tune up in frequency and see if the signal goes lower at the same rate and direction as the others. If it does, it is a signal on that frequency and you are confusing it with an image. An Image will always go “The wrong direction”. I.E; If you are rolling up in frequency the signals will slide to the right as the signals you are bypassing slide to the left. If you see signals cross each other or go in the direction you are tuning, it is an Image.

Q: I see signals I don’t think are really there. They keep rolling by and appear to be duplicates.

A: These are most likely RF in your audio system or sound card. They could also be rf generated by your computer. Note the frequency and signal characteristics, write it down, and then change computers. See if the exact signals are still there. Another thing you could do is unplug the audio cable – anything on the display after unplugging the audio cable is from your computer and not the SDR. BTW: You will see some transmitters that move up or down in frequency. These signals are actual communications, or equipment designed for this purpose such as Ionospheric Sounders, or Spread Spectrum Transmitters.

Q: My laptop is super- duper and has great sound, but I have all sorts of trash in my spectrum.

A: It has great sound, but it is being asked to process waveforms much higher in frequency than you can hear. The designers limit additional circuitry, shielding, and such to save weight, power, and cost. These deficiencies show up as bumps in the spectrum display. Also, laptops don’t have a 3 prong cord and the chassis ground is often not the same as a signal ground. This makes rf shielding tricky. Try an external sound card or a desktop computer, or a different laptop.

Q: When I move my mouse, I get weird things in my spectrum. But only when I move my mouse.

A: Cordless mice make RF that gets into the SDR. The SDR should be in a metal box, or shielded, or further away from the computer. You could also use a corded mouse and unplug the wireless sensor.

Q: What else causes interference? I don’t get it on my ham radio…

A: Your ham radio has a metal box around it and cost a whole lot more than your SDR. If you were to invest the same amount in your SDR shielding you would achieve similar results. Your radio probably can’t display a spectrum, process rtty or cw, and display kitten pictures, while ordering a pizza – it is a different tool and it does different things, some are the same as an SDR, many are not. Other things that cause interference include the DVR upstairs, the i-pod/i-pad next door, the LCD tv on the other side of the wall, the calculator next to you, and your monitor (that is even turned off). If it has a microcontroller in it, it makes and uses rf energy – in the hf spectrum. Try shielding, moving, unplugging, and upgrading offending devices. The SDR is designed to pick up and process RF energy. It is very sensitive so you must use your ham skills and figure out the cause and implement a solution.

Q: Is there a warranty?

A: an equipment protection plan is available for $20, but at the current sales price there is no warranty. You do get a demo that the SDR you are purchasing is working at the time of sale, and help with the SDR itself.

Q: I am having problems installing the free software that you didn’t write on a computer you have never seen at a location you do not know anything about. Can you help me?

A: At this price point it is assumed you have a standard setup with typical skills. If you are outside this definition, support is available at an additional cost. We are making a product that a person can “puzzle” their way through the installation, and if needed, maybe with the help of a friend or mentor, usually using the commonly available tools. Although this subject is “New”, it isn’t “Difficult” and many many people are able to succeed without any help whatsoever. Some people need a lot of help and this is available at an added cost but you only get so much for the price you pay.

Q: Okay, I am not a ham, or a computer operator, but the SDR is really something I want to learn, who do I call? Also, I plugged it in backwards, where do I get it fixed?

A: This product is sold by

3dB Wireless Inc.

144 Industrial Park Drive, Suite A2

Waynesville NC, 28786



We do not have a store front that is designed for walk-in customers and we usually sell direct mail, on our website, or at Hamfests and expositions. Currently our products are made in the US with components sourced globally. We also have other products and other services. Everybody at 3dB Wireless is a ham.

Please call or email with specific questions.