Soundcard SDR Basics, SDR Sharp

Connect to the Computer.

The first thing with soundcard SDRs is to connect the audio lines to a computer Check this link.

Most SDR programs will replay audio files so you may see how they should work. A few links here Files to Test Software Without a SDR You will probably just want to get on with testing..

Install and start a SDR program.

HDSDR, on this page is one option.

It supports transmit with a Softrock and other SDRs. From time to time it is updated.

SDR Sharp Tutorial

**2021 Now a good guide linked on the Airspy site.**

An easy to setup receive program is SDR# Go to "Download"

Read the other pages, for plugins and other information.

The downloaded zip contains all files, put them in a working folder, NOT in "Program Files".

Then make a shortcut to SDRSharp.exe. (Or just double Click this file.) Run "install-rtlsdr.bat" to setup for the RTL dongle.

September 2015 NOTE Windows XP is no longer supported link to last XP version here. EARLIER METHOD:- install.bat will not work, it just downloads the new versions and may overwrite your old version, only the old files already on your computer will work.

My notes below may help but relate to early versions.

An occasional fault stops SDR# from starting. Note there may be a crash report in the SDR# folder maybe this will help.

I am also running Win 7 X64 and had the same problem on my newly-installed SDR#. To fix it, just go to the MS link at and run the script to auto-install "European Union Expansion Font Update". It adds the Arial Regular font to your system quickly and at no cost. 8>)

A Funcube Dongle will work without any trouble.

This installation now works for the RTL dongle. A summary lower down this page. RTL Dongle)

For it to work with a Softrock For a Si570 controlled Softrock make sure the USB is plugged in.

Select "Softrock / Si570 (Or whatever radio you have.) from the drop-down. Click the +Audio tab and select the input from the Softrock, other soundcard SDR or FCD. (Not required for the RTL) Select the output to the speakers.

For crystal controlled SDRs select Other (Sound card), tick "Shift" and type in your crystal frequency in Hz. For example 40m 7040000 You would type the exact frequency.

Click ► "Start". Other settings may be left untouched, they do not need adjusting for general use.

If the display is not like mine below then there is a problem. SDR# is not connected to the soundcard or SDR. The incorrect one may have been selected or another program might be using it

If you have problems look below, TROUBLE?

Later versions of SDR# may look a little different. SDR# has collapsible panels on the left so the display is small enough to fit a netbook screen.

There is no longer a display of the centre frequency.

The SDR# window can be made much wider, and taller (or smaller) by dragging the borders. It may be made to span across two (maybe more?) monitors.

"Start" ► should start reception. Select mode. The "Gear" symbol next to ► will open any radio-specific configuration. Drag the grey area to tune, (this extends into the waterfall) use the mouse wheel for fine tuning. "Step size" determines the mouse wheel steps. Drag the scale to move up/down the band. Click on the display. The Zoom slider focuses on the selected frequency.

Click on the top or bottom of the tuning digits at the top.

Place the cursor over the first digit. Type in the frequency - Return key. You need to type leading zeros but not following zeros. Here I typed 014443 - Return.

If the cursor is placed over the second digit then a leading zero is not needed.

Copy and paste, arrow keys, enter, backspace and tab are all accepted while the cursor has focus.

The Zoom control does just that, gives a closer view if part of the spectrum.

Contrast adjusts the waterfall to your liking.

Speed adjusts... speed of the waterfall and spectrum.

Filter width, drag one edge of the grey area, use the arrows or type into the box.

Later versions have a Frequency Manager.

Radio Tab

If you get USB instead of LSB, (tuning will also be reversed) tick the "Swap I & Q" box.

Tick the "Correct IQ" box. Normally this should be left ticked so automatic image reduction is enabled.

"Snap to Grid" rounds up the frequency when clicking on the scale, determined by "Step Size".

"Shift" Used for fixed frequency SDRs and when a converter is used.

Audio Tab

Volume - adjusts output.

"Sample rate":- Only use rates you know your card is able to support. I think I'm safe to say ALL will work at 48KHZ.

"Filter Audio" reduces noise. If you are going to pass audio to a digital decoder then untick this box.

"Latency" may be adjusted if you have clicking on the audio. Normally not needed.

June 2014 from Yousseff:- A lot of stuff is hiding behind the "Filter Audio" option. In the case of AM demod, it's the DC removal and the audio BPF. In both cases the AGC does work on the detected carrier. To resume it a bit:

source -> DDC -> Main filter -> (optional plugin filter) -> detector -> AGC -> DC removal (IIR HPF) * -> Audio BPF * -> soundcard

The stages with (*) are bypassed when "Filter Audio" is checked/

When disabling the filtering makes sense? I'd say for digital amplitude modes (ASK, OOK, etc.)


You may experiment with AGC settings using settings in this tab.

FFT Display Tab

Has many more display adjustments. "Resolution" slows the display to give better resolution.


IQ baseband or audio. Wav files saved in the SDR# program folder. IQ playback selected by the input drop-down, top left.

Frequency Manager.

Store your frequencies here in separate folders.. Click "New" You may type a folder name in "Group" to make a selection of groups.


There are several "Plugins" available. Popular with RTL users are scanning. Look here for links, this site is mainly devoted to RTL installation and usage. June 2014 SDR# has been updated, only current plugins may be used. See the Yahoo group and the Wiki.

CPU Usage.

To reduce the load on slow computers reduce "Speed" to a minimum and use minimum FFT Resolution (512). On my computer these two settings make a great difference on reported CPU usage. I find other settings do not make too much difference. If you compare with other SDR software they will also have these kind of adjustments. A direct comparison is not easy!

An older page that describes the side panels in detail

Once a Funcube Dongle has been setup it is a quick way of getting that working.

NOTE:- The installation instructions below are only needed for use with the RTL dongle.

RTL Dongle

September 2015 No Windows XP support. Download SDR# as above. Unzip into a suitable folder and execute install-rtlsdr.bat

Zadig, the utility that installs the RTL driver is inside the downloaded package. Look at with link to "Usage" instructions.

This should be enough, a few links and notes at the bottom of this page may help if you have problems.

An old page showing operation of an older version of SDR# Ignore the old installation method but most of the rest is still relevant. Operation shows only the RTL dongle. a link to a PDF.

The older version had a different tuning procedure, June 2014 this is no longer available.

Below an older version. Jan 21 2013. (This version is best not used with the RTL dongle unless you know how to configure it.)

Type into "Frequency" but this only works within the bandwidth of the soundcard.

Si570, move up and down bands by altering "Center Frequency".

Change this by typing into the "Center" box - Enter USE " , " COMMA as a SEPARATOR.


If you have a crystal controlled Softrock select "Other Front End" and type in your crystal frequency in the "Center" box - Enter (Return key). For example 3778000 for 3.778MHz.

Other tuning features as the later version above.

Some tips here for using dongles with SDR#

The RTL dongle gives reasonable results considering its price! Above I show almost half the 2 metre band. 144.800 APRS on the left, tuned to a QSO on 145.250, and around 145.700 on the right.

Click "Front End" to bring up the RTL controls. The lower sample rates give the least strain on the CPU. The Frequency correction is set on a known signal. Here I have a precision beacon GB3VHF on 144.430MHz to use.

Generally it is best to remove the ticks from the AGC boxes and adjust the RF gain manually for best results on individual signals.

There are scanner plug-ins for RTL devices listed here they are popular.

Like the FCD this dongle will usually benefit from filters, maybe attenuators or preamps.

The RTL dongle works reasonably with a HF upconverter, on some frequencies an antenna attenuator and use of the "Front End" manual gain is useful.

RTL dongles with the R820 tuner are better. Will start at about 22MHz and seem more sensitive.

The FCD Pro is much the same in operation except only 80KHz is visible, the new version FCD Pro+ runs at 192KHz.

For transmit checks another program will be required. It is possible to use HDSDR (link above) Make sure you have the latest download and latest PE0FKO DLL. Note the Return key acts as a crude CW key.


This is a CW/PSK RXTX program. My information here.

I advise against using Power SDR until your SDR is tested. It has too many settings to confuse a beginner.

TROUBLE and notes about Windows 10 settings.

If you are not too familiar with Windows sound settings be prepared for problems! Most do not have trouble but some systems can be very frustrating.

Windows 10:- I suggest you make sure you get a computer with enough PCIe slots to accommodate your sound devices. Not easy, but if you use USB devices they can introduce a lot of problems, partly due to the way Windows handles USB sound and, it seems, partly the way some older software handles audio?

The major problem I find is the way USB audio devices change their order. This has always happened but with several USB devices it gets frustrating. Sometimes a device may stop working and the effect is as if it has been removed. All the other devices get re-ordered and Windows re-assigns it's default audio device and communications device. This means that every time you plug or unplug a USB audio device you must reset the default device to avoid Windows audio from being sent to your radio. Even resetting the default device seems to reset the order sometimes.

Here is how to access the Sound Properties:-

Right Click the Speaker Icon, Open Sound settings

Then on that page select "Sound Control Panel"

In the Playback and Recording tabs select the device that needs to be default and set it to "Default device" and Default Communications device". This will need to be done every time the USB devices are re-ordered.

Then set the required device in each of the softwares you are using.

Another problem is "Power Saving". If Windows thinks you are not using a device it may turn it off. Here is a description of the various Windows power saving settings. Re: #AudioIssues (

Note that even turning the screen off may re-order your sound devices. Most HDMI video cards are "soundcards". If you do not use HDMI sound you may disable it by right clicking it in the Sound Control Panel, otherwise you just have to turn off the monitor manually.

Basic SDR settings

To get a rough check of whether a SDR receiver is working connect phones to the output of it. Tuning through a busy band should produce some high pitched noises that may well sound something like radio signals. Stereo phones should reproduce sound in both channels. If your ears are old this needs care! The high frequencies may not be heard, or maybe just in one ear.

Use a good antenna. Ensure the band is "open".

Soundcard settings. Bruce KF1Z

In Windows volume control settings (Properties). XP Right click the Speaker Icon - Open Volume Control - Options - Properties - Recording Input.

First, you must use Line-input to the soundcard. Not microphone input.....

Make sure that in Windows volume controls for input, the ONLY thing that is checked is LINE-IN... [Set the slider to maximum]

If there is a "Stereo-MIX" make sure it's muted.

In OUTPUT [Playback] settings (still windows volume controls)

Make sure the only things checked is WAVE .... (and "master volume" if there is one..) [Set the sliders towards maximum]

Make SURE that LINE-IN is MUTED in playback (output) settings.

Then you need to make sure the proper card, and line in and out are selected in the SDR software as well. SAMPLE RATE leave at 48KHz. Almost all cards will work at this setting.

To check the soundcard input is correctly selected just feed something into it. Music from a MP3 player, or even just touching the free end of the cable should produce something on the SDR program's display.

The Soundblaster Live! 24 often seems to have a driver bug, it needs the Line In to be

unselected/selected to work.

Similarly, plug in speakers, or phones instead of the SDR input. When Rocky goes to TX VERY LOUD sounds should come out of both channels. Set the tuning (click on Rocky's spectrum) fairly close to centre, say 2-3KHz, if tuned near to the edge these sounds will be at a high frequency and may not be heard.

Signals heard but do not tune:- How to check and avoid an unwanted bypass between the soundcard's Line-In and Line-Out Input to output feedback on Audigy 2


They should be at least adequate for initial testing. Maybe good enough to satisfy..

My ACER 5553 has a stereo mic input and it works great with Rocky and other IQ software Neil, G3RIR

I am using a Compaq 6910p laptop and it says that it has stereo input.....

My old ACER 1683 gets LIN -IN, LINE-OUT and MIC_IN....Besides that although it is not the best it can work nicely with SR.

Dell Inspiron Mine is 1 to 2 years old. It has stereo input with mic and line software selected and stereo output. It has 24 bit ADC, but a max sample rate of only 48 kHz

Fujitsu Lifebook E8420. I works great with Softrock at 96kHz

Dell Latitude D600 Pentium Mobile has a real stereo input as well as real serial and parallel ports. The soundcard only goes to 48kHz

Dell Latitude 610 the docking station has a stereo jack for Line In/Mic In.

Lenovo Thinkpad Edge & X Series Notebook audio pinout Note these seem to be mono input.

ACER D270 NETBOOK, I purchased this for holiday internet access then found SDR worked well. Acer D270 and SDR

I also have a Sony Vaio also stereo.

My HP NC2400 is stereo too and works well enough to play around with. Dave kx3dx

I have a Toshiba Equium, that can use the same socket as a Mono MIC input, OR a Stereo Line input. But it's a fiddle to set up, Dave G0WBX.

If yours is not here look carefully in the manual, if it does not mention stereo input it may not have one. Google the make and model + "stereo input" you will probably find the answer. Dig into the sound control panels.

Some links here giving ways of accessing "Sound Properties"


Here is a method of testing a soundcard's suitability for SDR reception. Try different sample rates.

Every stereo sound system I have used has worked but very occasionally someone says they cannot get a system setup properly.


Dell Inspiron E1505 lap top with Sigmatel sound. Confirmed by two users, one had a

Gateway NX570X so it looks like a problem with Sigmatel. More here



Like RX the transmit image will be exactly opposite from centre to the wanted TX frequency.

Use AM/FM mode.

You find the image on a RX, make sure it really is the weaker image, that IQ swap is correct.

Then use the sliders to reduce this to a minimum.

This needs checking every time you move frequency and certainly will vary as you move bands.

Make notes of the settings at different frequencies.

This procedure is much the same for all SDR software with transmit capability.

Note with HDSDR is best to press "C" on the keyboard after selecting the TX frequency but before adjusting IQ. This moves the tuning so the TX frequency is at a constant audio frequency and reduces the variation as you change the tuning. PSDR-IQ does this automatically, keeping a preset offset.


Some hints, test equipment.

For reference, some notes and links about installing the RTL Dongle and SDR# if you have problems.

RTL Dongle ONLY:- CAREFULLY READ for instructions for obtaining the support files.

SUMMARY:- All links and instructions on above page. Do everything in the order described.

Or look here, using the installation script.

Install Zadig drivers, instructions on above page. This will normally only need to be done once unless an updated driver is made available. If you then use a different USB port Windows may be told to install the driver automatically. NOTE later versions of Windows, especially 64 bit have security features. Run as Administrator and right click to unblock downloaded files have been mentioned by users.

October 2015:- Now a direct zip download. Run install RTL_install.bat NOTE NO WINDOWS XP SUPPORT


4) RTLSDR Driver src\

Or direct link on page. Unzip this, find rtlsdr.dll and libusb-1.0.dll in the x32 or x64 folder and copy to the SDR# Program folder.

In the file is a folder "Config" Inside that is the file "SDRSharp.exe.Config" copy this into the SDR# folder, overwriting the one already there.

This should be already edited so you do not need to follow the instructions below. But if you have problems it may be worth checking.

Note the instructions for editing SDRSharp.exe.Config. This is actually a text file.

Right click, "Open With" Notepad. Find <!-- <add key="RTL-SDR / USB" value="SDRSharp.RTLSDR.RT1SdrIO, SDRSharp.RTLSDR! /> -> and remove the leading <!– and trailing –> so that it looks like

<add key="RTL-SDR / USB" value="SDRSharp.RTLSDR.RtlSdrIO,SDRSharp.RTLSDR" />

Check .NET installation for SDR# etc.

G4ZFQ February 2011

alan4alan at googlemail com

More of my pages related to SDR