Connecting Radios to Soundcards
Soundcard software has come a long way in the last few years, and has the ability now to manipulate and use audio inputs in a variety of ways. 2 questions come up time and again in many forums and mailing lists;
- I want to decode (or record) a signal I heard on my scanner - or -
- I want to decode (or record) a signal I heard on my HF radio
This article discusses the basics of setting up Windows to accept audio from your radio. At the bottom, there are links to articles with numerous software packages, some of which can be used with a soundcard input.
Before we proceed, it should be noted that settings may appear different in different OSs, and with different PC distributors,
who often put their own soundcard support software in their systems. The images -and text - in this article should be used as
a guide, not as specific examples. In addition, connecting a soundcard to a ham transceiver is a much more critical function, as isolation between the transceiver and PC is a must. For extensive discussions on the subject, please see the Understanding Soundcard Interfacing website.
There are two distinct conditions; using an older PC that has line/mic in jacks, and newer ones that don't.
PCs/Laptops with Input Jacks
- The use of shielded audio cable is strongly recommended. Make it as short as possible to minimize stray pickup.
- Older laptops and PCs that have Line/Mic in jacks require a stereo jack (1/8 inch) as input. Simply wire one side (either right or left). It may also be possible to short the 2 sides together. Check any available documentation on your soundcard for specifics.
- Laptops may require an attenuating patch cord, since their inputs may be designed to handle low-level inputs. If you hear distortion no matter what audio level you set, this is likely to be a cause.
- A resistor across the jack is an easy way to assemble an attenuating patch cord. One way to find the correct value would be to connect a 10k audio taper potentiometer across the jack, along with a Volt Ohm Meter (VOM). Begin with maximum resistance, and slowly decrease it until the audio sounds normal. You may need to also adjust the levels in the soundcard's control panel. When the audio is satisfactory, note the reading on the VOM. You now have an idea of the resistor's value.
- Be careful about connecting to a Mic In as sometimes these jacks have their audio boosted. Too much audio, and many decoding applications will produce either garbage or nothing at all. It's preferable to use the Line In jack, if your PC has one. This is because it's usually set to provide a low level, fixed input.
PCs/Laptops with No Input Jacks
In many cases, the use of a USB Soundcard is the only way to get audio into the laptop. Each model has their own drivers and installation.
How you get to your sound card (audio) settings varies depending on your Windows OS
- The Bit Rate is important; 8 and 16bit are the most common; high bitrates allow for smoother audio response and better throughput.
Getting Audio from a SDR
Once you have your SDR and control program running and active, your next step is to route the audio from the SDR to the decoder of choice. This depends on what the SDR has for outputs, and sometimes the software you are trying to use. in most cases, you will need to install software such as Virtual Audio Cable or VB Cable then change the settings in your control program to route audio to these devices. However;
- Some SDRs have an output that can be used to feed your sound card (i.e. Cross Country SDR 4 Plus).
- Some software will require the use of some Dynamic Link Libraries (DLLs) that must be installed (MultiPSK).
- Some packages can directly interface with certain SDRs without additional interfaces. You can see the list of such decoding software at the SDRs and Digital Decoding article.
- Some SDRs and one desktop receiver (the Alinco R8T) have an IQ output that may also be used. In the hobby level market, only Sorcerer and MultiPSK is known to be able to accept an IQ output for data analysis and decoding.
- SDRPlay owners should look at the Apps and Support Catalog for both PDFs and YouTube videos on setting up their units with Virtual Audio Cable, setting up virtual serial ports and much more.
Questions and Answers
- How can I get a date/time stamp on my recording?
- Most stand alone recording programs like RecAll or ScanCorder, will tag the audio file with date/time and duration.
- No audio is heard through the PC speakers using either 'Line In' or 'Mic In' jacks on the soundcard.
- Make sure that neither of these selections has been muted in the control panel for the soundcard
- An A/C type hum is heard, even when receiving nothing.
- Double click on your speaker icon on your taskbar, go to Options, Properties, change "Adjust volume" to Recording, hit OK, and under Mic, there should be an advanced, and see if 20 db boost is enabled. (Evan Platt via Scan-L)
- My Images Decoding with SSTV or MFSK Are Slanted
- My Stereo Mix Setting/Soundcard is Disabled. How can I enable it?
- You may need to right click on the setting in Properties and enable it. If that doesn't work, try updating the drivers from the distributor's website. Lastly, you may be able to use the Stereo Mix Plus software to create a virtual sound card.
- Scanner Related Issues
- How Can I Record Using an Uniden BC796D?
- The BC796D (and possibly the BC785D) has a tape output jack; however, it seems to activate after a 2 second delay. To get around this, connect to the speaker out jack instead
- Which RS Scanners can or cant log and record audio?
- Older Radio Shack scanners- with the exception of the PRO-2052 (which is really a Uniden clone) cannot log frequency or talkgroup information. It's not provided for in the firmware. However, the PRO-197, 106, 651, 652 as well as the Whistler WS-1040 and 1065 (which are RS clones of the GRE PSR-500 and 600) can do this with the proper software
- An A/C type hum is heard, even when receiving nothing.
- Many Uniden receivers put a resistor in the headphone jack circuit to limit the output. This is in the ground side of the jack and can cause hum if you are trying to use it for a tape input. According to the manual, the 796D has a programable tape output on the rear panel. See page 18 of the manual. If you still have hum, get a ground loop isolator such as these from Best Buy and the necessary adapters.
Amateur Radio Soundcard Interfaces
Many hams use dedicated terminal units or even sound card interfaces; and some (like the PK-232SC) have adjustable filters that can help reduce interference from adjacent stations. While that works well in the amateur service, those filters can actually cause an otherwise readable signal to be unintelligible. This is because those filters are often tuned to mark / space tone pairs common in the amateur radio service – but those tone pairs may not work for many non-ham digital modes. If you use such a device, first investigate whether these filters can be turned off or otherwise disabled.
Regardless of the application you are trying to execute, if you have Windows Vista You may need to check
to see if your software is compatible with it. XP support is far more widespread, with less problems; however it too has a
compatiblity feature that allows you to tell XP if your particular program need to run as if it were in Win95, 98, etc.
or in other modes/colors.
- Scanner software that includes audio recording capabilities;be sure to also check the scanner's wiki article for scanner-specific software...
- If you need to restore soundcard settings, or have a way to set different settings for different applications, then you should look into QuickMix.