Configure your AirSpy


Read this explanation of the different classes and roles of receivers for decoding and voice following.

Note that you can edit the Model field. The default text is "AirSpy" but you can edit that to whatever you like. Useful if you have more than one AirSpy.


AirSpy was the first receiver that Unitrunker supports with multiple VCOs. Many settings that appeared on the main Info tab of the reciever window have since been moved to VCO tabs. Each VCO tab is paired with a Scope tab to the immediate right. A VCO can tune to an separate RF channel. The acronym VCO stands for Voltage Controlled Oscillator - the part of a heterodyne receiver used to tune a specific frequency. An alternate name is VFO or Variable Frequency Oscillator. In SDRs like the AirSpy, the only constraint is all VCOs must fit inside the usable bandwidth of the receiver. This is about 80 percent of the sample rate. At 10 msps, that's about 8 Mhz of usable bandwidth. As of this writing, the number of VCOs is five.

Idle VCOs

Any VCOs surplus to your needs should be set to signal role and the park frequency set to 0.000 Mhz. This prevents the VCO from taking up compute and memory resources.

Signal VCO

Analog Voice VCO

Digital Voice VCO

The program does not provide decoding of digital coded voice channels. It can provide baseband audio suitable for other applications. Piping audio between applications requires a device driver that mimics a pair of audio devices - one input and one output. Two popular utilities are VB Cable and Virtual Audio Cable. The two popular digital voice programs are DSD and DSD+.


For analog voice, it's a good idea to set the squelch level so that the voice receiver becomes silent at the end of a transmission. It's also a good idea to do this for digital voice as the digital voice decoder won't mistake noise for a transmission. For the AirSpy - values between 50 and 100 work.

Squelch Procedure

If you change the receiver's gain or sample rate, you will need to readjust squelch. The same squelch setting will generally work for all VCOs on the same receiver.

Usable Bandwidth

The AirSpy samples RF at 2.5 or 10 msps. The usable bandwidth is about eighty percent of the sample bandwidth. The program tunes AirSpy to a center frequency (as displayed on the receiver window's Info tab). Individual VCOs tune to channels inside that usable bandwidth. If a VCO is directed to a frequency outside this usable bandwidth, the VCO is effectly idle. The program uses a sliding window in an attempt to fit as many VCOs as possible. It is possible to monitor multiple sites provided the voice and control channels are relatively close together. For example, monitoring a 851 Mhz trunking site, a 935 Mhz trunking site, and 455 Mhz site won't work. You would need three AirSpies.

In many cases, the voice and control channels for one or more sites will all fit inside the AirSpy's usable bandwidth.

Calibration Procedure

The AirSpy does not need to be calibrated.

© Copyright 2014-2015 Rick Parrish