Thursday, October 30, 2008

VHF/UHF Spectrum Analysis using the RF Space SDR-14

One of the most impressive developments in the radio communications community over the past few years is the advent of software defined receivers, which can provide great tools for spectrum analysis. Hobbyists today can not only view entire swaths of spectrum at one time to view activity, but can also record entire spectrum chunks for later playback and analysis using SDR tools.

This article will walk through the RF Space SDR-14 software defined receiver, and review how it can be used to analyze different user segments in the VHF/UHF spectrum.

To start, an introduction is in order. The RF Space SDR-14 is a 14-bit software defined radio receiver that operates in the 0.5-30 MHz band. It provides not only extensive spectrum analysis capabilities but also functions as a great receiver with numerous demodulation capabilities for the HF spectrum. Since the SDR-14 is a software defined radio, all controls and interfaces with the radio is done using software applications installed on a PC. The most popular application written to exploit the SDR-14 is SpectraVue.

As mentioned above, the SDR-14 functions as an HF software defined receiver, however it can be configured to accept the 10.7 MHz IF output from another receiver, and tune that receiver, to combine as a very powerful monitoring station and spectrum analysis platform for any band range. I have been using an AOR5000A in conjunction with the RF Space SDR-14 with excellent results, allowing me to click on certain portions of the spectrum and automatically tune the AOR receiver.

Showing some of the capabilities of this combination or AOR receiver and RF Space spectrum analysis tools, I'll review some annotated screen shots of different monitoring targets. You can click each screenshot to view the full size image.

The first we will review below is a screenshot of the SpectraVue application monitoring a 250 KHz wide chunk of spectrum between 260.350 and 260.600 MHz - where US Military UHF communications satellites have downlinks. The RF Space can realistically monitor about 10 MHz of spectrum from another radio's IF, however the narrow swath of 250 KHz allows us to monitor military satcom transponders transponders and see what is happening within each of them.

In this screenshot, we can see the 4 Active UHF SATCOM transponders:

1. Relaying unknown data bursts on 260.375
2. Relaying a Spanish bootlegger's communications on the 260.425 transponder but comms centered on 260.430 MHz. The transponder is 25 KHz wide so the communications come through loud and clear.
3. Relaying 16 KHz VINSON encrypted US Military voice
4. Relaying a Spanish bootlegger's communications on the 260.525 transponder but comms centered on 260.530 MHz.

It is interesting to note that Spanish, Portuguese, and Asian bootleggers at times use all the 25 KHz wide transponders, with communications in LSB, AM, and FM.
Next, let's take a look at the 5 KHz transponders on the Gapfiller Military SATCOM satellites. This screenshot shows (13) 5 KHz wide transponder in action, annotated with different traffic occurring on those. You can clearly see in the screenshot weaker active transponders for a different satellite on the left, and the 13 stronger transponders for the target satellite.

Now that we have reviewed some advanced monitoring targets, we can take a look at some more common monitoring targets that hobbyists focus on. Below is a screenshot of a 10 MHz wide section of spectrum in the VHF aircraft band. This shows a key benefit of using the SDR for spectrum analysis -- you can watch almost the entire VHF aircraft band on one screen, and click to tune a specific transmission on the AR5000 radio.

Further, why search the federal government VHF land mobile spectrum on a standard scanner when you can watch the entire band in one window? Below is a screenshot of the SDR monitoring 162-172 MHz, providing the ability to see all activity and click to tune the AOR radio to specific transmissions:

And finally, where I live, the federal UHF band in San Antonio TX is quite busy with a large wide area military trunking system active between 406-411 MHz. The screen capture shows activity over time in that spectrum, showing active data and voice channels.

In summary, you can see that the RF Space SDR-14 opens up a whole realm of possibilities for radio communications enthusiasts. The ability to watch entire blocks of spectrum and then point and click to tune an transmission makes finding new and unknown monitoring targets a breeze.

For those that are interested in adding this fine piece of communications equipment to their shack, Scanner Master offers the RF Space SDR-14 for sale on their fantastic Web site. Click the link below for more details on how to order.

RF Space SDR-14 on Scanner Master

Next up, we'll review the RF Space SDR-14 monitoring the HF bands. Utility, broadcast, and Ham listeners and operators will get a whole new perspective on how HF Spectrum is used.