Cruising the Wideband Spectrum

by Agent T.W. Lee / Interzone Intelligence

Those new RTL-SDR USB stick receivers are a neat toy, but the author was interested in being able to look at a wider piece of the spectrum at a given time than what the RTL-SDR allows.

The CIA and DOD have been using Frequency-Hopping Spread Spectrum (FHSS) since the 1980s, so the author proceeded to look for old-school tech that could be used for wideband reception.  Fortunately, such equipment can be readily found at hamfests and flea markets in this sector.

The old-school standbys are the wideband receivers and tuners made by Watkins-Johnson and CEI.  No one seems interested in them anymore, and they can be found for under $100.  Lesser-known brands such as NEMS-Clarke, Grimm, and Astro Communications Labs are also around.

Another piece of forgotten tech are the old analog NTSC TV service analyzers, especially those designed for CATV work.  If one finds an old Wavetek SAM for under $50, they should snap it up.  The CATV models have 3-300 MHz frequency coverage and can be used as a spectrum analyzer when hooked up to an inexpensive oscilloscope.  The old SAMs can't be used to test the new digital TV systems, and many are gathering dust in old TV repair shops.

Analog used to be that you could take your old click-tuner TV and tune between the channels.  You'd also see static.  Nowadays, you have preselected digital blue screen of death tuners.  Think about the white spaces and in-between places.  TVs used to go to channel 83.  They also used to go all the way down to 54 MHz.  54-88 MHz is bound to be useful now that the TV stations are gone.  It at least will be interesting!

When I mean wideband, I mean from 100 kHz to 24 GHz.  You never know where something interesting may be hiding in the spectrum!

The author once saw frequency-hopping spread spectrum in VHF high band.  It was during a CIA/UFO/USAF experimental aircraft test.  Took the author 20 years to find the equipment that did it at a New England hamfest.  Preston bought up all the cool surplus WJ toys a while back, but now that he's retired and fixing tube amps for rich old hippies, you can find the stuff again, and it's pretty cheap for the moment.

Some of the newer stuff is pretty good too.

The classic RadioShack PRO-2006 is found for under $100 at many a hamfest because it does not do P25.  You can always do an old-school discriminator tap and run any old police scanner into a PC soundboard and run DSD+ to decode P25, DMR, and MotoTRBO.  If you're smart, your PC will be running Linux.

Yaesu, a few years back, came out with this receiver called the VR-5000 - one of the few ham-grade receivers with an IF output just like WJ and all the other pro gear, plus 100 kHz to 2.6 GHz frequency coverage!  You can find them for sale cheap by scanner dweebs who weren't able to fully appreciate them.  Hamfests, eBay, and QRZ are full of good tech waiting for you to take out and use.

Here is what the author does: He goes to hamfests and looks around for likely prospects.

His budget for an item is $200, maybe $300 if it's really nice.  He does a quick function check.  Scanners should be able to pick up the local 162 MHz NOAA weather radio stations.  Shortwave receivers should be able to pick up WWV, some ham comms, and an international broadcaster like WBCQ with a few feet of wire stuck in the antenna connector.  If so, then it passes the function check.  Then knock about 30 percent off the asking price for a starting offer at the end of the hamfest.  The seller will probably settle at about 15 to 20 percent off his asking price.  What is a fair price?  Look at completed and sold auctions on eBay.  Average the prices you find and take another 30 to 40 percent off.  That will roughly be a fair hamfest price.  If the guy obviously has a good fair price on something, don't try to talk him down.  Just pay for it and get out of there.  Don't be an asshole!

The author prefers desktop receivers to portable units, as most of his radio research is done in a lab.  You, on the other hand, may find portable units more towards your preference.

Back in the days of his misspent youth, the author did a large amount of field work.  The portable receivers of preference were a RadioShack PRO-43 (yes, the diode was clipped for full 800 MHz coverage) and an Icom R10.  Old RadioShack scanners with 800 MHz were easy to mod for full coverage of the 800 MHz band by clipping a single diode.  They pretty much killed that after 1994.  The government does not make listening to certain frequencies illegal to "protect people's privacy."  They are probably hiding something there.  Now the RTL-SDR has full 800 MHz coverage, but it needs a PC to work.  Find yourself a RadioShack PRO-43, PRO-2005, or PRO-2006.  Older Icom and AOR receivers are also good, but still command fairly high resale prices unless you are fortunate.

The deciding factor as to whether or not you should go portable or fixed/lab depends on what interesting things are going on in your county or neighboring ones.  Go surf on over to: cufon.org/cufon/topufos.htm

This is a list of the top 300 counties in the U.S. for UFO sightings.

Since it is a known fact that the CIA and USAF have claimed responsibility for the vast majority of UFO-type sightings in the country, claiming they were experimental aircraft, this list right now is your best guide for determining if you should have a lab or a portable radio research setup.  Keep in mind that aircraft communications can be heard 100-plus miles away due to their altitude.  Land-based comms are 25 to 50 miles, maybe more, depending on the terrain.  You can figure it out with that list!

The author used to live deep in the heart of UFO territory, and heard/saw some amazing things.  You just have to keep watching the skies and listening to the airwaves, but some of the best things he "heard" were not voice communications, if you get my drift!

So now that you have some gear, where do you start?

A Google search of "spectrum use summary" (without the quotes) will show you a whole bunch of useful documents.  Download them and use them as a guideline.  Also, look for spectrum that appears to be underutilized, like TV broadcast "white space."  Now that people can't tune between the channels like they used to, it has become a good place to hide in plain sight.

The best receivers, the author has found, are those that are tunable - as in tuning dial.  The author started with 1960s and 1970s vintage multiband portable radios, and then upgraded to wideband surveillance receivers from CEI (Watkins-Johnson).  Usually these units are wideband tuners with a 21.4 MHz IF output that you use with a demodulator or a shortwave receiver.  The interceptor will discover lots more interesting emissions with this setup, especially when combined with a panoramic adapter/spectrum analyzer than he will with a police scanner on VHF/UHF+ frequency ranges.

O.K., so you have some equipment and are ready to go.

Start at the top end of your receiver's frequency range and tune down.  Many improvised emitters are rich in harmonics and easier to find this way.  Note every signal you find for later analysis.  What the author does is start with an old-school analog receiver, log as much as he can, and then go back later with an RTL-SDR for a more in-depth analysis.

He does this because he has discovered that the old-school analog gear works better for finding stuff than does the RTL-SDR.  However, the RTL-SDR is better for signal analysis, especially when recording the characteristics of a signal over a period of time.

The RTL-SDR has excellent Linux support, which is good because that is the OS you should be running.