Tuesday, June 29, 2010

How to build a $5,000 dollar UHF SATCOM antenna for under $20

Ultimate DIY: Military UHF SATCOM antenna
By Steve Douglass

I remember the first time I saw a Dorne & Margolin UHF portable SATCOM antenna. I know that may seem a bit weird and esoteric (an antenna leaving that kind of lasting impression) but the moment I saw one - I knew I wanted one.

It was many years ago at the annual “ROVING SANDS” military exercises held in southern New Mexico. I was there covering the games as an aviation journalist.

The world's largest air and missile defense exercise, ROVING SANDS overseen by the JFACC, combines Army, Navy, Marines and Air Force units and pits them against each other over the White Sands Missile Range and Biggs Army Ranges.

For many years Roving Sands afforded me a unique opportunity to observe (very up-close and personal) military aviation operations that didn’t require going through the laborious task of obtaining government-vetted-sanctioned press credentials, which is exactly what I didn’t want.

Once one is allowed on the inside - you only see the stuff they want you to see. Sure you have better access-but it is chaperoned access.

My job (then) was to look for the “unacknowledged” black-project aircraft that were rumored to be involved in the games, reporting for magazines such as Popular Science and Aviation Week & Space Technology.

Almost needless to say, my compatriots and I weren’t disappointed- but that’s different story for another day.

Anyway, (being a rabid military-monitoring hobbyist) I couldn’t help but spot the uber-cool milspec-looking-fishbone-yagi antenna on a building at the Roswell Industrial Airfield (where the Red Forces were based) pointing up at what I could easily deduce was a military satellite hanging 22,000 miles above the equator in geosynchronous orbit.

Later in the week, I summoned up my courage and asked an airman (eating his lunch near the antenna at a picnic table) what it was. Apparently he was the right man to ask.
He said it was a Dorne & Margolin portable antenna used for UHF-TACSAT/DAMA voice, data and telemetry work.

The airman (a com-tech) was proud of his MOS and even took time from his lunch to show me his radio rig. It was impressive, big and bulky over-built by Harris and looked like you cold have dropped it out of the back of a C-130 without damage.

He then graciously demonstrated it for me by doing a radio check (voice) with the Joint Training Analysis and Simulation Center (JTASC) in Suffolk, VA.

I was surprised at the high-fidelity and clarity of the return com-check, considering it was relayed off a rotating hunk of spinning metal and wires located some 22,000 miles in space, making the round-trip just under 50,000 miles.

As the tech continued with his demonstration, he rattled off a list of technical specifications, frequency ranges and communications parameters and protocols that I’m sure he thought I wouldn’t understand. I played dumb, scratched my head all the while trying as hard as I could to take it all in. He had no idea that he was talking to man who had written a hobbyists guide to military monitoring.

As impressive as the radio equipment was, I knew I’d never be able to afford one - even sometime in the far-flung future, when it had become obsolete and sold as surplus. It was kind of like taking a test drive in a Ferrari, all the while knowing you couldn’t even afford a Yugo.

But the antenna was a different matter entirely. I did own more than one receiver that could (with the right antenna) intercept satellite signals in the bands the airman had detailed (240 to 310 MHz) and had done so (with very limited success) from time to time.

The trouble was – UHF TACSAT satellite downlink transmissions were what was technically described as being (right-hand circularly polarized) making reception on commercial and consumer grade antennas (usually vertically or horizontally polarized) problematic at best.

Without getting too technical, rotating satellites have forced the use of circular polarization. The fundamental advantage of circular polarization is that all reflections change the direction of polarization, precluding the usual addition or subtraction of main and reflected signals. Therefore there is far less fading and flutter when circular polarization is used at each end of the link.

Over the years I tried building my own high-gain UHF Yagi antennas to receive military satellite communications with very limited success. Main trouble was, as the satellite rotated, the signal would swing out of phase and fade (rapidly) in and out and sound much like a record skipping – making interception just plain irritating.

To put it simply, it was like trying to have a conversation with someone riding on a merry-go-round. If you weren’t running along side them (constantly) all you would here were bits and bursts of voice.

Radio hobbyists (with more technical knowledge than moi) had built home-brew helical antennas and were reporting (via Internet news-groups) great success but the antennas were difficult to engineer and build, especially for a man who barely squeaked by with a C in high-school algebra.

For me, looking at the formulae for calculating the spacing and turns on a helical antenna was like trying to read Greek, but that wasn’t what turned me off to ever attempting to build one.

The main problem was, none of the antennas looked like the one I saw at Roving Sands, with the majority of the home-brew designs looking like the coils of razor wire ringing the local prison, plus they were huge -sometimes doubled-arrays hardly portable or easily mounted on the back balcony of my tiny apartment.

What I wanted was a Dorne & Margolin (now EDO) portable SATCOM antenna, transportable, easy to set up and tear down – and not to mention – tough-looking and black-like those used by covert operators, Rangers, SEAL teams and DELTA.

I wanted an antenna that didn’t say “ham radio operator” but instead said “government spy” and “If I tell you what it is I’d have to kill you – so don’t ask.” type of antenna.

Anyways –

Over the years I’ve held out hopes that some military surplus outlet advertising on the Internet would acquire one of these beauties (and not knowing what it was) offer it for sale at a reasonable price.

A few years ago – it happened. Dorne & Margolin/EDO and Trivec Avant (the major military contractors building SATCOM gear) surplus antennae began showing up sporadically on Ebay.

Unfortunately they were snapped up fast (and at premium prices) by the well-heeled radio hobbyists.

The going price was around 3K to (for pristine units) with even broken or heavily used and abused specimens going at over 1,000 dollars.

Refurbished (and new) antennas can also be (now) bought through various re-sellers, who equip shady-military-security for hire companies like Blackwater/Xe Services LLC.

These controversial firms are authorized to communicate with the military via SATCOM in places like Iraq and Afghanistan. Blackheart International (http://www.bhigear.com/) offers a mini-satcom antenna on their site for the walk-away price of $3,000. Heavy-duty antennas (Bigger-more gain) could be had for 5K.

I couldn’t (and still cannot) fathom why a simple assembly of electronics and aluminum sticks could cost so durn-much! For the life of me – they looked like a simple X-wing Yagi design. Was there something super-secret or complicated (hidden within the design) that made their construction complicated and thusly (and rightly-so) so expensive?

Still, hope springs eternal and I thought it would only be a matter of time before one popped up at a price I could afford.

In the meantime – I acquired a new super-scanning radio released by Uniden the BCD-996XT. The 996XT is a computer-controlled-programmable scanner with a 25,000-channel capability.

To quote Uniden: "This new scanner significantly raises the bar with much improved APCO-25 digital decoding as well as a host of new features and more memory. For those who like GPS scanning, a feature no other manufacturer offers, you can now enable and disable not only Systems but Groups as well depending on your location (the optional GPS antenna that we sell is required).

The radio offers a band-scope feature, a Fire Tone Out search feature to help you determine the tone out frequencies being used, improved Close Call, APCO-25 NAC code decoding, and more. The 996XT is a big leap forward."

The main reason I acquired the BCD-996XT was for its digital-decoding capabilities. I run a small news-gathering company for the local and (sometimes national) news media called “The Reporter’s Edge.” Recently, the Texas Department of Public Safety had “gone digital” employing APCO-25 digital encoding.

It is my job to scan the public safety bands for their producers and reporters and be a sort of safety net for the breaking-news stories that sometimes fall between the cracks while already over-tasked and under-staffed TV journalists took time to write, edit and produce the news as well have a life that didn’t dictate them spending their sacred off-time with their ears glued to a scanning radio.

Since I always have a scanning radio droning on in the background wherever I am- it was only natural I found a way to make my obsession (for intercepting radio communications) pay off. Once the Texas DPS went digital, the only way to listen in on their communications was with an APCO-25 digital scanning radio. The BCD-996XT filled the bill nicely.

The BC-996XT didn’t disappoint. In fact I can say without hesitation it is the finest scanning radio I have ever owned, only second to the handheld version Uniden’s BC396XT which I also own. Computer aided scanning software of choice is Butel’s ARC396, followed closely by Freescan.

The BCD996XT (with its’ more than ample 25,000 channel capacity) freed my BCT396XT for use as a MILCOM scanner, something I have wanted to do for a long while.

I love intercepting military aircraft (MILAIR) and associated communications on all the bands and to have a scanner dedicated to just MILCOM was a real treat.

I even went so far as to custom outfit a case (containing an ASUS netbook computer loaded with scanning software) that also housed the BCT396XT making it look somewhat like a retro SAC “nuclear football” capable of sending the emergency action messages triggering WWIII. It comes complete with an Cold-War era SAC badge that General Jack D. Ripper would trade his Cuban cigars to have.

Okay, I admit-its’ kind off geeky – but that’s just my way.

The “football” does have a utilitarian function. Underneath the netbook are two gel-cell batteries that can power the scanner and computer for up to twelve hours. Both can be charged by plugging it into a wall or a cigarette/accessory plug in an automobile.

(C) Steve Douglass

Continued soon in PART II



Anonymous said...

How about a thread dedicated to your "Nuclear Football"? battery info, and such.

Kelvin said...

I'm going to be honest, I know nothing about radios or antennas but I am interested in building a portable backpack type radio that could be charged by a solar panel to be used in cases of emergencies (ie:while hiking, during natural disasters, etc...). I'd like an antenna tha is portable, lightweight, and can be used ANYWHERE! I like this one, could it be used for the purpose I have described and what would you suggest as far as radios. Could I get the schematics for the antenna to build it? Or would it cause legal problems? If so, that's ok, I don't wish to get ANYONE in legal problems. Your imput would be greatly appreciated. Thank you.
no google account blindhntr@aol.com


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