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How to talk to a 36-year-old space probe with GNU Radio, a USRP and a big dish (jmalsbury.com)
226 points by liotier on July 13, 2014 | hide | past | web | favorite | 18 comments

Oh cool! They presented this at Dorkbot-SF a couple of weeks ago. A bit I particularly liked was that, because of the relative speed of the probe, a couple of km/sec, the frequencies sent and received had to be separately adjusted. And also, Arecibo was broadcasting with enough power to boil birds that flew over it.

It's cool space shit, is what I'm saying.

Edit: here's some video: https://www.youtube.com/watch?v=NTljlMH-0oM

"Arecibo was broadcasting with enough power to boil birds that flew over it"

Birds that flew over the parabola of the antenna or birds that flew between the focal point and the parabola? I can't imagine the amount of energy the former would take (and the latter is impressive by itself)!

Same thing with the Mig-21 radar, and I presume other fighters. If they powered it up on the ground, bird would drop.

During WWII, soldiers would stand in front of the radar to keep warm. This was before health and safety.

The first models of -21 had no radar, daytime/clear air only fighters. Someone's pulling your leg.

Edited to add in later years the soviets added one of the worst aerial radars ever flown (by the USSR anyway). Roughly the same performance as a modern marine radar. Think "Lowrance 3G level" performance. That outputs about 10 watts RF. (More like 20 watts DC in, and ancient microwave equipment was legendarily inefficient, so..)

Also the ground support vehicle runs the whole machine when the engine is off for ground maint, preflight, etc, and the max continuous is like 200 amps for the -21 ground support... so at 28 volts that's about 5 KW max for an entire aircraft.

Another way to look at it is tenth of a megawatt class TV stations were never surrounded by piles of dead birds. To shoot one outta the sky would take maybe 100 times the power.

So you're talking 10 megawatts out, minimum, given ancient RF gear that would require at least 100 megawatts power input... thats 100,000 horsepower or so. Also the waveguide feeding the antenna would arc over at those power levels, whoops.

This is why nobody uses beam weapons.

There's a darwin award for a security guard at (I think) a TV studio who decided on christmas eve that work was too hard and instead spent the night sleep in front of one of their microwave transmitters. I believe they found him dead and cooked right through in the morning.

Did that actually happen? I know someone who worked at a shortwave (a.k.a. microwave) radio station when that almost happened. They had to shut down the transmitters occasionally to paint the radio towers, but someone had the bright idea that they could just power down long enough for the painters to climb on. Then, when they weren't grounded, they could power it back up during the painting. They actually did a test run with chickens before it dawned on anyone that they would be cooking anything up there!

No it did not happen. Once again snopes to the rescue.


Why would they do a test run with chickens if it hadn't already dawned on them to some degree?

They were worried about electrical problems, not radiation problems.

I did read it in a darwin awards book, so I assumed it was true, but it's such an innocuous anecdote that I never felt it was worth checking.

if you think that's crazy, you should know an experiment I worked on had approval to fire an electron accelerator directly into the sky. Of course, we called it an "electron light source".

Silly people. If you'd called it a deathray instead you'd have been able to get way more funding.

Oh man. This is such a cool example of how open software platforms have made the world more accessible. Imagine how hard it would have been to rig up that modulation system from scratch 30 years ago.

Also, this article made me realize how you can do frequency addition/multiplication on arbitrary signals via complex multiplication/exponentiation! That part of the flow graph really confused me for a bit. So cool!

Some glossary to make it easier to read:

USRP, Universal Software Radio Perhipheral - https://en.wikipedia.org/wiki/Universal_Software_Radio_Perip...

SDR, Software Defined Radio - https://en.wikipedia.org/wiki/Software-defined_radio

Looks like we've already thrashed his server (oom errors); so here's a link to a cached version for the lazy: http://webcache.googleusercontent.com/search?q=cache:Qhe6rYL...

I got to get me one of those Arecibo dishes! I'm still impressed that they were able to get access to it.

it was amazing the way they accessed it

The hole thing they are doing is very cool and they write and post allot of stuff.

Unfortunately most of the text they post is quite boring and detail less.

It would be nice if they added someone new to the team that was a better writer.

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