Radio Archaeology

[Jeff M. Hopper]

I need some help with radio astronomy and SETI questions. I'd like to have an adventure seed based upon the characters recieving a radio transmission from a world parsecs away, but I need more information. How strong must a radio signal be to reach across parsecs of space? How sensitive do the ship's sensors have to be to recieve it? How big does the parsec-range radio transmitter have to be to send a signal of this kind (both the dish and the electronics)?

Now if all this is within the range of plausibility, then would a branch of radio astronomy become more radio archaeology with students of history setting up sensitive PEMS and radio recievers in the suspected path of radio signals that may have been broadcast from centuries ago?

 

[Piper]

This page has the math for figuring power, antenna size and so forth. Use the antenna link on this page if you have MS Word.

These numbers don't take into account environmental effects or background noise. Bandwidth is also a factor. High bandwidth allows faster data transmission. Low bandwidth is slower, down to morse-type code at the lowest levels.

The short answer is likely to be that one end (either transmit or receive) is going to be the size of a radio telescope. Both antennas will probably be highly directional so they'll have to be aimed at each other. For all that, we're still talking with the Voyager probes and they've only got 20 watt transmitters.

Lasers might be an option.

Hope this helps.

 

[sgbrown]

Not sure if this will help any - but radio waves can be very unusual things.

When I was a young Army Officer (Engineers), my platoon was building a headwall for a rock quarry in Honduras. Through some fluke of weather/atmospheric conditions I ended up speaking with a unit in central Oklahoma on a short range radio. This wasn't supposed to be possible, and definately wasn't reliable, but this particular day we could both hear each other just fine.

Even if it works out as improbable that the radio could be intercepted, that doesn't mean that it's impossible! Just unlikely - or maybe very, very unlikely. Point is a radio intercept is a plausible start for an adventure hook.

 

[Jeff M. Hopper]

Originally posted by Piper:
This page has the math for figuring power, antenna size and so forth. Use the antenna link on this page if you have MS Word.

Lasers might be an option.

Hope this helps.

Yes! This actually helps quite a bit. Thank you!

I've got to do more research on what frequencies work best for what applications and how we can detect the signals. My own experience is limited to the remote controls for bomb disposal robots, which doesn't really apply here. I'm learning rapidly that the signals used for broadcast TV (UHF mainly) are good for reaching recievers on a world's surface, but wouldn't do so good as a "beacon" for an off-world civilization located light-years away.

For shouting out "Hello", radio may be best. For communication to and from known stations, lasers or masers may be best. For energy efficient communication across intersteller distances, it may be most economical to just send a space probe!
Although a space probe may take a long time to get there with the message.

 

[TheEngineer]

Hi Jeff !

There are many variables here...
For long range commo it is a good idea to use frequencies, which are usually not around in natural astronomical environment, so that those are not completely lost in background noise.

The links above are pretty cool, and appearantly even commo with Mars is a task already.
Going further away makes things more tricky.

E.g. a 1 MW omnidirectional signal would result in a theoretical signal of around 8E-29 W/m² one parsec away. But thats still about 0,6 photons (long wave fequency 200 kHz) per second per square meter, so there is something to detect here...

Anyway, we could just take real world examples. E.g. the Arecibo radiotelescope acts as a directional (targeting M13) radio sender 500 kW, too. According to one source this signal is expected to be detectable with existing technology up to 15000 LJ away

.

I found another source (a German Commo magazine), where the author regulary discusses methods for interstellar communication.
His recent example of a directional radio link configuration was this one:
1 MW sender at 150 GHz (thus outside atmo)
Depending on the diameter of the parabolic antenna there were different maximal commo distances:
D = 6m 4,6 LJ
D = 25m 80 LJ
D= 90m 1000 LJ

I really dont do well with radio commo and DB stuff, but I guess one major aspect is to use directional commo and high frequencies in order to enhance signal strength at the target.

Perhaps I will find some more stuff...

regards,

TE

 

[Piper]

Don't be put off by the size of the antennas. A number of smaller antennae can be linked together and operated as the equivalent of a single, much larger antenna. This is used in the Very Large Array. The individual elements could be flat panels rather than dishes. Using a system like this, you could fit the equivalent of a 10-meter dish on the hull of a type-S scout.

 

[ElHombre]

There's also some canon that fits into your idea as well. There was mention made of system-wide arrays (think the VLA over an entire system) that were used for military and research purposes. Then there's also the Imperium's Longbow project which extended the array principle across the entire coreward border.

 

[robject]

El Hombre, whereabouts in Dallas are you at?

 

[Black Globe Generator]

Jack McDevitt mentions radio archaeology in his novel Polaris, but doesn't go into a great deal of detail.

Have you taken a look at Carl Sagan's Contact? You might some discussion in there about radio wave reception over interstellar distances.

 

[Andrew Boulton]

http://www.seti.org/site/apps/nl/content2.asp?c=ktJ2J9MMIsE&b=194993&ct=3242661

 

[Gadrin]

Jeff, keep us up to date on your ideas for this.

I'd be interested in hearing them. I read Polaris recently and really liked McDevitt's idea of Radio Arch, especially for other non-traveller RPGs.

But the idea of a micro-jump away to re-visit the signal (assuming it works) is a nice idea.

 

[Malenfant]

Originally posted by SGB - Steve B:
[QB]When I was a young Army Officer (Engineers), my platoon was building a headwall for a rock quarry in Honduras. Through some fluke of weather/atmospheric conditions I ended up speaking with a unit in central Oklahoma on a short range radio. This wasn't supposed to be possible, and definately wasn't reliable, but this particular day we could both hear each other just fine.

Sounds like the signal got bounced off the ionosphere? I'm not sure exactly how that works, but it has been the cause of other cases of long-range contact like that.

In space there's plenty of stuff that can absorb or scatter the signal (e.g. dust clouds), but nothing around that could amplify it or naturally reflect it while still maintaining signal coherency like that.

 

[MR TEK]

Could gravity lensing not amplify radio.

I am sure it would have a diffent amplification, (what little I know about lensing, it seems like it was frequency, or more accuratly wavelength dependant.)

Gavity lensing for those less knowlagable in astro physics is the effect where light passing near a star or other high gravity gets bent, and possably magnified.

I understand that entire galaxies can cause lensing as well. I do not know for sure if that runs down the em scale or how far it does, but I would guess there might be some effect in the millimetter to micro meter range.

 

[Jeff M. Hopper]

I've got to research the gravity lensing effect radio. I hadn't thought of that.

The big disappointment is that the usual frequencies used for broadcast television or radio (audio) are AM, FM, UHF, and VHF. These frequencies tend to both bounce off a world's atmosphere (the ionosphere) and can get overwhelmed by charged particles like what would happen during a solar flare. So claiming that we've been broadcasting extensively into space for the last almost 90 years doesn't mean that the signals have penetrated our own atmosphere (that great opening scene from the movie Cosmos doesn't fly too well). Now if those range bands are used on an airless world, it might work much better.

There are radio frequencies that work much better for transmission through space, they just don't work well for commercial tranmissions in an atmosphere.

 

[The Shaman]

For purposes of your plot hook, could the message the adventurers are meant to receive originate in space, such as between a ship and a station, where atmospheric interference isn't an issue?

 

[BlackBat242]

Just to show how outdated my astronomy education was, what is LJ? Is it a new name for LY... light year?

 

[Malenfant]

I think LJ is supposed to mean "Lightyear", I think TheEngineer just mistyped or something?

 

[Merxiless]

Jahre is Year in German.