2.115Ghz signal to be bounced off the moon on 3 March by JPL - Page 1
Forum section: electronics / general

author: TSL
author_rank: Regular Contributor
timestamp: February 27, 2015, 06:29:13 am
content: On March 3rd at 0630UTC JPL are going to bounce a 2.115Ghz signal off the moon.Given they're using about 20,000 watts into a 34m dish (dish DS-24) the reflected signal should be quite large, and detectable by modest equipment such as a re-purposed MDS down converter and a 20db grid dish.More from Jim Lux, JPL Engineer..."We're going to aim at Tycho from DSS-24 (34m antenna)We'll radiate at 2115 (not 2041).. from 0630UTC to 0900 UTCFor the first hour (until 0730UTC) we'll just have a CW carrier, shouldbe easy to see.For the next hour, we'll be transmitting a JPL ranging code with thechip rate at 2115/2048 MHz (a bit more than 1 MHz)..See the 810-005 handbook for detailshttp://deepspace.jpl.nasa.gov/dsndocs/810-005/214/214-1.pdfYou can probably see not only the carrier but the +/-1 MHz ranging tones(and probably at +/-2 MHz, too), and also the PN sequence if you've gotenough SNR (or post process.. the code period is about 1 second.. it'sabout a million chips long)Then, at 0830UTC we'll stop using the PN ranging, and go to Dopplercompensating the uplink so that the received signal at JPL will havezero Doppler.This is all "we hope".. it's experimental and a sort of procedural shakeout as well as giving me a chance to test my ground copy of a SoftwareDefined Radio that is flying on ISS."Check your moon rise and break out the S band kit - this should be fun to RXcheersTim

author: SNGLinks
author_rank: Regular Contributor
timestamp: February 27, 2015, 10:47:42 am
content: Moon not visible from Europe at this time

author: Howardlong
author_rank: Super Contributor
timestamp: February 27, 2015, 11:17:54 am
content: Interesting, but EME (earth-moon-earth) has been practiced for decades by radio hams with pretty modest equipment.It would however be interesting to see how small your receiver can be to get a discernable signal, I would have thought detecting the carrier would be easy!Around 2001, I used a postage stamp sized ceramic substrate patch antenna to receive a 10W beacon from a satellite out at 60,000km at 2.4GHz. I am sure the same could be achieved.I'm not an EME'er, and I am sure they have better ways of calculating this stuff than my back of envelope stuff here, but my rough calculation is that a 34m dish would have a gain of about 52dBi at 2.1GHz, so an eirp of 95dBW with 20kW at the feed point.Free space path loss at 2.1GHz (assuming 768000km total for both directions) is-246.6dB-216.6dB.Moon reflectivity apparently is 7% (via Wikipedia), so that's another -11.5dB.So that leaves 95 - 216.6 - 11.5 = -133.1dBW, or -103.1dBm.Given a modest 6dBi gain patch, that gets you to -97.1dBm, so I'd say you should be able to detect that carrier audibly with a patch antenna and SDRwith a reasonably low noise figure and narrow RBW of a 100Hz or so prettyVERY easily without any fancy modulation techniques at all, it should show up on the waterfall display.(Edit: corrected path loss figure, thanks to PA0PBZ)

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 27, 2015, 12:05:45 pm
content: I think your free space loss is 30dB off, I get -216.6dB.

author: Howardlong
author_rank: Super Contributor
timestamp: February 27, 2015, 12:11:41 pm
content: Quote from: PA0PBZ on February 27, 2015, 12:05:45 pmYou are right, in which case this is going to be a hell of a signal, I'll correct my earlier post.

author: blackdog
author_rank: Frequent Contributor
timestamp: February 27, 2015, 01:59:37 pm
content: HiMoon bouncing, that's easy...Ten years ago, i started a "qrp" Sirius bouncing project, still waiting on the reply...Kind regarts,Blackdog

author: John Coloccia
author_rank: Super Contributor
timestamp: February 27, 2015, 02:05:03 pm
content: Could someone explain what the purpose is? Is it an experiment to get data, or is there some specific application in mind?

author: SeanB
author_rank: Super Contributor
timestamp: February 27, 2015, 05:49:57 pm
content: Well, it will give both an indication of the velocity of the moon, and will scatter off the atmosphere so you will be able to see the local dispersion of the atmosphere on the transmit beam. Plus the polarisation of the echo gives info on the material at the moon reflection area, as the regolith will attenuate one polarisation slightly differently than the other. Plus with the timed numbered chirps you will get a measure of the distance down to the sub millimeter range, and will be able to get the velocity out of each chirp as well.

author: TSL
author_rank: Regular Contributor
timestamp: February 28, 2015, 02:03:06 am
content: Quote from: John Coloccia on February 27, 2015, 02:05:03 pmFrom the pdf link in my original quote..."The DSN ranging system provides a ranging signal for measuring the round-triplight time (RTLT) between a Deep Space Station (DSS) and a spacecraft. The ranging signal ofinterest in this module is a logical combination of a range clock and several pseudo-randomnoise (PN) codes. The DSS transmits an uplink carrier that has been phase modulated by thisranging signal. The modulated uplink carrier is received and processed by the spacecrafttransponder."also..."For example, if an X-Band uplink of 7,160 MHz is being used and suppose themeasurement obtained is 6,500,000 RU, then the equivalent RTLT delay is 6,153,467 ns, and theone-way distance (multiplying by c/2) is about 922,381.50 m."RU = "Range data are delivered to users in the form of Range Units (RU). Range unitsare defined, for historical reasons related to hardware design, as two cycles of the S-band uplinkfrequency (the only frequency band that was in use when the definition was established). As 2cycles of a 2 GHz frequency occur in a nanosecond, RUs are often described as beingapproximately 1 ns."Don't forget the moon is a big arsed satellite of earth with very stable known parameters so it makes sense to bounce a signal off it and see if your software agrees with those parameters.While EME is not a new thing as @HowardLong pointed out ( myself being a HAM I do realize this ) I thought this particular experiment is interesting and accessible by people without the usual HAM knowledge.JPL will be doing more experiments like this over the next few months and Jim has suggested that they are looking at using the 70m DS-34 at Tidbinbilla/Canberra, Australia with 400kw !!!!!I'd imagine we'll receive all sorts of interesting signal artifacts here in Oz given the power radiated.regardsTim

author: Zad
author_rank: Super Contributor
timestamp: March 01, 2015, 03:26:39 am
content: There are quite a few EME / moonbounce videos on YouTube. For example:

author: calexanian
author_rank: Super Contributor
timestamp: March 01, 2015, 04:42:26 pm
content: Even though it is commonplace to conduct EME comm you still have to admit, it's fun, and for people who do not have ready access to a transmitter site or know when the next scheduled transmission is this will give them a chance to play along.

author: John Coloccia
author_rank: Super Contributor
timestamp: March 01, 2015, 06:15:12 pm
content: Thanks for explaining, guys.