Tuesday, August 6, 2013

RF Maps of the Sky, Continued...

Here are a few more of the RF Noise Maps that I have been creating.  Each one is made by sweeping the 2m antenna array in a grid pattern across the sky, and recording the absolute level of RF noise seen by the antennas and SDR receiver.  The noise is measured in decibels (dB), with an arbitrary setpoint of roughly 21dB for the lowest noise seen (the "cold sky").

The first map shows a typical morning.  In the lower left is a bright red blob, corresponding to high noise coming out of a neighboring house (across the street, a few houses down).  In the upper right, there's a mild source of noise centered exactly around where the sun is located in the sky.  The cold sky in the upper left, away from most noise sources, is in the low 20's.

The next one was recorded during an evening when many TV's, fluorescent lamps, microwaves, and toaster ovens must have been running - there's very high noise near the horizon in all directions.

Next we have a nice morning with very low noise levels.  The sky is a very dark blue, indicating low RF signals at higher elevations.  Even the lower elevations have a nice (relatively!) low noise level.  My radios (and associated computer equipment) are located at 270 degrees azimuth on this map, and it's possible to see the orange "blob" from the RF that the computers, internet router, etc give off.

Next is a map created just as the sun appeared over the hills to the east in a July morning.  Accompanying the sunrise was a huge amount of radio noise that obliterated all EME reception right away.  Notice the huge red blob surrounding the sun in the sky, as viewed by the antennas:

One could argue that it's not sun noise at all in the lower right of the above plot.  Maybe it's my neighbor's TV?  Well, if we hypothesize that the noise is coming from the sun, then if we look at the same sky a few hours later, the noise should have moved and followed the sun.  This is exactly what we see, in the following plot from later on that morning:

Was the sun that noisy all day?  I took a reading a few hours later, and while there is still noise centered around the sun, the level has gone down quite a bit.  You can also see that my RF-generating neighbors at 248 degrees still have their noise going, and my neighbors to the south have turned something on as well:

The last plot is from a later July morning, with sun just coming over the hill but with little associated noise on that day.

The neighbor to the south at 180 degrees has whatever RF-noise box running, but on the whole noise levels are fairly low across the sky at 40 degrees elevation and above.

By way of reference, to hear a 4-yagi EME station, I pretty much need to have the Rf noise levels at that azimuth and elevation to be at 24dB or below (green or blue in the above plots).  When the noise is above 24dB (yellow, orange, and red in the plots above), I can only hear the strongest of the EME stations.

One nice thing about these plots is it lets me compare the local RF-noise environment from day to day, on a more or less absolute basis.  It helps to identify sources of noise, and to determine which noise sources are constant and which change over time.  It also helps to predict the best times and directions with which to listen for EME signals. Finally, it serves as a "reality check" that helps to verify system performance -- even if there's high noise that suddenly appears in one direction, by mapping the sky and seeing the rest of the noise levels are as expected, I can attribute the noise to a particular source rather than a system malfunction.

An example Excel 2003 spreadsheet that has these maps, and the macro that generates the color coding, is available here.  My previous post on this subject is located here.

Thursday, August 1, 2013

2013 Digital EME Contest

This was my first EME (earth-moon-earth) contest and I had a lot of fun but not much sleep!  The moon rose above my local hills past midnight local time, so on both days I was up the whole night long trying to make contacts.  The contest involved trying to make as many different contacts on the 2-meter (144 MHz) band as possible, using digital modes, and with one strict requirement:  all contacts must be complete two-way exchanges using only signals reflected off of the moon.

Out of the 29 QSO's, eight were new initials (stations not previously worked), including a new country (Uruguay) and two US states.  The most exciting contact was a local California station (Stanford W6YX), with very strong direct signals but also with a very weak lunar echo trace visible. Once the lunar echo was strong enough to decode, we could complete the QSO!

Below is the contest log:

Date            Time    Call    Grid    Sent    Rec'd
7/27/2013       6:50    UA3PTW  KO93    "O"     "O"
7/27/2013       7:56    I2FAK   JN45    "O"     "O"
7/27/2013       8:14    EB5EEO  IM98    "O"     "O"
7/27/2013       8:51    I3MEK   JN55    "O"     "O"
7/27/2013       8:57    DD0VF   JO61    "O"     "O"
7/27/2013       9:15    DL4KUG  JO64    "O"     "O"
7/27/2013       9:51    CX2SC   GF25    "O"     "O"
7/27/2013       10:05   WZ5Q    EM30    "O"     "O"
7/27/2013       10:18   CT1HZE  IM57    "O"     "O"
7/27/2013       10:49   K3RWR   FM18    "O"     "O"
7/27/2013       10:55   NZ5N    EL96    "O"     "O"
7/27/2013       11:06   AD4TJ   FM08    "O"     "O"
7/27/2013       13:43   K9MRI   EN70    "O"     "O"
7/27/2013       14:05   VK5APN  PF95    "O"     "O"
7/27/2013       15:01   W8WN    EM77    "O"     "O"
7/27/2013       15:25   KD9NH   EN44    "O"     "O"
7/27/2013       16:50   HL5QO   PM42    "O"     "O"
7/28/2013       7:18    HB9Q    JN47    "O"     "O"
7/28/2013       8:16    RU1MS   KO48    "O"     "O"
7/28/2013       9:01    OK1KIR  JO70    "O"     "O"
7/28/2013       9:11    UR7D    KN18    "O"     "O"
7/28/2013       9:15    F1DUZ   IN97    "O"     "O"
7/28/2013       9:44    G4SWX   JO02    "O"     "O"
7/28/2013       10:19   SM4GGC  JO69    "O"     "O"
7/28/2013       13:53   KE7NR   DM33    "O"     "O"
7/28/2013       14:00   VE1KG   FN84    "O"     "O"
7/28/2013       15:41   JA5EEU  PM63    "O"     "O"
7/28/2013       16:49   K5DNL   EM15    "O"     "O"
7/28/2013       17:36   W6YX    CM87    "O"     "O"

Here is a screenshot from a typical QSO.  This one is with VK5APN in Australia.  At 1402z you can see the trace that decoded as KB5WIA VK5APN PF95, when he replied to my CQ call.  At 1404z you can see the characteristic shorthand notation of "RO", where he acknowledged my OOO signal report.  And at 1406z you can see the shorthand notation for "73", indication completion of the QSO.  The lower left window is the WSJT9 software display from the FT-817ND analog radio, and the middle window is the MAP65 display from the FunCube Dongle Pro+ software-defined radio.

And next is a screenshot of the W6YX QSO.  In the SpecJT waterfall window, you can see the strong direct terrestrial JT65B signals clearly at about DF=80Hz.  At around -285Hz you can see a very faint trace, which decoded as KB5WIA W6YX CM87 at time 1731z.  The dT of the decoded trace is 2.0 seconds, in line with the expected 2.5-second round-trip of radio signals to the moon and back (the WSJT9 software clock is about 0.5 seconds behind the MAP65 clock, you can see this in the VK5APN windows above).  The Astronomical Data window in the upper right shows that the expected doppler shift between KB5WIA and W6YX was -369Hz at that instant.  The observed doppler shift of the faint trace is -285Hz - 80Hz = -365Hz, pretty much exactly as expected and further confirming the weak trace as a lunar echo.  Also of interest is the diagonal trace at 1733z, veering off the main sync line to the upper left; this is likely an airplane echo, doppler-shifted by the relative speed of the aircraft between the two stations.  To me, these QSO's are even more fascinating than EME DX contacts to the other side of the world -- since you can literally "see" the radios hearing signals coming direct through the air, the signals bouncing off of airplanes, and signals literally bouncing off the moon.

The MAP65 waterfall display (receiving signals from the FunCube Dongle Pro+) was really useful -- it helped to keep an eye on what signals were strong enough for easy decodes, and at times the messages display was full of QSO information.

All in all, it was a fun contest!  I'm pretty happy to make 29 unique QSO's via radio signals reflected off the moon, all in a single weekend!