Friday, April 18, 2014

Solar Flare HF Blackout

Sunday, April 6, 2014

rtl_power (more modifications)

I've been working on improving the 'quality' of the rendered 3D data from my version of rtl_power.  This morning I reduced the MAXIMUM_RATE by 800k samples per second.

#define MAXIMUM_RATE  2000000 /* trh changed from 2800000 */

After a quick recompile, and restart of the running rtl_power instances I had running here are some results to compare with.



Notice the MUCH better rendered resolution, and the much smaller gap between frequencies!

Also notice that in the 2.0msps you can EASILY see an intermittent carrier at around 42 Mhz that you can't see in the 2.8msps version.  These are two diff dongles using the same upconverter, LNA, and antenna, running simultaneously.   There is NOTHING wrong with the 2.8msps RTL Dongle being used in this comparison.

Lets look at a much smaller spectrum in the same data 40-44Mhz between the 2.8msps and the 2.0msps now.



It appears that this change is a massive improvement!  Note that there is a difference in the time span being used between these to graphs however this should not be enough to cause this much of a vast difference. (I mistakenly deleted the raw data from the first graph too soon, to be able replot it to match the time in the second graph), this however is not the sort of issue that would cause the 'washed out' appearance of the 2.8msps graph.

Since for this frequency span we're we only scanning a total of 55Mhz (5-60Mhz) the additional retunes required for this change do nothing to impact overall performance negatively.

I may attempt later today to further reduce to doing 1msps MAX.  The goal is to reduce the dark fringes you see in the graph immediately above this text as much as possible.

Saturday, April 5, 2014

WHY is monitoring Mexico TV Ch2 important? (PART 2)

If you haven't read (Part 1) it is located here:

So in my previous post (similar title) I described the basic 'old school' methods of using Analog TV video carriers as a propagation indicator.

In this post I'll show you some of the newer ways that this can be done (fairly cheaply) without tying up an expensive receiver.

So using the the same sort of Yagi antenna I mentioned before and the same feedline "coax" that runs to a receiver, we can connect that feedline to an SDR Radio.  These days simple SDR radio's can come in all sorts of shapes and sizes and price ranges.  The cheapest that I'm aware of is something called an "RTL DVB-T TV DONGLE".  Of these in my humble opinion the most reliable and well built are created by a company named "NooElec" found HERE.  They are also on Ebay HERE.

I've been using THIS RTL Dongle now for quite a while with excellent results!  The smaller size is quite handy for the uses I have.  

I'm not going to go into the finer details on how to set this up in this post.  That's a whole 'nuther' set of posts, but you can find a TON of detail on how to use these inexpensive devices simply by Googling "RTL SDR".

Here is an image showing some of my current setup, although for monitoring XETV I currently only use ONE RTL dongle and an LNA (not really required).

This image shows 12 RTL dongles connected to 3 powered USB 3.0 hubs.  Along with several splitters, and LNA (low noise amplifiers) and lower-right is a Nooelec "Ham-It-Up" which up-converts 0-60 Mhz by 125 Mhz quite well and is used mostly for HF monitoring.

The top 1U rackmounted server is a small DELL Poweredge 860 with a Intel Xeon 2.4Ghz 4 core CPU and 4Gb of Ram.  This box connects to the USB hubs above.

Next I use a self-modified version of Osmocomm's RTL-SDR software.  I've modified the file format that 'rtl_power' generates when it runs to conform to the GNUPLOT '3D' file format.  I've also added a few command line options like -u <freq> which will take into account that I'm using a 125 Mhz upconverted and log the frequencies in the log file correctly.  I've also added the ability to do sub-second (millisecond) scans to the -i option.

Anyway...the net result of all of this is that I can run rtl_power to do 'frequency scans' and the code logs the date/time, frequency (corrected for upconversion if used), and dbm (the power level noted by the RTL Dongle).

Since rtl_power will then log the data in a GNUPLOT "3D" file format I can simple using 'plot' or 'splot' within GNUPLOT to create some VERY nice graphs of what is actually going on.

Here are a few examples (not all are related to XETV monitoring, but are shown to give you some ideas of your own for it's use)

Anyway you probably get the idea here.

The next steps I plan on doing is using the logged data NOT to create graphs, but to alert when a frequency like 55.250 Mhz reaches a certain minimum threshold and remains above that level for a certain amount of time.  Long enough above the minimum so that we can infer that this is NOT a meteor enhanced event.  Typically a Meteor will only cause an ionization that will last between milliseconds and <= 3 Minutes.  So some time greater than 3 (probably more like 5 Minutes).

Believe it not, in my experience I've noted elevated XETV during events such as:

  • Back Scatter on XETV at 260 degrees stronger than direct, coinciding with New Zealand and Australian (south pacific) 50 Mhz "openings".
  • Back Scatter on XETV at 80-100 degrees during 50 Mhz opening to N. AF and EU.
  • Back Scatter on XETV at 320 degrees during 50 Mhz openings to Japan!
While I DO NOT advocate that we limit our monitoring to XETV alone, XETV has proven to be amazingly accurate and helpful in my search for 50 Mhz Radio propagation.  Others that I would like to note are Canadian Channel 2 TV (VETV) there are still several VETV stations active.  I've heard Greenland TV as well, and some others I still have not identified in that same general direction.

THE DOWN SIDE (and more)

Is that the world is changing.  And analog TV is becoming a dinosaur now, with more and more countries migrating to Digital HDTV formats.  While this is a bummer, it's not the end of the world.  There are still 'pilot carriers' related to these on-air TV stations.  And they undoubtable will become more and more useful as the older analog carriers fade into history.

WHY is monitoring Mexico TV Ch2 important?

Over the years I've learned (as have MANY others who are interested in 50 Mhz Radio Propagation) that monitoring 55 Mhz (and 45, 58,49 Mhz) Analog TV carriers is an important tool when hunting for long distance radio contacts in the 50 Mhz Ham Radio spectrum.  It should be fairly obvious that if the "Maximum Usable Frequency" or "MUF" :-) is greater than 50Mhz that with a bit of luck and hunting around we might find those long distance "DX" contacts we tirelessly search for.

The following is a brief case study in how this can be done, and how useful it can be.

To give you a brief synopsis of how I am monitoring for Mexican TV (here after known as "XE" or "XETV") I'll list some of the hardware and software items I'm currently using and demostrate how they are used, as well as some followup comments and ideas I have on the subject.

Please keep in mind that this is ONLY a case study in the usefulness of monitoring XETV.  However, there are MANY such TV carriers still active around the world and similar use applies to them as well.

Lets take a look at several ways of monitoring for these carriers.  These methods are all fairly simple although some are more complex that others.

The simplest method is to connect a radio capable of tuning to 55.250 Mhz (in this example) there are MANY others for example: (48.25, 49.75, 55.24, 55.26, and on up into the UHF range)  XETV Channel 2 uses several different 'offsets' 55.24, 55.25, 55.26 Mhz.  For this example we'll just talk about 55.25 Mhz for the time-being.

So now we have a radio, and some 'feedline' (aka "Coax") connected to an antenna someplace.  I have used many types of antennas, from Dipoles, to Loops, to Discones, to Yagi antennas.  I've had the best luck using "Yagi" antennas.  A simple 3 element 50 Mhz Yagi will do just fine!  The primary reasons for using this type of antenna is that it provides some directivity.  This means that in the direction of interest where the antenna is pointed we should have the most 'gain' from the antenna.  Meanwhile other directions have NULL's and reduced gain the net effect of which all aid us in focusing the energy we want into our receiver, while avoiding unwanted signals and noise.  Reducing noise, has the added effect of improving our detection of the signals we are hunting for.

So the age old method of hunting for these signals is basically what I've described so far.  We have an antenna, some feedline "coax" connected to our Receiver that can listen to 55.250 Mhz.  Personally I prefer to use "CW" mode to listen for these carriers, while others like to use SSB.  Using "CW" and my Ear I can tune to the most exact frequency that I can, aided by using narrow CW filters.  In this way I can be quite sure of the TV carrier I'm actually hearing, as most TV carriers are just ever so slightly off in frequency that the offset can help us in determining which one we're hearing (over time, we can with a fair amount of accuracy determine the location of the actual transmitter which is QUITE helpful!)

So we tune to the frequency we want to monitor and then we sit there and listen.  Duh?  Yep...that's it.  With any luck we'll hear what are commonly called "pings".  Pings are the effect of a meteor passing over 'someplace' and creating an 'ionized trail of dense particles which may reflect the distance TV carrier we're hunting for.  These tend to be quite random for the most part.  And while they are useful for some types of radio propagation, namely "Meteor Scatter" they aren't really what most avid "DX'ers" are looking for.  But this is the initial sign that your system WILL work!  So this is an excellent sign so far.

"foEs" or "Es" is a layer in the ionosphere that is capable when packed with dense electrons, of reflecting radio signals back to earth one, or many times.  THIS IS WHAT WE'RE SEARCING FOR at least at this point.  These densely packed electrons are able to reflect radio waves long distances.  A single hop typically is about 1000-2300km. (more or less).  From where I live in Missouri it is about 2100km to one of the common TV Channel 2 transmitters I hear that is located in the Yucatan peninsula.  This distance is perfect for monitoring for Meteor Scatter as well as "Es".   So from here that is 176 degrees from North.  THAT is where I aim my small Yagi antenna a lot of the time.

Here is a FULL ON XETV opening

An example of an "Es" type "opening" is while listening to 55.250 Mhz I may initially hear a few "pings" or a very faint steady carrier.  This signal begins to build, sometimes gradually to a very strong signal.  Other times the signal can just go from noise to instantly strong.  Still other times the signal may 'waffle' up and down in intensity, Hams call this "QSB" which basically means your signal is fading from time to time.  Based on the stability of this carrier, and it's strength this can help to determine how well the ionosphere is behaving (for what we're looking for).  What we basically want is a SOLID, STRONG (or extremely strong) carrier.

Here is an example of a fairly strong XETV "Es" propagated carrier on the right side you will see a display that shows the 55.250 Mhz Video carrier, and on the left side (top) is the 59.750 Mhz WFM audio carrier.  (bottom) is spectrum analysis of the 55.250 TV carrier and it's offsets.

So these are some VISUAL tools that can be used to help monitor LIVE signals that you are HEARING on the radio.  They can all provide some insight into how strong the radio propagation is (at least to the transmitter sites).

The KEY here, is that you know you are 'at least' getting as far as that transmitter.  The downside yet is that you know for certain if you are getting beyond that.  But there is a good chance that you will be able to.  So this is a very important tool that I use DAILY.

Some more examples of some "foEs" and even better (longer distances) "foF2" (which is a much higher layer in the ionosphere that reflects signals around 1.5-2x+ as far as foEs 'on average' per hop).

Last night we had an 'opening' to South America as far south as Uruguay here.  The following graph was created from power samples that came from 55.250 Mhz over about 4 hours in duration.

(click the graph for a larger view)

This graph shows an initial brief surge around 00:15z, followed by another surge around 00:25z.  Then between 00:30z and about 02:40z a fairly well sustained opening existed.  In this graph you can see some of the "QSB" (fading) that can occur during such an opening.

At 01:13z I contacted a ham via Morse Code located in Chile.  His callsign is "CE2AWW".  Here is a short video of that event.

Referring back the graph above you can PLAINLY see that this contact was definitely 'aided' by "Es" around Mexico.  The "MUF" was well above 80 Mhz into Mexico at this time.

In my next post "Part 2" of this series I'll further detail how I currently monitor XETV.  And how I intend to provide 'Automated' alerts to these types of events.

Continue to "Part 2" Here: