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.