Monday, June 24, 2013

6 Meters and the Power of the Reverse Beacon Network

by Paul Carreiro, N6EV
The Reverse Beacon Network has evolved to become a powerful tool with quite a few Amateur Radio applications, mostly on the HF bands.  Antenna comparisons; spotting contest and DX stations; checking to see where your transmission is being heard; and seeing which bands might be open to particular parts of the world at any given time are just a few examples of the RBN’s usefulness.  The RBN also provides a very unique opportunity for real time propagation awareness on VHF, and in particular on 6 meters.
“The Magic Band”
6 meters is known as the ‘Magic Band’.  It got this nickname in part because of the wide range and transitory nature of its propagation modes. F2, Sporadic-E, Transequatorial, Tropospheric, Back Scatter, and Meteor Scatter are all propagation modes regularly observed on the band, often at the same time or in combination!  The power of RBN’s ever-listening ear, combined with the existing constellation of active beacon stations, enables an awareness of 6 meter band conditions unheard of before now.    
In the case of sporadic-E, the added path information helps more than just those operators geographically close to the RBN node and spotted station.  The center of a sporadic-E path is generally where the ‘E Cloud’ resides.  As a result, operators around the spotted path are alerted to probable centers of sporadic-E ‘cloud' activity.  This allows them to anticipate additional paths that share the common 'cloud' center; or even connect multiple ‘cloud’ centers into multi-hop paths.
RBN and 6 Meters in Action
Here are a couple of excellent examples of 6 meter propagation as shown on the 6 meter maps at  Often, RBN spots (green callsign paths on the map), particularly of beacons, are some of the first to show up, indicating the start of a sporadic-E opening.

Note how the intersection of the paths clearly locates the sporadic-E cloud area. also offers a real time EMUF map view showing the upper cutoff frequencies for each sporadic-E center of activity.
Of course, it works in Europe too.

The Reverse Beacon Network coupled with equals fantastic real time 6 meter propagation awareness!

Unique Issues for 6 Meter RBN Nodes
You’ll note in the maps above that some of the spots in both Europe and the U.S. were derived from active beacons.  In order to spot beacon stations on the band, Skimmer must be configured to pass all callsigns, not just CQing stations.  However, disabling this filter opens up the possibility of Skimmer falsely spotting a callsign it decodes from digital spurs created by consumer electronics that seem to be prevalent on 6 meters.  The callsigns of these false spots often contain lots of dits (e.g. EI5I, ES5I, EE5E).  
 A situation can also arise where Skimmer decodes not only the callsign of the station being heard, but also of the unheard station being worked.  This is the result of the heard station sending the unheard station’s callsign repeatedly in an exchange.  This is common on HF too, but would be considered a particularly unhelpful false spot on 6 meters as the propagation path between the RBN node and the unheard station does not exist.

The steps to help eliminate false spots for a 6 meter RBN node are relatively simple.
1.    Turn ON Skimmer’s Aggressive Call Validation – this forces Skimmer to decode the callsign more times in a row before it is announced.  It also puts a higher weighting to callsigns in the Watch List (see next item)

2.    Populate the Skimmer Watch List with a list of callsigns of known beacons and other stations heard on the band operating CW.  With aggressive call validation active, any call in the Watch List will be validated more quickly.  A good source for this is the current World Wide 6 Meter Beacon List maintained by G3USF, stripped of all the text except the callsigns.  In addition to beacon calls, you can add the calls of CW ops worked or spotted from your location.  This way subsequent spots are validated quicker.  The Watch List can be managed easily as an external text file with a text editor.  Include comment text to help organize the list into sections.  Cut and paste into Skimmer when updated.

3.    In Aggregator, under the Spot Filters tab:

     a.    Enable the filter to eliminate callsigns that look like grid squares.  Many beacons send grid squares identifiers which are occasionally misinterpreted by Skimmer as callsigns.

     b.    Enable the filter to not send VHF+ callsigns with 1dB SNR or less.  Many of the digital spurs on the band are close to the noise floor.   Typical false spots with lots of dits show up with 1dB SNR
     c.    If you have known digital spurs that repeatedly are the source of falls spots you can populate those frequencies in the bad frequency list and click the appropriate filter to not spot those frequencies.

     d.    If you have persistent false spots from partial callsigns, or incorrect beacon call signs (usually from poor automatic beacon CW spacing), you can add those bad callsigns to the bad callsign list and click the appropriate filter to eliminate them.

4.    Monitor the 6 meter spots from your RBN node on a regular basis.  Look for false spots and analyze if any adjustment in filtering is necessary.  You can also collect additional spotted callsigns to include in your Watch List.

5.    Update the beacon callsigns in your Watch List to represent exactly what is spotted and/or sent over the air.  Many beacons send a call suffix of /B not represented in the G3USF list.

6.    Keep your Skimmer and Aggregator software up to date.   Features, filters and algorithms are improved and added from time to time.

Performing these few steps will eliminate most of the false spots typically reported by new RBN nodes on 6 meters.

6 Meters Needs Your Help!
We need additional 6 meter RBN nodes in North America!  Europe currently has much better RBN node coverage on the band and as a result enjoys very good early warning of 6 meter openings.  At the moment a handful of full time and part time nodes are in operation in the continental U.S.  We could really use additional coverage in the Mid-west, Gulf, Plains and Western states (is that all?!).  The more diverse and plentiful the nodes are the better.  It’s summer time.  And that means sporadic-E season is upon us.  Activity on 6 meters is hot.  So now is the time to set up a 6 meter RBN node!  If you have a QS1R coupled with Skimmer Server, consider giving up one of the lower frequency bands in favor of 6 meters from mid-May through August (sporadic-E season) each year.  Softrock offers a single band VHF SDR kit at a reasonable price, making it a good choice for a full time 6 meter RBN node.

6 Meters for the Uninitiated
For those not familiar with the 6 meter band layout, CW activity can be found between 50.000 and 50.126 MHz.  International beacons are found between 50.000 and 50.060.  The U.S. beacon band runs from 50.060 to 50.080.  Point-to-point CW QSOs are found between 50.080 and 50.100.  The DX window, which includes CW activity, runs between 50.100 and 50.125.  50.125 is the U.S. SSB calling frequency.  Some CW ops often call CQ on the SSB calling frequency (an accepted practice) to drum up activity when there aren't many signals on the band.  

In Skimmer, configure the 6 meter CW band limits between 50.000 and 50.127 without any beacon band annotation.  Depending on available bandwidth, your 6 meter RBN should concentrate on 50.059 to 50.127 (in the U.S.), and if you have the available bandwidth, run Skimmer between 50.000 and 50.127. Note: Even if you can run 192-KHz bandwidth, the default Skimsrv.ini file has the 6m CWSegment set to 50.0-50.1 MHz.  You'll need to edit that line to 50000000-50130000 before Skimmer Server will decode above 50.1 MHz.

Antennas for a 6 meter RBN node don’t need to be elaborate.  Even though the vast majority of weak signal work (CW/SSB) on 6 meters is done with horizontal polarization, a vertical works well for skimming and has the advantage of the omnidirectional pattern.  I’ve used a simple Cushcraft Ringo Ranger for my 6 meter RBN node the past three years with great success.  A halo for omnidirectional horizontal polarization is commercially available and is also easy to build.  If you don’t have a 6 meter-specific antenna, the use of a preamp is advisable.

Contact me, the RBN team or Mark, N2QT, who also operates a full time 6 meter node, if you need help setting one up.

73 – Paul,  N6EV

Sunday, June 23, 2013

A Low-Cost Specialized Skimmer Computer

I thought others might be interested in the specs and design criteria of my new Skimmer computer. 

First, I should say that my old Skimmer computer, running an E2200 dual-core Pentium, was distinctly unhappy in contests at 96 KHz coverage of 6 bands, and was absolutely knocked flat at 192 KHz.

I couldn't spend a lot of money, but wanted to do better.  Here's what I came up with:

  • An AMD FX-8350 8-core processor.  This processor has a Passmark score of over 9141, compared to the E2200's 1160.  The AMD is far more cost-effective than Intels of comparable performance, and it even comes with its own cooler
  • An ASUS M5A78L-MLX Plus motherboard.  This is quite an old design, but is the only one I could find that still has onboard video and audio and takes decently fast memory.  And it is really cheap.  I've always liked Asus, not least for their comprehensive user manuals.
  • 8 GB of DDR3 1666 MHz memory.  I have never seen more than about 3 GB of memory in use by Skimmer, but memory is cheap these days, so why not.
I reused my case, power supply, PCI wifi adapter and the DVD drive from the old computer.  Total cost, including a new full copy of Windows 7 Home Premium, was US$ 375.

How does it work?  This weekend, with over 1000 decoders and over 1100 QSOs per 30 minutes, and 192 KHz bandwidth on 7 bands, Skimmer Server was consuming 8-11 percent of the CPU.  I think this bodes very well.

73, Pete N4ZR