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 dxmaps.com. 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. Dxmaps.com 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 DXMaps.com 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.
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
