Tuesday, March 6, 2012

All the Details Fit to Print!

There is a new feature on the RBN web site, one intended specifically to help Reverse Beacon operators.  If you click on the Skimmers menu on the main page, you'll be given the choice of Simple or Detailed List.  If you choose the Simple option, you'll be taken to the same page as before, but with a new link titled "Check here for detailed Skimmers list".  Click either "Detailed" link and you'll be taken to a new page that has a lot more information about each Skimmer.

Let's look at an entry:

Callsign     Skimmer      Aggregator  Bands          Skew    Began        Last Seen
N4ZR       v.
       ALL spots
2.1b7       7000~7070

    3 years ago   online

Now let's break it down. Incidentally, you may have noticed that callsigns move around on the Skimmer list.  This is because it is dynamic, based on the most recent spots, to the nearest minute.  In effect it looks at the RBN web-site's main page and lists the stations it sees online at that moment.

Next over, the "Skimmer" column displays the release of Skimmer or Skimmer Server being used by the station.  Below that is the validation level in use, and below that it reports whether the Skimmer is sending all spots to the Aggregator, or just CQ spots.  I'm sending all spots from the Skimmer to the Aggregator, and relying on the Aggregator to forward only CQ spots and regular beacon spots below 50 MHz, and all spots on 50 MHz and above.

The next column reports  the Aggregator version in use at the Reverse Beacon station.  We're encouraging everyone to be on at least version 2.01, but there are always stragglers.  I'm running 2.1 beta 7, which is a new one coming out soon.

Next is the Bands Column.  Here are listed the exact bands covered by the RBN station's Skimmer.  For technical reasons, a 96-KHz Skimmer bandwidth only produces a maximum of 91 KHz coverage, which is why the odd numbers.

The next column is where it really gets interesting.  "Skews" is a term that Felipe PY1NB invented to describe the difference between frequencies being reported by a given Skimmer for a given station, and the frequency reported by a reference station.  What's a reference station?  Well, we start with two all-band Skimmers, one in Europe and one in the United States, which have well-established frequency calibration.  Each time another station and one of these reference stations both make the same spot, the server compares their frequency reports.  They don't necessarily have to make the spot at the same time; in fact, if a non-reference station makes a spot, the server will try to validate it for some minutes against another spot of a station, before giving up.  And here's the clever part.  In addition to the two reference stations, any station that is found to agree with them exactly is named a temporary reference station, and for a substantial period it, too, can serve as a reference.  This helps to deal with propagation "holes" that might otherwise prevent validation of spots against one of the two principal reference stations.  When a band is open, we typically have 20-30 stations that are temporarily given this status.

So what does the column show?  If there is a "0" in the column it means that the RBN station is currently a reference station on that band.  If there is a "-", that means that the server has not yet been able to compare that station's spots on that band with one of the reference stations.  And finally, if there is a number, like "-0.2", it means that the last spot on that band by that station was off by that amount (in this case,  0.2 KHz low.

Because the DX cluster network only handles frequencies to an accuracy of 0.1 KHz, any station that has either a "0" or a +/- 0.1 entry should consider that its calibration is "right on."  Skews of 0.2 or more should probably be dealt with.  If you are using a QS1R, you will find that your skews, if any, will increase as you go up in frequency - so a 0.2 skew on 20 meters might be 0.4 on 10.

If you want to correct your calibration, an easy method was explained in a post on this blog in March, 2011.  You can read it at http://reversebeacon.blogspot.com/2011_03_01_archive.html

One interesting question that this raises.  If a station's calibration is off by a few tenths of a KHz, should the server apply a correction?  Opinions welcome!


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