Topband: Spot Light Effects...

Ford Peterson ford at
Mon Jan 3 11:01:02 EST 2005

>From Tom-W8JI's comment on the beacon thread:


> I wonder is a lot of the "search light" effect is really
> just normal small or modest level increases. I wish I could
> record absolute signal levels over a long period of time,
> but I can't.
> 73 Tom

Tom, and others...

I have been following the 'beacon' thread for some weeks now.  It's interesting to observe (it would be more interesting to participate) but the distances to MN are a waste of time at such low levels.  In my view, the close-in path of very low level signals is not very interesting.  I have NO problem working anyone within 1000 miles of here, even at QRP levels.  So the scientific nature of these close-in paths is not extremely interesting to this op.

What is of interest is the so-called spot light effects on longer paths, of which I am a firm believer, but fail to understand the physics.  There are loads of speculations but little 'proof' and even considerable numbers of people that believe these effects to be nothing short of fairy tale--pure randomness.  I have worked enough 160M contests to know that NFL/WCF/FL in general is a difficult path to MN for some reason.  I can also demonstrate from numerous logs on different weekends that the MN/SC, MN/FL, MN/AL, MN/MS, MN/LA (and others) can be a similar difficult path.  Nothing in the log and then suddenly 3 or 4 stations (or more) from a single section will appear consecutively with good signal strength--never to be heard from again the entire night.  Weird and too coincidental to simply dismiss as a fairy tale.

For the last couple of weeks, I have been investigating an experiment to attempt to document what is happening in hopes of solidifying the nature of the physics.  While contest logs are somewhat interesting, they only document completed QSOs.  My 'experiment' involves a beacon running all night.  Special software would be utilized to allow receiving stations to set and forget the project rest of the night.  The software would listen and document the S-Meter reading on the radio throughout the evening--posting an average reading to a data file every few seconds perhaps?  A file transfer the next day via email would permit a cumulative database of these 'reports.'

The point Tom makes about variations in antenna patterns, and equipment sensitivity, makes the results only relative from station-to-station.  Absolute levels are not necessarily comparable at all.  But with enough reports, I believe a series of maps could be developed that performs some average results--perhaps by using grid squares--over the course of an entire evening--for the entire continent.  By orchestrating different beacon locations on different nights, and coordinating the reporting efforts from a central clearing house, I believe the maps could serve to illustrate the effectiveness of that path through the entire period of darkness.

Power level would be set at the beacon to facilitate a reliable path but remain well within the AGC range of most distant radios  (100W maybe? 50W? 25W? 10W?)  I don't know yet.  Perhaps the software can track many beacons all at once?  E.g. a beacon in CT, SC, GA, SFL, TX, MO, MN, AZ, CO, WA, CA all on the same night but a different frequency for each.  The software at each receiving station would be programmed to QSY to each frequency in sequence, document the SMeter reading and QSY to the next.  Tens of Thousands of data points throughout the evening from hundreds of reporting stations would document the various paths over time and in unison.  The resulting database would be large, but easily managed using any beefy computer.  A summary of paths could then be placed on a grid map to document the path condition to each beacon--perhaps using color to identify relative intensity of the signals.  Correlating these results to propagation conditions throughout the evening.  Documenting 6M or 10M conditions simultaneously may prove interesting as well, but increases the complexity of the project substantially.

I have contacted Alex-VE3NEA (the DX Atlas guy) and discussed the project and am waiting for his educated advice on the matter.  I've worked with Alex before on software projects--he's a magician with software.  He may be too consumed with his other projects (like Peter I) to take this on.  But perhaps others would like to give it a shot?  I think it would be a worthwhile effort as long as whoever acts as the clearing house of the data is willing to also share the resulting data collected.  If I am the clearing house, I can assure all that the data would be available to all who participate--and only those that participate (an incentive to participate).

ford at

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