Using Beamfinder and Beamfinder Plus

For Beamfinder, you will need Plane Plotter with a suitable receiver.  Currently the SBS1, PGR, AVR/Beast, miniADSB, microADSB, SSRx allow use of the Beamfinder facility.

For Beamfinder Plus, you need a receiver also capable of capturing the mode A/C transponder pings.  Currently, only The ADS-B Beast allows this.

Beamfinder FAQ

What does the Display Ping Log file show for identifiers?

Use the Display Ping Log file after capturing the identifier pings to see whether a particular II or SI file shows a clear "hole" centred on a radar site.  There's an example here showing the "hole" around Inverness, Scotland radar.

Beamfinder Plus FAQ

I see quite a list of PRFs when the "z" key is pressed, but some are quite similar?

The acceptance of a matching PRF (pulse repetition frequency) has a tolerance of 2 microseconds.  Similar values may be from different radars or they be members of the family of intervals created by the jitter pattern that some radars use to avoid synchronous confusion with other sites.
For example, here in Adelaide, one of the transmitters has a nominal PRF of 3323 us and the other transmitter has a nominal PRF of 3325 µs.  The transmitters are used on alternate days, I think.  Both of them have a 5-fold jitter pattern of +10, +20, -20, -10, 0 µs.  This leads to the following observed pulse intervals for the first transmission:
  6656, 6676, 6646, 6616, 6636 µs
and these for the second transmission:
  6660, 6680, 6650, 6620, 6640 µs

Do radars from the same manufacturer have the same PRF?

The manufacturer does not define the PRF.  The systems analysts who design the overall system will specify PRFs such that synchronous interference between overlapping sites is avoided or controlled.

Why are the entries in the "z" list apparently in a random order?

They are not random, they are sorted in descending order of frequency of occurrence, with the most common interval at the top of the list.  Sorted in this way, analysing them in the order given gives you the best results first and when the analysis starts to fail, you can usually ignore the rest.

Why do I see multiple PRFs from the same site?

Radars can do all sorts of interesting things. They can introduce a systematic jitter in the interval between pulses and they can use various strategies for separately interrogating Mode-A and Mode-C responses from aircraft.

Imagine a radar that is alternately polling Mode-A and Mode-C. Suppose that it also has an interval jitter that contains a number of steps that is not a multiple of two. You can easily imagine that there are several apparent intervals, measured from A-ping to A-ping and from C-ping to C-ping, manifested by the same site.

In the case where the polls go C,C,A,C,C,A then it would not be surprising if the interval between pings from the same site was seen to be both "t" (C-ping to adjacent C-ping) and also "2t" (C-ping to non-adjacent C-ping) and also "3t" (A-ping to A ping).

The only thing that matters is what intervals PP sees coming out of the receiver and whether or not they turn out to be unique to a site and therefore capable of uniquely identifying that site.

(from a message from Bev in this thread on the Plane Plotter Yahoo group)

Should I include entries in Radar.txt for the multiple PRFs I see?

Multiple PRFs are only to be expected.  Given the number of message collisions, it is going to be fairly likely that one ping is not received, either at the aircraft, so the aircraft responds after 2t or at the ground even if the aircraft responds after t.  The observed pulse interval will then be twice the nominal value.  It is worth including these so that a "beam" results even when one ping is lost.

What does the Display Ping Log file show for pulse rates?

Use the Display Ping Log file after capturing the pulse rate pings to see whether there are lines pointing towards a radar site.  There's an example here showing the lines pointing at Dublin.  Not very clear!  Anyone have a better example?

How are the different message types used in the Beamfinder functions?

Please see this page.