Last updated Sunday, 27 July 2008
On these pages:- Info about using and setting up the 5MHz beacon (GB3RAL) monitoring program. Info about the beacons.
Info about setting up a dedicated monitoring computer, remote control of it using VNC, networking notes, making charts with "Excel"
"GB3RAL" beacon software by Peter, G3PLX It is available in the middle of http://www.rsgb-spectrumforum.org.uk/5mhz%20beacon%20monitoring.htm This now includes a download of G3PLX's I/Q version for use with a "Softrock", or similar SDR receiver. Also note there is a recommended method for forwarding .LOG files. The mention of "Calibrating" refers to counting the number of 6db steps heard against the s/n ratio recorded by the beacon program. (Steps are the number of tones heard minus one.)
"GB3RAL" software is easy to run. All that is needed is to set it so the time display on the title bar is at UTC. Enable the text log. . Once you have setup everything, including the filenames, close and restart the program to check all is saved as required. Note there is an I/Q version for an SDR.
Setting up beacon (GB3RAL.EXE) software. Read the "Help" first!
Until you are accustomed to the program I recommend using the USB mode with a "TrackFreq." of 1500Hz +/- any normally slight adjustment that may be needed. An SDR will require a "centre frequency" to give around 1-3KHz offset. Anyone uncertain about the recordings they are making is free to send me their .LOG file, or a screenshot. "Hoversnap" at http://www.hoverdesk.net is just one free Screen Capture program. PNG format suits the program well, good quality and small file size.
Setting up Signal Levels.
I do not use Peter's recommended method, but try to keep signal levels as low as possible to avoid possible overload in the receiver (no AGC!) or soundcard.
I have used a switched attenuator in the antenna circuit, a variable one could be made from a couple of 100 ohm pots. Exact impedance matching is not needed. I am now using the 10db attenuator in the RX and reducing RF gain, but some RXs may not have an RF control. I find a "Softrock" SDR does not need an attenuator, may even benefit from a Norton preamp of a few db gain.
Adjust when noise levels are low, eg. early afternoon when no thunderstorms or local noise is evident. Observe the noise level on the program's Spectrum Display, increase antenna attenuation until the noise reaches a minimum then decrease it so that the noise level increases a few db. I find adjusting by ear gives similar results.
If you use Peter's method (And most do!) after reducing the RX RF gain try removing the antenna and looking at the noise level, it should reduce (from about 30db?). If it does not reduce then the settings are not correct, you are looking at RX noise.
Set the audio level so the noise peaks are low on the Spectrum Display at 5-10 db. If the Windows Record Volume slider is near it's minimum I suggest reducing the audio input with an attenuator.
As I said this is not Peter's method, Peter has said that provided one is certain that it is antenna noise that is registering on the display the actual level is not critical. I have two cards I cannot drive to the levels Peter suggests.
Apart from setting the time accurately on the Title Bar, some seem to have trouble finding the correct "Track Freq" setting when using CW mode or a poorly calibrated receiver. To get it near, a spectrum display program could be run when receiving the beacon. http://www.weaksignals.com/ For "Argo", "Spectran" etc. The "Track Freq" setting just needs to be set at the audio frequency that the receiver is producing from the beacon signal. Or, the receiver adjusted to give the tone that "Track Freq" is set.
Beacon carrier frequency 5.290 MHz Most rigs will display this frequency in CW mode, tone produced depends on rig settings. USB produces audio tone of 1500HZ when tuned to 5.2885MHz
I never remember whether to add or subtract the "Track Frequency" to centre the signal when setting up!
Below, the signal or marker is about 60Hz off frequency, but what way?
If the signal is the other side of the zero, interchange words ADD/SUBTRACT.
To tune the RX. USB:- A positive value means the received signal is high. LSB:- Means signal is lower than the centre "0". CW, depends!
Below, a shot of a correctly received beacon signal.
Your SNR
Chart should look something like this, ensure that the noise level IS reduced
with no antenna and that you have definite peaks when signal levels are high.
SOME systems will not allow peaks to reach 100db. Some RX/soundcard combinations
will not have enough gain.
Don't forget you are running the RX with no AGC, it's gain, or signal input, must be reduced.
GB3RAL Loc. IO91IN 51.34N 1.32W Rutherford Laboratory Oxfordshire. SU475870
Beacon carrier frequency 5.290 MHz Most rigs will display this frequency in CW mode, tone produced depends on rig settings. USB produces audio tone of 1500HZ when tuned to 5.2885MHz
There are nine dashes. The sequence is repeated on the 1/4 hour. Time is GPS
locked. TX frequency is not yet, slight drift approx -5Hz to +10Hz? (The
others are more accurate, 1.0-1.5Hz low?)
The beacon is running 10W into a full sized dipole oriented East West.
The following was obtained by Doug, MM0BJA:-
GB3RAL antenna should be treated as a dipole at 40ft . Orientation NNW/SSE.
It seems to be over a 30ft flat roof which acts a ground plane. Actual size
of antenna not known but if it is 30ft it about 1/3 wavelength. Assuming 1/2
wave though for modelling. [I believe it is a full size dipole G4ZFQ]
Amateurs (with or without 5MHz NoVs) are invited to send reception reports using the Station logging form, preferably electronically rather than handwritten, which is available along with guidance on reporting on the 5MHz Website,
Announcement from G3WGV 30 Oct 2004.
Reports are requested, either here or direct to me at john
at g3wgv.com
(mailto:john at g3wgv.com) . It's jolly
loud here :-)
GB3WES, the Westmorland beacon, made its debut on 5290kHz at precisely
1631Z
today.
GB3WES is one of a planned chain of (currently) three beacons, the other
being GB3RAL, Oxfordshire and GB3ORK, Orkney. GB3ORK is not yet QRV.
Information on GB3WES: See http://g3wgv.com/gb3wes.htm
and the rest of John's interesting site.
* Operates from the QTH of G3WGV, IO84QN
* Ground height: 205m ASL
* Antenna height: 9m AGL at apex
* Antenna: Full size dipole
* Power: 10W at full carrier
* Transmit time: 1 minute past the hour for a period of one minute.
Repeats
every 15 minutes. For information, GB3RAL transmits exactly on the
hour and
GB3ORK will transmit at 2 minutes past the hour, so the three beacons fire
up one after the other.
* Format of transmission:
0 seconds - Callsign sent at approximately 16WPM, followed by a period of
full power carrier
7 to 15 seconds - Nine transmission intervals with a 6dB reduction in
power
for each step, giving 48dB overall power reduction at the final interval.
For each step a 100ms break in transmission is followed by 900ms of
carrier at
the appropriate level.
16 to 24 seconds - Repeat of the power step sequence
25 to 30 seconds - 5 seconds of continuous transmission at full power –
this
is the interval used by G3PLX’s beacon monitoring software.
30 to 60 seconds - Sounder sequence consisting of a 500us wide pulse of
full
power carrier repeated at a 40Hz repetition rate.
(Rob MM1RAH is working on software to monitor this sounder. http://www.netronic.co.uk/mm1rah/scattergram.htm )
Some notes from Peter G3PLX
Re The Pulse Sounder Experiment.
The pulse sounder sequence from the GB3RAL beacon on 5290kHz transmits from
T+30 secs to T+60 secs, where T is on the hour and every 15 minutes.
The signal is a simple short pulse repeating at 40Hz (25mS repetition
interval).
The object of this experiment is to look at multipath.
If you trigger a scope from a stable 40Hz and look at the receiver audio, you
will see the pulse and any multipath echoes, but not very strong or very clear,
and we can do a lot better by processing the signal better. If anyone would like
to try experiments with the signal, here is an idea to start with, although it
does require some knowledge of mathematics and programming.
Effectively this idea sums-up all the pulses over the 30 second transmission
(1200 of them) in order to gain a considerable improvement in the display. It
means we can do this kind of experiment with a 10 watt pulse transmitter rather
than a 12kW pulse transmitter, so long as the ionosphere remains stable (or
moving at a steady rate) for 30 seconds.
First of all, record the whole 30 seconds onto a WAV file. The idea is to then
work on the whole file off-line. The first job is to sort the data in the file
into individual records, each containing 1200 audio samples.
Each record will be a "comb" of samples taken at 25mS intervals.
Effectively we have laid out the whole 30 seconds of audio in strips along a
rectangular array 25mS long by 1200 samples wide, then sliced the rectangle
cross-ways, to give us strips containing 1200 samples, each representing one
"element" of the 25mS pulse repetition interval over the whole 30
seconds.
There are several ways we could then analyse these. One way would be to
calculate the r.m.s. power in each one, and display the result as a graph.
This would show the shape of the pulse, including any multipath echoes.
Another way which gives a much more detailed view of the propagation, is to
compute the spectrum of each element, and display that as horizontal line of
pixels, with the stronger signal levels shown darker, displaying all elements as
a vertical stack of horizontal lines of pixels, building up to give a
two-dimensional picture with frequency along the horizontal axis, and time-delay
vertically, showing the signal levels at all combinations of time-delay and
frequency-offset. The vertical extent of this image is 25mS and the horizontal
extent is 40Hz, and the entire image is known as a scattergram, since it shows
the extent to which the propagation scatters the signal in both the time (mulipath)
and frequency (Doppler) dimensions.
On such a display, a clean direct path will show as a single dot, and a path
with an echo will show as a pair of dots, but because different paths via the
ionosphere are subject to differing Doppler shifts, the two dots may not be one
above the other, and this makes them much easier to distinguish from each other.
We can also see the O and X components of the F-layer reflection as separate
dots at the same height, and such things as Auroral echoes show as horizontal
streaks with a wide Doppler spread at a sharply-defined range.
Note that there is no synchronisation in this simple experiment, so the dot
pattern may appear anywhere at random in the vertical extent of the image, and
if the transmitter and receiver frequencies are not accurately-locked, the dot
pattern may appear anywhere in the horizontal extent of the image, but
individual scattergram images can be "cleaned-up" to centre the dot
pattern by scrolling then up/down or left/right. If your soundcard clock
is a bit off, the dot pattern will be smeared in the vertical direction, and
this will also be the case if the SSB filter in your receiver is too narrow or
suffering excessive group delay distortion, but there are ways round these
problems.
The GB3RAL signal is accurately timed from GPS, so a local time reference could
be used for the vertical axis, and it will then be possible to measure the
actual propagation-time of the path. Mike hopes to lock the frequency
source of GB3RAL to GPS too, and if the receiver is also locked to a
high-stability reference, it will be possible to read-off the actual Doppler
shift.
A third beacon located in the Orkneys is now operational. GB3ORK
The antenna is an inverted Vee 90ft overall, with a 1:1 current balun at the feed point. Centre height is 21ft above ground, orientation E-W.
First official transmission 3mins after the start of 3rd Dec 2004.
The RX is an Icom ICR70. Mode CW with 500HZ
filter. AGC Off. 10db attenuation and RF gain reduced so when band noise is low it is just audible.
CW mode is "LSB" Since May 2007 I have been using a
"Softrock" SDR. I have found this to be good but not quite sensitive
enough to see my daytime local noise floor. An 8db preamp with a LPF is added.
This RX drifts during warm up, only about 50Hz, but enough to move outside the beacon's "passband". If you are using a "drifty" receiver but have a more accurate transceiver run it in CW mode at 5.2900MHz at low power into a dummy load. This will give a marker to centre on, and also confirm whether it is necessary to add or subtract the difference from the "Track Frequency" box! It is a pain having to wait 15 minutes to find the compensation has been done in the opposite direction! I use a marker based on the G4JNT MSF frequency standard, divided down to 10KHz provides a marker on the beacon's nominal frequency. I now have a prototype standard based on a 10KHz output from a GPS, (when it stays locked!)
Antenna is the top section of a nest of dipoles
at 9m. The centre 20m is horizontal, the ends hang down vertically.
It has changed several times over the years and from March 2008 has been a 20m
long wire fed with coax at one end.
Maplin do a good line in Radio controlled Clocks and watches, ideal for checking program timing. The one on the left was £9.99 on special offer.
Click here for (Perhaps) a real-time update screenshot. And links to other "Real Time" sites.
Latest G4ZFQ Recordings of beacons, Links to Archived Graphs and Text Files Moved from this page.
Some notes on using a remote monitoring computer and a beginner's notes on using "Excel"
Comparisons GB3RAL and G4JNT with Vertical/horizontal antennas. G4JNT made and tested beacons 16 miles away.
G4ZFQ's PAGES AT QSL NET (You may have come from here)
Click link to email If you see no link or it does not work Click HERE GB3RAL - G4ZFQ