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DJ2JA > BAKEN 30.03.06 15:57l 107 Lines 5476 Bytes #999 (0) @ EU
BID : IWY428DB0SIF
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Subj: GB3VHF a new 2m beacon
Path: DB0FHN<DB0FOR<DB0SIF
Sent: 060330/1454z @:DB0SIF.#HES.DEU.EU [GIESSEN JO40IO] DP6.00 $:IWY428DB0SIF
From: DJ2JA @ DB0SIF.#HES.DEU.EU (Roland)
To: BAKEN @ EU
Amateur Radio Press Release
GB3VHF - A new replacement beacon designed for the 21st century
After several decades of excellent service, the 144.430 MHz beacon
located at Wrotham in Kent (JO01DH), was replaced on Sunday
26th February 2006 with a new state of the art beacon incorporating
several new RF and digital features.
The beacon which is the result of a year of design and construction by
a team of four radio amateurs, provides facilities some of which have
never been used in amateur radio beacons before.
At the heart of the beacon is a direct digital synthesiser designed,
constructed and programmed by Andy Talbot G4JNT. This generates a signal
directly at 72MHz and is L/C and crystal filtered and doubled to 144MHz
before passing to the PA. The DDS clock source will be locked to GPS with
a short time-constant phase-locked loop, and will normally maintain an
accuracy to within a few parts in 10-9 over a period of a few tens of
seconds, and better than 10-12 long term. The frequency of the CW carrier
(mark) being exactly on 144.430000MHz.
The most important feature of the new beacon is that by using the DDS,
the beacon can be programmed to transmit new modes. As before, the beacon
sends its callsign and locator in Morse, but using A1A (on /off) keying
rather than FSK.
To enable the beacon to be monitored at extreme ranges, the beacon
additionally transmits it's callsign and locator using WSJT JT65B mode.
The GPS also provides for the precise timing of the keying sequence,
such that the JT65B sequence will start at every even minute past the
hour for 48 seconds duration.
The Morse sequence will commence at the start of each odd minute past
the hour and last for 13 seconds.
At the start of each odd minute 30 seconds past the hour, at a precisely
timed point, 140 microseconds after the UTC one-second reference as
signalled by the GPS receiver, the phase of the carrier is reversed,
28 times in total to fill up the 30 second time slot. The result is a
1 bit/second pattern of 101010.. The BPSK mode has been incorporated to
allow users to become familiar with using precise timing methods to
assist in experimentation with coherent signal recovery, to measure time
of flight information and propagation testing.
In the event of GPS lock being lost, the beacon will suspend the JT65B
sequence and replace it with the Morse sequence, until such time as GPS
lock is re-established.
The RF section which was designed by Sam Jewell G4DDK, relies on a
Mitsubishi RA30H1317 power amplifier module for the PA. The use of
extensive RF L/C and crystal filtering throughout, ensures that the
beacon complies with the most stringent CEPT regulations for transmitters
operating in the VHF frequency range. The beacon has undergone exhaustive
tests in this respect. The RF power output of the beacon is 30 Watts.
The power supplies delivering both 12 amp; 24 volts for the entire
beacon, have been designed and built by David Bowman G0MRF who has
ensured that generous component under rating and spare current capacity
will help to provide the high reliability needed.
Over-sized heat sinks mean that no fan cooling is required, whatever the
ambient temperature.
Chris Whitmarsh G0FDZ, the beacon keeper, integrated the various modules
and units, and produced the metalwork and housing facilities for the
beacon. Ease of maintenance was very much in mind when designing the
beacon, so as to ensure minimal outage times when any faults occur.
This new beacon hardware is only the fourth to be employed, since the
beacon first became operational in 1959 at the end of International
Geo-physical Year (IGY).
The beacon antennas which comprise of two 3 element yagis beaming 288
and 348 degrees and located approximately 48 metres AGL are unchanged,
and have been employed since the mid 1980's when the current mast
replaced the original. The base of the mast is approximately 213 metres
ASL.
Software to decode the JT65B is easily obtainable on the Internet at the
WSJT website www.pulsar.princeton.edu/~joe/K1JT
To decode the JT65B, tune the carrier to obtain a tone of 1500Hz with
the receiver set to USB, and the dial frequency reading 144.4285. The
JT65B will then be tuned in correctly.
This beacon has been financed by the four participants only, but the
team gratefully acknowledge the donation of some parts for building the
beacon from Russ G4PBP, Derek G3GRO, Dave at Quartslab Ltd and Simon
G3LQR.
For details of the beacon DDS please see Andy Talbot's website at
www.scrbg.org/g4jnt
and for more information and photos of the beacon please see the beacon
website www.g0afh.com/gb3vhf
Chris Whitmarsh Sam Jewell
G0FDZ G4DDK
(Beacon Keeper GB3VHF)
Andy Talbot David Bowman
G4JNT G0MRF
Reception reports are most welcome.
www.g0afh.com/index.html
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