This photo shows a WDG009 multiplier constructed
by G3PHO. It is built in a homemade tinplate box and produces 50mW at 12GHz
from an input of 10mW at 2.4GHz
This information paper was written by the RSGB for the IARU Region 1 conference held in September 1995. It describes the changes which have taken place in 24GHz operation in the UK in recent years. It is still very much applicable, and is included here, with one update - an additional note about the G3WDG/PA0EZ contact in 1997.
Until recently, most operation on the 24GHz band was portable, mainly from hill and mountain top sites. In the UK, much of this operation had been using simple wideband FM equipment, with paths limited to line of sight of 100 to 150km distance.
In the UK, there are now a number of home stations operational, using narrowband equipment with power levels of typically 50 to 150mW, and several up to 1W. The benefits of this have already been seen, with regular scheduled tests and beacon observation, and a number of long distance contacts made.
The designs from DB6NT have been of especial importance in stimulating activity - the Mk II transverter [1], and low noise and high power amplifiers [2].
The simple DB6NT Mk II transverter provides an easy way of getting operational on 24GHz. This design provides a basic receiver and very low power transmitter (typically 0.2 to 0.6mW) using a diode subharmonic mixer. Addition of a low noise amplifier and high power amplifier improves the system, with noise figures of typically 3 to 4 dB, and a power output of some 50 to 100mW or more achieved.
The 12GHz local oscillator is typically generated using a G4DDK004 2.4GHz LO [3], followed by a G3WDG009 x5 multiplier [4 and photo below], providing a reliable 40 to 80mW output required at 12GHz.
This photo shows a WDG009 multiplier constructed
by G3PHO. It is built in a homemade tinplate box and produces 50mW at 12GHz
from an input of 10mW at 2.4GHz
Simple narrowband equipment using a basic DB6NT Mk II transverter has superior capability than the typical wideband FM equipment used in the UK in the past. It seems likely that within the next few years, much of the UK operation will be using narrowband equipment.
While most activity on the band was portable, this had the effect of limiting operation to those days when conditions look as if they may be good and two (or more) stations were able to travel to their respective sites. It is likely that good propagation days have been missed because of incorrect assumptions about good conditions.
Regular fixed station operation, with regular scheduled contacts, or an effective programme of beacon observation are needed in order to determine the real nature of 24GHz propagation.
The capability of the more advanced equipment, using powers of some 50mW to 1W, and noise figures down to around 3dB, allows many more paths to be tested with a chance of success.
SSB QSO's have taken place over the G3WDG/G4DDK and G3WDG/G3LQR paths (circa 130km) with powers as low as 100mW, indicating that the present generation of low cost FET power amplifiers, HEMT LNA's together with modest 25cm dishes are adequate to ensure a reasonable operational range when conditions are right.
Regular observation of the Schipol beacon PI7EHG on 24.192070GHz by several home stations located near the English east coast has already shown that super refraction at 24GHz does indeed occur over this mixed land/sea path.
Observations by G3LQR (JO02QF) throughout the summer of 1994 revealed no signals. On 24/12/1994, PI7EHG appeared for about an hour at strengths up to S5. The distance from Schipol to G3LQR is about 250km, of which about 50km is overland at the Dutch end and 15km at the UK end. The weather was cold and clear with temperatures of around 05C at each end of the path.
On 23/03/1995, the beacon was heard again, by both G3LQR and G4DDK (JO02PA). PA0EHG (the beacon keeper) travelled to the coast (JO22FF) and proceeded to work G3LQR for a first contact on the band between the UK and the Netherlands. The distance was 207km. G4DDK also heard PA0EHG at up to S9. At the time of these contacts the Schipol 10GHz beacon was up to 30dB over S9 at both G4DDK and G3LQR and although cold, the humidity was not judged to be particularly low. Indeed there was some low level mist at the UK end of the path.
Since this first contact, QSO's have now been made by G4DDK with ON6UG/P in JO10 and JO11 at distances of 210 and 157km respectively. Contact has also been made between G4DDK and PA0EHG/P (215km, JO22ff) and between G4DDK and PA0EZ (JO22) at 268km. This last contact is notable as being between two home stations.
Additional note: early in 1997, a new UK record was set when G3WDG (IO92RG) worked PA0EZ (JO22QF) over a distance of 391km on 24GHz. This is the first contact across the North Sea where both stations are located significantly inland.
Long distance propagation is not limited to super refraction at 24GHz. G3WDG installed a high power (1W) attended beacon on 24GHz at his home to allow long distance reception tests to be made. Both G3LQR and G4DDK have heard this beacon at up to 30dBN (2.5kHz) over the 130km path when overland ducting on 10GHz has been present. G3LQR has also observed strong precipitation scatter over this same path during conditions of heavy hail/sleet. Signal levels were higher than by tropospheric ducting by several dB on this particular path.
The tests have demonstrated the importance of stations in neighbouring countries operating in a common frequency band, and for these tests, in Northern Europe, 24.192GHz was used. There is long term concern that we are not using the primary allocation.
The advent of narrowband equipment and home stations in the UK has meant regular tests and beacon monitoring has become possible over both inland paths and sea paths to nearby mainland Europe. These tests have resulted in significant new contacts being made, with super refraction, tropospheric ducting and precipitation scatter being observed.
[1] 24GHz Transverter (MK II), Michael Kuhne DB6NT, Dubus 1/1993.
[2] Modules for 24GHz, Michael Kuhne DB6NT, Dubus 4/1993.
[3] Microwave Handbook Vol 2, Chapter 8, Sam Jewell G4DDK (Edited
by Mike Dixon G3PFR), RSGB 1991.
[4] Not yet published. Information from Charles Suckling G3WDG, 314A Newton
Road, Rushden, Northants, NN10 0SY, UK.
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