10GHz Narrowband Equipment
The equipment shown on the left comprises a basic G3WDG transmit and receive system with the addition of a 1W Qualcomm amplifier. An G8ACE ovened oscillator with a Luis Cupido type PLL is used for the LO and this can be locked to a 10MHz GPS locked source. Another solution would be to use a REVDDS system. Its a pretty horrid looking assembly of parts as its "grown" over the years and been re-boxed several times, the last time to accomodate the 1W Qualcomm PA seen on the left.
For portable operation a 60cm offset antenna shown here, is used with a dual mode feed. Best Dx with this gear has been ~350km while out /P. With signals also copied off the moon, when the 20m dish at Bochum in Germany was activated with 200W!
A better design of feed horn by G4NNS has been tried instead of the dual mode feed but as yet a full evaluation has not been completed
Recent experiments have been looking at the more compact "Sky" dish....shown on the right. This has been tried with the same dual mode feed for 10Ghz and also a dual band feed for 10 and 24Ghz. To reduce pointing problems associated with getting the elevation correct, the dish is used at 90degrees to its normal operating position.
A Simple 10GHz Transverter
Some experimentation has been done recently with a very simple 2-GaAs FET transverter. This was published in the March 1989 Microwave Newsletter from a German design way back in the late 80's by DC0DA, but updated here with some more modern components. Output power is about 0.8mW and it gives a good account of itself on a single 20dB gain horn on both receive and transmit. Of course the performance is not up to a fully fledged transverter but creditable nevertheless and despite the low output power it can be classed as a "narrowband system" thus benefiting from the gains one gets over a wideband system of frequency stability and narrow operating bandwidth. The pcb is made on 0.79mm Teflon PCB with Er = 2.55 and of dimensions ~ 40 x 70mm. The power supply required is +5V and -1.5V. A suitable circuit operating from 12V is shown on page 18.108 of the RSGB Microwave Handbook Volume 3,using a 3 terminal 5V regulator and a 7660 negative voltage generator. If serious operation is contemplated, it would be advisable to fit a WG16 filter tuned to 10368.1Mhz ahead of the unit to prevent radiation of the LO frequency.
In addition to the parts shown here, one would need an LO producing 10224Mhz output at about 8mW from a 106.5Mhz crystal. This can be obtained from a xtal oscillator, a X24 multiplier and a X4 multiplier Or one can convert a 12GHz DB6NT LO/ multiplier module to 10Ghz as shown in the October 2009 Scatterpoint.
Wideband 10Ghz Equipment
The equipment below is a Mark 2 version of that used in the 1970 and 80's. The Mark 1 version used a simple diode mixer in waveguide 16 on receive and a cross-coupler but still achieved contacts in excess of 150km.
The Mark 2 version receiver comprises an ex-SATV LNB with the the DRO disabled and image filter by-passed. The output from a tunable Gunn oscillator is injected into the mixer via an isolator to reduce frequency pulling. The Gunn cavity is coarse tuned with a micrometer in the cavity with fine tuning done by varying the Gunn voltage +/- 1volt via a potentiomter. The IF output from the LNB is at 30MHz and this is amplified in a 30Mhz preamp before being down converted to 10.7Mhz where FM detection takes place in a standard wideband FM frequency discriminator.
The Tx side comprises a fixed tuned Gunn oscillator generating approx. 10mW output on 10.15GHz. This is FM modulated with either speech or an audio tone.
Coupling of both the Tx and Rx to the antenna is via a waveguide 16 circulator.
JT4G digital mode at 10GHz
Some recent tests have been made, receiving JT4G from G8IMR/G4JNT over a 32km partially obstructed path, under rainscatter conditions to investigate how well the mode stands up to anomolous propagation. As can be seen below, despite the signal being severly doppler shifted due to the heavy rain between the two stations, copy is still 100%
JT4G generation at 10GHz
The set-up below shows bench testing of a test signal source using a G8ACE 108MHz OCXO locked to a 10Mhz standard via a prototype RDDS module equipped with a PIC to generate a JT4G signal. This is then multiplied up to 10Ghz in a DDK004 source and WDG X4 multiplier. Accurate timing is produced by linking the RDDS module via its RS232 serial link (blue / green wires) to a Jupiter GPS system.