An idea for a low cost stable 10GHz receiver

The satellite Es’Hail-2 is expected to be launched by the end of 2016. This will be the first geostationary satellite carrying an amateur radio transponder. As the launch date comes nearer, it becomes interesting to find a low cost solution to receive its 10GHz downlink.

Several amateurs have been experimenting with low cost LNBFs designed to receive satellite TV. These operate in the Ku band and usually cover the frequencies 10.7GHz-12.75GHz. However, many of these LNBFs have also good performance in the X band, and particularly in the amateur 10GHz band (10GHz-10.5GHz). In fact, the ASTRA-type LNBFs have a local oscillator which can be setted to either 9.75GHz or 10.6GHz. The 9.75GHz local oscillator mixes 10.386GHz (the narrowband terrestrial subband) to 618MHz, which is a frequency covered by most SDRs and conventional scanners. The satellite subband, which is 10.45GHz-10.5GHz gets mixed down to 700MHz-750MHz, a frequency which is also easy to deal with.

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Building the G0MRF comb generator

A comb generator is essentially an RF oscillator whose output is amplified in a non-linear fashion, so that plenty of harmonics are produced. This is an easy way of producing microwave signals. The G0MRF comb generator was originally designed as a 2.4GHz signal source, to help in the alignment of receivers for the amateur radio satellite S-band. It has a 96.013MHz crystal oscillator, so its 25th harmonic falls at 2400.325MHz, right in the satellite allocation of the 13cm amateur band. Its harmonics are usable up to at least 10GHz, so this can be an useful tool when working with microwave equipment.

In fact, several other harmonics fall on the amateur bands: The 13th harmonic is 1248.169MHz. This is inside the 23cm amateur band, but quite far from the narrow-band segment, which is at 1296MHz. The 24th harmonic is 2304.312MHz. This falls inside the 13cm band. Indeed, 2302MHz is used for EME in some parts of the world. The 36th harmonic is 3456.468MHz, in the 9cm band, but far from the narrow-band segment. The 59th harmonic is 5664.767MHz, in the 6cm band. This is in the satellite uplink segment and quite near the first narrow-band segment, which is at 5668MHz. The 60th harmonic is 5760.780MHz, right in the second narrow-band segment of the 6cm band. The 105th-109th harmonics all fall in the 3cm band. In particular, the 108th harmonic is 10369.404MHz, which is in the narrow-band segment of the 3cm band.

This is a nice kit which is quite easy to build. Most of the components are through-hole, and it can be put together fairly quickly. I built my kit during the Christmas holidays, but I’ve had the PCB lying around until I installed it in a project box yesterday. Here I describe the kit briefly and show the extruded aluminium case I’ve used.

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