10 GHz receiving

 

General considerations

In the 10 GHz band, it is mandatory to be in a line-of-sight path from the transmitter: good clearing or portable. To receive television signals in the 10 GHz band is today on the other hand relatively easy, thanks to the available cheap satellite kits in hypermarkets and other home depot stores.

For the choice of the components, to privilege the simplicity: standard steel offset satellite parabola with a 80 or 85 cm (32") diameter, biband head with a metallic case, closed by screws, rudimentary demodulator, the all without flourish. Let's avoid the satellite heads enveloped in a plastic shell. The case is then in light alloy and often of small size and is badly suitable to the modifications described lower. The first price satellite kits, below 70 Euros, are often perfect. 

The only difficulty resides in the frequency lowering of the "low" local oscillator, from 9.75 GHz to 9.00 GHz. The very classic method and abundantly described elsewhere is presented below.

Modification of a satellite head

The principle of the modification is very simple: it is sufficient to glue the high band DRO (10.6 GHz), on the tuning screw of the low band and to adjust the screw to make oscillate the low band oscillator on 9.00 GHz. The biband head contains all the necessary ingredients. All heads are not however comfortably modifiable and some oscillators are reticent to function to this rate. Some instabilities can also appear, in particular when the mobile DRO is approached very close to the fixed DRO. So, be indulgent with yourself if you encounter some failures !

An hard to modify head :

This biband head is not easily modifiable because the space is too small to lodge the two superposed DRO in the tiny light alloy case. Nevertheless, let's recover the high band DRO!

(click to enlarge)

 

An antediluvian Astra head !

Let's try to transplant the DRO recovered previously on this old monoband Astra head!

 

The opened head:

The glued high band DRO:

 

Tuning the local oscillator:

A small antenna placed in front of the small horn captures the head local oscillator leakage. The amplitude of this leakage is far from being negligible!

 

 

A spectrum analyzer and a frequency counter connected on the SA LO output allow a perfect tuning of the head in a trice !

 

You don't have a spectrum analyzer. No problem! You are going to tune your head in a few minutes:

Take a non modified satellite head connected on a demodulator satellite, itself connected on a TV set. With the demodulator remote control, select the high band (local oscillator on 10.600 GHz). Adjust the demodulator satellite frequency on 1600 MHz. You have now a sensitive receiver on 9.000 GHz (10.6 - 1.6) that is going to allow you to discover the local oscillator leakage of the head that you want to adjust exactly on 9.000 GHz. The gotten precision is of some MHz. You will be able to improve the result later by means of a known received frequency.

Antenna mounting

The available satellite offset antennas are designed to receive satellites situated in the sky, to an angle of roughly 45° relative to the horizon. When one wishes to use these antennas to receive a terrestrial transmitter, we need to topple the plan of the paraboloid. We can choose to bring up these "upside-down", that is to say with the head placed up, as shown on the photograph below:

 

 

Small mechanical amenities are however necessary:

- cut or deplace the vertical fixing tube "otherwise the arm support touches in top"

- create with a file a buttonhole to allow the elevation set up and "in the right sense"

 

Far away, the mount Aigoual:

 

 

How to evaluate the received signal strength ?

A small adaptation of your satellite demodulator is proposed.

 

B5+ et 73 de Jean-François Fourcadier, F4DAY

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