TinySA: How to increase the frequency range

The TinySA (https://www.tinysa.org/wiki/) is a wonderful device. At an absolutely amazing price it offers a complete spectrum analyser which is (very small – almost tiny), features a built-in LCD, a battery and the measurements are quite precise.

But there is a catch: the supported frequency range is rather reduced. It can operate in the 0.1MHZ-350MHz range with increased precision or in the 240MHz-960MHz range with less precision.

This covers most amateur radio needs and even allows CATV measurements. But what about the L-Band? This band, as you know covers 950MHz-2150MHz and is used by satellite receivers for satellite TV. The LNB will down-convert from the C, Ku or Ka band into L-Band and the receiver-se tuner will then lock on whatever transponder that is required for the selected TV channel.

All the satellite TV aficionados are not served by the TinySA. Unless of course, they use an RF mixer! Such a device will down/up-convert a signal on the input connector and present the both the original and the down/up-converted signal on its output.

For this to work, a third connector on the mixer requires the input of a frequency. This frequency determines by how much the input signal is down/up-converted.

You therefor need a signal generator that produces for instance a 700MHz signal. This is fed into the mixer. On the input connector you attach the LNB LOOPTHROUGH of the satellite receiver (note that you must use a DC blocker, otherwise you will break the mixer and/or the TinySA).

The output connector of the mixer will present you with a signal composed of the original input signal and two copies of it: one at (950MHz-2150MHz) minus 700MHz = 250MHz-1450MHz and at (950MHz-2150MHz) plus 700MHz =1650MHz- 2850MHz.

If you follow the simple math, you will notice an overlap from 950MHz-1450MHz for the down-converted signal and 1650MHz-2150MHz for the up-converted signal. However, since we are only interested in the down-converted signal and because the TinySA can only support an input up to 960MHz, that is not really a problem, apart from the fact that the frequency range of the TinySA is too small to render the complete down-converted L-Band.

This means we need to work with two different frequencies on the signal generator, each down-converting half of the L-band into the 240MHz-960MHz frequency range of the TinySA.

Naturally, down-converting a signal with this setup comes with a cost: the mixer will attenuate the input signal, eventually it will attenuate the input signal considerably. To compensate, it might be required to first amplify the input signal to compensate for such attenuation.

Anyway, the easiest approach to extending the frequency range of the TinySA is to use moRFeus (https://othernet.is/products/morfeus-1), a device that combines a signal generator (up to 6GHz) and a mixer.

Effectively it is possible to down-convert any signal by up to 6GHz, so that the TinySA can render it! Note, however, that any signal over 2-3GHz is borderline magic and suitable cables, connectors, etc. will be required, otherwise the attenuation will move the signal under the noise floor.

Here is my setup to look at satellite signals with the TinySA:

The satellite receiver powers the LNB and the LNB LOOPTHROUGH connector goes from the receiver to the moRFeus input, which is protected by an inline DC blocker.

On the moRFeus, the MIXER mode is selected and the signal generator frequency is set to 700MHz, as described above.

The TinySA can now render the satellite transponders! Note that the displayed frequencies need to be compensated, by adding 700MHz.

Here is the same spectrum as rendered on my VMA Simple Spectrum Analyser software for the TinySA.

Notice that the frequencies are wrong, as the software does not compensate for the 700MHz down-conversion.

By entering a LOF of 700MHz, the frequency scale is correctly compensated. 

This allows the automatic satellite recognition algorithm to correctly identify the satellite, in this case Astra at 19.2E.

By entering a LOF of 9750MHz+700MHz = 10450MHz, the Ku-band frequencies are displayed for the Low-Band and by entering a LOF of 10600MHz+700MHz = 11300MHz the software shows the corresponding High-Band frequencies.

Conclusion:

• The TinySA can indeed be used to look at frequency ranges beyond its capability, by down/up-converting the required freqeuncy ranges using a mixer
• The moRFeus is a cost-effective device to down/up-convert RF signals, as it unites a signal gernerator and a mixer onto one single device
• The down/up-conversion introduces attentuation, which increases with frequency