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  • TinySA Spectrum Analyser Review

    Date Posted:

    The TinySA is a low cost portable spectrum analyser that also functions as a signal generator, this is a true spectrum analyser that has a wide dynamic range and can measure a signal up to 960 MHz, it is developed by Erik Kaashoek and has open source firmware but not hardware.

    It features a 2.8″ LCD color touchscreen in a 90×58 mm plastic case, it includes a rechargeable internal 650mAh battery for portable use but can also be powered and recharged by the included USB C cable, it has two SMA female ports for input and output and a jog switch for additional control.

    Hardware

    The TinySA is primarily designed to operate between 0.1 to 350 MHz, input and output for this range uses the low SMA port, this includes a 0-31dB attenuator (1dB steps), the minimum RBW (Resolution BandWidth) is 3 kHz giving it a reasonably good signal resolution, it has a maximum of 290 measurement points when not connected to a PC and overall RF performance is decent, keeping in mind this is portable and low cost.

    The high port operates between 240 to 960 MHz and is lower quality than the low port, but still quite functional for many usage cases, this also includes the calibration signal generator fed from a 30MHz TCXO which is used to calibrate the level of the low port, a single level attenuator is included which varies from 22.5dB to 40dB depending on frequency, image suppression of this port is poor so it should be considered as a free extra rather than the main purpose of the TinySA.

    Overall the hardware is exceptionally good for the price, but you should not expect similar performance to a modern spectrum analyser, it is however more than good enough for most applications that do not require high precision measurements.

    Included with the package is two SMA male cables and a SMA female to female adapter, as well as a small SMA extendable antenna, although mine broke pretty quickly.

    Signal Generator

    The TinySA also functions as an excellent signal generator, note that this cannot be used at the same time as the spectrum analyser function, the low port can put out a 0.1 to 350 MHz sine signal between -76 and -7dBm, it can also perform a frequency and level sweep as well as AM, Narrowband FM and Wideband FM modulation making it extremely versatile.

    The high port can also put out a signal between 240 to 960 MHz square wave, with a level between -38 and +16dBm, as well as frequency sweep and narrow and wide FM modulation, it’s important to note that being a square wave there is a very high harmonic content which easily exceeds 2GHz making this capable of producing a signal in the many GHz range, as such it should never be used to drive a power amplifier and antenna.

    Harmonic output at 1.75GHz with FM modulation

    Software

    The software is extremely well made and easy to use, and for the most part reliable although I have had the occasional freeze, even with the small touchscreen it’s quite usable by those possessing fat fingers, the firmware is easy to update and impossible to brick due to mistakes making it very user friendly.

    Software for PC use is also available for Windows and limited use with Linux, this can extend the number of measurement points to many thousands giving even more resolution.

    High port connected to an antenna and PC, 3000 points

    Overall

    I’m very impressed by the value for money offered by the TinySA, normally for a spectrum analyser you’d need to pay several hundred pounds, to get a reasonably similar alternative for $50 is huge, even though it’s more limited, the functionality is perfectly good for many usage applications such as verifying the output of a radio, tuning filters, RFI and EMI testing and much more, as such any electronics lab should have one of these as a must buy item.

    Beware that there are some poor clones being sold out there that may perform much worse, an official list of sellers is available on the wiki.

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  • Thrustmaster TCA Quadrant Airbus Edition Review

    Date Posted:

    After having endless issues with my Saitek X56 HOTAS I decided to pick this up, it’s available at the relatively low price of around £100, I got mine from scan.co.uk.

    Build Quality

    The overall build quality is very decent, even though it’s mostly plastic it feels like good quality plastic that does not creak and bend when pressure is applied, the paint job is of high quality and I suspect will last a long time.

    It’s quite compact which works well on a cramped desk and despite it’s low weight it doesn’t move much on my wooden desk, a mounting hole is provided if needed, the throttle leavers move quite smoothly to the point when I had to increase the tension adjustment quite a bit, but once done it feels good just don’t over tighten it or you will break it.

    The only real negative I can find is the mechanism to link the throttles together, it’s possible with a bit of pressure to move one throttle slightly but it isn’t generally a big deal in practical usage.

    Functionality

    Four push buttons are included, two on the throttle levers, and two on the lower pedestal, there is also two switches and a three position switch, not a lot but it’s sufficient, it’s possible to link two throttles together to give yourself four throttle levers which is ideal for something like the A380.

    Thrustmaster also sell an addon module which includes speedbrake, gear, flaps, parking brake and more for around the same price, although at the time of writing this there was no stock available.

    Another useful feature is it allows you to plug in a Thrustmaster T.Flight rudder pedals helping to save your usb ports, speaking of USB it uses a type C connector (on the product side) which is a nice touch.

    The throttle includes detents which are found in the real Airbus aircraft, these can be disabled by removing four screws and switching some plastic parts around, this could be a bit annoying if you switch a lot so I would have liked to have seen a different mechanism to do this, the included detent range is also not ideal as it leaves little room for the manual thrust range, fortunately someone has already produced a mod to fix this minor issue if it really annoys you, personally it seems ok to me.

    The thrust reverser can be disabled to allow you usage of the whole range if desired.

    Overall

    Given the relatively low price this is a good throttle that offers some degree of extension if you need more controls in future, I’ve used it a fair amount in MSFS now and it appears to work just fine, some complaints about certain functions not working appear to have been resolved, overall I have no hesitation in recommending this.

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  • Plotting Orbits – Part 1

    Date Posted:

    This article has been reworked on 21 March 2021
- Fixed error in first equation

    Using the orbital equation it is possible to plot the orbits of planets, moons and other objects to a reasonable degree of precision, this however only works for visualising orbits that are relatively stable or at an instant in time.

    Accurate orbit data (ephemeris) can be obtained from NASA JPL Horizons system, in this case we’re interested in the Kerlerian elements rather than the state vectors which are more suitable for simulation.

    In this part I will only be plotting the orbit in two dimensions, I will cover the plotting of orbits in three dimensions in another part.

    Plotting an ellipse

    Most orbits are elliptical, although some are relatively close to circular such as the earth-sun and geosynchronous satellites, none are exactly perfect and will drift over time due to orbital perturbations, the following equation can plot a circle, ellipse, parabola or hyperbola depending on the eccentricity value, if you are not familar eccentricity is a unitless value that determines the shape of an orbit, 0 is a circle, between 0 and 1 is an ellipse, exactly 1 is a parabola and greater than 1 is a hyperbola.

    To plot in polar form the equation is:

    $$ r = \frac{a(1-\varepsilon^2)}{1+\varepsilon \cos \theta} $$

    Where a is the semi-major axis of the ellipse (the radius from the focal point) and ε (epsilon) is the eccentricity of the orbit, this can be converted to rectangular form with:

    $$ x = r \cos \theta $$

    $$ y = r \sin \theta $$

    The maximum and minimum distance from the focal point can be calculated with:

    $$r_{min} = \frac{a(1-\varepsilon^2)}{1+\varepsilon}$$

    $$r_{max} = \frac{a(1-\varepsilon^2)}{1-\varepsilon}$$

    An example of the results can be seen below:

    Rectangular form

    If you’d rather plot directly in rectangular rather than polar you can use this equation:

    $$ \frac{(x+F_1)^2}{a^2} + \frac{y^2}{b^2}=1 $$

    Where b is the semi-minor axis, and F1 is one of the two focal points, in this case the one on the right is chosen to match up with the polar equation which uses the right focal point also, the semi-minor axis can be calculated with:

    $$ b = a \sqrt{1- \varepsilon^2} $$

    And for the focal point:

    $$ F_1 = \sqrt{a^2 – b^2} $$

    Since it’s centred on the focal point F1, the centre of the ellipse is at (-F1,0) whilst F2 is at (-2*F1,0), it’s important to note that this equation does not work with an eccentricity equal or above 1.

    Alternative equation

    The alternative form given in the Wikipedia article is somewhat more complicated but yields the same results, in order for this to work you need to know the velocity at periapsis.

    To calculate the velocity you can use the vis-viva equation, using the distance to periapsis:

    $$v =\sqrt{\mu \frac{2}{r_{min}}-\frac{1}{a}}$$

    Where μ is the gravitational parameter:

    $$\mu = GM$$

    For example for earth:

    $$v =\sqrt{1.327184555 \times 10^{20} \frac{2}{1.47095 \times 10^{11}}-\frac{1}{1.49598023 \times ^{11}}} = \approx 30287.94 \text{m}/\text{s}$$

    The equation to plot the orbit is:

    $$r = \frac{\ell^2}{m^2\mu}\frac{1}{1+\varepsilon\cos{\theta}}$$

    Where m is the mass of the secondary body and the angular momentum ℓ is:

    $$\ell = m v r_{min}$$

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