Softrock TXRX v6.1 Kit Review

The world is indebted to Tony Parks KB9YIG for the development and production of the Softrock kits. I shied away from development work myself awaiting the arrival of something where the bugs have been ironed out. The Softrock is truly well designed and no less than superb in performance.
Would be constructors are warned about SMD components and the need for construction skills, they truly are for advanced constructors, Small SMD components and toroidal transformers that have to be wound will tax some builders. One reads reports of “wrecked the winding of the coils must go buy some more wire and start again.” Yes even adequate wire is provided in the kit for one try.
They are not ‘anyone can build’ Heathkit type projects. Instructions are downloaded from the web and some knowledge of electronics/radio is assumed and required. If you have never wound miniature bi-fila transformers with little room for the windings even if they are carefully and meticulously done, maybe you should get some practice in on that front. Likewise this is not the project to try out the mounting of tiny surface mount integrated circuits and components.

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SDR a Simple Explanation

Radios have increased in complexity and component count since the simple crystal set of the early days. Problem is, every component used, even the humble resistor can add to the noise generated within the receiver. Every stage used in a receiver adds noise to the wanted signal.
With Superhet techniques came the harmonics and image responses. With Frequency Synthesised injection for mixers came phase jitter noise.

The SDR takes away many of these problems. The Aerial goes directly into a low noise Mixer the output of which goes via balanced low noise Audio Amplifiers to a Computer which takes over all the work of selectivity and signal processing.

The Crystal controlled Mixer Oscillator injection is from a divider which provides I and Q signals, In and Quadrature (out) of phase. The resultant audio output, I and Q components are accurately balanced by the computer software; producing a spectrum, as wide as the sample rate of the sound card, either side of the central point, as seen in the first screen shot below.

A small frequency segment at the centre point, 0Hz +/- is unusable for obvious reasons. So if you wish to use that frequency what do you do.

(Note the ‘hole at the centre point, poor sound cards and earth loops produce a hump.)

Answer, change the Crystal frequency, there are 2 on board.

Transmit function is the exact opposite process using another identical Mixer chip this time to mix I an Q audio signals from the computer with the Oscillator to produce the RF envelope.
Thus in theory any mode conceived or yet to be thought of can be received and transmitted by the SDR system, gone is the Mode switch on the Hardware.

Software Defined Radio

Rocky Software displaying the spectrum of the 40m band. input from my TX/RX. A CW contest is raging down the bottom end.  (Right click on images to view full width)

rocky

I have been watching the Software Defined Radio (SDR) scene for a while. The ideas and hardware have finally reached a stage where we can produce a high performance unit for ourselves.

What is needed is (a) Low noise, high speed mixers. (b) High speed computers. (c) Fast Computer. (d) Low noise fast sampling Sound Cards.

More on these later.

Rocky, display expanded showing an SSB station. Input again from my RX/TX.

I have built the Softrock TX/RX v 6.01 transceiver for 40 Meters. Fairly intricate surface mount work this. It set up perfectly and worked first time on initial test the receive side is very sensitive. I carefully set the image balance and tested PSK31 data on air.
I saw a German station calling CQ and thought, why not.
He was running 100 Watts from a portable holiday location. He returned to my call and gave me a 549 report, not bad for less than ).5 Watt and the first contact.

Rocky decoding and displaying PSK31 data from my RX/TX.