Charly 25 RADIO^lab 14Transceiver kit - Basic, (no STEMlab, no Preselector)

The Software Defined Radio core

The Software Defined Radio core – can be either STEMlab 125-14 or STEMlab 122.88-16 SDR. Specs as defined by Red Pitaya. RADIOlab kits will be pre-configured to fit the requested SDR platform.
A later conversion from STEMlab 125-14 to STEMlab 122.88-16 SDR is always possible and can be either done by the experienced end user or will be offered as a service from Smart Radio Concepts (Repairs necessary because of board damage done by the end user will be charged extra).

Charly 25 Mainboard

A 4 layer PCB which is completely controlled by I2C, has been developed to make full use of the functionality offered by either STEMlab 125-14 or STEMlab 122.88-16 SDR cores.
The board includes the following functional blocks:

Power control
- Input 13,8V – a built in DC/DC Converter 2x 5V/2A will provide internal 5V for STEMlab and other parts of the device requiring 5V.
- This enables the operation through a Battery (12 V Car Battery)
- Deep discharge protection is included
- Over Voltage and reverse polarity protection is included as well
- Current consumption of both – the complete board and the Power Amplifier is measured through an on board 12Bit A/D converter. Measured values can be displayed in Power SDR.
- Current consumption approx. 0,3A for receive, 3A @ 20Wpep for SSB and 5A for 20W CW

RX
- 2x RX Channel with a bandwidth of approx. 50KHz to 55MHz
- An anti-aliasing filter, necessary for STEMlab 122.88-16 SDR is included
- 2 x Pre-amplifier for each channel (total of 4 amplifiers with a gain of 17dB +/-1dB) – OIP3 about +43dBm.
- 2 Attenuators for each channel (12dB/24dB)
- Sensitivity / MDS about -139dBm @500Hz Bandwidth
- In order to avoid additional intermodulation caused by switching diodes, all switching is done using HF capable signal relays
- RX Filter connections for both RX channels are available on the board as well

TX
- The power amplifier uses a very robust VHF Transistor from NXP (AFT05M075), capable to withstand any SWR from open to short without damage
- Output 20W CW/SSB
- Specified for 160m to 6m operation (no damage will be caused if testing is done @ 600m, PA will work no specs defined )
- Overcurrent protection ensures that the transistor cannot be damaged ( eg. switching in the wrong low pass, at full output power)
- Antenna1/Antenna2 relay integrated – controlled by Power SDR

Additional features
- An onboard predistortion attenuator, controlled by Power SDR can be switched in 1dB steps from 0dB to 31dB (process automated through Power SDR)
- Output signal for experiments with envelope modulation
- -32dB coupler output for predistortion
- -32dB Phase Output
- BCD output to handover frequency to external PA
- PTT capable of 500V/8A max.
- Transverter Outputs for TX & RX
- Direct Access to STEMlab in order to allow usage of standard applications (eg. for VNA usage)
- Additional PA Driver for STEMlab 122.88-16 SDR (required because of reduced TX output of STEMlab 122.88-16 SDR) – very low IMD -55dBc@+16dBm output

Charly 25 CODEC board

A 4 layer board with excellent reduction of unwanted noise by consequently separating analogue and digital grounds. - CODEC Chip used is WM8731.
Fits either on top or underneath of STEMlab XX. Can be set up for HPSDR or Power SDR (on board bridges to be taken in- or out)
The board provides:

- 2x 7Watt/4 to 8 Ohm Audio Output (Speaker, headphone etc.)
- A high quality passive low pass filter reduces unwanted quantization noise from the D/A converter and ensures a smooth listening experience
- Microphone Input
- Inputs for CW lampic- as well as standard key
- AF inputs and Outputs for generic use (external signal processing, active speakers etc.)
- Onboard I2C buffer to support heavy bus loads (required to drive C25 Mainboard from STEMlab XX)

Charly 25 power distribution board

This board is just used for ease of DC cabling inside the transceiver.
An on board power source can be switched to 8V,6V,5V,3,3V and provides adequate voltage for different electret based microphones.
In addition, the board provides HF decoupling between various internal TRX building blocks.

Charly 25 RX Preselector/Filterboard

In order to achieve an outstanding performance on all 11 Amateur Bands, the Charly 25 team had to move to an unusual PI based filter architecture which until recently was only available to Microwave – and /or commercial and military customers.
This filter offers extreme far off attenuation (>80dB) and a sharp selection of each of the 11 amateur bands.
A path through allows to listen to stations outside the Amateur Bands.
Each of the 2 available receiver channels in a RADIOlab can be configured with a separate bandpass filter, allowing for smooth listening on all bands except the one which is actually being used to transmit.
The filter accepts an Antenna input of up to 10Watts, therefore the RX is save even in very harsh environments with other stations operating on bands nearby with high power. The filter board is I2C controlled by Power SDR.

Power SDR in the Charly 25 Edition

The Software used for these Transceivers is based on HPSDR and is open source. All changes implemented by the Charly 25 team are well documented on Git Hub and available to everybody.However, an enormous amount of effort has been spent to adopt the Software and allow for the usage of all available HW features. Power SDR controls all boards inside the RADIOlab via I2C.

It:
- Automatically detects the HW installed
- Comes with auto update features to allow for a seamless user experience
- Will always be kept up to date by the C25 team
- Provides additional functionality
   • Automatic predistortion
   • Automatic diversity
   • TX can be used as wobbulator to measure antenna SWR
   • Separate TX and RX frequency correction capability
   • S-meter calibration including all attenuators and pre-amplifiers eliminating any possible error. This makes RADIOlab a great test and measurement receiver - >100dB S-meter dynamic
   • S-meter precision only limited by the quality of the calibration kit

Best of all: Power SDR in the Charly 25 Edition comes for free and can be tested on any standalone STEMlab XX!!