SDRT2
| SDRT2 Release status: experimental [box doku] | |
|---|---|
| Description | use the VGA port to transmit I/Q signals on any frequency |
| Author(s) | siro (siro) |
| Last Version | 0.1 () |
| License | GPL |
Software Defined Radio Transmitter
Description
Hardware to transmit anything on any frequency. That means any information / modulation can be transmited on a channel between 100 and 2400 Mhz, which is the possible internal PLL frequency-range for ADRF6755. The I/Q signals are feed through a VGA-compatible 15pole-DSUB connector.
This board is intended to be used with VGAtoBaseband.
While SDRT was configured using a teensy this board is connected to the VGA i2c and can be controlled from any Software that has access to this bus.
The board has a 50Ohms SMA connector transmitting about todo using VGA signals (0.8Vpp).
[[Datei:|thumb]]
Board
Overview
- VGA DSUB connector, baseband input
- power jack DC 6 - 7 V > 600mA
- 3 LEDS
- power
- opamp power
- PLL locked
- SMA connector, rf output
- switch (rf disable/enable)
Clock
26 Mhz TCXO +-2 ppm 1.8V
As there is a frequency error of at least +-2ppm the software has to add a compensation offset to the selected rf frequency. The adrf6755 can be configured in 1Hz steps. The offset has to be measured initially using precise frequency counters.
Low pass
The low pass is critical as it phase-shifts the high frequencies.
Phase shifts can be ignored in analog audio applications, but not in digital transmissions. It might be necessary that the software compensates this phase-shift.
The channels are terminated using 110 and 120 Ohms to have a voltage level of about 0.8Vpp.
Differential Opamps
Opamps are used to generate two differential signal with a common mode voltage of 0.5V. Each signal is filtered and then feed into the Adrf6755.
SPI/I2c
The ADRF6755 can be configured by I2c or by SPI. External pins are connected to this port. Upon startup the ADRF6755 is in I2c mode. Once in SPI mode the board has to be powered to use I2c again. Place resistors (R49, R31, R50, R51) accordingly to use VGA port or external port. The SPI interface should have series resistance of more than 50 Ohms.
ADRF6755
- reference design
- internal vco and pll is used
- LO path is disabled
- input multiplier 1:1
- internal LO divider 1:4
- fin: 26Mhz ac coupled
- internal gain control
- lo output freq:
fout = fin / 4 * ( INT + (mod / frac) ) where: INT, MOD, FRAC are register values
HF Power amplifier
The ADL5601 amplifies the HF signals by about +15 dB.
- 83 mA @ 5V
Layout
todo