SDRT

     

SDRT Release status: obsolete [box doku]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 750 and 1150 Mhz, which is the possible internal PLL frequency-range for ADRF6701. The I/Q signals are feed through a VGA-compatible 15pole-DSUB connector.
This board is intended to be used with VGAtoBaseband.
This is a prototype with a teensy controlling the ADRF6701. The frequency can be adjusted using a USB terminal connection. The board has a 50Ohms SMA connector transmitting about 0dBm using VGA signals (0.7Vpp).

Board

Overview

• VGA DSUB connector, baseband input
• power jack DC 5.5V - 6.0V, > 300mA
• 4 LEDS
  • power
  • teensy alive
  • rf enabled
  • unused
• teensy
• SMA connector, rf output
• switch (rf disable/enable)

Clock

26 Mhz TCXO +-2 ppm 1.8V

Low pass

I'm using one 9Mhz 3rd order Bessel low pass filter on each channel. This isn't included in the schematics. All three channels are terminated using 75 Ohms.

SPI

The SPI interface should have series resistance of more than 50 Ohms.

ADRF6701

• 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
• lo output freq:

fout = fin / 4 * ( INT + (mod / frac) )
where:
INT, MOD, FRAC are register values

Layout

todo

TODOs

• use ADRF6755
• shrink board size
• don't use eeprom 24C02
• don't use teensy, maybe Attiny
• don't use sot-123 diodes
• rf power amplifier
• use a display to show the current freq.
• rotary switch

Summary

• new i/q filter design is critical
• adrf6703 doesn't work as intended (write only, no debug pins)
• new design done -> this part is now obsolete

Links

• http://www.kickstarter.com/projects/1085541682/bladerf-usb-30-software-defined-radio