Unterschiede

Hier werden die Unterschiede zwischen zwei Versionen angezeigt.

--- projekte:3cmbeacon:start [2023/01/06 18:26] – thasti
+++ projekte:3cmbeacon:start [2023/01/23 19:42] (aktuell) – [Architecture] thasti
@@ Zeile 1: / Zeile 1: @@
 ====== Integrated 10 GHz Beacon Transmitter ======
-After the decline in use of ATV in Germany, an idea of building a 3 cm beacon at [[https://db0hdf.de/service-beacon-10g/|DB0HDF]] emerged. A survey of the equipment landscape revealed some shortcomings: Currently, no commercial all-in-one 10 GHz beacon transmitter is available. Documented designs exist, but often are built from a) many individual components (tin-can style) and/or b) obsolete and unavailable parts.
+After the decline in use of ATV in Germany, an idea of building a 3 cm beacon at [[https://db0hdf.de/service-beacon-10g/|DB0HDF]] emerged. A survey of the equipment landscape revealed some shortcomings: Currently, no commercial all-in-one 10 GHz beacon transmitter is available. Documented home-brew designs exist, but often are built from a) many individual components (tin-can style) and/or b) obsolete and unavailable parts.
 The goal of this project was building a 10 GHz beacon transmitter suitable for long-term unsupervised operation from commercially available integrated circuits. To make full use of the transmit power constraints in Germany, an output power of 1-2 W was targeted. Support for contemporary digital beacon transmission modes such as [[https://rudius.net/oz2m/ngnb/pi4.htm|PI-4]] was also a requirement for the design. Remote monitoring (telemetry) and control functionality was the third critical item on the feature list for a complete design.
-{{:projekte:3cmbeacon:pcb_v1_small.jpeg?400 |}} {{ :projekte:3cmbeacon:pcb_v2_small.jpeg?400|}}
 **Quick Pointers:**
@@ Zeile 15: / Zeile 12: @@
 A simple block diagram of the beacon transmitter is shown in the figure below.
-~TODO~
+{{ :projekte:3cmbeacon:hw_architecture.png?1090 |}}
 The beacon transmitter accepts an external 100 MHz reference clock provided by a GNSS-disciplined oscillator. GNSS stabilization is the de-facto standard for beacons on 10 GHz and above due to their narrow spacing and small bandwidth. It also enables receiving stations to use the beacon as a frequency reference for aligning their own equipment.
-A Silicon Labs Si5342 is used as a crystal-driven reference PLL, which takes care of reference clock jitter cleaning and modulation generation. The high-resolution fractional divider allows synthesizing sub-Hz frequency steps of the output RF carrier, which are required for modern modulation formats. Due to the architecture of the synthesizer, no appreciable fractional spurs are generated in the process, yielding a very clean output spectrum with excellent phase noise. This IC generates in intermediate frequency of about 162 MHz, which is an integer multiplication factor lower than the final RF output frequency. A Linear LTC6948 RF PLL IC is used to multiply this signal by 16, up to a frequency of 2.592 GHz. From this point on, an Analog Devices HMC443 multiplier is used to create the final 10.368 GHz frequency. The multiplication creates some harmonic content at +-N*2.592 GHz away from the carrier, which are suppressed by a Mini-Circuits BFCN-Series MLCC bandpass filter. At this point, the final PA (Analog HMC952A) amplifies the signal up to around 1.5 W before reaching an SMA antenna connector.
+{{ :projekte:3cmbeacon:odu_tx_ref.jpg?500|Fully assembled transmitter PCB on temporary heat sink}}
+A Silicon Labs Si5342 is used as a crystal-driven reference PLL, which takes care of reference clock jitter cleaning and modulation generation. The high-resolution fractional divider allows synthesizing sub-Hz frequency steps of the output RF carrier, which are required for modern modulation formats. Due to the architecture of the synthesizer, no appreciable fractional spurs are generated in the process, yielding a very clean output spectrum with excellent phase noise. This IC generates in intermediate frequency of about 162 MHz, which is an integer multiplication factor lower than the final RF output frequency. A Linear LTC6948 RF PLL IC is used to multiply this signal by 16, up to a frequency of 2.592 GHz. From this point on, an Analog Devices HMC443 multiplier is used to create the final 10.368 GHz frequency. The multiplication creates some harmonic content at +-N*2.592 GHz away from the carrier, which are suppressed by a Mini-Circuits BFCN-Series LTCC bandpass filter. At this point, the final PA (Analog HMC952A) amplifies the signal up to around 1.5 W before reaching an SMA antenna connector.
 The HMC952A also has a built-in output RF power detector, which is read out by an on-board controller with integrated ADC. This simplifies the design since no external coupler is required to monitor forward power. The MCU further takes care of reading out the various DC power sensors on the board (to monitor voltages and currents of the SMPSes) and runs the sequencing of the beacon transmitter itself. It (optionally) communicates with a remote device through RS-422 (differential signalling).
 ===== RF Design =====
+{{ :projekte:3cmbeacon:pcb_v1_small.jpeg?425|}}\\
 One of the key design features that helps with driving down cost is working with a commercial four-layer FR4 stackup. These have become ubiquitous and cheap to use, so one supplier (JLCPCB from China) was chosen and their PCB process characterized for RF performance. Two dedicated RF test coupons were designed: Based on the results of long simulations, prototype designs for SMA connector footprints, microstrip, coplanar waveguides etc were designed.
@@ Zeile 68: / Zeile 69: @@
 ===== Testing =====
+{{ :projekte:3cmbeacon:pcb_v2_small.jpeg?400|}}
 Before going into continuous operation at DB0HDF, the transmitter hard- and software were extensively tested on the lab workbench. The output power, phase noise and spurious performance was first evaluated, with a particular emphasis on varying input voltage conditions. Long supply wires could possibly cause regulator instabilities in final installations, and (resistive) voltage drop could across the cable could cause unexpected input voltage conditions.
@@ Zeile 89: / Zeile 92: @@
 ===== Transmitter Integration at DB0HDF =====
 With the PCB battle-tested, the beacon needed to be assembled in a setup suitable for extended outdoor installation. A small add-on PCB allows supplying power and serial data through a common Cat.5 Ethernet cable with RJ-45 connectors. On the receiving end, a Raspberry Pi shield was designed that houses a relay for power control and RS-422 level conversion for the on-board serial port.
-{{:projekte:3cmbeacon:odu_tx_ref.jpg?600|Fully assembled transmitter PCB on temporary heat sink}}
 {{:projekte:3cmbeacon:idu_shield_ref.jpg?600|Raspberry Pi Shield}}