Usage
The SuperDARN Canada receive path amplification circuitry. This device is used to condition the received signal from the antenna by amplifying and filtering the signal. The circuit is designed to work with the pulsed radar system, where the received signal is only amplified when the radar is receiving (RX mode), and suppress the signal when the radar is transmitting (TX mode). Additionally, circuitry protects the circuit against high-power inputs and ensures devices operate within their limits.
Features:
- Frequency range: 2 - 22 MHz
- Internal 22 MHz low-pass filter
- Gain during RX mode: 30 dB
- Isolation during TX mode: -80 dB
- Switching time between TX and RX modes: 30 ns
- Internal circuit protection via pin-diode limiters
- TX/RX mode switching via two different input options
- Circuit protected against up to 1 W input power
A simplified block diagram of the RF devices contained within the circuit is shown below.
Figure 1: RX path v4.2 flow chart
Figure 2: RX path enclosure plate
| Input/Output | Connector | Description |
|---|---|---|
| RF In | SMA-F | RF input to the circuit. |
| RF Out | SMA-F | RF output from the circuit. |
| TR In | Molex Nano / SMA-F | Differential / Single-ended TX/RX control signal |
| PWR In | 2mm Barrel Jack | DC power input to the circuit. |
The following plots are the average of 20x assembled v4.2 boards measured with a VNA. Notable plots:
- S21 Log Mag: Gain/Isolation of the circuit
- S11 SWR: Input VSWR of the circuit
Figure 3: S11 and S21 measurements during RX mode
Figure 4: S11 and S21 measurements during TX mode
Parts list: digikey_component_list.csv
Circuit KiCad project: receive_path
There are two options for assembling the receive path board:
- Order a bare PCB, order components (i.e. from Digikey), and populate the board by hand (either soldering or reflow oven)
- Order a PCB and assembly together (i.e. from Elecrow), where the assembly company sources all components and populates the surface-mount parts. Through-hole components are populated by hand soldering
The cost breakdown for these two options is shown below. This breakdown is for a 50-count order, with factory assembly costs based on an Elecrow quote from 2024.
| Cost per board (x50 assemblies) | Hand assembly | Factory assembly |
|---|---|---|
| PCB + Assembly | $5.05 | $9.25 |
| Components | $130.43 | $103.51 |
| Enclosure, connectors, cables | $47.06 | $47.06 |
| Total | $182.54 | $159.81 |
Despite the extra cost to assemble the PCBs, factory assembly is cheaper as Elecrow is able to source components at a better cost than available on Digikey. Additionally, having a factory assemble the PCBs is much faster and of higher quality than hand assembly.
Figure 5: Populated RX path PCB
Figure 6: Assembled RX path boards
The enclosures required some minor preparation ahead of use:
- The extruded enclosure isn't pre-threaded, so the provided screws were used with a drill to thread the screw holes
- The enclosure sizes vary slightly, so the PCBs all needed to be sanded down slightly on the sides to fit them in nicely to the enclosure
- The front enclosure face PCB's mounting holes were drilled with a 82° countersink to better fit the screws
The following cables were used for the Clyde River and Rankin Inlet installations.
Power: 20AWG red/black dual hook-up strand
Differential TR Signal: 20AWG green and white hook-up strand. Spun them together using a drill to make the cable twisted-pair. The colours were chosed for consistency with the TR cabling within the transmitters.
RF: Used the existing SMA cables at site
Power: Power Plug: KLDX-PA-0202-A-LT. The center conductor is soldered to the red wire of the power cable. A small piece of heat-shrink insulation is sealed around that connection before the black wire is soldered to the outer conductor of the power connector. Heat shrink insulation is used to cover up the connector fully. The black plastic sheath that comes with the power connector was not used.
Differential TR: Molex connector: 1053071202. 20-22 AWG socket contacts were used with this connector. The were attached to the green/white twister-pair cable using the Engineer PA-09 Connector Crimping Pliers after stripping the cable. Special care was made that all connectors had the same colour on the same side of the connector.
To check that the boards are working correctly, using a VNA, verify the following:
- During RX mode, S21 Log Mag (Gain) is ~30 dB
- During TX mode, S21 Log Mag (Isolation) is <-60 dB
- Check that the board can switch between TX and RX mode using the selected TR input
It is possible to minimize the phase difference between a selected set of RX path boards. This is useful if a large order of RX path boards is being assembled at the same time for multiple radar sites. To do this:
- Measure the S21 Phase of all RX path boards
- Collect the data for all boards and sort the boards by their phase value at a specific frequency (i.e. 12 MHz)
- Group RX path boards with similar phase values
Using this method, the phase variance of a set of 20 RX path boards (taken from a larger group of 50) can be reduced to 1°-2°.
For the main array antennas, the receive path enclosures were all installed within their own respective transmitter. The connections for the receive path were as follows:
- Power: connected to internal 15V rails of transmitter
- TR: differential signal connected to internal TR contacts
- RF in/out: replaced existing pre-amp connections
For the SuperDARN Canada radar sites, we have two distinct models of transmitter: cabinet-style, and rackmount-style (drawer-style). Clyde River's transmitters are rackmount, and the installation is shown below in Figure 7.
Figure 7: Clyde River rackmount installation
Rankin Inlet's transmitters are cabinet-style, installation shown below in Figure 8.
Figure 8: Rankin Inlet cabinet installation
For the interferometer antennas, the receive path enclosures are installed on their own dedicated rackmount plate. They replaced the existing pre-amp design. The connections for the receive path are as follows:
- Power: 15V DC power supply on the rackmount plate
- TR: SMA connection from back of N200s
- RF in/out: replaced existing pre-amp connections
Figure 9: Interferometer pre-amp plate before/after
