Figure: Data Receiver (A3018A) and Data Acquisition System. The A3018A is the metal box with its lid off.
Warning: Connect no more than two A3018s to a single LWDAQ Driver (A2037E). The A3018 exceeds the LWDAQ current consumption limits.
Warning: The A3018 does not perform well when it shares a LWDAQ Driver (A2037E) with an RF Spectrometer (A3008). The A3008 introduces noise into the LWDAQ power supplies that disturbs the operation of the A3018.
The Data Receiver (A3018) receives messages from transmitters such as the Subcutaneous Transmitter (A3013) and Subcutaneous Transmitter (A3009). The A3018 is an example of a data recorder, as used with the Recorder Instrument. The A3018 records messages in a first-in first-out buffer. You read out the buffer with LWDAQ hardware and a TCPIP connection.
The A3010 receives RF signals through a cable-mounting antenna, such as the A3015. A BNC socket on the side of the A3010 enclosure provides connection for the antenna. The LWDAQ connection is through an RJ-45 socket on the opposite side from the antenna. There are four indicator LEDs next to the RJ-45 socket. The green one closest to the socket is the power indicator (POWER). The red LED shines when the message buffer is empty (EMPTY). The orange LED shines when the A3018 is uploading messages from the buffer to the LWDAQ driver (UPLOAD). The far green LED shines when the A3018 is storing messages in the buffer (RECEIVE).
The A3018 combines three circuits, as shown in the picture above. The RF input passes to a Demodulating Receiver (A3017). The A3017 receives its local oscillator input from a SAW Oscillator (A3016SO). The demodulated output of the A3017 connects to a Data Recorder (A3007C). The A3008C connects to the LWDAQ.
The A3018 replaces the Data Recorder (A3010). Unlike the A3010, the A3018 operates equally well with its lid on or off. It requires no warm-up before you begin recording messages. In addition, its operating range is greater, as we discuss here.
Note: All our schematics and Gerber files are distributed for free under the GNU General Public License.
S3017_1: RF Amplifier, Downshifter, IF Amplifier, and Discriminator sections of the Demodulating Receiver (A3017).
S3017_2: Demodulator and Power Supply sections of the Demodulating Receiver (A3017).
S3007_1: Demodulated Input, LWDAQ Connection, Programmable Logic, Reference Oscillator, and RAM sections of the Data Recorder (A3007).
S3007_2: Clock Oscillator, Power Distribution, and Indicator Lamp sections of the Data Recorder (A3007).
S3016_3: SAW Oscillator section of RF Combo (A3016).
Plug the Data Receiver (A3018) into the LWDAQ. Wait a few seconds. Check that the power light is on. If not, reset the LWDAQ driver by unplugging its main power and plugging it in again. If your LWDAQ driver has firmware version 10 or higher, you can achieve the same power-cycle effect by pressing its hardware reset button.
Plug in an antenna. Turn on a transmitter. You should see the RECEIVE light come on. Move the transmitter around. Interpose your body between it and the antenna. You should see the RECEIVE light flicker every now and then as you hit a reception dead spot.
Turn on the LWDAQ, open the Recorder Instrument. Point the Recorder Instrument to the A3018 and press Acquire. You should see the transmitter trace on the screen. The A3018 stores 128 clock messages in its message buffer every second. Its clock tick frequency is 32.768 kHz.
See Subcutaneous Transmitter for more operating instructions.
The Local Oscillator provides the LO input to its Demodulating Receiver. The local oscillator is an A3016SO with a B3563 SAW Filter from Epcos in place of L100. The LO output is +9±1 dBm at 864±1 MHz. We use solder lumps in place of C100 and C104. The oscillator output power is +10 dBm when supplied with +5V, but when the power supply drops to 4.5 V, as it can do with long cables and multiplexers between the driver and the A3018, the oscillator output power can drop to +6 dBm. Even at +6 dBm, the power is sufficient to drive the mixer on the Demodulating Receiver.
We discuss the Demodulating Receiver in detail here. It consists of an antenna amplifier, a mixer, a limiting amplifier, and a demodulator. The antenna amplifier amplifies the antenna signal by 20 dB, passes the signal through a 902-928 MHz SAW filter, and amplifies the signal again. The mixer takes this 902-928 MHz signal and down-shifts it to 38-64 MHz using the 864 MHz LO signal provided by the Local Oscillator.
Note: Initial versions of the antenna amplifier used three 100-Ω resistors in series to bias the ERA-3SM amplifiers. The amplifier quiescent current was 40 mA. But the recommended operating point of the amplifiers is 35 mA. We found that some amplifiers were failed after a few days running, while others kept going indefinitely. We raised the bias resistance to 350 Ω, giving us a 34 mA current, and no amplifiers failed after two weeks running.
The gain from the antenna input to the IF output from the mixer should be +29 dB at the center of the SAW filter pass-band. You will find a trace of the IF output with a sweeping RF input here.
The limiting amplifier takes the IF signal from the mixer and amplifies it by up to 60 dB until it saturates.
Note: Initial versions of the limiting amplifier used 1-nF decoupling capacitors on the power supplies to the limiting op-amps. With 10-nF decoupling capacitors, the noise at the output of the first stage of the limiting amplifier decreased by 10 dB. We changed the schematic and modified existing circuits so they used 10-nF capacitors.
The demodulator takes the limited IF signal and passes it through a resonant circuit and then a full-wave rectifier. The resonant circuit is a resistor, capacitor, and inductor.
The Data Recorder takes the output of the Demodulating Receiver, converts the signal into a sequence of logic levels with a comparator, and looks for transmitter messages in the logic signal. We describe how the Data Recorder detects messages in the Signal Path section of Subcutaneous Transmitters. We provide links to the Data Recorder schematics and firmware in the Data Recorder (A3007C) Manual.
We measured the current consumed by three A3018s, and found them to be within a few milliamps of one another on all three power supply voltages.
| −15 V | +5 V | +15 V |
|---|---|---|
| 72 mA | 166 mA | 107 mA |
