The TH7122 is a single-chip FM/FSK/ASK transceiver designed for SRDs operating in the range of 300-930MHz. The device can operate down to 27MHz using an external varactor diode. Like the ADF7012, the device includes a built in VCO and PLL, circuitry to control the RF chain via an SPI interface, and the addition of a receive chain including LNA, mixer, and limiting IF amplifier. Using few external components, the device can also generate and receive analog FM, which will be used in this application. The device datasheet and application notes give a wide variety of example circuits and theory of operation, including examples to extend the frequency range to 144MHz, and examples to generate and receive analog FM.
The Murata SFVLF10M7MF00-B0 10.7MHz IF filter was tested using an Anritsu MS4622B vector network analyzer. The insertion loss and 3dB bandwidth were measured as follows (datasheet specifications in parenthesis):
- Center Frequency = 10.7MHz (10.7MHz)
- Insertion Loss = 4.19dB (5dB)
- 3dB Bandwidth = 51kHz (50kHz)
Since the filter is a 330 ohm device, 280 ohms of resistance was used in series of either side of the device in order for the device to "see" a 330 ohm system impedance. A correction factor of +16.3909dB was added to the raw data to remove the losses due to the addition of the extra resistors. This technique was verified in LTspiceIV with a 330 ohm Chebyshev filter as an example.
Bill of Materials
|Part||Quantity||Unit Cost||Total Cost||Source|
|0603 Capacitor||19||$0.0096||$0.18||eBay - mib_instruments|
|1206 Tantalum Capacitor||1||$0.44||$0.44||Digi-Key|
|0603 Inductor (Taiyo Yuden HK Series)||5||$0.064||$0.32||Digi-Key|
|0603 Resistor||7||$0.00294||$0.02||eBay - mib_instruments|
|100k SMD Potentiometer||1||$0.25||$0.25||Digi-Key|
|SMA Male Connector||2/5||$2.51||$1.00||Dealextreme|
|10.7MHz Ceramic Filter||1||$1.83||$1.83||Digi-Key|
|Total Unit Cost||$22.94|
- TH7122 PCB Top.jpg
Top of unpopulated PCB
- Melexis Microelectronic Systems, "TH7122 27 to 930MHz FSK/FM/ASK Transceiver," Feb. 2009. [Online]. Available: http://www.melexis.com/Wireless-ICs-Sensing/RFID-Sensor-Tag-ICs-433MHz/TH7122-121.aspx. [Accessed 11 March 2012].