Intro: UHF Remote Control Receiver
This UHFremote control receiver works in conjunction with the UHF transmitter described in my previous post. Circuit is quite simple but you must observe all recommendations on UHF construction layout (ground plane, stray capacity, inductance etc). For calibration & setup we will only need our trusty RF Sniffer. When properly built & calibrated you will achieve a range of 10 meters without any external antennas and with a transmitter supply voltage of only 3v. It can be used for DATA or as a simple ON-OFF action.
Step 1: Overview
The RF stage should not be assembled on a solderless breadboard. Use "Manhattan-style" construction or a double sided PCB with ground plane.
Step 2: Circuit Diagram & Main Components
Q1: 2SC-3358high frequency high gain NPN transistor.
IC1: LM358N dual OP-AMP
Z1: 3.3v zener diode
C1: 2.7pF - 7pF trimmer capacitor (blue color coded)
L1: UHF frequency loop inductor made from 1.5mm diameter copper wire or wide PCB trace.
Large diameter is required to minimize "skin effect". Dimensions should match those of transmitter tank coil (which is variable with a shorting bar).
L2: 20 turns 30AWG enameled wire on 3mm diameter form. (not critical)
Supply voltage: any between 5V and 24v . (for more than 6v adjust value of R6 to minimize dissipation).
Step 3: RF Stage
Step 4: Tank
Resonating frequency of tankL1-C1 should be the same as the carrier frequency of transmitter. Use the RF sniffer to verify (more on this later)
Step 5: Super-Regenerative Receiver
This circuit is basically a Super Regenerative receiver.
Step 6: Output Comparator
Step 7: Quench Frequency Filter
Step 8: Tank L1-C1 Details
Our goal is to have the tank resonating at the transmitter frequency with the trimmer cap in its center position. This will give us margin for fine-tuning when it is in-circuit. If it resonates in an extreme position, or doesn´t resonate at all then the dimensions of L1 are wrong. Tweak until you get the right frequency or else nothing will work at all.
Step 9: Verify Tank Frequency Vs Transmitter Frequency
Step 10: Tune C1 for Brightest LED
after tuning, C1 should be close to its center position
Step 11: Understanding Position of C1
Step 12: L2 Details
Step 13: Setup & Calibration
Step 14: Modulation Options
transmitter modulation is OOK(on off keying). For simple ON-OFF applications tie modulation input of transmitter to +3v and power it through a switch. For multichannel operation, use data encoding-decoding or simpler tone encoding-decoding with 555 and 567 chips. Reduce R7 value to 10k for data rate up to 1000bits/s