ES-31       UHF Radio Control Experiment
             (momentary mode )   ( Transmitter : DC 9V,    Receiver : DC 12V )

<<<<<< MORE kits .....  view other available kits >>>>>>

Recommended  ceramic tip alignment tool for this kit
 A must for RF projects
(for trimmer cap or coil adjustment)
    details & price

The kit consists of two separate units : 
(1) a transmitter   &   (2)  a receiver

Pressing the tact switch on the transmitter, the receiver will respond by energizing a relay (& light up the LED)
Releasing the switch, the relay on the receiver unit return to its inactive state

The transmitter consists of 2 sections :
1) The AF section comprising logic gates IC1c & IC1d which generates a tone signal with frequency around 1 ~ 2KHz.
2) The RF section : C4 & L1 & Q4 form a LC oscillator which generates a UHF radio wave of around 300 MHz.

The RF signal is modulated by the tone signal in the OOK mode (ON/OFF Keying) and then transmitted to the receiver unit located from a distance

The receiver circuit is a simple super-regerative AM receiver which has very high sensitivity.
The tone signal detected is amplified by Q2 and fed to the input of tone decoder IC NE567 ( IC2) 
The tone decoder  compares the tone signal received (at pin 3 of IC2) with PLL  VCO frequency (pin 5).
If the frequencies of both signal match or close enough, output pin (No.8) drops low & energizes the miniature relay (& illuminates the LED).
      Click here for  NE567 datasheet (pdf)



Since frequency counters are not available to most hobbyists, we simplified the alignment procedure
so that it can be done without any instrument.

Step (1) : Powering up the transmitter & receiver units
Transmitter : Connect a 9V battery to the battery clip
Receiver : connect a stable DC 12V supply to the terminals marked+ 12V -
You may use batteries or a DC 12V adaptor (@200 mA)

Step (2) Adjustment of PLL osc frequency. Place the transmitter on top of the receiver so that the
printed coils of both units come closest to each other.
Now press & hold the transmitter tact switch & slowly adjust the trim pot VR of the receiver until
relay actuates & LED on. Press & release the switch several times to ensure the relay responds promptly.

Step (3) Adjustment of RF frequency. Next, move the transmitter away from the receiver so that
both units are approximately 1 m apart.
Again press & hold the transmitter tact switch & slowly adjust the VC (trim cap) on the
receiver until relay actuates. To increase the control range : move the transmitter further away & do a
fine tuning on VC.