Page 199 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits

percent duty-cycle square wave at 14.3 MHz. This 14.3-MHz square-wave signal will

be used later to generate a gO-degree phase-shifted version of the 7.150 MHz .. A
second frequency-divider circuit U2A further frequency divides the 14.3-MHz signal
from U lA to provide a 7.150-MHz signal at a reference phase of 0 degree. By
feeding this reference phase 7.150-MHz signal to a latch flip-flop circuit and
clocking the latch with an inverted-phase 14.3-MHz signa'l, the output of the latch
circuit provides a 90-degree phase-shifted signal at 7.150 MHz. The actual
frequency of the crystal is 28.636 MHz, which results in 7.159 MHz instead of 7.150

MHz.
The 0- and gO-degree signals from U2A and U2B, along with output signals from
U1A, are fed to a decoder circuit consisting of four AND gates, U3. The outputs of
the AND gate provide the 0-, 90-, 180-, and 270-degree nonoverlapping signals for

the analog switch mixer U4.
This front-end circuit was able to receive single-sideband transmissions on the
40-meter band. However, this circuit is just a starting point. Improvements can be
made, and if time penmits, another front-end circuit for receiving the 40-meter
band will be presented.
It is suggested that the reader may just want to purchase DIY SDR front-end kits ..

One vendor is SoftRock, which sells receivers and transceivers for the amateur
radio enthusiast.

To transmit below the 10-meter band (i.e., transmit below 28 MHz), the reader
must hold at least a general class amateur radio license. And to transmit on any
amateur radio band, a license is required. Consult the ARRL, the Amercian Radio
Relay League, at www.arrl.net for more information on licensing.
If the reader is just interested in operating receivers, no license is required. And

SoftRock sells many receiver kits.
Well, this ends the first part of this book, which is geared more for the hobbyist to
just build or experiment with radio circuits. It has been an interesting ride for the
last 12 weeks for me in designing, building, testing, and writing about radio circuits.