Instruction manual

It is the goal of this project to educate the builder in
all of the principles needed to design and build this
kit. The radio is broken down into four blocks. Each
block contains:
1. Explanation of circuit to be assembled
(Theory of Operation).
2. Detailed assembly instructions for each
circuit.
3. Specifications and testing procedure for each
circuit.
4. Troubleshooting guide for each circuit.
5. Quiz on circuit (answers included).
A final quiz is included (with answers) to help
demonstrate the overall knowledge gained by
building this kit. With this in mind, let’s start by
defining exactly what this radio kit is.
THE AR-2N6
-2-
Figure 1
Dual Conversion The original radio frequency in converted first to a 10.7MHz intermediate
frequency (i-f) and amplified (Block 4). The 10.7MHz signal is then converted to
455kHz and amplified (Block 3). Noise is removed and the modulated signal is
recovered from the 455kHz i-f signal (Block 2). The audio signal is amplified to
drive a speaker (Block 1).
The AR-2N6 is a dual conversion narr
ow band
FM radio receiver designed to detect signals in
the 2 meter
and 6 meter bands.
Why Convert Twice? In the attempt to obtain the desired intermediate frequency (i-f) signal by mixing
the local oscillator with the desired radio frequency, an unwanted output may
result due to a transmission spaced one intermediate frequency (i-f) on the
opposite side of the oscillator (image). By using a large i-f frequency, this image
is moved further out of the band of desired frequencies. The second conversion
provides the selectivity to filter out the desired narrow band transmission.
Figure 2
BLOCK 4
CONVERT TO 455
AND AMPLIFY
REMOVE NOISE &
DEMODULATE
CONVERT TO 10.7
AND AMPLIFY
AUDIO
AMP
BLOCK 3 BLOCK 2 BLOCK 1
Antenna
Speaker
Desired Band of Frequencies
Local Oscillator
Image
Frequency
Desired
Frequency
Single Conversion with 455kHz
Intermediate Frequency
Double Conversion puts the Image Outside of Desired Band
and still allows Narrow Band Output
SECOND CONVERSION
TO 455kHz
Crystal
Oscillator
at 10.245
10.7MHz
10.7MHz
Desired Frequency
Desired Band of Frequencies
Local Oscillator #1
Image
Frequency