Page 182 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits

frequency limit to the Ilowest frequency limit of about 10: 1 for a frequency range of

300 Hz to 3,000 Hz with an error of about 0.1 degree. And it should be noted that
although 300 Hz to 3,000 Hz typically is a range for a single-sideband audio phase
shifter, for the SDR, a range of about 3,000 Hz to 30 kHz is more useful.
In order to scale the original range of 300 Hz to 3,000 Hz to a new range, just scale
either the resistors or the capacitors coupled to the positive (+) terminal of the
amplifier to the reciprocal of the scaling factor. For example, if 3,000 to 30,000 Hz

is needed, then this is a scaling factor of 10. So just divide all the resistor values at
the (+) terminal of the amplifiers by 10, or alternatively, divide all capacitor value
at the (+) terminal of the amplifiers by 10.

Do not divide both the values of the resistors and capaCitors.
Table 12-2 illustrates a phase-shifting circuit that holds a gO-degree phase
difference within about ±0.1 degree.
TABLE 12-2 Resistor and Capacitor Values for the Phase-Shifting Circuit that
Maintains a gO-Degree Phase Difference between the I and Q Signal Outputs within

0.1 Degree

Frequency Range Frequency Range Frequency Range
300 Hz to 3 kHz 3 kHz to 30 kHz 9 kHz to 90 kHz

R1A: 16.2 kO R1A: 1.62 kO R1A: 1.62 kn
R1B: 54.9 k!1 RIB: 5.49 kn RIB: 5.49 k!1
R2A: 118 kn R2A: 11.8 kn R2A: 11.8 k!1

R2B: 237 kO R2B: 23.7 kO R2B: 23.7 k!1
R3A: 511 kO R3A: 51.1 kO R3A: 51.1 kn

R3B: 1.74 MO R3B: 174 k!1 R3B: 174 kO
All capacitors: 1,000 pF 1 % ALL capacitors: 1,000 pF 1 % ALL capacitors: 330 pF 1%
The first column of the table shows the original resistor and capacitor values for a

frequency range of 300 to 3,000 Hz. To scale the frequency range 10-fold for 3 to
30 kHz, the resistors are divided by 10, but the capacitors remain the same. The
third column shows how to scale the frequency range of 3 kHz to 30 kHz to 9 kHz
to 90 kHz simply by taking the (same) resistor values of the second column and
dividing the capaCitor values by 3 (1,000 IJF/3 = IV 330 IJF).

Op amps for these circuits (in Table 12-2) should have at least a 10-MHz gain
bandwidth product. For example, an AD823 op amp may be used. For the values
shown for the frequency ranges of 3 kHz to 30 kHz and 9 kHz to 90 kHz, one can
use an NE5532 or LM833 op amp.