Here the output of the analyzer is audio, so it can use any scope for the display. The analyzer functions as a Tunable RF Voltmeter. This makes it function as a natural receiver / transmitter tracing signals. A display of the frequency is provided using the analyzer on a transmitter. Owing to the high sensitivity of the instrument signal tracing receiver circuits are permitted from the antenna through the low-level Radio Frequency stages. Whereas a conventional RF voltmeter adds up all the individual voltages as a summation without indicating the components it is not the case with a spectrum analyzer. Additionally the analyzer displays local oscillator signal and its frequency and injection levels.
A tracking generator added to the basic spectrum analyzer makes a powerful receiver system for measurements of stimulus-responses. The tracking generator is a signal source whose RF output tracks the tuning of the analyzer. Since the instantaneous output frequency is matched with the input frequency of the analyzer, this swept frequency test system actually substitutes for an effective synchronous detector. This ideally caters to the measurement of the frequency response of devices such as amplifiers, attenuators, mixers, transmission lines, couplers and even antennas used with an external bridge. Two or more oscillators mixed together generate the output. Typical application of the tracking generator consists of the RF output being connected to the device under test and its output in turn connected to input of the spectrum analyzer. The display resulting is the instantaneous plotting of the frequency response of the device under test. If one were looking out for a CRT display all that was needed was a 3 digit readout that could display 0 to 500 MHZ directly covering anywhere from a few MHZ to several hundred.
Besides the conventional all-digital circuit solution there exists an alternate solution based on the Precision Frequency-to-voltage converter IC, along with the output of the pre-scaler IC. This is a low cost alternative for directly displaying the received frequency of almost any receiver. Simple adjustments to a potentiometer is all that is required to accommodate any IF frequency from zero to hundreds of MHZ. When the circuit is designed with a digital voltmeter and the DVM set on the 20 volt scale, 0 to 500 MHZ will be displayed as 0.00 to 5.00 volts.
Front Panel Layout
Instead nowadays we have the digital panel meter module such as the above which is ideal and reads directly in MHZ.
Typical Design specifications for a Spectrum Analyzer
R3132: 9 kHz to 3 GHz
R3132N: 9 kHz to 2.2 GHz (75 ohms)
R3162: 9 kHz to 8 GHz
Signal Purity - 105 dBc/Hz 20 kHz Offset 100 dBc/Hz 10 kHz Offset
Total Level Accuracy - Maximum 1.5 dB
High-speed GPIB, Effective for System Applications
High Speed Measurement - 20 Traces per Second
6.5-inch TFT Color LCD
Built-in Frequency Counter
3 GHz Tracking Generator (Option)
Floppy Disk for Data Saving
Large Numeric Display for Measurement Results (In Counter and Power Measurement Mode)
20 dB Preamp
QP detector and EMC filters
Spectrum analyzers are used widely to make measurements of radio frequencies. Performances at high levels are guaranteed as compared to a few years ago.