National Radio Institute 34 Signal Analyzer
Signal Tracer


For the convenience of those interested, o wiring diagram of the Model 33 is shown in Fig. 1. To use your Signal Tracer it is not necessary to refer to this schematic. However, as you can see, this instrument is actually a special kind of all«wave, tuned radio frequency (t.r.f.) receiver, complete with audio Amplifier end loudspeaker. Any on« of the following four frequency bands way be selected by the BAND SELECTOR switch. Band A 170-490 kc. Band B 490-1470 kc. Band C 1470 kc.-3.9 me. Band D 3.8-11.3 «c. What is normally an antenna load is actual by the R.F. probe, and any r.f. signals within the frequency range of the instrument maybe fed into it through this Probe. When the R.F. Probe is connected to a resonant circuit, very little detuning will occur because of the 2 micro-microfarad series condenser built into the Probe handle. The COARSE R.F. ATTENUATOR (SW-l) is a capacity type voltage divider which controls the amount of signal fed to the first r.f. Amplifier tube. The FINE R.F. ATTENUATOR (Hj) controls the bias, and hence the gain, of the first r.f. tube. The use of these controls in making gain measurements will be described later. When the R.F. Probe is used, the tuning eye indicates the relative strength of the signal reaching the 6SQ7 diode detector plate (pin No. 4). After demodulation, the audio signal passes on through the a.f. Amplifier section to the loudspeaker. when the HF-AF switch is in the A.F. position, it disconnects the r.f. Amplifier and makes it possible to use the audio section of the Signal Tracer independently. In this case a.f. signals are fed through the A. F. Probe and blocking condenser C29 *.© the calibrated volume control (A.F. ATTENUATOR), and are amplified and reproduced by the loudspeaker. The method of using the calibrated markings on the A. F. ATTENUATOR to measure a.f. gain is discussed later. Part of the amplified signal is fed back from output transformer Tj and rectified by the other diode plate of the 6SQ7 (pin No. 5). This rectified voltage is used to close the tuning eye to indicate the relative strength of the a.f. signal being examined. While the over-all sensitivity of the Model 33 is exceptionally high for on instrument of this type, there is no attempt made to keep the sensitivity constant with variations in frequency. To do so would add considerable coat to the instrument. However, as gain measurements are generally made at a single frequency, this proves to be no drawback.

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Serwis i User Manual
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Serwis i User Manual
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2016 10 03