Microwave oscilloscope detector. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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I did not intend to draw this simple detector. But the mass of letters with questions about setting up my MMDS converters showed that even novice radio amateurs are trying to repeat them. I would not advise beginners in radio engineering to take on microwave devices. Experienced radio amateurs always have at hand similar homemade "chips" like this detector. Here for those who still do not have such a prefix, this publication.

I made this sampler to set up the v.h. paths of their satellite receivers and used in conjunction with a swept frequency generator. It turned out that it is convenient to use it not only for microwaves, but also for other radio devices, even for those for which I had factory measuring instruments. And for the next 15 years, I used it constantly.

The basis of the probe is a microwave diode from direction finders or radar installations. In old military equipment, it was often used. Putting a PVC tube on it, I wrapped it with a copper tape with a grounding tail and soldered the KM-4a isolation capacitor and resistor directly to the thin terminal of the diode. The conclusion of this capacitor concerned the circuit under study. The second output of the diode and the resulting cylinder of the copper screen were completed with springy contacts. This nozzle was put on the coaxial head of the oscilloscope probe. Then I made such detectors with different diodes as independent oscilloscope probes.

Why do you need an oscilloscope? It turned out that the use of an oscilloscope as an indicator of rectified direct current has many advantages. Firstly, the oscilloscope has a high-resistance input (usually 1 MΩ) and the resulting probe loads the circuit being measured a little. In addition, the high-resistance load of the detector ensures its linearity, which makes it possible to measure very small voltages (millivolts).

The high sensitivity of the oscilloscope and the dynamic display of the envelope of the measured signal make it possible to use the probe to compare frequencies by beating on the harmonics of a radio frequency generator (GSS), to observe the processes of self-excitation of circuits, large noises and, in general, the signal in dynamics. The detector diode is designed for operating wavelengths of ~3 cm (10 GHz), so the detector is fairly linear over a wide frequency band. And although this is only an indicator, it can also accurately measure the voltage or gain of devices using the substitution method. Direct measurement on the oscilloscope scales gives only an approximate estimate of the signal level. When using the detector, do not apply more than 1 volt to it, otherwise the diode will be damaged.

To tune more powerful devices, make another probe with a higher voltage diode suitable for your purpose. In the detector, I used diodes D405A, D405B, D605, D602, KD514A, D18. The last two are at frequencies below 1 GHz. Also, the range of permissible input voltages can be expanded by using a capacitive voltage divider at the input of the detector. The length of the leads for connecting to the circuit should be as short as possible, normally 1-2 cm. The ground lead is made in the form of a 10 mm wide bar, and when measuring it must be connected first.

The measuring probe is driven into the insulating washer and we fix it in the body by punching in a circle. Mechanical loads on the capacitor C1 must be excluded so as not to damage its lining. In this probe, the output signal has a negative polarity. To reverse the display polarity, either reverse the diode or use the oscilloscope's inverted input. All parts and the body of the detector itself are assembled by soldering with low-melting solder. This is especially important for the diode.

Author: 73! UO5OHX ex RO5OWG; Publication: shustikov.by.ru

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