Computer TV tuner as a frequency meter. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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It just so happens that I do not have a frequency counter with the ability to measure frequencies above 100 MHz. And that's not the problem at all. that there is nothing to assemble the necessary frequency divider from and add one more bit to the already existing home-made frequency meter on the 1030BE31 microprocessor. The thing is. that frequencies above 100 MHz have to be measured no more than once every few years. and there seems to be no need for such a device. But still, no, no, and yes, it will be needed, but how then to be?

Once in one of the magazines for radio amateurs it was told about that. that the frequency can be measured using a VHF receiver with a digital frequency indication. It was about pocket "Chinese" radios popular in the 90s of the last century with low IF and auto-scanning of the VHF band (65 ... 110 MHz). 8 At present, to measure a much larger range of frequencies, you can use a computer TV tuner designed to receive analog terrestrial or cable television signals.

If there is an internal PCI or PCI-Express tuner, then to turn it into a frequency meter, it is enough to make a simple adapter according to the diagram shown in Fig. 1.

The adapter consists of a piece of coaxial cable up to 2 m long, a resistor, a capacitor, a standard antenna plug, a crocodile clip, a probe needle and 4-5 600NN ferrite cylinders from the IF circuits of old radios. The cylinders are strung on the cable from the connection side to the tuner. The coaxial cable is connected to the tuner's antenna jack, the alligator cable is connected to the common wire ("mass") of the device under test, and the probe is connected to the places where the RF signal passes. due to the high sensitivity of TV tuners, in most cases the probe needle does not even have to be connected, for example, to the terminals of the circuit windings, the terminals of a transistor or quartz. It is enough just to bring the probe to a distance of 2 ... 10 mm, and it, like an antenna, will "catch" the measured frequency.

To take measurements, you do not need to look for specialized software, just what came with the tuner or almost any third-party software.

Figure 2 shows an example of using the FLY 2000 TV program in the frequency counter mode.

"Frequency counter mode" is nothing but a TV station search mode with the "Blank screen when no video signal" option disabled. This will make it possible to observe characteristic noise in the "TV" window, the absence of which will mean that the tuner is tuned to the frequency of the oscillation source. Frequency scanning in the FLY 2000 TV software is very convenient. For example, you can manually scan in 10 MHz, 1 MHz steps. 50 kHz. enter the frequency manually or perform an autoscan.

My tuner allows you to scan a continuous frequency range from 45 MHz to 895 MHz. If you have an external computer tuner connected to your computer via a USB-2 or IEEE1394 port, it will be even more convenient to use it in frequency counter mode, since there is no need for a high-frequency connecting cable. In order not to accidentally take the "reflex camera" as the measured frequency, you need to strive for the minimum level of the useful signal at the tuner input, i.e. move the probe needle as far as possible from the measured point. After a little training, you will learn how to easily distinguish the frequencies of a useful signal from harmonics and interference by the nature of the picture and sound background. If you at least approximately know at what frequency the node under test should operate, then there is no need to scan the entire range (more than 800 MHz).

In some TV models, you can also smoothly scan the range in manual mode with an indication of the current frequency, although using the TV as a frequency meter is still less convenient.

Literature

1. A. Butov. UHF TV signal modulator Samsung RUS736 and CBL. - Circuitry, 2005, No. 9, P.55.
2. V.Kuts. TV tuners - to be or not to be? - Radioworld. Your computer, 2004, No. 9, p.2.

Author: A. Butov, village of Kurba, Yaroslavl region.

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