Unplug the radio and discharge the storage capacitors in its power supply.
Disconnect the inlet and outlet petofile or filter centered selection from other receiver nodes. To the input, connect the generator of standard signals (in parallel, it is desirable to attach a frequency counter), and to the output of the millivoltmeter with the detector head. The generator is pre-set amplitude of the output signal of about 0.5 V.
Find out the value of the intermediate frequency receiver of the documentation or markings on the filters. In modern devices, the intermediate frequency tract AM usually equals 450, 455, 460 or 465 kHz and tract FM is 10.7 MHz. In older designs, there are values of the intermediate frequency tract of the world Cup, or 8,4 or 6.5 MHz.
Set the generator frequency to about 20 percent below the nominal value of the intermediate frequency of the receiver. Gently rotate the handle in the direction of increasing frequency. Notice the moment the readings of the millivoltmeter will increase dramatically. Record the frequency to which the thus configured generator. Find out the scale of the generator or, in the presence of frequency - according to his testimony (or rather they). This is the lower band edge bandwidth.
Continue to increase the frequency of the generator. Notice the moment the readings of the millivoltmeter will fall sharply. Similarly, define the upper limit of the band transmission.
If necessary, calculate the bandwidth, subtract the lower border of the upper.
Considerable assistance in defining the strip transmission may have a device, consisting of a frequency sweep generator, label generator and oscilloscope. Knowing, what is the frequency difference between adjacent labels on the screen, make a proportion and calculate the width shown on the same screen, the strip transmission filter. This device also allows to observe the shape of the band boundaries (whether smooth or sharp downturns).
After the experiment, turn off the power to all devices, disconnect them, and connect the filter back to the rest of the elements of the receiver.
Do not work under tension.