So far, we have used only audible and ultrasonic sounds in our experiments, but they are not the only kinds of signals that can be used in experiments involving EVP.
Many experimenters have found the voices using a radio receiver (MW, SW, or FM) tuned between stations or even using radio receivers with the tuning circuit adjusted in such a way that all the stations were mixed.
The background noise generated by the circuit (by thermal agitation or picked up by the antenna as atmospheric noise) added to the mixed radio station signals can be used to reveal the voices.
It seems that all kinds of random signals, independent of their nature or frequency band, can support the stochastic resonance phenomenon and thereby be used to reveal the voices. The mechanism that causes this phenomenon is an interesting subject to be investigated.
It is not clear if the voices appear due to the noise produced by the loudspeaker of a radio receiver when tuned between stations, or if they arrive with the high- frequency noise tuned by the receiver. This is a question remaining to be investigated.
Experiments involving high-frequency signals start with two possible sources.
One of them is radio transmitters or natural atmospheric or circuit noise. The other involves the use of transmitters that can fill the ambient with the necessary signals to support the EVP to be revealed.
Related experiments have used radio transmitters to produce electromagnetic signals to fill an ambient. These signals also can be used as carriers for the voices, which appear when demodulated by a receiver. Many researchers have related good results using 20 to 100 MHZ transmitters.
Experiments with very low frequency (VLF) transmitters can also be conducted.
An alternative is to employ a circuit that produces RF (radio frequency) or high-frequency signals. The signals must be picked up by special receiver from which the audio or low-frequency signals are transferred to a tape recorder or simply listened to by the researcher. Another possibility is the use of a computer to analyze the picked-up signal.
See in TEL041E in this site and BM007 how to build transmitters for the experiments.
