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Cordless phone BUG

Cordless phone BUG

Many Cordless phones are still analogue and use the frequency from 30-50MHz. The signal is FM-modulated and can easy be picked up with any FM-receiver. The author will present a FM-receiver wich can be adjusted within this frequency range.The cordless phones can have different number of channels. In the oldest type you will find a single crystall ,one channel.The multi-channel phones uses a synthesizer chip to set a frequency wich is not occupied. The receiver I present is not crystall controlled. The receiving frequency is set manually by a potensiometer. This way you can easy find any signal within the frequency range.
Six-channel systems are pre-1984, and are all but obsolete. They differ from the other systems in that they use radio spectrum just above the AM radio band for the base transmit frequency. An AM radio slighly detuned or shortwave receiver is all it takes to capture a signal from one of these, and their transmit range can be quite good.
Ten-channel systems became available around 1985 and replaced the AM mode used in the base with FM. They offer better clarity, less noise, and a range of about 1000 feet or so, although under ideal conditions the signal can go much farther.
Twenty-five channel systems came out around 1995-1996 after the FCC opened up additional frequency space to relieve the overcrowed ten-channel systems. They keep the original channels from the ten-channel system (now setup as channels 16-25), and added fifteen new ones using the 43, 44 and 48 Mhz bands. They offer the same basic range, with the only difference being the expanded selection of channels.
Because cordless phones operate on the lower end of the VHF spectrum, those rubber duckie antennas that ship with most handheld scanners are usually not enough to tune this band (unless you are right nextdoor to the base unit).
For the real dedicated listener, consider purchasing good quality low-band antenna, such as the Grove Scanner Beam, the Channel Master 5094A, or the new 46 MHz antenna from Cellular Security Group.


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