This article is presented for information only. The new Electronic Communications Privacy Act makes it illegal to monitor cellular telephone calls.
A UHF TV tuner can be used as a converter to listen to cellular telephone calls. Salvage a UHF tuner from and old TV set. Connect it to a power supply. Typical voltage requirements are 12 - 25 volts. If the set is still working, measure the voltage before removing the tuner. Connect the output cable from the tuner to the external antenna input of a scanner or tunable monitor. Tune the scanner or monitor to a frequency between 41 and 46 MHz which is the IF output of the tuner. If you are within a few miles of a base station, a pair of test leads clipped to the antenna terminals of the tuner will serve as an antenna. Turn off the squelch on the scanner or monitor and carefully tune through UHF channels 70 - 83.
It is easier to use a tunable monitor than a scanner for this application because the monitor allows you to compensate for drift in the tuner. Either will provide an adequate means of checking out the cellular activity in your area.
There are several crystal controlled converters available which will convert cellular frequencies to the UHF range of many scanners. There is a slight problem involved with these. The spacing between cellular frequencies is 30 KHz. Most scanners have a stepping interval of 12.5 Khz at UHF. This means that on most channels the frequency tuned to by the scanner will not be a perfect match. I have been assured by one of the converter manufacturers that this is not a serious problem. When using this type of converter, the scanner can be used in scan or search modes as usual.
I wanted to find out how much discrepancy exists between the output of the converters and the tuning intervals of most scanners. I took the specs of a typical converter and put my computer to work doing the calculations. What follows is the result of this examination. Listed are the cellular base frequencies followed by the frequencies after conversion followed by the closest tuning point of a scanner with a tuning interval of 12.5 KHz. Each of the base frequencies listed is paired with a mobile frequency located 45 MHz lower. The mobile frequencies are not listed.
All 666 base frequencies were checked. Only the first 33 of these are listed. The pattern repeats throughout the list.
CELLULAR FREQ. CONVERTER OUT CLOSEST SCANNER FREQ.
