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.
------------- ------------- --------------------
870.030 486.030 486.0250
870.060 486.060 486.0625
870.090 486.090 486.0875
870.120 486.120 486.1250
870.150 486.150 486.1500
870.180 486.180 486.1750
870.210 486.210 486.2125
870.240 486.240 486.2375
870.270 486.270 486.2750
870.300 486.300 486.3000
870.330 486.330 486.3250
870.360 486.360 486.3625
870.390 486.390 486.3875
870.420 486.420 486.4250
870.450 486.450 486.4500
870.480 486.480 486.4750
870.510 486.510 486.5125
870.540 486.540 486.5375
870.570 486.570 486.5750
870.600 486.600 486.6000
870.630 486.630 486.6250
870.660 486.660 486.6625
870.690 486.690 486.6875
870.720 486.720 486.7250
870.750 486.750 486.7500
870.780 486.780 486.7750
870.810 486.810 486.8125
870.840 486.840 486.8375
870.870 486.870 486.8750
870.900 486.900 486.9000
870.930 486.930 486.9250
870.960 486.960 486.9625
870.990 486.990 486.9875
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