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Monitoring cordless phones
NOTICE: TO ALL CONCERNED Certain text files and messages contained on this site deal with activities and devices which would be in violation of various Federal, State, and local laws if actually carried out or constructed. The webmasters of this site do not advocate the breaking of any law. Our text files and message bases are for informational purposes only. We recommend that you contact your local law enforcement officials before undertaking any project based upon any information obtained from this or any other web site. We do not guarantee that any of the information contained on this system is correct, workable, or factual. We are not responsible for, nor do we assume any liability for, damages resulting from the use of any information on this site.
MONITORING CHORDLESS TELEPHONE CALLS
by THE RESEARCHER
Written for P-80 Systems 2-19-87
Chordls telephone calls can be monitored on any radio scanner that covers the VHF low band (30 - 50 MHz).Dring recent experiments, I was surprised at just how far these low power devices can be heard. Wit aproper antenna these signals will trip your squelch about 1/2 mile away. They become noisey but radale at a distance of .2 to .3 mile. At .1 to .2 mile reception is loud and clear. One tenth mile s th length of a typical city block.
Using the simple whip antenna that came with my scanner, can ear calls within a radius of about one block. By connecting an external ground plane antenna, can icrease that coverage out to about 3 to 4 blocks.
Chordless telephones have been assignedfrequenies on ten channels. Each channel consists of two frequencies. One for the base unit and anoher for he handset. My experiments have shown that the base unit puts out the stronger signal. It aso carrie both sides of the conversation while the handset is weaker and carries only the conversaton of the erson using it. Earlier this week I decided to find out what I cold hear by oing mobile. I bought a magnetic mount scanner antenna at Radio Shack and stuck it on th top of my cr. I used a cigarette lighter plug to provide power for the scanner. I programmed the sanner with th ten base frequencies and went driving through residential neighborhoods. Everywhere Iwent I found cordless phones active. I quickly became adept at tracking them down and getting closeenough to cleary monitor the conversations.
The next day I removed the center loaded whip fromthe base of the ntenna by loosening the set screw which holds it in place and replaced it with an ajustable whip. Th improvement in reception was dramatic. With the antenna adjusted to any length beween 2 1/4 and 5 fet the reception distance was approximately double that of the original center loded antenna. Accordng to theory, the optimum length for an antenna of this type when used at 46 MHzwould be about 5 fee. In my experiments, I could detect no loss in performance until the length wasreduced to less than 1/4 feet.
For convenient reference, I am listing the cordless telephone requencies here. All fequencies are in MHz. Keep in mind that the base frequencies are the ones to onitor.
Channel Base Handset
------- ---- -------
1 46.61 49.670
2 46.63 49.85
3 46.67 49.860 4 46.71 49.770
5 46.73 49.875
6 46.77 49.830
7 46.83 49.890
8 6.87 49.930
9 46.93 49.990
10 46.97 49.970
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