Low cost surveillance
Remote Audio Surveillance Basics
Digital, UHF and VHF
Transmitters : VHF Room Transmitter
Transmitters : VHF Telephone Transmitter
Transmitters : VHF Room Power Transmitters
Receivers : VHF General Purpose
Receivers : Mini VHF Receiver
Mirophones and recording
The Simplest FM Transmitter
This article will focus on the effective use of low priced surveillance equipment. The major setback to buying surveillance equipment is that they are usually very expensive, a cheaper alternative does exist and can be used with great results.
Remote Audio Surveillance Basics
A simple remote surveillance setup includes a transmitter and a receiver. The transmitter collects the audio and sends it with electromagnetic waves to the receiver which in turn converts the waves into audio. There are different versions of these pairs.
Digital, UHF and VHF.
Digital transmitters and receivers are the best on the market, although they have many advantages they are very expensive. UHF or Ultra High Frequency pairs are very effective but are also purchased at a very high price. VHF or Very High Frequency have several disadvantages but are very low priced. The main disadvantage of VHF equipment is that the signal from the transmitter can tend to drift over time meaning that the receiver would have to be retuned if used over a long duration of time. Another disadvantage is the low penetration strength of the signal, that means in a highly built up area the VHF signal will have a short range of operation. Finally another disadvantage of UHF and VHF equipment is that they can be listened in on by third parties if they posses the same type of equipment. Even with all these disadvantages VHF is a very good choice due to its very low price. Both UHF and VHF can be detected using a bug sweep device but the digital device can store the audio for transmission at a later time avoiding detection (Burst Transmitter).
Transmitters : VHF Room Transmitter
The Room Transmitter (such as the TX4 model) is a small black box an inch in size with a bundle of wire connected to it. There is a connector on it which allows the hookup of a standard 9 Volt battery. This device can typically have a range of 300 meters and a battery life of 60 Hours with a transmitter frequency capability of between 110 and 140 Mhz with FM (Frequency Modulation). To use this device a battery is simply attached and it is hidden in the room to be monitored. There are complications; the transmitter can get overmodulated in a smaller space which means that the output will be distorted, luckily this can be overcome by covering the transmitter with tissue paper or a light cloth. The use of FM (Frequency Modulation) does not mean that anyone with a standard FM radio can listen in since the frequency of FM being used is outside the range of radio FM.
Transmitters : VHF Telephone Transmitter
This is usually in the form of a telephone adapter or wire that can be attached to a phone terminal. The Frequency capability is as the Room transmitter between 110 and 140 Mhz (VHF), range 300 meters and an advantage being no battery is required, the power is drawn from the phone line. The device can be very simple and only requires that it be plugged into the standard phone socket to which the phone is attached. Due to the nature of phone sockets two versions are available, British model and US model which have the same circuitry but different shapes to adapt to the local phone socket type. A major advantage to such a device is that it does not get overmodulated so the signal on the receiver side is as clear as possible, this happens because the amplitude (how loud the audio is) of the phone signal is a set standard and can be designed for in the telephone transmitter.
Transmitter : VHF Room Power Transmitter
The design of this device is similar to the basic Room Transmitter discussed earlier with the major advantage that it draws power from the electricity socket. Such a device can take on the shape of a power adaptor that provides multiple connections from a single power socket. This device is usually fully functional as a power adaptor and the built in transmitter does not require batteries.
Receivers : VHF General Purpose
The General purpose receiver is an FM receiver capable of receiving a wide range of frequencies based on the VHF Signal, this can be used over longer ranges and can be attached to a permanent power supply to avoid using batteries, and includes external connectors of recording. In addition includes volume and tuning control. The advantage to using such a broadband receiver is that you can listen in on a lot of signals such as the conversations between commercial jets and the traffic control tower in airports.
Receivers : Mini VHF Receivers
Mini receivers are specially built to receive the Transmitter VHF signal and do not cover a broad range of VHF signals as the general purpose receiver does. It cannot run from a power source requiring batteries to operate. The idea behind this device is that it can be used in the field with an earphone, it is very compact unlike the bulky general purpose receiver and can be carried in any size pocket un-noticed by the target and bystanders.
Microphones and Recording
Finally an extremely cheap alternative to remote surveillance. The use of a recording tape with a room microphone attached to the microphone socket. These devices are extremely cheap and easy to acquire and produce high quality results. Any standard walkman can be used with a room microphone attached. Major disadvantages include incapability to operate on a long term basis, the size of the device leads to it being discovered easily. A high priced alternative is the digital recording stick which is a battery powered block that can record many more hours than a normal tape recorder but is of course more expensive.
The Simplest FM Transmitter
A few online shops sell a standard FM transmitter which can be used with a normal FM radio. The transmitter runs off batteries and some manufacturers have designed such devices with a high operating range typically 600 meters. This device is more suited to entertaining purposes as any FM radio in range can pick up the signal. However this device is extremely cheap and can be found to be as low as 10-20 US Dollars.
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