by Steve Uhrig
In response to several requests, copied below is a message I sent to someone recently discussing my experience with sweeping for the low cost 2.4 GHz video and audio transmitters:
Hope this is of service to someone. For a few hundred dollars max you can build the receiver and a video monitor package. Use the best 2.4 GHz antenna you can with as short a pingpong paddle, as a convenient way to paint the walls and ceiling when sweeping. A larger patch antenna is good, keeping in mind the pattern of the thing. Use audio too, into a speaker, as there are audio-only bugs built from the video transmitters.
Regarding 2.4 GHz surveillance equipment:
99% of this 2.4 GHz wireless video garbage is made from converted Wavecom or virtually identical generic modules, sometimes with the attenuator pads bypassed to give 20-50 mW RF out. What is described here will work regardless of the manufacturer of the 2.4 GHz video devices.
The Wavecom TX are on 4 distinct transmit channels.
The Wavecom RX are the same 4 channels, but the front ends and I.F. filtering on the receivers is so crappy that the receivers will hear one and usually two adjacent channels fine, including stuff well above and below the ISM band allocation.
Due to the fact that the Wavecom units frequently power up on channel 1 by default, chances are good any surveillance or monitoring will be on channel 1. They are 4 channel devices where you can select channels 1-2-3-4 by a stepper switch, but on power up they frequently revert to channel 1 unless some mods have been done to change this feature.
The best and cheapest sweep goodie for 2.4 GHz wireless video is a Wavecom (or same thing with another name on the label) receiver module with battery pack and small battery operated video monitor. Use the original garbage patch antenna if you can't afford anything better and move around area being inspected.
Take a $3 hardware store bimetal lamp flasher, turn out all lights in the target area, and plug one lamp into the flasher. You easily will see on the Wavetek receiver/monitor the pattern of the flashing light if there is an "open camera" anywhere in the vicinity. Once you see something, kill the flashing lamp and shine a flashlight around till you hit the camera. Start with channel 1 on the Wavecom RX and advance through its 4 channels doing a separate sweep on each channel. An average room will only take a few minutes to sweep.
You may not see a clear picture depending on many factors, but you will see the light/raster flashing, and that is a giveaway to inspect further. Anything other than noise on the video monitor is cause for further investigation.
This test almost is child's play and in testing we have been able to identify a test transmitter at the fringe of the coverage area. This test setup is more sensitive than the stock Wavecom (because of the gain antenna you are pointing manually) so you will be able to sniff from further away than the listening post likely would be.
If the above does not reveal anything, it is extremely unlikely there is any illicit 2.4 GHz surveillance activity in the vicinity. Remember range of FCC Type Accepted stuff on 2.4 GHz is like 300 feet MAX and probably less. Even bumping up the effective radiated power (ERP) does not increase range that much. For indoor applications of 2.4 GHz, the listening post almost always will be no further away than through one or two interior walls.
A way to test the Wavecom receiver setup is to heat a cup of water in a microwave. Depending on leakage from the microwave, you should see hash in the Wavecom image for up to several rooms away. Remember the 2.4 GHz video stuff is on the precise frequency as a microwave oven. 2.4 GHz video and microwave ovens cannot peacefully co-exist in the same area.
There also is some crappy audio-only packages made around the Wavecom models. The Wavecom receiver will still hear them but of course you go for audio feedback instead of watching for the flashing lamp on the video.
Virtually all the Wavecom-type devices are the same manufacture and freqs regardless of packaging, so you can buy the cheapest one from a catalog anywhere and have good results. Be sure to get the crummy Wavecom receiver though, not a better receiver of another brand (not too likely as practically everything at these frequencies are built down to a consumer price, not up to a performance level standard). You want the high sensitivity (cheap) and the poor selectivity (high selectivity is expensive) which goes along with the crummy receiver. In this application, both work to the sweeper's advantage.
Using a decent patch antenna on a pingpong paddle will improve sensitivity significantly. Larger is better. Look for 6-8 dBd if possible. As the patch antenna will be fairly directional, stand in the middle of each room being swept and 'paint' the walls and ceilings by slowly rotating and moving the pingpong paddle up and down as you rotate. Look for anything other than noise on the video monitor. I wear the receiver over my shoulder and use an older Sony battery powered video monitor around my neck on a strap, leaving my hands free to operate the antenna and step through the channels on the receiver.
Hope this helps. Do as described, and you don't need anything else.
Steve
******************************************************************* Steve Uhrig, SWS Security, Maryland (USA) Mfrs of electronic surveillance equip mailto:Steve@swssec.com website http://www.swssec.com tel +1+410-879-4035, fax +1+410-836-1190 "In God we trust, all others we monitor" *******************************************************************