FM Transmitter Circuit Confidential Photos - BBG
BBG FM (NBFM ) VHF
Crystal Controlled 1/2 WattTransmitter - Confidential Photos
All Of The Photos Below Represent Various Law Enforcement Type Body Wires, Or NBFM Crystal Controlled FM Transmitters. The frequency span of all of these devices run anywhere from around 150.00 to 174 MHz. None of the units shown below generate more that 1/2 Watt.
That Is Not To Say, That This Is A Standard and you are looking at the norm. They can come in any shape or form. They are built in anything from belt buckles, to whatever you can dream up. Recall that in the link below in different configurations of the BBG, that the BBG 1/2 watt unit has been built in the cardboard tube of a coat hanger.
Take A Look At The Photo Directly Below This Text. This is a small unit that I have built and mounted in a baseball cap for years. It only has a power output of around a few milliwatts, and it does the job and quite efficient.
1:1 Actual Size
The Rule Of Thumb In These Very Small Transmitters and the methods, places, and spaces to conceal them is that the actual power outputs range from about 5 Mw to around a maximum of about 15Mw, the problem being the size of the power source, therefore the reception or overall distance away that the unit can be received is made up with a boosted receiver or hi-gain antenna. In a lot of cases a repeater is used nearby.
On The Flip Side Of The Coin, where security, life and limb, danger or any number of imminent problems may crop up, the standard and more powerful body bug ( Wire ) such as the ones shown below. The reason being because of it's power source, usually a 9 Volt battery or 18 volts ( Two 9 volts in series ) which allows us to generate a hell of a lot of transmit power. I have actually provided the BBG in a 2 Watt Model in the past several times but always felt uncomfortable building the unit in that power range due to the heat it generated. They were built on special request, and the teams were aware of the excess heat limiting the life of the unit, so their problem - made clear in a waiver on my behalf.
You Will Notice On A Couple Of The Enclosures, Such As The One On The Lower Right, That Has A Slide Switch That Says CH1 and CH2. That means that this particular unit operates on two switchable frequencies. To those who purchase dual channel transmitters such as the above, it is usually a couple of hundred dollars more. To us who design and build them, it is a $1.00 Switch and an additional hole punched in the box.
Dual Crystals Can Be Mounted as long as the frequencies are within 3 to 5Khz, and only requires one crystal to be aligned for the other to work when switched over. I have had success with higher spreads with no other alignment required.
Shown Below Is A Drawing That Shows Exactly How It Is Done: I Have Used The BBG Schematic, To Show How A Single Frequency Transmitter Can Be Modified To Operate "Dual Channel."