Here we present you a long range that can cover a reasonable distance of 2 miles and beyond, with a power of one watt RF with full circuit details, bill of material and test procedure.
A single FM transmitter (such as Belkin) connects your home entertainment system to a portable radio that can be worn around the house and in the backyard. For example, you can listen to music on the CD changer in your living room and listen to a portable radio by a back-yard barbecue with 100mW, 10-meter range car FM Transmitter easily available on eBay, Amazon, Wall Mart, Ross, etc. of the target. With a bit of hacking the range can be increased up to 100 meters.
Step 1: Block Diagram & Circuit Details
This FM transmitter has three levels of RF.
- A variable frequency (VFO) oscillator (30 MW),
- A class C pilot stage (150 MW) in the buffer and
- A class C final RF power amplifier (1 Watt)
Necessarily, every FM transmitter must have an oscillator controlled voltage (VCO). It is a high-frequency oscillator whose output frequency changes based on the voltage applied to a particular control point. It is a variable frequency oscillator (VFO). Q1 with is associated with components form the VFO. The VFO output is powered at Q2. Q2 being a buffer does not load the VFO but boosts the power only. This output is fed to the final Q3 RF power amplifier, whose output powers the tuned circuit. Several C 4,8,9,10 capacitors are used on the supply rail for HF filtrations. If the VFO transistor Q1 is powered directly with a microphone at its base, it becomes an FM transmitter circuit.
At V1 at 12 volts DC, it will deliver a current of 1 watt RF. With Yagi antenna, looking like TV antenna starts with aluminum pipes both at the end of transmitter and receiver looking for each other at a distance from the line of sight, the range can be up to 5 KM.
Step 2: List of Components
The Q2 pack should be ” 92-b” type (slightly larger than BC547 pack) and not simple at 92 which is slightly smaller in size (just like BC547 pack).P lease note that the pinouts are different for these 2 types, TO92 pack is used then increase the value of R7 56 ohms 1/2 watt. Otherwise, it will burn, but this TO92 pack can affect the range
The 3rd quarter should be 2N3866 with a heat sink for the correct range. However 2N 2219 usable that could compromise the range considerably.
Step 3: Test
Initially put a single 75CM single wire directly under the antenna to get a range of about 100-200 meters indoor. Similar telescopic antenna length is also OK for the test that will only give on the range of 100-200 meters. But never again 79 CM antenna wire is thinking it will cover the upper range. In fact, in this case, the range will fall.
Transmitter frequency can be set with 88 to 108 MHz FM band by adjusting the TR1 (Hedge Trimmer 1) of the VFO or by changing the spacing between the L1 coil.
One adjustable frequency
Note: Do not try to test the device in the evening for the night because at that time a lot of powerful FM stations will be active. Test only at the time of the day. Some people have had trouble with this circuit otherwise appropriately soldered. Not the biggest problem is whether it is even oscillating since the frequency is outside the scope of most simple oscilloscopes. You may require the use of an RF frequency counter which is very expensive. So, to know that it oscillates and that it is enough to know how often, the easiest way is to put a mobile phone having FM radio (or any FM radio) in search mode near your transmitter to hear sounds while you press the microphone. Please note very close to the transmitter will have several frequencies answering the microphone and we will get confused. So go, at least 30 meters from the transmitter after the initial test as above is verified. It displays only one frequency at which it gets the best sound and all other frequencies giving whistling sound and that’s how often the transmitter is running. Set the mower TR1a very very very (about 1 degree) little to the right or left, the transmission frequency will change. Then put the cell phone further search and find the frequency. If it’s very close to a powerful transmitter, you will not get the range. Change the frequency again to 106 MHz where no commercial transmission usually occurs.
Two adjustments of the distance, after connecting a Yagi or GP antenna
Transmission range is adjusted from TR2. For this purpose a multimeter in current 250 mA DC mode in series with the 12-volt power supply and then adjust the TR2 potentiometer while the current is the peak. Adjust the current to about 75 mA (at 12 volts DC supplied by a good adapter), or mower peak current 2 say about 85 mA. After peaking while turning in the current clockwise direction may fall or while you put needles it will fall as well. And it is the best position of TR2 for the delivery of all the power of the antenna. Please note Q3; round metal body must be fully covered by the provided black heater, without which it will get heated up badly and finally get burned. In around 100mA at 12 volts, it covers an area of good and must be hot but beyond that current even though it may cover a greater range it must feel very badly heated and is doomed to fail. Initially attempt to touch the radiator and feel the heat as warm only. If it decays up to badly cut and reduce the current.
(Do not use a metallic screwdriver. You must use a non-small piece iron metal object to work as a screwdriver – this will not change the frequency as you take your hand near or far from the mower that often happens in a metal). It is best to copper or aluminum screwdriver with the insulated top.
Step 4: For Long Range
For Long Range use a Yagi antenna
The output is connected to a coaxial cable (usually used for television) that corresponds almost to the Yagi antenna impedance (although 300 ohms) of 75 ohms mower 2 TR of the listening circuit for maximum power delivery of the charge, ie, the Yagi / GP antenna. The transmitter must never be powered without the antenna (i.e., the load) in which case the total power constitutes a fixed wave ratio SWR on the power transistor Q3 it heats badly to cause the failure.