This is an old electronic scheme of the Handy Talky (HT) circuit. This electronic circuit is quite popular among electronic hobbies in the 90s. If you have already built this scheme, maybe you are old enough now

This handy talky scheme is an original scan of the kit on the market, so this scheme is guaranteed to function properly. Because this kit circulates in Indonesia, some information in this scheme uses Indonesian. Please use Google Translate to translate it

Hopefully useful for readers

This is a simple low cost circuit of an active FM booster that can be used to amplify the FM band signal, so you can listen the FM channels/programs from distant FM stations clearly. The circuit make use of a common-emitter tuned RF preamplifier wired around VHF/UHF transistor 2SC2570. (Only C2570 is annotated on the transistor body).

For good result, you may construct the circuit on a good-quality PCB (preferably, glass-epoxy). The input/output trimmers (VC1/VC2) can be adjusted to get the maximum gain.

Input coil L1 consists of four turns of 20SWG enamelled copper wire (slightly space wound) over 5mm diameter former. It is tapped at the first turn from ground lead side. Coil L2 is similar to L1, but has only three turns. Pin configuration of transistor 2SC2570 shown on the above image.

This active FM booster circuit operated with 12V DC supply. You may use power supply or directly connected to the 12 lead acid battery.

This long-range FM radio transmitter has an additional RF power amplifier stage, after the oscillator stage. The extra RF power amplifier used to strenght up the power output to become 200-250 milliwatts. With a great matching multi-element Yagi antenna or 50-ohm ground?plane antenna, this transmitter can give great good signal strength up to a distance of about 2 kilometres.

The circuit designed using transistor T1 (BF494) as a basic low-power variable frequency VHF oscillator. A varicap diode circuit is included to change the frequency of the transmitter and to provide frequency modulation by audio signals. The output of the oscillator is about 50 milliwatts. Transistor T2 (2N3866) forms a VHF-class A power amplifier. It boosts the oscillator signals” power four to five times. Thus, 200-250 milliwatts of power is produced at the collector of transistor T2.

Here the coil winding specifications:
L1 ? 4 turns of 20 SWG wire close wound over 8mm diameter plastic former.
L2 ? 2 turns of 24 SWG wire near top end of L1. (Note: No core (i.e. air core) is used for the above coils)
L3 ? 7 turns of 24 SWG wire close wound with 3mm diameter air core.
L4 ? 7 turns of 24 SWG wire-wound on a ferrite bead (as choke)

Potentiometer VR1 is utilized to set the centre frequency whereas potentiometer VR2 is used for power control. For humfree operation, operate the transmitter on a 12V rechargeable battery pack of 10 x 1.2-volt Ni-Cd cells. Transistor T2 must be mounted on a heat sink. Do not switch on the transmitter without a matching antenna. Adjust both trimmers (VC1 and VC2) for maximum transmission power. Adjust potentiometer VR1 to set the centre frequency near 100 MHz.

For better comes about, build the circuit on a good-quality glass epoxy board and house the transmitter inside an aluminium case. Shield the oscillator stage using an aluminium sheet.

Figure A

Figure A is the schematic of the microstrip single stage RF amplifier. The amplifier is based on the M/A-Com LF2810A MOSFET. The transistor is actually a 10 watt, 28 volt part, but provides adequate gain for this application at 12 VDC. The amplifier provides greater than 40% efficiency at the desired output power. Trimmer capacitors are used for input and output matching. Output power is adjusted by a trimpot which sets the gate bias voltage.

Figure B

Figure B is the layout for the microstrip circuit board. The board material is 0.030 inch Duroid. The circuit board is compression soldered onto a similarly sized copper heat spreader. The board and spreader are milled and drilled to accept the flange-mount transistor.

About LF2810A:

LF2810A is a RF Power MOSFET Transistor 10W, 500-1000MHz, 28V.

LF2810A Features:

• N-Channel enhancement mode device
• DMOS structure
• Lower capacitances for broadband operation
• Common source configuration
• Lower noise floor
• Applications – Broadband linear operation 500 MHz to 1200 MHz

Download LF2810A RF Power MOSFET Datasheet:

LF2810A Datasheet

1 file(s) 136.42 KB

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source: http://www.ham-radio.com/wb6zsu/components/exciter/exciter_mods.html

The circuit is composed of a mic amplifier circuit, a variable frequency oscillator, and modulation amplifier stages. Transistor T1 (BF195) is put to use as a simple RF oscillator. Resistors R6 and R7 determine base bias, while resistor R9 is utilized for stability. Feedback is provided by 150pF capacitor C11 to maintain oscillations. The primary of shortwave oscillator coil and variable condenser VC1 (365pF, 1/2J gang) form the frequency determining network.

By altering the coil inductance or the capacitance of gang condenser, the frequency of oscillation can be modified. The carrier RF signal from the oscillator is inductively coupled through the secondary of transformer X1 to the next RF amplifier-cum-modulation stage assembled around transistor T2 that is run in class “A” mode. Audio signal from the audio amplifier assembled around IC BEL1895 is coupled to the emitter of transistor 2N2222 (T2) for RF modulation.

IC BEL1895 is a monolithic audio power amplifier intendeded for sensitive AM radio applications. It can deliver 1W power to 4 ohms at 9V power supply, with low distortion and noise characteristics. Since the amplifier’s voltage gain is of the order of 600, the signal from condenser mic can be straightly linked to its input without any amplification.

The SW transmitter’s stability is managed by the quality of the tuned circuit parts as well as the degree of regulation of the supply voltage. A 9V regulated power source is required. RF output to the aerial consists of harmonics, because transistor T2 doesn’t have tuned coil in its collector circuit. However, for short-range communication, it does not create any trouble. The harmonic content of the output may be lowered by means of a high-Q L-C filter or resonant L-C traps tuned to each of the prominent harmonics. The power output of this transmitter is about 100 milliwatts.

Here the short wave AM Transmitter circuit design diagram. The circuit is quite simple and easy to build since it applies only a few electronic components. The primary feature of this transmitter is that it really is absolutely free from the LC (inductor, capacitor) tuned circuit and runs using a fixed frequency of 12 MHz that is very stable. An LC based tuned circuit is inherently unstable because of drift of resonant frequency due to temperature and humidity variations.

Resistors R1 and R2 are utilized for DC biasing of transistor T1. The capacitor C1 gives coupling in between the condenser microphone and the base of transistor T1. In the same way, resistors R3, R4 and R5 give DC biasing to transistor T2.

The oscillator segment is a combination of transistor T2, crystal XTAL, capacitor C2, C3 and resistors R3, R4 and R5. The crystal is excited by a portion of energy from the collector of transistor T2 via the feedback capacitor C2. The crystal vibrates at its essential frequency and the oscillations happening because of the crystal are placed to the base of transistor T2 across resistor R4. Using this method, continuous undamped oscillations are acquired. Any crystal having the frequency in short wave range could be substituted in this circuit, even though the operation was tried using a 12 MHz crystal.

The Transistor T1 has 3 capabilities:

1. The transistor features the DC path for extending +VCC source to transistor T2.
2. It amplifies the audio signals which is generated by condenser mic.
3. It injects the audio signal into the high frequency carrier signal for modulation.

The condenser microphone transforms the voice message into the electrical signal that is amplified by transistor T1. This amplified audio signal modulates the carrier frequency produced by transistor T2. The amplitude modulated output is acquired at the collector of transistor T2 and is transmitted by a loop antenna into space in the form of electromagnetic waves. The antenna could be tuned to a specific frequency by fine-tuning the trimmer C5 and also by modifying the length of ferrite rod into the coil.

The transmitted signals could be received on any short wave receiver without having distortion and noise. The range of this transmitter is 25 to 30 metres and may be expanded even more in case the length of the antenna wire is suitably extended together with good matching.

This the Good Quality FM transmitter for your stereo or any other amplifier gives you a pretty good signal strength up to a range of 500 metres having a power output of about 200 mW. This circuit can be operated with a 9V battery.

The audio-frequency modulation stage is constructed close to transistor BF494 (T1), that is wired as a VHF oscillator and modulates the audio signal present at the base. Working with preset VR1, you’ll be able to alter the audio signal level.

The VHF frequency is decided by coil L1 and variable capacitor VC1. Decrease the value of VR2 to obtain a higher power output.

The next stage is designed close to transistor BC548 (T2), which serves to be a Class-A power amplifier. This stage is inductively coupled towards the audio-frequency modulation stage. The antenna matching network contains variable capacitor VC2 and capacitor C9. Fine-tune VC2 for the optimum transmission of power or signal strength at the receiver.

For frequency stability, use a regulated DC power supply and house the transmitter inside of a metallic cabinet. For better antenna gain, utilize a telescopic antenna in place of the simple wire. Coils L1 and L2 are to be wound over the same air core such that windings for coil L2 start from the end point for coil L1.

Here the coil winding specification:

• L1: 5 turns of 24 SWG wire closely wound over a 5mm diameter air core
• L2: 2 turns of 24 SWG wire closely wound over the 5mm diameter air core
• L3: 7 turns of 24 SWG wire closely wound over a 4mm diameter air core
• L4: 5 turns of 28 SWG wire on an intermediate-frequency transmitter (IFT) ferrite core

This good quality 500M FM transmitter circuit absolutely works fine since it already tested.

This is the FM transmitter circuit which apply 4 radio frequency stages, that are a VHF oscillator designed around transistor BF494 (T1), a preamplifier designed around transistor BF200 (T2), a driver designed around transistor 2N2219 (T3) and also a power amplifier designed around transistor 2N3866 (T4). A condenser microphone is wired at the input of the oscillator.

The Operational of this FM transmitter circuit is very simple. At the time you speak close to the microphone, frequency-modulated signals are produced at the collector of oscillator transistor T1. The FM signals are amplified by the VHF preamplifier and also the pre-driver stage. You’ll be able to also use transistor 2N5109 as a placement of 2N2219.

The preamplifier works as a tuned class-A RF amplifier while the driver works as a class-C amplifier. Signals are finally fed towards the class-C RF power amplifier, which delivers RF power to a 50-ohm horizontal dipole or ground plane antenna.

Regulator IC 78C09 gives you stable 9V supply to the oscillator, so variation in the supply voltage is not going to have an impact on the frequency produced. You are able to also use a 12V battery to power the circuit.

Use a heat-sink with transistor 2N3866 for heat dissipation. Alter the trimmer VC1 connected across L1 to produce frequency within 88-108 MHz with care. Also alter trimmers VC2 through VC7 to obtain maximum output at maximum assortment.

Assemble the circuit on a generalpurpose PCB. Set up the antenna correctly for optimum range. Coils L1 through L5 are built with 20 SWG copper-enamelled wire wound over air-cores that have 8mm diameter. They will have 4, 6, 6, 5 and 7 turns of wire, respectively.

This 4 stage FM transmitter tested by Electronics For You mag and should be work. You can download this circuit in PDF version from the following link:

Four Stage FM Transmitter Circuit Project

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PCB Design:

Easy Build FM Transmitter Circuit Notes

• L1 and L2 are 5 turns of 28 AWG enamel coated magnet wire wound with a inside diameter of about 4mm. The inside of a ballpoint pen works well (the plastic tube that holds the ink). Remove the form after winding then install the coil on the circuit board, being careful not to bend it.
• C5 is used for tuning. This transmitter operates on the normal broadcast frequencies (88-108MHz).
• You may want to bypass the battery with a .01uF capacitor.
• An antenna may not be required for operation.

Easy build FM transmitter circuit source: http://www.aaroncake.net/circuits/fmtrans.asp

This two chips AM radio receiver circuit is a tuned radio frequency (TRF) receiver of the standard AM (amplitude modulation) radio with broadcast frequencies at 550kHz-600kHz. This is a simple and easy to build AM radio circuit which only using two integrated circuits (IC). This circuit works with 9V voltage supply, you could use 9V standard battery to supply this AM radio circuit.

Parts list:

Two Chips AM Radio Receiver Circuit Works

The coils on the ferrite rod antenna (L1 and L2) and the variable capacitors (C2) make up a “tuned circuit”. It is a very selective filter. The frequency is selectable over a certain range by adjusting the tuning capacitor. The selectable signal is passed into IC1 (integrated circuit 484) where it is amplified and then detected. The 484 is a monolithic integral circuit equal to a ten transistor tuned radio frequency circuit. The resistor R2 and the capacitor C3 set the automatic gain control of IC1. The 484 requires a low voltage power supply (1.1 -1.8V). The voltage drop across diodes D1, D2, and resistor R4 is the correct supply voltage to IC1.

The output from a diode detector of the 484 is typically 40 – 60mV. This audio signal is too weak to drive a speaker directly. Capacitor C3 filters out the radio frequency component of the signal, leaving a clean audio signal.

The amount of gain control is varied by potentiometer R3, which also varies the audio level and consequently the volume. Capacitor C5 couples the audio signal from the volume control to the input of the audio amplifier. Our kit uses the standard design for the audio amplifier on the base of the integral circuit LM-386. To make the LM-386 a more versitile amplifier, two pins (1 and 8) are provided for gain control. With pins 1 and 8 open, the gain at 20, the capacitor will go up to 200. Capacitor C7 blocks the DC from the speaker while allowing the AC to pass.

Download the MK484 datasheet:

MK484 Datasheet

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This circuit available in kit module, you can purchase the kit at electronickits.com, or download the kit manual

Two Chips AM Radio Kit

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