capacitor is a first step in setting up the resonant frequency of the SA602’s internal oscillator, using the resonant LC circuit to be created along with C1, C3 and L1.

ˆ12. Install C1, 100pF disc capacitor (marked 100 or 101K).

ˆ13. Install C3, .001µF disc capacitor (marked 102 or .001 or 1nF).

ˆ14. Install L2, shielded oscillator coil (marked K6883 or K6886).

ˆ15. Install C4, 100pFdisc capacitor (marked 100 or 101). C4 adds variable capacitance of the varactor tuning network to the oscillator circuit already formed by L2, C1, C2 and the SA602.

ˆ16. Install D1, the 1N4002 diode, making sure that the cathode or banded end is oriented towards the back of the PC board. This diode performs the function of a varactor diode. A varactor diode acts like a variable capacitor whose capacitance is controlled by the voltage across it. There is nothing fancy about the varactor diodes, so we are using a common rectifier diode as a varactor.

ˆ17. Install R5, 10k ohms (brown-black-orange)

ˆ18. Install R2, 10k potentiometer tuning control.

ˆ19. Install R3, 10k potentiometer volume control. This control varies the level of audio from pin 4 of the SA602 to the LM386 audio amplifier.

ˆ20. Using a scrap piece of wire, snipped from an installed component, install JMP-1. Jumpers are required sometimes in PC board layout to make a connection that has to cross over other PC-board traces.This particular jumper brings 9 volts from the power switch to the long circuit trace supplying voltage to the entire circuit. Notice how the jumper crosses over the other traces leading from the volume control.

ˆ21. Install S1, the power switch.

ˆ22. Install the 9-volt battery snap connector, making sure that the red (+) and black (-) leads are correctly installed.

ˆ23. Install C7, .01µF disc capacitor (marked 103 or .01 or 10nF).

ˆ24. Install C8, a small 4.7-10µF electrolytic capacitor. Observe correct polarity.

ˆ25. Install R6, 10K ohm resistor (brown-black-orange).

ˆ26. nstall U2, the LM386 audio amplifier IC chip. Just like the SA602, you must correctly position the notched or banded end.

ˆ27. Install C12, 100-220µF electrolytic capacitor; observe polarity. This capacitor couples the output of the LM-386 to the speaker jack.

ˆ28. Install C9, 4.7-10µF electrolytic capacitor; observe polarity.

HR40 • 12

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Ramsey Electronics HR40 manual
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HR40 specifications

The Ramsey Electronics HR40 is a versatile and high-performance FM transmitter that has gained recognition among hobbyists and professionals looking to broadcast audio signals. With its robust features and user-friendly design, the HR40 stands as an excellent choice for a range of applications, from low-power broadcasting to personal audio projects.

One of the standout features of the HR40 is its frequency range, typically allowing for transmission on the FM band from 88 to 108 MHz. This broad range ensures compatibility with a variety of receivers and allows users to select an optimal frequency for their needs, minimizing potential interference. The transmitter is designed to offer excellent audio fidelity, with a frequency response that meets and exceeds industry standards, ensuring clear and crisp sound quality.

The HR40 utilizes advanced modulation techniques, which contribute to its performance in terms of signal clarity and range. The use of frequency modulation allows the HR40 to transmit audio signals with minimal distortion, even at higher volume levels. Additionally, the transmitter is equipped with a built-in audio preamplifier, which enhances audio quality by providing a clean and powerful signal before transmission.

Another notable characteristic of the HR40 is its adjustable output power. Users can modify the power level to suit their specific broadcasting needs, whether for indoor use or outdoor applications. This flexibility is particularly useful in managing transmission range, allowing users to tailor their setup without excessive overkill or underperformance.

The compact design of the HR40 also stands out, making it a popular choice for those who need a portable broadcasting solution. The unit is lightweight and easy to transport, while its durable construction ensures longevity and resilience in various environments.

In terms of ease of use, the Ramsey Electronics HR40 offers simple installation and operation. It comes with a clear instruction manual, allowing users to set up their transmitters quickly. The intuitive interface and minimal setup requirements enable beginners to jump right in, while advanced users can take advantage of its expandability and customization options.

Overall, the Ramsey Electronics HR40 combines user-friendliness with a range of powerful features aimed at both amateur and experienced broadcasters. Its excellent audio quality, adjustable output power, and compact design make it a favorite for many seeking reliable FM transmission capabilities.
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