A 1928 Hartley

After seeing my 1934 transmitter a friend asked if I was doing anything special for the Bruce Kelley Memorial 1929 QSO Party coming up in December. Last year I put my TNT transmitter and SW3 on the air. This year it might be interesting to try a Hartley oscillator.As ham radio approached January 1, 1929, and the more rigorous standards,...

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Designing a Combiner for VHF/UHF

Here's is one way of combining several antennas on VHF/UHF is by using a power combiner (or power splitter if you prefer to look at it from that angle). Using the principle of impedance transformation in a quater wavelength transmission line, a proper matching can be made between antennas and the downlead cable.To build a RF combiner you...

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40-900 MHz Signal Amplifier-Booster

This is a small amplifier of signal that cover the frequencies from 40 to 900 MHz. Those frequencies include TV in VHF and UHF and also radio in the frequencies of 88 - 108 MHz, strip of FM. The signals in up to 20 dB, becoming possible to receive even the weakest signals. Below is the circuit diagram.The circuit is built in turn of an UHF...

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FM Transmitter With BF494

This is a small circuit fm transmitter using transistor BF494 . The reach of the transmitter will depend a lot on this antenna, of the feeding of the circuit and of the place where will happen your operation.With a feeding of 6 V (4 piles AA) and an antenna of about 40 cm of length, we can arrive to the 200 meters. With a smaller antenna,...

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FM Transmitter 2N2218

Here's simple FM transmitter circuit using transistor 2N2218. Micropohone is a microphone of electret of two terminals and the antenna should possess from 15 to 40 cm.Below is schematic circuit of the fm transmitterPrinted Circuit Board (PCB) and Component Layout of the fm tranmitter Parts List of the fm transmitterResistorsR1 = 2,2 kΩ R2...

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Camping and Picnic Table QRP

This last weekend we planned a campout at Frontenac State Park. We've picniced there several times but have never camped over night. No camping trip packing list is complete without my K1. (This time we did forget the blankets and pillows but the K1 was loaded.)I ended up getting several chances to ham. After a quick listen on 20 and discovering the CQ WW RTTY contest in full swing I moved to 30 mtrs for the weekend. The antenna...

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Making 1 to 4 Balun for Matching Impedance

Here's the way to match 75 Ohm to 300 Ohm impedance. In case of making balun for 200-300 Ohm folded dipole antenna to 75 Ohm transmission cable.Please see table on image above to determine velocity factor for different cable type.Please check out my 4 Watt FM transmitt...

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Audio Limiter/Compressor for Electret Desk Microphones

This electronic circuit is audio limiter compressor specifically designed to use with very low-cost electret desk microphones. Overcomes the heavy attack/decay problems with diode rectifier VOGAD circuits.A TL074 IC was used with a dual supply of +/-5v Note the lack of rectifier diodes in the feedback loop, instead the circuit uses high gain...

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VHF Video Transmitter 60-200 MHz

Here's a simple video transmitter for VHF TV channel will accept baseband video input, hence it can be driven by most CCD cameras and VCR video outputs. It ouputs roughly 80mW and when used with a 40cm telescopic antenna over 100 metres range is possible.The transistor of the video transmitter can be a BC108, BC546, BC337 or a 2N2222. L1...

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40W Broadband FM RF Power Amplifier

Here's broadband RF power amplifier for FM amplifier design is based on Motorola MRF171A MOSFET. The amplifier was constructed in a small aluminium diecast box. RF input from transmitter and output connections are made by coaxial sockets. The power supply is routed through a ceramic feedthrough capacitor bolted in the wall of the box.This...

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More 1934 Transmitter

Remember the safety problem with my 1934 transmitter? One of the phone plugs is for metering and the other is for the key. If, in the heat of the moment, I get the two mixed up and plug the key into a B+ metering jack, I'll have over 300 volts on the key.To protect myself I tied a length of string and a plastic cable clamp to the key phone...

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RF Low Pass Filter 1.8-145 MHz

This lowpass filter circuit is a very basic filter. It required to remove the harmonic frequency content of the transmitter and can be used on frequency 1.8 - 145 MHz.The cut off frequency of the filter can be achieved by making C2 and C4 variable trimmer acurate filtering. All coils are 22 SWG wound on 10mm Air former spaced at 2mm. For...

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A 1934 transmitter - On the Air

Yesterday I set up my 1934 transmitter up with my NC101X and tried the pair out on 80 meters using my endfed 105' inverted "L" antenna only about 10'-20' off the ground. The station worked fine.At 21:45 I had a nice QSO on 3570 with NG9D in Plainfield, IL. Lynn's signal varied from 589 to 599+. He reported that my 589 signal sounded fine/stable.Also...

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More 1934 transmitter - It Works!

I've finished wiring my 1934 transmitter, powered it up and it works! With about 300 volts on the plates of the 46s and the 47 it loads to 15-20 watts input and 7-10 watts output. It sounds great also.One change I made from the Bill Orr design is to connect the 47 screen to regulated 150V rather than a resistor network off of B+.This transmitter...

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FM Bandpass Filter 97.5 MHz

This type of filter circuit is a bandpass filter for FM band 88-108 MHz. This bandpass filter is in fact a combined highpass and lowpass filter. The first stages are a high pass and the last stages a low pass. We ripped it out the newsgroup alt.radio.pirate too bad, we can't remember who posted it. We tested the schematic with a simulation...

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