Archive for the ‘Transmitter’ Category:

2021-04-28 Colpitts Oscillator For FM BCB

This is a low power oscillator using an air core coil and silver mica capacitors for stability. Parts values are subject to the frequency needed. There is no modulation. For FM the 10 pF capacitor would be lower and include a reverse biased diode as a varicap in parallel. The audio should be across this

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2020-05-22 PIM Passive InterModulation Explained

Good article on passive intermodulation, AKA the Rusty Bolt Effect.

2018-09-28 LM386 Used As Modulator of Final RF Output

From FB group Building Transistor Radios 2018-09-28 I see nothing wrong with using the ‘386 to directly drive the power output stage. It’s cheaper than a transformer. But I was thinking about how the current was flowing in the ‘386’s output transistors. Normally an electrolytic capacitor blocks any DC from flowing out of pin 5.

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2018-01-08 RF Oscillator For AM Band

For FB group Building Transistor Radios When I started building regen receivers, the first thing I found I needed was a simple  signal generator.  I have a function generator, but every time I want a different frequency, I had to readjust the controls.  So I built a few RF oscillators to put close to the

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2017-12-03 AM Oscillator Instead Of Aux Input

From FB group Vintage Transistor Radios  For the last few months, ever since I started experimenting with oscillators on the AM broadcast band, my attitude towards auxiliary audio inputs has changed.  Earlier I thought  that it would be convenient to have an aux input.  But I was leery of making changes to the collectibles radio

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2017-06-02 I Built Another Oscillator For AM BCB

I pulled a pill bottle out of my junk box, it had a single layer of solid enameled wire wound on it, and it measured 85 microhenrys.  So I added the transistor, resistors and the capacitors to get it to oscillate at the low end of the AM BCB, around 540 kHz. The schem is

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2017-01-15 Tuned Circuit Tester

I’m building a tuned circuit tester, which is a Franklin Oscillator without the parallel tuned circuit.  I based it on the schematic I found at this URL.  The first amp is a JFET in common drain or source follower configuration, which then drives the 2nd stage, a PNP transistor in common base configuration, so there

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2016-09-29 FM Quality Stereo Tx

When I googled I found a ‘stereo input’ FM transmitter. Most of the FM ‘bugs’ on the web and YouTube have a microphone.  The circuit I linked to has left and right inputs, but mixes them to make a monophonic (not stereo) signal.  After looking at the schematic I noticed a mistake, so I thought

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