Archive for the ‘Radio Frequency’ Category:

2019-11-27 “Oscilator Colpitts” Doesn’t!

I found this schematic on a website and it’s recognizable because the author misspelled it oscilator – he left out one of the Ls (I corrected it on my copy). So I built it as shown but it wouldn’t oscillate. The values of base bias resistors R1 and R2 gave a saturated transistor. I had

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2019-11-01 Microwave Motion Detector (BigClive)

Here is a good explanation of a microwave motion detector with a schematic. A few important things: This gadget detects *anything* that moves that interferes with microwaves. It isn’t limited to living bodies. The microwaves will go through drywall or other insulating surfaces. It will be attenuated by glass, presumably because glass has lead and

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2019-10-12 RF Oscillator Won’t Make A Sine Wave, Only Sawtooth

I wanted to make an RF Oscillator that puts out a sinewave at about 734 kHz, which uses two convenient values, 100 uH coil and 470 pF capacitor. I used the toroid core with 16 turns of 30 AWG wire, with a tap at 4 turns then later 8 turns. I built the circuit in

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2019-10-07 Zenith Royal 500H Troubleshooting

I got this from eBay, it doesn’t make any sound at all. It has a small crack in one corner but the case is otherwise okay. The screw on the bottom is corroded but the battery holder is in halfway decent shape. It needs a bit of cleaning, the metal is a bit tarnished but

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2019-10-05 Huge Corcom Filters For RFI

from FB group post to Building Transistor Radios 2019 Oct 5 I spent quite a bit of time adding filtering to my 0 to 30VDC, 10A SMPS to get rid of the RF interference. It was successful, I got rid of most of it, but not all. So I think I found the solution. This

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2019-09-30 RF Modulator

For the oscillator I used the Hartley oscillator circuit that is used in the Eico 330 signal generator. I didn’t need any of the range switches – I left that out. It used MPS6513 transistors which are cheap but very uncommon – I can’t remember ever seeing them in any schematics or in PC boards.

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2019-09-03 ‘The Cosmic Inventor’ Fessenden Book

I got the book on Reginald Fessenden and I’ve been reading it the last few days. It’s a thin book, the story was first published in a journal. Fessenden was an early pioneer of wireless AKA radio. He deserved more credit than he received, he was before Marconi but Marconi got most of the publicity.

2019-06-20

June 20 Olek Kopyto What is the reason for using higher L and lower C? For parallel resonant circuits, it’s better to use high C and low L, for series resonant it’s the other way around. Higher C means the stray capacitances of the temperature sensitive components such as the transistors have less influence on

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2019-06-12 Plug-in Coils Pros And Cons

from FB group Regenerative Radio… Jun 13 I’ve thought about using plug-in coils, but I’ve had experience with Grid dip meters and there are a few important issues that must be dealt with. One is, what happens to the unused coils when the equipment is not in use. They get separated from the equipment and

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2019-06-11 Selenium Rectifier Burned Up, How To Replace

from FB group Vintage Transistor Radios Jun 12 Bob Kirsch has the right idea, but the single replacement diode *must* be rated for 400 V peak inverse voltage or more. A 1N4007 is cheap and readily available. I assume you’re in a country where the AC line voltage is 120 VAC, because the rectified DC

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