Archive for the ‘Radio Frequency’ Category:

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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2019-05-31 DIY Plastic Variable Capacitor

I hear others complain about the high cost of variable capacitors, especially the older air variables with metal plates. So I decided to DIY and make one. This is my first attempt so forgive the lack of elegance and unfinished look. I’m sure it could be improved on and made better with some effort. The

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2019-05-29 Another Oscillator For AM Band

Also posted part to FB group Building Transistor Radios May 30 I built this coil by winding 20 turns 28 AWG enamel coated wire on a soda bottle cap. It has an inductance of about 17 microhenrys. I wound a tap for the antenna, but it would be more stable if a separate coil with

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2019-05-26 Low Power AM Transmitter

I Can’t Find One I’ve seen several AM broadcast band transmitters on websites and on YouTube, but all of them require a 1 MHz oscillator module, which is difficult to obtain. I see modules for every other frequency not in the 550 to 1600 kHz AM band, but it seems all of the ones (and

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2019-05-02 Regen Using PN2222A Connected Backwards

from FB group Regenerative Rcvr Initiative May 3 Cyril Hodson Superregen receivers are always past the point of regenerative amplification. The AGC for a Regen should keep the regen high but prevent it from oscillating. I was thinking that a CdS photocell could be put in series with the Regen pot, and light from a

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2019-04-21 Adjustable Switching Power Supply RFI Suppression

I’ve been experimenting with a switching power supply I got for $51.00, Model QW-MS3010D. It puts out 0 to 30VDC at 0 to 10 amps, adjustable voltage and current limiting. As would be expected, it puts out a lot of RF interference. I’m using an old Motorola AM radio as the receiver. I set the

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2019-04-20 DC to DC Converter for Tube B+

from FB group Building Transistor Radios Jon Edwards I’ve built a lot of JTs, they are useful for low power, under 100 mW. I got about 50% efficiency. What you have to do is make sure the reverse voltage emitter to base doesn’t exceed 5V, so it doesn’t waste power. A better way is to

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2019-04-09 Event Horizon Telescope Hoopla Tomorrow

There has been a big media buildup to the scheduled release of the “picture” of a black hole. This was synthesized from data taken by multiple radiotelescopes around the world, and processed by supercomputers. More information. Update Apr 10 evening – As I had expected, the media made quite a big issue out of a

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