Archive for the ‘Radio Frequency’ Category:

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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2019-04-05

from FB group Vintage Transistor Radios April 6 I clicked on the link and I looked at the schematic. I’m surprised that in 1959 they had a radio that used the OTL amplifier to drive the spkr. I remember OTL was used in the early ’60s for Hi Fi amps, but I didn’t think that

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2019-04-01 Microwave Versus Radar Power

from FB group Bell Telephone of … Apr 2 Sam Corcione The Radars I worked on in the army were putting out peak power at 5 megawatts, but because it was listening most of the time, the average power was “only” 5 kilowatts, still equal to several microwave ovens. But it had to illuminate a

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2019-03-31

from FB group Vintage transistor Radios April 3 Are all ‘polyvaricon’ tuning capacitors the same? They’re all about the same size. Charles Vesser Japan Industry Standard… The few that I have examined were 140 pF antenna and about 70 pF oscillator. In parallel give 210 pF. They’re probably made to match up with the loopstick

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2019-03-27

From FB group transistor radios Mar 29 Lin Holcomb One never knows what secrets the US government has hidden. They could have some other plans for using the WWV stations. Decades ago I worked for a radio engineer, and we had a frequency counter traceable to NBS (now NIST). He noticed that the frequency of

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2019-03-22 Tuned Circuit For 702 kHz

from FB group Building Transistor Radios Stoffel van Aswegen I used the free Android app ElectroDroid to do these calculations. For 702 kHz, a 220 pF fixed capacitor (NP0 or C0G) and a 230 microhenrys coil are needed. The standard ferrite loopstick is 230 uH, but you can wind your own on a coil form

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2019-03-19 Radio Alignment Questions

From FB group Building Transistor Radios Mar 20 Bob Kirsch Any recommendation for doing a complete alignment? Documents? I used a HP sweep gen decades ago but I don’t have one now, just an old signal gen. I thought about building a sweep gen but I need to get a few parts. I have bought

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2019-03-11 Dipper, Wavemeter PT. 1

from FB group Building Transistor Radios Mar 11 I watched a YouTube video from Alan Yates VK2ZAY, he built a combination Dipper, wavemeter, receiver and RF generator. I built his schematic ‘right side up,’ he admitted he built it upside down with positive ground and drew the schematic, see: https://youtu.be/0pJw0m2Lz6o I didn’t attempt to build

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2019-03-07 Make a 4 Millihenry RF Choke

From FB group Building Transistor Radios Mar 7 I got some of these toroid cores a few months ago, and I got around to experimenting with them. I wound one with 21 inches (51 cm) of 30 AWG (.25 mm diameter) enameled wire. This covered the core with a single layer of wire. I measured

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