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 huge slice of the sky.

In contrast the microwave sets that my roommates trained on were putting out only a few hundred milliwatts to a few tens of watts, depending on the distance. I put my finger in the horn of a radar training set putting out 1 watt, and I could just barely tell it was warmer than the ambient temperature. It used a reflex klystron tube similar to those used in a microwave radio for the telephone equipment. The reason they can go so far with so little power is because the dish antenna has huge gain, thousands of times, and the beam is directed at a small spot on the horizon. I would guesstimate that the radio sets for these antennas were putting out less than a hundred watts, which would take a long time to cook a chicken.



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 and oscillator coil, so the radios will track correctly over the whole AM band without labor intensive adjustment at the factory.



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 a radio station in San Francisco was periodically shifting a few Hz. He could understand the frequency drifting, but not changes that looked like they were not random. He talked to the station engineer but he was “not aware…”. My engineer boss theorized it was a way for the Navy to communicate secretly with ships or submarines. So no, I’m not some conspiracy theorist with a tin hat. 😀


2019-03-26 Fukushima Daiichi NPP Article


“You traveled to Fukushima to film. What was your big takeaway from there?”

“I found it incredibly chilling to be there. The plant itself is very strange. You don’t smell or see or touch radiation, so you don’t know. But [there’s] this whole process of getting completely suited up, and there are literally thousands of workers there, and they have to dress like that every day. I think they’re only allowed to work there for about a month at a time before they’ve been exposed for too long; it’s too dangerous. It’s almost like slave labor. It’s all men, and now, more and more, much older men who have decided, “Well, I’m not long for this world. I guess I’ll just work at cleaning up Fukushima.” And it’s going to take maybe 80 years to clean it up.



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 such as a toilet paper roll. For a TP roll 44 mm diameter and coil 70 mm length, it takes 92 turns. But beginning at the 85th turn you make a tap every 2-1/8 turns, up to about 100 turns. Then you can connect the capacitor to one of the taps to tune the circuit to the right frequency.


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 a few radios on eBay and when the caps started going bad and volume got weak, the owner diddled with the IFs, not realizing it wouldn’t help, only make it worse. So the only thing I’ve seen have been simple instructions in the Sam’s schematics.



From FB group Building Transistor Radios 2019-03-19

John Ferguson
Yeah, I used to use the Sylvania ECG and the NTE catalogs to cross-reference transistors. But then I got some better product manuals from the makers, especially Motorola and National Semi. And I got hold of the professional industry documents. ECG and NTE give a ‘one size fits all’ cross-reference, and that’s just too iffy for a good substitute.


2019-03-15 The Tape Recorder 6V6 Making Crackling Noise

from FB group Building Transistor Radios

Tuck Choy
I was a reel to reel tape recorder fanatic when I was a kid, and had a recorder with a 6V6 output to the spkr. The first thing I did was modify the recorder to add an external spkr. One time I plugged in a clip leads with no spkr. When I played back my recording I heard crackling noise inside. Well, that wasn’t supposed to happen, so I looked inside. The unloaded output transformer’s counter EMF was causing the plate pin of the 6V6 socket to arc to the chassis as the audio got louder! 😱😱😱


2019-03-14 Pi Day!

3.14 is Pi day.


2019-03-13 Regen Receiver Schematic

from FB group Building Transistor Radios post by Tuck Choy. I sharpened and lightened it to make it more readable. From EPE Mag. Sep 2005 by Thomas Scarborough.

Since only four of the 6 inverters of the CD4069 are used, the CD4001 or CD4011 quadruple NOR or NAND gates should substitute, if the other unused gate is grounded or tied to positive. I have a few CD4049 hex inverters, I should try one of those and see if it will work.

Update Mar 13 – Tuck Choy posted the complete article as a .PDF file.

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