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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 following photo and experimented with it a lot, changing values for the various parts and every time it would not oscillate or it would put out a sawtooth wave. I was monitoring the waveform at the emitter with my oscilloscope. The supply voltage was the same 4.5 volts throughout the experiment.

I started with the coil of 16 turns with a tap at 4 turns. Later I changed to 16 turns tapped at 8 turns. I started with the 2N4401 for the transistor and then changed it to a 2N3904 to see if it would change anything – it didn’t. The waveform stayed a sawtooth, with only changes to the frequency and amplitude. I varied the base bias resistor, starting at 150k, then I connected a 100k in parallel for about 68k, then I replaced those with two 22k in series for 44k.

I started out with a 10 nF or .01 uF DC blocking capacitor between the top of the coil and the base. When I reduced it to 1 nF or .001 uF, the sawtooth frequency went up. I put a 100 to 10k variable resistor in series with this capacitor and it varied the amplitude and frequency of the sawtooth, or else the sawtooth fell to nothing. I did a few other things that I haven’t mentioned. The only tendency I saw was the sawtooth got a slight wiggle in it somewhat like a damped sinewave.

This was supposed to be a Hartley oscillator. I’ve come to the conclusion that this circuit makes a very reliable sawtooth generator.

Update Oct 12 – I moved the .01 uF from emitter to +4.5V to emitter to – across the 1k resistor. I moved the scope probe from the emitter to the collector. Now the scope shows a sine wave on the sawtooth wave. Then while I was messing with it the sawtooth stopped and I saw for the first time just a sine wave! Yes! But the sawtooth came back, it just reappeared. It still is an unstable circuit. At this point I had set the 100 to 10k variable resistor to 100, so I increased it to 270 ohms. The sine wave was more stable, and it didn’t want to go into the sawtooth mode. I disconnected and reconnected the +4.5V several times, and most but not all of the times it put out only the sine wave. So it is still not stable and wants to go into sawtooth oscillation even though to sine waves are at the collector.

Update Oct 13 – I experimented with the values a lot and I have gotten a better feel for what puts the circuit into the sawtooth oscillation mode. I’m currently using the following circuit. It seems to be more stable and less prone to make sawtooth waves. The .01 uF from the top of the coil to the base has a lot to do with the sawtooth. I put a larger capacitor in parallel and it brought the sawtooth frequency down. Apparently this capacitor is charging and discharging. The 1k in series with the .01 uF reduces the gain enough to stop the sawtooth waves.

The waveform for the following circuit is sine wave but the bottom is skewed because it’s being clipped. Another odd thing is the L and C values should give a frequency of 734 kHz. But I measure 638 kHz with the DMM. This is too low and far off what it should be. I don’t understand what is causing the big difference. Normally the circuit is off no more than ten kHz.

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2019-10-09 Not Enough Ports, Too Many Wall Jacks!

from FB group Bell Telephone…

This reminds me of one of the netheads in our dept. I get a request to connect an additional jack on the patch panel up to the switch. I go over to the IDF and find that all of the ports on all 3 of the 48 port switches were being used. So I forward the trouble ticket with the “all ports in use” back to the help desk, and they forward it to the netheads. The nethead gets it and looks at the switch stats and sees a port has no activity since the last powerup, 30 days ago. So nethead forwards it to me to use port 37. I go back over and disconnect the patch cord for port 37 from the patch panel and plug it into the jack that needs to be live. So far, everything is okay.

Two weeks later the help desk sends me a trouble ticket that some printer is not working, no one can print to it. You guessed it, that nethead had me disconnect a jack used for a working printer! Okay, I forward it back to netheads for them to resolve because there are too many piglets and not enough teats on mama hog!! 😫😫😣

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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 it’s all there – pretty good for more than 57 years old. Made in ’62, it’s S/N 811910.

The first thing I found was the earphone jack switch contacts were not closed so the audio output couldn’t get to the speaker. So I scraped the contacts and bent them so they make contact as long as the earphone plug is not plugged in. But I think that after a plug is plugged in, the contacts may no longer make contact. But for now it’s okay.

The next problem was there was still no sound from the speaker. I stripped it down to get to the PC board. I tested the speaker with the DMM and it measured a dozen or so ohms so it seemed okay. I pulled the speaker out of the cabinet to give it a visual and it’s really weird. The voice coil is not in the center, it’s off to one end of the oval cone. I found that there were iron filings all over the cone and voice coil, so I removed them and some dust and put the speaker back.

I still wasn’t hearing anything from the speaker. The electrolytic capacitors had the black plastic cases and those are the ones that usually go bad, so I replaced some and the radio was now making a bit of noise in the speaker when turned on but still no audio. But when I held the PC board in a certain place I heard audio. So I probed around on the board for an intermittent connection and resoldered a few joints, and I think I got rid of the bad connection.

The volume control was noisy so I gave it a shot of Deoxit and it quieted down. It’s now acting halfway like it should, but it needs an alignment to make it more sensitive. The schematic I downloaded has alignment instructions so I’ll try that soon. I’ll have to replace the earphone jack to get it to be reliable.

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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 is huge and weighs 5.5 pounds or 2.5 kg. It’s a monster! Fifty amps! 😱👍👍👍

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2019-10-03 Fry’s Electronics Lied!

I had to go over near there so on the way home I stopped by Fry’s Electronics in Anaheim. I was shocked by the sparseness of the shelves, like they were not restocking many areas. It was afternoon and there were only two checkouts open, and of course there was a line of waiting people.

I looked at a sign that said “We will match internet prices” and to see store associate. I found a Samsung 32GB EVO micro SD card and they were marked $14.99, so I looked the model up on the internet and found Amazon was selling it for $8.00. So I took 2 and went to the checkout.

I showed the young guy the Amazon ad on my phone, he said let me check online and went to a workstation a few feet away. When he came back he looked at the Amazon ad and said, but this is being sold by this (some company name) and fulfilled by Amazon. I said, what are you telling me? He said, we can’t match that price. I said, why? He mumbled that it was company policy. So I said Sorry about that and walked out of the store.

I got home and looked for the same micro SD card on eBay since I’ve found that I can usually find items cheaper than Amazon on eBay. I found the same exact model number for $7.60, or if I buy two, I get a slight discount. So I bought the same two SD cards for half Fry’s price and free shipping, and they’ll be here by Oct 7.

So Fry’s is turning into a Radio Shack where stuff is overpriced. And they try to suck you into believing that you will get a cheaper price at the checkout counter. Then when you checkout, they will trick you and go back on their promise to match internet prices. If you ask why they’ll give you some lame excuse. I bet if I had showed the guy the ad from eBay, he would have given me a different lame excuse why he would not match the eBay price. It’s no wonder they aren’t as popular as they used to be.

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2019-10-02 Biolite Review by Crazy Russian Hacker

Crazy Russian Hacker reviews the BioLite, it’s a small stove that has a thermopile (copper rod) that is in the fire and generates enough electric power to power a fan, a light and charge the phone from a USB port.

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2019-10-01 Renewable Energy Denial

https://www.resilience.org/stories/2019-09-12/what-is-energy-denial/

I left a Comment:

This myths list makes no room for solutions, it ignores what is already being done to address many of its concerns. The claim about the Mojave Desert is one example. California is leading the way to making renewables a major part of the energy consumed. Hundreds of thousands of homes have solar panels on roofs and in urban areas, which take up no land that is for habitat. The claim about “coal plants are ten times less than clean energy…” ignores the fact that a coal plant consumes many times its weight in coal every day during its whole lifetime, solar and wind don’t. And the open pit coal mines take up a huge amount of land and cause major disruption of the environment.
I could go on, but this article is too one-sided and critical of clean energy and portrays it as being evil, without merit or without solution. As was said at the end, much could be done by reducing energy use. One problem not confined to clean energy is overpopulation, and that must be solved for all of humanity.
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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. The Eico 330 stages were designed for a 77 MHz bandwidth, which my signal generator doesn’t need. So the circuit looks much simpler.

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2019-09-27 Phase Shift Oscillator For RF Signal Generator

2019-09-27 PSO

I tack soldered the parts together for a PSO, and made modifications to get it go work at 500 Hz. My goal is to get a steady tone to use to amplitude modulate the RF signal generator that I have built (see this blog). The sine wave from this PSO is beautiful – the most beautiful I’ve ever seen from a PSO. Usually the PSO’s sine wave is clipped because there is no automatic gain control and the amplitude grows until it is clipped.

Once I got it working at the right frequency I unsoldered the parts and put them on the same PC board that is holding the RF signal generator. I got done and it works. But every time I get close to it, the zone wave drops to zero. It’s like a proximity detector that drops out of oscillating when I get close to it. Evidently I chose part values that are putting the circuit right at the point of oscillating, the circuit is getting just the right amount of positive feedback to oscillate. But when anything changes the feedback to just a tiny bit less, the oscillations can’t sustain themselves and they drop to zero.

So I increased the 3.3k collector load resistor to 3.9k, then 4.3k. The waveform is slightly clipped at the bottom but that’s okay. The oscillations are much more stable, they don’t die when I put my hand near it. But the oscillations rapidly stop when I turn on the RF oscillator. There are two .22 uF bypass capacitors across the supply to filter out the RF. Apparently there is still enough RF to disturb the PSO. So I’m thinking about using some RF chokes in the supply lines.

I put a 1 mH choke in the supply line to the PSO, and it seemed to help. the PSO stays running. Now I have to do the power amp and modulator circuit after the RF oscillator.

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2019-09-24 Climate Change More Expensive To Fix The Damage

from FB reply to a comment Sep 27

I watched the video of the press conference on SROCC. What he said is that if the CC deniers delay the changes needed to halt climate change, it’s going to cost many times the amount needed to fix the mess later.

“… Over time, paying for climate related damages is much more – several fold more – expensive than increasing investments into renewables, into technologies that support rapid reduction of emissions. And considering this comparison should be a strong motivation to find the right path into the future.”
— Hans-O. Pörtner
Co-chair of the IPCC Working Group 2
This was from this video in his reply to a question near the end.

https://youtu.be/JYFMCU8L0zU

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