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20185-10-13 Limiting Global Warming To 1.5 Deg. C

I was reading this article about the catastrophe that awaits us in the near future, in the next 20 to 35 years. It states that limiting the global warming will be hard, really hard. But it’s something that has to be done if life as we know it is to be saved.

As the article shows in the charts, the climate change will adversely affect food production by farms and reduce the fish that can be caught.

We should be more like Europe, where gasoline costs much more than what we are now paying, as much as 7 to 8 dollars a gallon in some European countries. We should raise the taxes on vehicle fuels to force drivers to conserve fuel, and the taxes we collect should be used to mitigate climate change.

If we don’t start action immediately, the results will be very bad. It will probably be catastrophic.

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2018-10-12 Finding Transistor Substitutes

From FB group Building Transistor Radios 2018-10-12

Michael P. Hamilton
After I got a National transistor catalog decades ago, I started to understand the way they were making and packaging transistors.

They had lists of discretes, BJTs, FETs, etc. At the beginning of the line was the part number, then the parameters, and then at the end of the line it gave the process number. I could then look at the sections of processes and see the specifications for the process, including the drawing of the chip. I realized that all these hundreds of transistors are made from the same few dozens of chip dies. The difference was the testing of the dies and packaging. So it’s not difficult for me to come up with a close equivalent of a transistor to use for a substitute.

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2018-10-08 Air Band Radio Kit HMOOABRA_4.3 Part 5

from FB group Building Transistor Radios comment 2018-10-08

Bob Johansen
Receive frequency? I can’t receive a signal, so the receive frequency is not known. This receiver has no tuned circuit in the RF side of the NE612, other than the bandpass filter made up of the coils on the PCB and their capacitors. The bandpass is supposed to be 118 to 136 MHz, but as I said before, the dipmeter shows the coils dipping above the 2M band, somewhere near 200 MHz. However that may be caused by interactions between the filter elements.

I have measured the LO oscillating over the full range of the tuning pot, up to 158 MHz. But this is what seems odd. With squelch at minimum I put the DMM on the tuning pot wiper and get the tuning voltage from 1.85 at min to 8V at max. At 1.85V I hear hiss, and it peaks at 3.5V. But above 4V it falls off to silence.

Bob Johansen
Yeah the funny part is I can’t hear any FM stations either through the front end filter or bypassing the filter. I have heard an occasional change in the noise level, like one would get if a very weak signal was buried in the noise. But then I’ve heard a lowering in the noise level when I touched the tip of metal screwdriver to some parts near the LO, and the change stays after I remove the tip. I also noticed the same effect when I touched the brass slug with the tip of the screwdriver but not with a nylon tuning wand. I thought that it might be caused by wear on the coil by the slug, but when I removed the slug to see, it wasn’t touching the coil.

I can get noise and hum when I touch the tip to Out A, pin 4, so the 10.7 MHz side is sensitive. It seems that the NE612 is where the signal isn’t getting through. So I ordered some NE612 chips on eBay, they are stocked in the US even though the seller is in China. The chips should be arriving in a week. I may remove the chip and install the socket and try the SA602 from the Vectronics receiver just to see if it’s a bad chip.

BTW I measured the supply current, it was about 50 mA dead silent, and up to 70 mA when very noisy. The 78L08 gets quite warm.

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2018-10-07 Air Band Radio Kit HMOOABRA_4.3 Part 3

From FB group Building Transistor Radios comment 2018-10-07

Bob Johansen
I don’t have a way of calibrating an RF signal level. Back when I worked on Aircraft radios we had General Radio VHF signal generators, attenuators and RF signal strength meters and a Panoramic spectrum analyzer. This would have been a piece of cake to t/s. Right now I’m thinking about unsoldering the NE612 and putting the socket in, and borrowing the NE602 from the Vectronics kit I built last month. I’m getting good sensitivity at the pin 4, IF output of the NE, but not good sensitivity at the RF input to the Q1 RF amp. All the voltages look normal at Q1. I may pull out the parts and Q1, I think I have all of them on hand, even a 2SC3355. I’ve been occupied with some other real life things that have priority right now.

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2018-10-06 Air Band Radio Kit HMOOABRA_4.3 Part 2

Posted to FB group Building Transistor Radios 2018-10-06

First part is here.

I noticed that my photo didn’t get added to the photos tab, So I’m trying again to add it.

I got a fresh start this Sat. morning. I used another little air band receiver to listen for the LO from this one. I turned the tuning pot to minimum which should be 118.00 MHz. I then set the other receiver to 118 + 10.7 or 128.7 MHz. I used a nylon tuning wand to tune the LO coil’s brass slug until I heard the LO fully quiet at 128.7. The speaker has hiss at this setting.

I then set the little receiver for 130, 132, 134, 136, and 138.0 MHz (highest it would go), and each time I could hear the LO in the little receiver as I advanced the tune pot. So the LO is oscillating all the way up to 138. But with the brass slug out most of the way, as soon as I tuned to 130, the hiss from the speaker went down to nothing and stayed quiet for all the other frequencies, too. This is puzzling.

I could hear transmissions on some frequencies in the little receiver. There is activity in the band. This little receiver uses a pair of ear buds for listening, and the antenna is the wires of the ear buds. So the transmissions have plenty of strength to be heard on a short lengths of wire, which is what I’m using for this receiver. But I have heard nothing but hiss on this receiver or no hiss, wherever I have tuned it.

I’m even more puzzled.

Update late afternoon – I forgot I had my Gy560 frequency counter in the drawer. I pulled it out and I touched its antenna to the slug and it gave me a reading. With the tune pot at minimum I set the slug for 118 + 10.7 or 128.7 MHz. As I tuned the pot, I could see the LO frequency go up and up. It should go as high as 136 + 10.7 or 146.7 MHz. But it kept going higher, all the way up to 158.7 MHz. That’s okay, but I would rather have the pot have a smaller range with greater resolution. So I’ll have to change the resistors to get the right range. But first I have to get it to receive a signal.

One thing that bothered me was the PCB coils dipping as high as 200 MHz. So I removed one leg of the C5 DC blocking capacitor, and I soldered a tiny switch to the leg so I can choose to have the antenna signal go through the coils on the PCB or bypass the coils and go directly to Q1. I tried a short length of antenna into the Q1 and it still does not receive any signals across the band. But I can hear the strong signal from my dipmeter at two places on the band, one below and one above the LO frequency, so it seems to be receiving very strong signals.

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2018-10-05 Air Band Radio Kit HMOOABRA_4.3 Part 1

Will also post to FB.

I ordered this air band radio kit from China a few weeks ago and received it a few days ago. Yesterday I spent most of the day assembling it. I’m an experienced kit builder and believe me, it was difficult. The kit came with a single sheet of paper, on one side was a discription and the other side was the schematic. The description was written in Chinglish and was no help in assembling the kit. The PC board had a part number, like C27, but no value. So each part had to be looked up on the schematic to find out what the value was. But the schematic on the paper and online was blurry and the part numbers and values were nearly impossible to read. This made the kit very difficult to assemble correctly and most inexperienced kit builders would find it too difficult, with many mistakes being made.

I spent more than 2 hours going to the schematic and puzzling out the part numbers, then puzzling out the proper values for the parts. This was in addition to the time I spent finding each part, inserting it properly, soldering it in and clipping off the leads. This kit was easier to do than my previous kit because there were no coils to wind. The coils were a part of the printed circuit traces, spirals on the board. No tuning to do, just solder the capacitors.

I finally finished with the assembly. I had to double check as I was assembling, tracing the leads between parts to see that they corresponded to the parts on the schematic, so my checks after assembly were more like the third time. I hooked it up to a short antenna, speaker and the power supply and prepared for the sight and smell of smoke. But I didn’t get anything, other than a click on the speaker. Volume was up and the squelch was off, so I used a small screwdriver to turn the slug in the IF can. After adjusting the slug for the most hiss, I didn’t have the volume control turned up, maybe a quarter turn. No matter where I adjusted the tuning, I heard nothing but hiss.

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2018-09-28 LM386 Used As Modulator of Final RF Output

From FB group Building Transistor Radios 2018-09-28

I see nothing wrong with using the ‘386 to directly drive the power output stage. It’s cheaper than a transformer.

But I was thinking about how the current was flowing in the ‘386’s output transistors. Normally an electrolytic capacitor blocks any DC from flowing out of pin 5. But when the ‘386 is used to directly modulate the final, the current that would normally flow through the chip’s bottom (current sink or pulldown) transistor instead flows out pin 5 and through the final. The bottom transistor is not doing anything, it can’t current sink or pulldown because the pin 5 has current flowing out only, nothing flows in to be sunk or pulled down. So the ‘386 is effectively running as a current source with just the top (current source or pull-up) transistor.

The point is that the ‘386 chip could be replaced with a single transistor, or two if more gain is needed.

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2018-09-11 Vectronics Aircraft Radio Kit

I got the Vectronics VEC-131K aircraft band radio kit in the mail yesterday and warmed up the soldering iron to assemble it. It came at a decent price, so some of my complaints seem to be cost cutting measures. It comes with a decent assembly instruction manual, but some of the pages including the schematic were printed from a low resolution graphic, which makes them difficult to read. The Parts Placement Diagram page was not readable and useless. The part numbers are marked on the PC board, so I had to use that.

The assembly time was about 3 hours, but would have been less if I hadn’t hit a few snags – I’ll talk about those later. I would estimate this to be a medium difficulty kit, because it has a lot of parts and there other reasons I’ll get to next.

The instructions get to the point where the two glass diodes are installed. It says to pick the larger glass diode, the 1N270, and I’ll need a magnifying glass to read the markings. But both diodes are the same size, and neither one said 1N270. One said F 5235 so I assumed that was the 1N5235 zener diode. The other diode said 41 BAT, which was not 1N270, so I assumed it was a substitute for the 1N270. I installed it and the zener in their proper places and hoped I got it right.

Another snag was the winding of the three coils. The instructions said to use the length of 24 gauge enameled wire, but I found none in the bags. There were three short lengths of purple hookup wire in the bag, but they didn’t look like it was possible for them to do the job. The instructions say to wind the coils on a 6-32 screw, but the heavy hookup wire would not fit into the threads like they said. So I found some 24 AWG enameled wire that I had and used it instead.

There were seven “103” .01 uF ceramic disk capacitors to be installed into the board. The bag had seven big blue .01 uF capacitors that were rated at 1000 volts and their leads were very wide, making it difficult to install them close to the board. So I got seven smaller .01 uF capacitors from my parts box and used them instead. They could still be a lot smaller, so I may replace them later.

With the rest of the parts properly installed, I finished up the assembly. then the instructions take me through the testing and alignment. I used a short lengths if wire for the antenna, plugged in a speaker, powered it up and turned up the volume but I heard nothing. I heard some clicks and buzzes but that was my cellphone, so I moved it away. I did the procedure “10.7 MHz IF Stage Alignment By Ear” and suddenly the receiver started to put out noise, which was a good sign. There is no squelch control on this radio.

The instructions said to “Set the Local Oscillator Tuning Range Using the Signal Generator” but I don’t have a signal generator that can go to 120 MHz. So instead I used the “Setting the LO Tuning Range Using Off-air Signals” procedure. I tuned the frequency control, but it was super sensitive and a very small change covered many channels. I think this 10k potentiometer needs to be replaced with a multiturn pot that will give finer control of the frequency setting. Also the volume control seems to be linear, not logarithmic. When I turn it to minimum the speaker is silent. But if I turn the pot just slightly above minimum the volume gets very loud very quickly. If it was logarithmic, the volume would be normal over a much wider range of the pot.

I have been listening to the local airport radio traffic with just a few feet of wire connected to the RCA antenna jack. But I don’t know what frequency I’m listening to. I need to get some way of calibrating the dial so I can choose 121.8 MHz, the frequency for the big jets.

Update 12 Sep.

I made a modification to the volume control. I soldered a 680 ohm resistor between the center wiper pin and the pin that’s common negative. This makes the volume control less sensitive so it doesn’t get so loud when it’s barely turned up. The resistor could be lower, maybe 560 or 470 ohms, to make it even less sensitive.

The second modification was to add a 1k pot in series with R7. I unsoldered the negative lead of the 2.2k resistor R7 and soldered a short piece of wire to the lead and to the center wiper pin of a 1k pot. I soldered another short wire to the other ‘cold’ pin of the pot and to the hole where the 2.2k resistor lead was. This is much easier to tune to a channel than the main 10k tuning pot.

Now I need to print a list of the John Wayne Airport frequencies.

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2018-09-08 Skunk!

From FB comment to Kate Jesse’s skunk visiting her back yard, 2018-09-12

One time I was on guard duty at the Artillery Hq. in Minneapolis, standing in the 3′ by 3′ guard house at the front gate. I saw something crawling under the fence several yards away, and when I saw the white stripes, I knew it was a skunk! I wasn’t sure what to do, run or what. No door on the guardhouse, the skunk could’ve walked right in! The M1 carbine was useless, no ammo! I just hoped and prayed he’d leave me alone. Skunk waddled off into the brush, and I breathed a sigh of relief. 😱

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2018-09-07 Q of an Inductor

from FB group Building Transistor Radios, 2018-09-07

Tom Miller
Say a capacitor or inductor has a Q of 100. The losses are about 1/100 of the energy in the component. In a tuned circuit the capacitor Q is usually much higher than this – it has lower losses, so the more important is the Q of the inductor.

The inductor’s copper wire has resistance so there is some loss in the resistance. If it has a core other than air, the losses in the core’s magnetic field add to the total. The core is made of small particles of material to reduce eddy currents, which reduces the losses. The copper wire losses can get higher because of skin effect, which is why Litz wire is used to reduce the skin effect.

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