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2017-01-22 FM Regenerative Receiver

I’ve been building another FM regenerative receiver. This one is supposed to use a BF244 JFET. But they were declared obsolete years ago, and aren’t available in quantities at a reasonable price. So I ordered some 2N3819 JFETs from Mouser and got them a few days ago. The 2N3819 is also a VHF JFET, so it should do the job.

I used this circuit. This is a superregenerative circuit – it self quenches at a supersonic frequency, as shown by the waveform.
image Here’s the website where I obtained this.

The antenna is shown as a collapsible type from a portable radio, but I used a short piece of wire, abut 10 inches or 25 cm long. For the 1.2 pF antenna coupling capacitor I used a 0.2 to 5 pF miniature variable capacitor set to a low value. I will be using these a lot — I bought a bag of 500 of them for a few dollars.

I made L1 from 18 AWG wire, 5 turns wound on a Bic pen, about .36 in. diameter. It measured about 190 nanohenrys, but it’s less than that after I stretched it to lower its inductance. For C1 I used a 15 pF ceramic in parallel with one of the 0.2 to 5 pF mini variable capacitors (see changes below).

Added Audio Stage
I added a stage of audio amplification after the regen, in place of the ‘auriculare’ headphones that the schematic shows. It’s a SS9014D high gain audio transistor with the emitter grounded. The collector load resistor is 4.7k, and the base bias resistor between collector and base is 1 Megohm. It should be higher, probably 2.2 M. The DC blocking capacitors at both base and collector are 0.56 uF MLCCs. It’s loud enough to drive a 120 ohm earphone from a telephone handset.

Performance
After building a few of these, this is the first one that is sort of acting as a receiver. I got a little hiss and noise when I swept my dip meter’s frequency dial past this regenerative receivers frequency. I’m happy to find that it’s tuned to a frequency on the low end of the FM band. But I still haven’t heard any FM stations. It’s like these regen receivers are very insensitive. Some schematics I’ve seen have an RF preamplifier before the regen stage, but the impression that I got was this preamplifier was more for preventing the RF generated by the regen stage from going out from the antenna. I can hear this regen noise when I listen with a pocket FM radio, so it definitely radiates RF.

When I finished building it, I used a 10 inch wire for the antenna. I set the variable antenna coupling cap to a low value, probably about 1 pF. With the 10 inch wire, I get a 120 Hz buzz, which stops when I turn off my soldering iron. When I add a foot long alligator cliplead to the wire, the receiver goes silent, like it stopped oscillating. I need to find out why it’s sensitive to the antenna length.

It looks like I’m going to have to do some tweaking to get this receiver to work better.

I varied the supply voltage from 9 down to 4.5 volts, adjusting the tuning as I lowered it. I think it is a bit better when the supply is 6 volts DC. After adjusting the tuning, I could hear an FM station weakly mixed with the hum, noise and sputtering. This “first hear” is a defining moment, but whenever I move my hands, arms or body, the signal starts splattering loudly, so right now I have a proximity detector more than a radio receiver.

Next Day
Jan 24 morning I found that no matter what the supply voltage was, it still had problems with hum, noise, and dropping out. It’s supposed to quench at several tens of kHz, but I didn’t see that with a DMM or ‘scope. The original schematic had a pair of piezo earphones connected to the output. These are very high impedance and a minimal load. This audio preamplifier may be too low an impedance load. So I inserted a 10k resistor in series with the coupling capacitor C4. See here for an example (uses 22k res.)

I thought that part of the problem might be the L2 choke was not high enough value, only about half a microhenry. I removed it and wound more turns on a short length of soda straw. It measured 1.5 uH, three times the original. I put that in and it seemed to be less sensitive to my movements, and I heard a radio station a bit clearer. But as I tuned the 5 pF tuning capacitor, I found that the frequency was below the FM band, as low as 85 MHz. I removed the L1 coil and wound on a smaller diameter shaft of a drill bit about 0.3 inches diameter. I cut off some of the extra wire and reinstalled it in the circuit. Now the tuning is covering much more of the bottom on the FM band.

I tuned a pocket FM radio to a station at the bottom of the band, 88.5 MHz. I can now tune the regen receiver to that same station. But the regen receiver radiates RFI and causes the pocket radio’s audio to become quieter. The regen receiver’s audio is very weak, too. These two problems may mean that the regen receiver should have a RF preamplifier before the regen stage to prevent the interference from escaping and amplify the signal.

An My earlier regenerative receiver project.

I’ll continue this on the next blog tomorrow Jan 24.

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2017-01-18 Simulating An Analog Meter

A detector or discriminator in an electronic device might need to be adjusted to a very few points on a scale of a hundred or more points.  A digital indicator typically indicates only a fraction of that, possibly 16 points.  This is why the analog meter is still useful: it can indicate a small change on a much larger scale.  I would like to make a device that is much cheaper than the analog meter, yet can indicate a small change in a much larger voltage or current.

I had a thought.  With today’s 3d technology and super strong magnets, it might be easy to do this.  Back in ‘the old days’ they used to make super sensitive meters by replacing the meter needle with a mirror.  Then a light went through a narrow slit and reflected off the mirror onto a somewhat distant surface, and movement that couldn’t be seen on the needle was easily seen on the light line on the surface. 

Another idea.  If the circuit is designed like a Wheatstone bridge, where the meter is showing only a small fraction of the total reading, then a 16 bar digital meter might be usable.  In other words, if the 16 bar meter shows 1/8 of the full scale reading, then it would be like looking at a part of the scale of a 128 bar meter.

But the problem is the measured quantity might suddenly change to a much different value which would no longer be in the small scale.  Therefore the small scale should be able to readjust itself to cover the new point.  There could be a ‘zero’ button to let the user recenter the 16 bar display on the changed value.

Some form of automatic feedback correction should be able to do this readjustment.  The adjustment could be done manually, but it seems that it can easily be done automatically.  The adjustment and settling times should be quick enough to not interfere with the user’s measurements.

One thing that occurred to me is that a good sensor of small level changes might be the ear. I could try connecting the voltage output to a voltage to frequency converter. The slight voltage changes would change the frequency and the ear could discriminate very small changes in the tone. A simple oscillator such as an astable multivibrator could be used.

Another idea. I’d like to investigate how sensitive the visual system is to flash rate. I found that the reason they use a starting pistol for races is that the mind processes sounds much faster than visual signals. That’s because there is much less brain used in processing sound, so there are less delays. But can a person do a visual comparison of the flash rates of a flashing LED? Or perhaps compare the flash rate of two LEDs?

Another possible solution, which seems to be very similar to the magic eye displays. The single LED would be mounted on a rotating disk. It could be mounted so the LED is seen on the edge of the disk. The disk spins and the led moves from Left to right. As the LED appears on the left, the circuit turns it on, and it remains on for the time determined by the voltage. Zero volts would have a very short time and the LED would turn off at the left side. Maximum voltage would turn off on the far right and other voltages would be in between. So the user would see something similar to a bar graph, with a varying length of light depending on the voltage. I realize that the mechanism might be complicated, but the rotating LED might be replaced with a stationary LED and a rotating mirror. Or the LED might be mounted on a lever that is driven by electromagnetics similar to a speaker’s voice coil. The whole idea here is to simplify and miniaturize the display.

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2017-01-15 Tuned Circuit Tester

I’m building a tuned circuit tester, which is a Franklin Oscillator without the parallel tuned circuit.  I based it on the schematic I found at this URL.  The first amp is a JFET in common drain or source follower configuration, which then drives the 2nd stage, a PNP transistor in common base configuration, so there is no signal inversion and the common base has voltage gain.  Some signal is used to drive the third emitter follower stage, and its output is used to drive a frequency counter. 

The following photo shows the changes I made.  Most are increased capacitor values, such as coupling and bypass, which don’t affect the circuit very much.

I used an MPF102 JFET for the first amp, and a 2SC3355 for the emitter follower.  Instead of a 1N4148 I used a 1SS98 UHF diode for the JFET’s gate.

After completing the basic circuit, I double checked it and found a bias resistor that needed to be soldered.  It pays to double-check!  I then soldered a coil of 6 turns of 20AWG bare copper wire in parallel with a 24 pF trimmer capacitor across the ‘unknown tuned circuit’ pins.  I applied 9 volts and checked with a dip meter and FM radio, and tuned the circuit to the bottom of the FM band.  It oscillates just fine – I got a strong signal.  I tried adjusting the trimpot, but it doesn’t do a lot, just changes the power.

I changed the tuned circuit to a 2.6 uH toroid coil in parallel with a 100 pF disk capacitor.  This should resonate at 9.7 MHz.  I put a short wire through the toroid and made a  single turn loop by soldering the ends together.  This allows me to put the coil of the dip meter inside of the loop to pickup the signal.  I powered it up, but I got nothing.  I thought it may be because the loop is acting as a shorted turn and stops the oscillator.

I removed the single turn loop from the toroid. I thought, what would be a good way to indicate that the circuit is oscillating? I decided that a half wave doubler and LED should be fine. I added two 1N914 diodes, a filter capacitor and red LED to the output. I checked the LED to make sure it would light up. When I powered it up, the circuit did not seem to be oscillating and the LED did not light. I decided to go back to the 6 turns and trimmer capacitor. I powered it up and adjusted the trimmer so I could hear the dead carrier in my radio. I got a strong carrier, but the LED still didn’t light up. My thoughts are the circuit is oscillating but the amplitude is not high enough to make the half wave doubler rectify and light the LED. Maybe I need an amplifier after the diodes? …

Things are turned around. Circuits typically oscillate easier at low frequencies, and harder at high frequencies, but not in this case. Weird.

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2000-01-01 watsonspics.blogspot.com

This is a link to my pictures I posted.

watsonspics

Pictures, for the most part, of schematics I’ve drawn, using ExpressPCB, free software. There is little or no text. A few may have been drawn by others. Those from Quantsuff (quantsuff.com) have a QS in the name. I’ve received permission from QS to use them. Solid State Systems is a name I used many years ago.

I can no longer access these pictures.  The evil blogger.com deleted my watsonseblog.blogspot.com account.

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2009-01-10 Experimental Joule Thief

Date 2017-01-12
Link to
Experimental Joule Thief

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2017-01-10 Work Light

Here’s a shot of one of my very bright work lights.  It’s a 10 watt multi chip LED mounted on a heat sink, which gets a bit warm.  I mounted the heat sink on a piece of 6 AWG bare copper wire which lets me reposition the light a bit.

It’s a daylight color temperature, but I have some of the same LEDs that are warm white.  I powered it with a 12 volt wall wart and a switchmode DC – DC converter.  I can adjust the current and brightness.

image

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2016-12-25 Merry Christmas

Jingle Bell,

It’s cold as hell,

45 degrees today;

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2016-12-10 Snowden – Courage And Fear

Someone I know posted this to Facebook:

“Courage is not living without fear. Courage is being scared to death and doing the right thing anyway.”

What does this have to do with Snowden?  Well, think about it.  Did he weigh the consequences of his actions?  Did he think about what would happen if he went ahead with his revelations?  I’m sure he realized that there would be negative consequences for his actions.  When he made the choice, I’m certain he knew that there would be repercussions and his choice would have a negative impact on him.  But as he made the discoveries that would send him down this path, did he know that the evidence he had uncovered would be worth risking his life and future?

I’m sure he didn’t make a sudden snap decision.  He must’ve spent some time looking at data he had access to, and developed a sense over time that the information was so important that he had to do what he did.  I’m very curious because it was a life changing decision that he made.

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2016-12-05 Regenerative Receiver

After I unsoldered the parts from my failed ‘noisy regenerative receiver’ circuit, I decided to build a more conventional regenerative receiver, one that uses a single transistor for the regenerative stage. I chose the circuit from a website that I had found, and saved the schematic. But I forgot to document the URL of the website. So I’ve attached the schematic which has the author’s name and ham call letters to identify it.

image

I used the following values for the parts.

C1 100 nF
C2 not used
C3 4.7 uF
C4 1000 pF
C5 27 pF fixed, 4 to 14 pF var. cap in parallel.
C6 25 pF mica variable capacitor
C7 two 2.2 nF in parallel.
C8 5 pF variable capacitor set to max
C9 not needed, already in the audio amp

R1 10k, 25 turn trimpot
R2 0 ohms (not used)
R3 44k – two 22k in series
R4 no value given, used 1k in series with a 5k pot, giving 1k to 6k
R5 10k

L1 14 turns 20 AWG on 3/8 in. diam. wood dowel – about 0.8 uH.
RFC1 33 uH RF bead with several turns threaded through the center hole
Q1 I used a C9018 VHF transistor.

I reused my amplifier and earphone from the nonworking regenerative receiver. The supply is a three AA cell holder, so fresh cells will give a bit more than 4.5 volts.

I got noise from the regenerative circuit as soon as I powered it up. With a little tweaking, I tuned it, and got noise but received no communications. I did hear bursts of RF coming from my cell phone. The antenna is only about 7 inches long. I think the receiving frequency is not in the CB band. My dip meter showed the coil as resonating at about 27 MHz. I guess I’ll have to make a transmitter that puts out a known frequency in the 27 MHz band. I looked for some schematics of VFOs that hams build and I found one that is supposed to be very stable if it is built properly.

Update Dec 7 – I mounted most of the pieces on a piece of plywood, and put a piece of sheet metal on it for a front panel. I got the Batteries, audio amp and volume pot mounted. I drilled a hole in the plywood that is the size of the dowel that holds the coil, and I can press the dowel into the hole so that it fits snugly. I have to rearrange some of the parts so they aren’t in the way. The RF part is sensitive to movement, so this ‘breadboard’ should help a lot in making it more stable. I measured the total battery drain at about 2.5 mA.

I changed the fixed resistor R4 to 1k and a 5k pot in series and mounted the pot on the front panel. I get hiss, but I still haven’t received any signals. After adjustments my dip meter said the coil was resonating at about 27 MHz, but the meter isn’t accurate and is probably off a bit. When the dip meter is on, it quiets the hiss, so I guess that means the regenerative circuit is doing something.

I have been looking at other regen schematics, and I found that the ones that use a JFET do not need a diode detector, but the others that use a BJT have a diode as the detector. Except for the one I’m experimenting with, which is missing the diode. I think I’m going to have to add a diode somewhere, and I’ll have to do some experimenting to find out where.

Update 2017-01-22 I’m building another FM regenerative receiver, see here.

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2016-12-01 NEJM Antivaccine Article

Whole article from
https://web.archive.org/web/20140423082318/http://www.nejm.org/doi/full/10.1056/NEJMp1010594

***Begin quote***:
“Perspective

The Age-Old Struggle against the Antivaccinationists

Gregory A. Poland, M.D., and Robert M. Jacobson, M.D.

N Engl J Med 2011; 364:97-99January 13, 2011DOI: 10.1056/NEJMp1010594

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ArticleReferencesCiting Articles (41)

Since the introduction of the first vaccine, there has been opposition to vaccination. In the 19th century, despite clear evidence of benefit, routine inoculation with cowpox to protect people against smallpox was hindered by a burgeoning antivaccination movement. The result was ongoing smallpox outbreaks and needless deaths. In 1910, Sir William Osler publicly expressed his frustration with the irrationality of the antivaccinationists by offering to take 10 vaccinated and 10 unvaccinated people with him into the next severe smallpox epidemic, to care for the latter when they inevitably succumbed to the disease, and ultimately to arrange for the funerals of those among them who would die (see the Medical Notes section of the Dec. 22, 1910, issue of the Journal). A century later, smallpox has been eradicated through vaccination, but we are still contending with antivaccinationists.

The Cow Pock — or — the Wonderful Effects of the New Inoculation.

Since the 18th century, fear and mistrust have arisen every time a new vaccine has been introduced. Antivaccine thinking receded in importance between the 1940s and the early 1980s because of three trends: a boom in vaccine science, discovery, and manufacture; public awareness of widespread outbreaks of infectious diseases (measles, mumps, rubella, pertussis, polio, and others) and the desire to protect children from these highly prevalent ills; and a baby boom, accompanied by increasing levels of education and wealth. These events led to public acceptance of vaccines and their use, which resulted in significant decreases in disease outbreaks, illnesses, and deaths. This golden age was relatively short-lived, however. With fewer highly visible outbreaks of infectious disease threatening the public, more vaccines being developed and added to the vaccine schedule, and the media permitting widespread dissemination of poor science and anecdotal claims of harm from vaccines, antivaccine thinking began flourishing once again in the 1970s.1

Little has changed since that time, although now the antivaccinationists’ media of choice are typically television and the Internet, including its social media outlets, which are used to sway public opinion and distract attention from scientific evidence. A 1982 television program on diphtheria–pertussis–tetanus (DPT) vaccination entitled “DPT: Vaccine Roulette” led to a national debate on the use of the vaccine, focused on a litany of unproven claims against it. Many countries dropped their programs of universal DPT vaccination in the face of public protests after a period in which pertussis had been well controlled through vaccination2 — the public had become complacent about the risks of the disease and focused on adverse events purportedly associated with vaccination. Countries that dropped routine pertussis vaccination in the 1970s and 1980s then suffered 10 to 100 times the pertussis incidence of countries that maintained high immunization rates; ultimately, the countries that had eliminated their pertussis vaccination programs reinstated them.2 In the United States, vaccine manufacturers faced an onslaught of lawsuits, which led the majority of them to cease vaccine production. These losses prompted the development of new programs, such as the Vaccine Injury Compensation Program (VICP), in an attempt to keep manufacturers in the U.S. market.

The 1998 publication of an article, recently retracted by the Lancet, by Wakefield et al.3created a worldwide controversy over the measles–mumps–rubella (MMR) vaccine by claiming that it played a causative role in autism. This claim led to decreased use of MMR vaccine in Britain, Ireland, the United States, and other countries. Ireland, in particular, experienced measles outbreaks in which there were more than 300 cases, 100 hospitalizations, and 3 deaths.4

Today, the spectrum of antivaccinationists ranges from people who are simply ignorant about science (or “innumerate” — unable to understand and incorporate concepts of risk and probability into science-grounded decision making) to a radical fringe element who use deliberate mistruths, intimidation, falsified data, and threats of violence in efforts to prevent the use of vaccines and to silence critics. Antivaccinationists tend toward complete mistrust of government and manufacturers, conspiratorial thinking, denialism, low cognitive complexity in thinking patterns, reasoning flaws, and a habit of substituting emotional anecdotes for data.5Their efforts have had disruptive and costly effects, including damage to individual and community well-being from outbreaks of previously controlled diseases, withdrawal of vaccine manufacturers from the market, compromising of national security (in the case of anthrax and smallpox vaccines), and lost productivity.2

The H1N1 influenza pandemic of 2009 and 2010 revealed a strong public fear of vaccination, stoked by antivaccinationists. In the United States, 70 million doses of vaccine were wasted, although there was no evidence of harm from vaccination. Meanwhile, even though more than a dozen studies have demonstrated an absence of harm from MMR vaccination, Wakefield and his supporters continue to steer the public away from the vaccine. As a result, a generation of parents and their children have grown up afraid of vaccines, and the resulting outbreaks of measles and mumps have damaged and destroyed young lives. The reemergence of other previously controlled diseases has led to hospitalizations, missed days of school and work, medical complications, societal disruptions, and deaths. The worst pertussis outbreaks in the past 50 years are now occurring in California, where 10 deaths have already been reported among infants and young children.

In the face of such a legacy, what can we do to hasten the funeral of antivaccination campaigns? First, we must continue to fund and publish high-quality studies to investigate concerns about vaccine safety. Second, we must maintain, if not improve, monitoring programs, such as the Vaccine Adverse Events Reporting System (VAERS) and the Clinical Immunization Safety Assessment Network, to ensure coverage of real but rare adverse events that may be related to vaccination, and we should expand the VAERS to make compensation available to anyone, regardless of age, who is legitimately injured by a vaccine. Third, we must teach health care professionals, parents, and patients how to counter antivaccinationists’ false and injurious claims. The scientific method must inform evidence-based decision making and a numerate society if good public policy decisions are to be made and the public health held safe. Syncretism between the scientific method and unorthodox medicine can be dangerous.

Fourth, we must enhance public education and public persuasion. Patients and parents are seeking to balance risks and benefits. This process must start with increasing scientific literacy at all levels of education. In addition, public–private partnerships of scientists and physicians could be developed to make accurate vaccine information accessible to the public in multiple languages, on a range of reading levels, and through various media. We must counter misinformation where it is transmitted and consider using legal remedies when appropriate.

The diseases that we now seek to prevent with vaccination pose far less risk to antivaccinationists than smallpox did through the early 1900s. Unfortunately, this means that they can continue to disseminate false science without much personal risk, while putting children, the elderly, and the frail in harm’s way. We can propose no Oslerian challenge to demonstrate our point but have instead a story of science and contrasting worldviews: on the one hand, a long history of stunning triumphs, such as the eradication of smallpox and control of many epidemic diseases that had previously maimed and killed millions of people; on the other hand, the reality that none of the antivaccinationists’ claims of widespread injury from vaccines have withstood the tests of time and science. We believe that antivaccinationists have done significant harm to the public health. Ultimately, society must recognize that science is not a democracy in which the side with the most votes or the loudest voices gets to decide what is right.

Disclosure forms provided by the authors are available with the full text of this article at NEJM.org.

SOURCE INFORMATION

From the Mayo Clinic Vaccine Research Group (G.A.P., R.M.J.), the Department of Medicine (G.A.P.), and the Department of Pediatric and Adolescent Medicine (G.A.P., R.M.J.), Mayo Clinic, Rochester, MN.”
***End quote***

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