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Hand on the loading coil

Discussion in 'Radio and Wireless' started by aurelZ, Feb 10, 2020.

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  1. aurelZ

    aurelZ

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    Jun 10, 2019
    -Your hand on the loading coil seems to be creating some sort of tuning, likely capacitive?

    hello
    I have similar problems with my receivers, is that mean if tune well with hand on tuning coil that something is wrong with
    signal grounding ?
    or is that mean that gain is to small?
    ..anyone can explain that effect ?
     
  2. davenn

    davenn Moderator

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    bringing your hand/finger close is capacitively changing the tuning of the circuit
     
  3. aurelZ

    aurelZ

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    ok, i understand this , but is ther a way on same way create antenna connection?
     
  4. hevans1944

    hevans1944 Hop - AC8NS

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    Please post a schematic of your receiver and its specifications. What range of frequencies is it supposed to tune to? What type of signal modulation is it supposed to respond to? Do you have any idea what you are trying to do? Why is your hand a part of the circuit you are tuning? All radio-frequency circuits and their components should be shielded and inaccessible to the end user. Compare your receiver with similar commercial products to see the difference. There are many ways "create antenna connection" and to inject an antenna signal into a receiver, but your hand should not be one of them.
     
  5. davenn

    davenn Moderator

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    Sep 5, 2009

    that doesn't make sense … try again :)
     
  6. aurelZ

    aurelZ

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    -Do you have any idea what you are trying to do?
    No i don't have ,,,ah sorry i ask on wrong place..
    forget
     
  7. hevans1944

    hevans1944 Hop - AC8NS

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    To which you posted the schematic image below of a "one transistor superhet."

    [​IMG]
    Your link points to another EP thread that you started. The thread has a link to a Japanese article claiming to offer a toroid-wound transformer to use with an "improved" FM ratio detector. Which is supposed to mean you can wind your own ratio transformer by following a few some simple instructions. The circuit in the Japanese article is for a center-frequency of 10.7 MHz, which is a typical intermediate frequency for consumer FM radios. Two very similar iron-powder toroid cores were suggested for constructing the transformer and its attached 3.3μH inductor: the Amidon FT-23-61 for the inductor and the Amidon T25-6 for the transformer.

    Below is the FM ratio-detector circuit as shown in the Japanese article. There is no mention of an FM radio that can be or is implemented with this circuit.

    [​IMG]

    From which one of the two suggested toroid cores did you wind your center-tapped transformer? Which one did you use for the inductor? How many turns did you use? What gauge insulated wire did you use? What was the final end-to-end inductance? Got any pictures of what you made?

    Where did you find the circuit on the left side of your modified schematic, purportedly showing a "one transistor FM superhet" receiver?

    A superheterodyne or superhet receiver uses a local oscillator injected into a non-linear device to mix with the received signal and produce sum and difference frequencies. The difference frequency is called an intermediate frequency and represents the received signal spectrum translated to a new, intermediate, band of frequencies much lower in frequency than the original received frequency.

    The sum frequency is discarded by filtering. Because the local oscillator is always tuned to a frequency 10.7 MHz higher (or lower) than the received frequency, the band of intermediate frequencies is always located in a known location, namely 10.7 MHz plus or minus the bandwidth of the received signal in the Japanese example. This makes the task of designing and implementing circuits for amplifying and demodulating the received signal much easier.

    How is the transistor in your circuit supposed to oscillate, at some frequency above or below the received FM signal, to create a 10.7 MHz (intermediate) frequency that is the difference between the received FM signal and your (alleged but unspecified) oscillator frequency? What range of DC voltages do you apply to the "poly- plastic FM vari-cap" to tune your receiver? What is the part number and the manufacturer of your vari-cap?

    There does not appear to be any feedback to make your circuit oscillate, but without an oscilloscope and a built circuit in front of me to test with, I must confess that I cannot determine if your circuit will oscillate at any frequency.

    Good luck with your project, but please try to keep every thing in one thread. Multiple threads discussing the same thing are confusing to most people and a clear waste of time trying to sort things out.
    More information, please. Describe what you are trying to DO.
     
    Harald Kapp likes this.
  8. aurelZ

    aurelZ

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    Wow you asking question like you never see before such a oscillator,it is colpitts of course
    and oscillate ..od course, i am really dissapointed in you mister hevans,use imagination once
    and build this circuit and you will see that work, you probably have all parts including BFR91A.
    toroid core is from old fluo home lamp 15W and is perfect..and here is a complete circuit
     

    Attached Files:

  9. hevans1944

    hevans1944 Hop - AC8NS

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    It's really unfortunate that the circuit diagram you just uploaded is not the same circuit as the one you posted earlier. I guess those "monkey see, monkey do" details don't matter much to you. Did you try to copy your circuit from this blog post? Or maybe it was this one?

    I am quite familiar with all sorts of oscillators, but not all variations of them of course. I had never seen one quite like yours, which is apparently a common-collector configuration that oscillates in your FM band to provide a 10.7 MHz IF for the following ratio detector.. My apologies for not recognizing your circuit. I would breadboard your circuit if I could find the Motorola UHF transistor that I purchased some time in the previous century but never used. I kept it because IIRC I paid what was then a "small fortune" for it. I run across it from time-to-time because IIRC I have it stashed in a small vial... or maybe that's the way it came to me. Whatever, it isn't handy at the moment and I don't have a BFR91A to play with.

    Another detail you seem to have decided is not worth including in your FM receiver is the 10.7 MHz bandpass filter shown in the blog schematic, located between the mixer/local oscillator IF output and the ratio detector transformer input. Or is that the little unidentified triangle on your schematic, located at the junction of the collector resistor and the transistor collector?

    When specifying toroid cores, it is best to use Amidon part numbers instead of specifying a "core from a 15W fluorescent lamp." I harvest parts from LED as well as curly-bulb fluorescent lamps, but I would test the cores and try to specify the nearest Amidon equivalent rather than provide a vague description in any circuit I developed that required such a core. I buy a few cores every year at amateur radio fests that I attend, but I always purchase Amidon part numbered cores. That's not to say I won't get taken by an unscrupulous seller who packages salvaged fluorescent-light cores and sells them as Amidon cores. It's always caveat emptor when buying stuff at ham fests.
    Are you trying to do electronics from Croatia? If so, I can understand the difficulties you might experience in obtaining parts, as well as language problems. However, you English is good enough for Electronics Point and certainly better than my Croation or Serbian or whatever language your native tongue is, because my foreign language skills are non-existent.
     
  10. aurelZ

    aurelZ

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    Hi hevans44 ,yes that is my blogspot..or better to say My https://.aurelsoft.ucoz.com ...my nickname here is aurelZ...do you get it now?
    also i have one facebook group called Aurel DIY Radios.
    My primary hobby is programming and you can see that on my site too.
    No here in Croatia we can buy electronic components which are Europen or from Asia(China).
    BFR91 is a philips transistor and i don't know what might be american equivalent.
    We can also buy BFG65,BFR93...etc
    In genaral ...every VHF/UHF transistor used in TV antenna amplifier should work in this circuit.
    One member of my group from Oregon(USA) build complete superhet radio with
    similar oscillator using 2N3904 using 6V battery pack,of course with all stages.
     
    Last edited: Feb 17, 2020
  11. hevans1944

    hevans1944 Hop - AC8NS

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    Thanks for the reply @aurelZ. I did see an example of your programming on your blog, but as I said elsewhere I am not a programmer... maybe a program hacker could describe what I can do if sufficiently motivated, but I've long ago turned to others (such as yourself) if any serious programming was required.

    Glad to see that there is good parts availability in Croatia. Here in the States we tend to be insulated from the rest of the world because everyone gets their "news" from the same sources, just different names attached... ABC, CBS, NBC, CNN, Fox News... etc. Back in the day, there was short-wave radio to receive (literally) other points of view. Not so much today, unless you go looking for it on the Internet, and even then there is likely to be "paywall" between your money and their site. <sigh> It's a good thing you, and similar minded folks, are keeping analog radio alive.

    I have an Elecraft KX3, low-power, portable amateur radio transceiver that is mostly digital, but there is no way I could begin to duplicate its functionality with analog circuits. Still, that's what I grew up on... taking apart old, discarded, radios and TVs and using their parts to learn about electronics. By the time I entered the Air Force in 1963 at age 19 I thought I knew it all when it came to electronics. I was wrong. Military weapon systems are always on the cutting (some say bleeding) edge of current technology. In 1963 I was trained to work on the latest B-52H bombers and exposed to a wide range of technology that I was barely aware existed. I left the Air Force in 1967, thinking again that now I really did know it all when it came to electronics. I was wrong again. Twelve years working my up from entry-level technician to degreed electrical engineer at the University of Dayton Research Institute exposed me to stuff that was beyond the state-of-the-art being used by our troops in the field. Laser weapons were the most fascinating, but they have one significant limitation: no appreciable momentum is transferred in the laser beam. Armies are in business to break things. Lasers have their place, but they definitely don't "break things" like momentum-based weapons do. Burn holes if left on target long enough, and that can cause things to self-destruct, but lasers don't break things and their beams can literally be deflected by a mirror.

    Phillips and other European manufacturer parts are readily available here. I hadn't thought about taking a TV apart to harvest some VHF/UHF components... those aren't the parts that usually fail, leading the TV to being discarded, so that could be a real gold mine. Thanks for the tip! I have a large flat-screen Samsung LCD TV that failed last year because it displayed a single pixel-wide vertical line on the left side of its screen. A YouTube video allegedly showed how to "fix" the circuit board trace that was causing the problem, but it required disassembling the TV from the back towards the front just to gain access to the suspect trace. I already had a "spare" TV with a somewhat smaller screen in the bedroom, so my wife moved that one into the living room and we now watch it.

    But back to your "problem" of your hand changing the tuning of the RF circuit. This is quite common with lumped-element construction where everything is a discrete capacitor or discrete inductor that is exposed. Hams have been fighting it for years. It was a problem when TVs were serviced by repair shops... plastic wands (screwdrivers) were used to adjust the ferrite cores of IF transformers, even when those transformers were mounted inside shielded aluminum cases. The only solution I know of that actually works is to keep your paws away and perform any adjustments with a long plastic rod. It also helps to enclose the RF circuits in aluminum cases, although steel Altoids® mint cases (after you eat the mints of course) work pretty good too.

    As I, and others, have said here many times: HAVE FUN! Electronics is supposed to be FUN! Even programming electronics can be FUN if you are so inclined.:D

    Hop -- AC8NS
     
  12. aurelZ

    aurelZ

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    Jun 10, 2019
    WOW..hevans ..nice story to read
    i don't programming electronics ..then i like to play with code editors,interpreters,parsers etc..
    yes i agree with you about shilding,it should be there..

    ..ahh about LCD TV,most of errors is in bad power supply electrolyte capacitors...
    which one is bad is easy to find ,it is wider on top.
     
  13. hevans1944

    hevans1944 Hop - AC8NS

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    Thank you for the kind remarks. I LOVE telling stories, and hope it helps those coming up to discover where this wonderful industry came from. Back in the day, when I was in high school, none of my fellow students had ever heard of Nikola Tesla. This upset me a lot because I knew that Tesla, almost single handedly (with help from George Westinghouse), invented three-phase, high-voltage, AC power distribution. Not to mention the induction motor which went on to revolutionize industrial manufacturing. He died penniless and perhaps a little crazy in the end, but there is no denying his early genius.

    There was an electronics surplus store (Mendelsons) in Dayton that had a humongous stock of electrolytic capacitors, mostly old "new stock," but also some pulls from power supplies. At one time, NCR Corporation in Dayton was a big-time semiconductor user and manufacturer trying to make the transition from mechanical cash registers to something... anything... more modern. Unfortunately, they just didn't have the corporate mentality required to make such a transition. When NCR decided to abandon those efforts a whole lot of power supplies flooded the Dayton market. These "boat anchors" were typically series-regulated 5 VDC supplies with output currents starting at 10 A and going up to several 100 A. No one wanted to pay the freight cost to move them around the country, so a goodly quantity ended up at Mendelsons. Later they were disassembled for parts and those parts become part of the warehouse inventory open for sale to the public. I knew from some sad experiences going back into the 1950s that electrolytics of unknown pedigree, age, and usage were not to be trusted, so I never bought any from Mendelsons even when the price was ridiculously low. The best approach now when "restoring" or "refurbishing" (make like new) electronics is to simply replace ALL the electrolytic capacitors with factory-new capacitors. Be sure to make your customer aware that the reason for doing this is to avoid repeat maintenance visits, not to rip them off with new parts they may not need. You can use test equipment to find "iffy" electrolytics, but it is usually simpler to just replace them.

    Sadly, Mendelsons is soon to be no more. Sandy Mendelson sold the building for seven million dollars in 2019, with the new owners planning to spend around two hundred million dollars to spruce it up for public usage. I've sort of missed it since retiring to Florida in 2016, but there are more reliable (if not exactly cheaper) sources of parts available on the Internet. Mendelsons was the kind of place you visited on a rainy Saturday morning, spending hours walking up and down aisles that were two or three hundred yards long and full of all manner of interesting "stuff" at rock-bottom prices. Every price was negotiable at checkout, too! A few years ago, while I was still living in Dayton, I had the honor of guiding @(*steve*) (who is an EP moderator) to Mendelsons. I think he liked it because he left with an arm load of blank circuit boards and maybe some other goodies that he shipped back to New Zealand or maybe Australia (I forget where Steve lives, but it is far, far, away). I hope he got to see the Elton John Farewell Yellow Brick Road tour. Sir John is in poor health and I don't have a good feeling for his prospects of making it through another year. All my favorite performing musicians are dead or dying. This may have started for me with The King, Elvis Presley, but I am sure that the 1959 deaths of Buddy Holly, Ritchie Valens, and "The Big Bopper" J. P. Richardson in a chartered airplane crash that actually occurred earlier may have affected more people.

    I say all this because I am dusting off my turntable to play some vinyl records from the 1960s I had stashed in Dayton. Probably need a new diamond stylus for the tone cartridge, and those are probably unobtainable now. Probably have to buy a new tone cartridge, but vinyl is making a comeback here in the States, so that should be doable. More on this project later as it develops.
     
    (*steve*) likes this.
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Nooooooooooooooooo!

    Yeah, it was a great place to visit and you were the perfect host. And those bits and pieces got shipped back to Australia.

    No, I didn't go to see Elton when he was here, but I swear I could hear it from where I live (about 5 miles away).
     
  15. hevans1944

    hevans1944 Hop - AC8NS

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    Yep, those touring events can attract huge crowds and the band needs a lot of volume to heard over the crowd noise. I used to stand next to a set a speakers on a small stage, listening to music played by a local house band in a nightclub in the late 1960s. Wonderful feeling to actually feel the music, but it probably ruined my hearing.

    I have never quite been able to reproduce the same intensity with my home sound system, but that's probably because I don't have all the speakers of the surround sound system wired up. Or maybe 300 watts ain't enuf power to move me. Some fans would say I need at least a kilowatt to get the desired effect, and a monster speaker (or two or four) like Marty had in the original Back to the Future movie. I have often wondered if that speaker was real or just a movie prop, like the "flux capacitor" that allegedly propelled the D'Lorean backwards (and, later, forwards) in time.

    Stories about alternate realities and time travel are fun to read, and when translated to the "big screen" almost believable, at least for the two hours spent to watch them when suspension of belief is essential to enjoyment. That may be why some folks can't stand this type of fiction, but maybe I will try writing some because it is my favorite genre.

    Thanks for remembering our short visit together. I enjoyed showing you around Dayton. I think I would enjoy visiting Australia, but Mexico and Canada are as far as we can afford to travel. I spent a couple of weeks on a job in Mexico during the mid 1990s, and my hosts were very pleasant, arranging transportation and a hotel room for me. Unless you speak Spanish, I found it difficult to fully enjoy their culture. And now it is getting very dangerous to be an American in Mexico... or so I have heard. Actually, it's become tough to be an American anywhere abroad... or so I have heard.

    Dad apparently spent some time in Australia during the Korean conflict, flying as the bombardier on B-29s, from who-knows-where... maybe Guam or the Philippines. I was just a kid when all that was going on, and he didn't talk about what he did when he came back home. But he took a lot of Kodachrome slides that were unfortunately destroyed in a fire at the nightclub I mentioned above. But that's another (tragic) story. Dad said he always wanted to return to Australia, and in his later years he could certainly afford it. But he never made the trip.

    Hmmm. Might be time to close this thread since it has wandered a bit off-topic. I am sure @aurelZ will post here again, perhaps with an interesting programming problem or a unique analog circuit...

    Hop -- ACNS
     
    Last edited: Feb 18, 2020
  16. hevans1944

    hevans1944 Hop - AC8NS

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    Sure, your hand acts as one plate of a capacitor, grounded to earth through your body. The wire of the coil acts as the other plate, also eventually referenced to earth ground but also part of resonant tuned circuit. So changing any of the physical parameters, such as the position of your hand with respect to the coil and the distance of your hand from the coil, will cause a change in the capacitance your hand presents to the circuit. Generally the capacitance increases as your hand moves closer, lowering the resonant frequency of the tuned circuit.

    The exotic musical instrument called a Theremin works on this principle, beating two high-frequency (RF) oscillators against each other to create an audible note whose frequency (pitch) is determined by the location of the musician's hand near an "antenna" that is connected to one of the oscillator's tuned circuit. A similar (but different) circuit allows the audio amplitude to be controlled with the other hand. Some very strange sound effects can be produced by a skilled Theremin player, mostly useful as background "music" for science-fiction movies.
     
    Last edited: Feb 18, 2020
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