a Prototype VLF Superhet. https://bfreebandingtalktheplanet.runboard.com/t2307 Runboard| a Prototype VLF Superhet. en-us Fri, 29 Mar 2024 01:50:34 +0000 Fri, 29 Mar 2024 01:50:34 +0000 https://www.runboard.com/ rssfeeds_managingeditor@runboard.com (Runboard.com RSS feeds managing editor) rssfeeds_webmaster@runboard.com (Runboard.com RSS feeds webmaster) akBBS 60 Re: a Prototype VLF Superhet.https://bfreebandingtalktheplanet.runboard.com/p16329,from=rss#post16329https://bfreebandingtalktheplanet.runboard.com/p16329,from=rss#post16329Thanks each all being well I`ll be committing the circuit over to a more perm board (just the pre drilled perf-board), and doing that "Module" at a time, I`ll also present my cct diags as modules as well, keeps things simple IMO. I like to work from the Output backwards, so I`ll be starting with the Speaker and LM386 circuit first and working towards the front. I like doing it this way because you have a better way to Test early should a mistake or something happen in transposing over, or maybe a bad joint, part failure etc... early warning as nice, and Much better than trying to de-bug an entire circuit in one whole chunk. of course you may be different and have your method too as for what I listen to on there, I tend to stick around the 10KHz frequency, my antenna gives a great response there for some reason, and it`s ideal for weather disturbances too. although mostly I get manmade noises, I don`t begrudge these as I`v tracked a few and know what they are, I use them as Markers. in fact if it wasn`t for these I wouldn`t have much of an idea if I was in the right place or not without bringing a load of test equipment to bear, so I thank my local dentist and his X-Ray machine, and the railroad crossings about 1/4 mile away, even the compact fluorescent bulb in my darkroom for giving a nice 7.5KHz marker ref. what I like to do, is build these things in the winter months and then take them out of a Lads Roadtrip (just me and my mate and no Women!) to Shell Island in wales, and then set up the radio equipment and beer then generally abuse it, Nag Free! anyway, back to it, I haven`t been lazy, I`v just built a nice little 455KHz BFO kit that I bought on eBay from an american guy, it works well and saves me a load of faffing around making my own PCBs, + the price was good! as for Comms on there, you get the usual RTTY type signals and time markers and nav beacons, I`v never really had a go at sending a transmission though (beyond my trusty CFL in the darkroom), although the laptops Touch pad seems to work around the 10K mark and I can send morse over a couple of feet by simply touching it with my other hand by the antenna wire when I DO decide to eventually get to that point, I have a few ideas already of the ways I want to try, I`ll be using Valves for that I think (I prefer them for most applications anyway). nondisclosed_email@example.com (YT2095)Tue, 14 Dec 2010 12:43:44 +0000 Re: a Prototype VLF Superhet.https://bfreebandingtalktheplanet.runboard.com/p16328,from=rss#post16328https://bfreebandingtalktheplanet.runboard.com/p16328,from=rss#post16328Holy.... it's forever since I saw a breadboard like that! I remember I used to have an S-dec. Cut my teeth great on that thing. I still got the first "rig" I ever had... 1977, I was 14, homebrew am tx with a 27.184mhz rock. It was close enuf. I'll try and find it to take a pic. The receiver was my trusty old EC10 which I still have too! What frequencies do you listen to on VLF? Apart from the "au naturel" signals, do you do any comms on that band? Regards Ian nondisclosed_email@example.com (bear632002)Mon, 13 Dec 2010 23:07:56 +0000 Re: a Prototype VLF Superhet.https://bfreebandingtalktheplanet.runboard.com/p16307,from=rss#post16307https://bfreebandingtalktheplanet.runboard.com/p16307,from=rss#post16307Thats a tidy job, i also like a bit of Homebrew, I know most things can be bought for a reasonable price these days, buts its the feeling you get when something you make springs to 'Life' when you power it up, and the satisfaction it gives you. be it a simple or complex project, its all good stuff and may it continue. Mark Gw0wvlnondisclosed_email@example.com (madmark1)Sun, 12 Dec 2010 19:17:55 +0000 Re: a Prototype VLF Superhet.https://bfreebandingtalktheplanet.runboard.com/p16303,from=rss#post16303https://bfreebandingtalktheplanet.runboard.com/p16303,from=rss#post16303Thats fantastic , good old home brew stuff. Thats the sort of thing that got me interested in radio in the first place. For a job, i work with cutting edge, ultra high speed digital products. This sort of stuff is my relaxation, and actually being able to go back to stuff that people can work with, and design themselves, without some fantastic state of the art computer programme to do it for you.   I work as a Test Engineer and frequently have to design and build circuits to test products. The 555 is one of my main-stay design favorites. Sometimes i get the odd funny look when using 'old skool' components in my designs,instead of going down the 'software simulation' road, but if it works.....it works nondisclosed_email@example.com (26FB1981)Sun, 12 Dec 2010 18:39:53 +0000 a Prototype VLF Superhet.https://bfreebandingtalktheplanet.runboard.com/p16288,from=rss#post16288https://bfreebandingtalktheplanet.runboard.com/p16288,from=rss#post16288There are few chips out there that are really memorable in my opinion, the likes of the 555, the 741 op amp, the tda7000 and the lm386 to name a few. but I have to add SA612 to that list now, it has other icarnations too, such as the ne602, ne612 and sa602, but they`re all essentially the same chip. the 612 is lovely little chip that`s quite forgiving and the heart of many a radio product commercial and otherwise, and does exactly what it says on the box, a "Double-balanced mixer and oscillator". after reading up a little about it, I saw quite some potential for my VLF work and set about experimenting with it, like all chips it has pins for Power (+ and -) 2 inputs for the signal, 2 for the oscillator and 2 for the balanced output (or product). it Should be possible to make a VLF superhet I thought, so using my long-wire antenna, through a homemade coil and capacitor filter I fed that to the signal input. the Coil pictured on the left is made from one of those tubes you get in packs of rocket fireworks, and around it are wound 8 cells of 100 turns each very thin copper wire, and then a ferrite rod pushed into the tube, the coil is 260mH, quite a large value of over a quarter of a Henry. since VLF is in the audio range anyway, I don`t need a particularly high I.F, in fact I can have an I.F in the Audio range, so an Audio pass filter was added to the Product Out pins, that`s made up with Audio transformer seen just below the left-most chip. now all I needed was something to Hetrodyne against, again, since we`re in the Audio band, what better than the old 555 timer! that`s the chip in the middle. no although the output from the audio transformer is good enough to drive a crystal headphone, I thought it would be nice to use an LM386 to give it a level of amplification to drive a speaker, that`s the Right-most chip. the 2 pots are Volume and Frequency, the whole lot powers off 4`D` cells (6 volts). the Blue wire in the top left going to the Black connector is the Earth, the white wire (bottom left) is the longwire. the LED is just to remind me to turn it off at night here`s the pic: Once I`v fininshed "messing" I`ll draw up a circuit diagram and try post that in here too. but the idea is really so simple when broken down into Modules like this, that a cct diag shouldn`t realy be necessary exactly. nondisclosed_email@example.com (YT2095)Sun, 12 Dec 2010 13:13:45 +0000