[HN Gopher] A 74xx-Defined Radio (2021)
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A 74xx-Defined Radio (2021)
Author : _Microft
Score : 97 points
Date : 2022-07-13 18:45 UTC (4 hours ago)
(HTM) web link (acidbourbon.wordpress.com)
(TXT) w3m dump (acidbourbon.wordpress.com)
| dpifke wrote:
| I've always heard this technique referred to as a "Tayloe
| converter" (or "Tayloe mixer"), and it is commonly seen in SDR
| radios.
|
| I believe this is the original article from the 90's which
| popularized the idea:
| https://norcalqrp.org/files/Tayloe_mixer_x3a.pdf [PDF]
| jschroedl wrote:
| I'll have to build one of these when I find the time. I wonder
| how hard it would be to turn it into a SSB receiver.
| gnramires wrote:
| I don't have much circuit expertise, but in theory I believe
| demodulating SSB can be done by mixing (multiplying) a sine
| wave 2x the SSB center frequency, and summing that with the
| original signal (and then filtering the large frequency
| residues of course). This brings the opposite bands next to
| each other (then you can demodulate as DSB normally).
| orionion wrote:
| Spock: "I am attempting to construct a Mnemonic memory circuit
| using stone knives and bear skins."
| H_Pylori wrote:
| grendelt wrote:
| This is basically what the SoftRock SDR kit is.
|
| The build instructions' schematic is basically a color-coded
| block diagram of what all is needed for an SDR. A super fun,
| informative build.
|
| http://www.wb5rvz.org/softrock_lite_ii/index/projectId=8
| deepspace wrote:
| I knew there was going to be a 74HC4046 in there before clicking
| the link. It is a venerable old workhorse.
|
| When I was studying EE, 40 years ago, one of our professors
| always wore a lab coat with a pocket full of 4046s. He used to
| roam the labs and offer one to students struggling with designs.
|
| It is such a versatile chip, with a VCO and _three different_
| phase comparators. If you have to do anything related to
| modulation and /or demodulation of signals below a few 10s of
| MHz, it may just solve your problem.
| nousermane wrote:
| Analog multiplexer employed as an RF mixer is pure genius.
|
| Of course you can only drive it with square-wave, and mixing with
| square-wave, intuitively, feels like a terrible idea (think of
| all the harmonics!). But surprisingly, listening to the recording
| of the whole thing working, end result sounds A-okay!
| jleahy wrote:
| If you think about how a diode mixer works then you're using a
| square wave LO, same for a Gilbert cell.
|
| Remember, a square wave is just a sum of odd harmonics. The
| only downside is that a strong signal at a multiple of the
| signal of interest might get aliased into your IF. Hence
| bandpass filtering on the input is important.
| lxe wrote:
| I always prefer the FFT/waterfall visualizations instead of
| amplitude/time scope graphs when talking about mixing and
| modulation. Makes it way simpler to reason about I think.
| gaudat wrote:
| There is a high level mixer (I think it's called that) design
| that uses a 3157 video switch chip. I tried to build one a while
| ago and found some manufacturers putting the chip under the 74LVC
| series. I thought this article is about that chip but this is
| mone amazing.
| nynyny7 wrote:
| When I had my "I want to build my own SDR" phase ;) ca. 15 years
| ago, I also used analog switches as a switching mixer - with a
| PLL running at 4x the desired frequency so I could utilize
| dividers to get nice 0deg, 90deg, 180deg, 270deg LO signals for
| IQ mixing. Brings back memories...
| cardiffspaceman wrote:
| In the 70's the company I worked for made a receiver for fixed
| frequencies within 10KHz-13KHz. The architecture roughly was
| discrete time analog, and an analog switch was available that
| took a digital selection and routed the indicated analog input
| to the analog output. That block was used to control the
| sampling for a filter by cycling through the selections. The
| rest of the design was over my head in those days, since I was
| the software guy and the software wasn't controlling that.
| ranger207 wrote:
| How do you learn something like this? I'm ok at digital
| electronics, but doing all this weird radio analog stuff is
| something I don't even know where to start to learn about
| nomel wrote:
| Dig deep into understanding capacitors, inductors, and all the
| first order math around them, then impedance, then get a grasp
| of the hidden capacitors in inductors, and the hidden inductors
| in capacitors, and you'll be in a pretty good position, with a
| path that you should be able to see fairly well.
| solomonb wrote:
| The ARRL Handbook is a wonderful place to start.
| Ao7bei3s wrote:
| Of course there's EE university courses, but generally,
| experimentation. You can get really far in electronics with
| learning by doing.
|
| If you don't know where to start, ham radio is one traditional
| gateway.
|
| Whether or not you get the license is secondary (I think most
| interested people should get it; especially in the US where the
| lowest license class is ridiculously easy - if you know basic
| electronics already and cram today with https://hamstudy.org/,
| you could probably have a Technician class license by end of
| tomorrow - and then you can legally build your own transmitters
| or buy some cheap radios and transmit with those. Transmitting
| is more fun than only receiving.).
|
| The real value is all the structure around it (e.g. 1. there
| are books that start from zero electronics knowledge and end at
| several types of complete transmitters/receivers. The ARRL
| publishes some; 2. the license is a tangible learning milestone
| to work towards; 3. all basic transmitters/receivers have been
| done thousands of times so you can find something online and
| copy it to learn from it. The ham community also has many DIY
| kits you can just buy and build and experiment with.)
|
| Eventually you'll find that you have enough background to use
| more "professional" resources (e.g. data sheets, real academic
| textbooks / professional books, etc.) (at least if you have
| some math background from another field, e.g. CS), build more
| complicated things etc.
| JKCalhoun wrote:
| I like the little prototyping modules. One has a few pots,
| another the logic chips ... they seem to all take their power
| with wire pairs that join a narrow "power-bus module". 3D printed
| boxes with prototyping PCBs... Looks like fun.
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