Small RF/radio projects you remember as very rewarding - Page 1
Forum section: electronics / rf-microwave

author: RoGeorge
author_rank: Super Contributor
timestamp: June 22, 2023, 10:28:35 am
content: Looking for project themes. Something that can be built in a few hours, a weekend at most. Can be either educational, a standalone module, a small radio, or an interesting circuit, etc.There are plenty of schematics online, asking in particular for projects you tried and found them to be the most enjoyable or the most interesting.

author: CountChocula
author_rank: Unknown
timestamp: June 22, 2023, 11:11:21 am
content: I still remember building my first crystal AM radio with my dad when I was around 6 years old… I was duly amazed, but found understanding how it worked so hard that it ended up putting me off electronics for 40 yearsAnyway, I'm pretty sure that's a classic and you've already thought about it, but it's definitely something that can be built in an afternoon—at least as long as there are still AM radio stations around!—CC

author: CaptDon
author_rank: Super Contributor
timestamp: June 22, 2023, 06:23:06 pm
content: Two things come to mind, a two tube super-regen receiver (one tube was an audio amplifier section) with the interchangeable coils wound on old octal tube bases that we used to save from dead tubes. I think we built it from an article in QST or perhaps 73 magazine. The second was a one tube (6AQ5A) 5-8 watt crystal controlled novice (40 meter band) transmitter. Several of us 'novices' built these and used them with receivers like Heath HR-10B, Hallicrafters S-38 and so forth and we practiced code with each other within about 25km / 15 stat miles of each other. Most were tuning into long wires but I was a lucky dog already having an 18AVQ multiband antenna used for SWL. I remember well the days of digging through thousands of crystals at hamfests to find a few that matched in frequency. Had some mild success at raising crystal frequencies by grinding on glass with toothpaste. My HR-10B was such a dog, things really came alive when I bought a well maintained National NC-300 for $50 at a local second hand radio store.

author: coppercone2
author_rank: Super Contributor
timestamp: June 23, 2023, 03:50:47 am
content: an antenna

author: Kim Christensen
author_rank: Super Contributor
timestamp: June 23, 2023, 04:20:05 am
content: I remember as a kid having a blast building little 2 transistor FM transmitters. I'd try and make them as small as possible and then plant the "bug" in another room to listen in.

author: floobydust
author_rank: Super Contributor
timestamp: June 23, 2023, 04:45:18 am
content: As a kid, this wireless burglar alarm. All with using a single transistor.

author: Bicurico
author_rank: Super Contributor
timestamp: June 23, 2023, 07:12:00 am
content: About 15 years ago, my favourite electronics shop used to sell a "soldering training kit", which really was a decoder for analog encrypted PayTV. It used an Atmel and was built inside an included 3-way SCART box. You would hook up your TV and could watch all 5 or so premium channels. That was very rewarding and indeed served it's "soldering training" purpose. I assembled 3 kits, but never watched much TV afterwards. A few years later they fully switched to digital modulation and encryption.Main point is: radio receivers are probably a bit boring if your goal is to get kids interested in electronics.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: June 23, 2023, 09:29:53 am
content: FM bugs are great fun. I recommend the ones described on the Talking Electronics website:https://www.talkingelectronics.com/Others have suggested small receivers. I second that. Starts off with a crystal set (if you've got room for a wire antenna at home) or try a simple 2 or 3 transistor type.The MK484 IC can really simplify small receivers as it's almost a whole set in a chip. Here's mine.Later you could try shortwave receivers - either regenerative, direct conversion or even software defined type that you can plug into your computer and use SDR software to hear signals with.Very simple and a lot of fun. One I built quite recently:Superregen receivers can be fiddly but fun for the FM broadcast and aircraft bands. A demo here:If you have a small transmitter (could be CB or ham) then a Squeakie is super simple and cheap with a 555 IC. It detects RF.If you're more the science type and want to measure VHF / UHF frequencies with some wood, wire nails and LED you can with a Lecher line. You will need a small UHF transmitter for this.But really good for teaching radio physics. I described it here:Little 433 MHz UHF modules can be fun, especially if you have a UHF FM receiver (eg a cheap Baofeng handheld).Some experiments here:https://vk3ye.com/projects/projuhf.htm

author: radiolistener
author_rank: Super Contributor
timestamp: June 23, 2023, 10:31:22 am
content: You can build some antenna, for example wi-fi antenna from a used can.

author: A.Z.
author_rank: Super Contributor
timestamp: June 24, 2023, 01:15:17 pm
content: Quote from: RoGeorge on June 22, 2023, 10:28:35 amI've built the regen receiver and the varactor tuned loop antenna found herehttp://techlib.com/electronics/index.htmlboth worked well and are quite straightforward and easy to build

author: radiogeek381
author_rank: Regular Contributor
timestamp: June 24, 2023, 06:13:07 pm
content: I remember building a 10MHz direct conversion receiver from a kit. It used an NE602 and could not have been simpler.

author: @rt
author_rank: Super Contributor
timestamp: June 25, 2023, 12:26:12 am
content: Not easy to find the crystal, but when I came across an old 100kHz xtal, I used it as in an LO to mix with a 359 kHz beacon that could be received here. The tiny module I made could then output the still modulated beacon at 459kHz, which could be fed into the first IF filter of any AM broadcast receiver. It was just a robot voice so I didn’t notice any effect of the IF filter centre f being 4kHz off.

author: tautech
author_rank: Super Contributor
timestamp: July 04, 2023, 07:32:42 am
content: Antenna, no other simple improvement gains so much RF range.I pondered how to get a 200m rated keyfob remote to work reliably at 500m when I got my first VNA.Kind members held my hand and pointed me towards a Slim Jim/J-Pole design.Shared in detail here:https://www.eevblog.com/forum/rf-microwave/antenna-project-log/

author: RoGeorge
author_rank: Super Contributor
timestamp: July 04, 2023, 08:19:47 am
content: For RF (car) key fob you can also get a substantial increase in range if you touch the remote to your head while pressing a button.Not kidding, it works. My guess is the body and the arm with the remote (like a loop) makes an antenna that helps radiate better. Did this many times in parking lots, to discover where the car was park when a normal button press didn't work. The car key fob was on 433MHz.

author: tautech
author_rank: Super Contributor
timestamp: July 04, 2023, 08:35:26 am
content: Quote from: RoGeorge on July 04, 2023, 08:19:47 amYes an old trick.Just dreamt up another antenna project.....garage door opener range extension.It would be nice to signal the door opener at some range, 50m or so to have it open for when your arrive instead of, in our case be quite close to it with an aftermarket keyfob remote. The OEM remote is much better however still only offers some 10-15m range.Shit, just remembered I sold my VNA and its replacement got sold too, the day before it arrived.

author: AndyBeez
author_rank: Frequent Contributor
timestamp: July 04, 2023, 08:47:28 am
content: An AM receiver built around the legendary 'single chip' ZN414https://en.m.wikipedia.org/wiki/ZN414

author: jonovid
author_rank: Super Contributor
timestamp: July 04, 2023, 08:59:56 am
content: as a 1970's teenager I remember building a grid dip meter with a EM84 magic eye tube from an old reel to reel tape recorder , and a unknown 5 pin triode from a 1960's AWA radiosonde.the grid dip meter circuit was put in an aluminum box the size of a coffee mug. with plug-in DIY coils one was 10MHz to 35MHz the other was 1 to 0.3 for the 455KHz IF .I used as a shortwave BFO. then discovering SSB & Amateur radio operators on 7MHz under garbled sounds on my shortwave receiver.the other plug-in DIY coil I used to test my AM 27MHz CB radio (transceiver) and other regenerative shortwave receiver projects. most was one transistor type circuits.as I was circuit bending transistorized Dick Smith kits at the time.the grid dip meter's power supply was other aluminum box with choke and diode tube, AC power transformer with 6.3V AC and 200V for the HT.an audio transformer on the HT line was used as audio modulation. a 3 wire cable was used if i can remember correctly.I later used another unknown 5 pin triode from a 1960's AWA radiosonde as a VHF oscillator with its 100MHz FM radio signal traveling up to 1 km. with a brass rod antenna.to an FM radio cassette recorder. fun at the time. in the 1960s used radiosondes were commonplace in western Victoria before weather satellites came in.each weather balloon radiosonde had two vacuum tubes and a dark green military radio battery 90 volt HT & 6.3 volt LT. if you could get to one with-in 24hr'sthe battery would still have life in it. plus a free parachute!update-vacuum tube circuits I did use for the grid dip meter and FM VHF oscillator came fromMy father's collection of Electronics Australia magazines , also used Talking Electronics magazine for most transistorized circuits at the time.there was no internet or cellphone's back then!update-fixed text errors & context

author: ftg
author_rank: Frequent Contributor
timestamp: July 05, 2023, 10:17:00 am
content: Every deliberately built oscillator is always fun.The joy of oscillation is very true.One of the most fun radio builds was building the "fixed" version of thishttps://www.cool386.com/kits/ace.htmlaround a PCC88 tv tuner frontend valve.Worked on first try!And it was tuned to a station, so when I started increasing the regen pot up I got music.No other radio project before and since has been that rewarding and worked that well from the start.First valve I ever owned and first vacuum tube project in general.Edit:I think I learned about this project from some video by Peter Parker, VK3YE.

author: A.Z.
author_rank: Super Contributor
timestamp: July 09, 2023, 08:44:38 am
content: check thishttps://www.radiolocman.com/shem/pdf.html?di=169057

author: profdc9
author_rank: Frequent Contributor
timestamp: July 09, 2023, 11:43:57 pm
content: You could build a T-match antenna tuner for $5 and an hour or two at most:https://github.com/profdc9/TMatchPCB

author: RoGeorge
author_rank: Super Contributor
timestamp: July 10, 2023, 06:21:02 am
content: What band/frequency is the PCB T-match for?

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: July 10, 2023, 06:55:19 am
content: Quote from: A.Z. on July 09, 2023, 08:44:38 amAnd a video demonstration of a similar LM386 regen but for the MW band

author: RoGeorge
author_rank: Super Contributor
timestamp: July 10, 2023, 08:01:27 am
content: Another unusual radio is this one using a 555 timer.Picture fromhttps://tubetime.us/index.php/2011/02/23/555-contest-entry/

author: ftg
author_rank: Frequent Contributor
timestamp: July 31, 2023, 07:33:30 am
content: Quote from: RoGeorge on July 10, 2023, 08:01:27 amHow about a single 4069UB hex inverter?