Building me an FM aerial
I’ve just replaced the knackered, cheap, nasty, old hi-fi in my home office. It was an all-in-one system, but the turntable was no good (and hasn’t seen any use since 1997 when I bought a couple of turntables and a mixer) the cd player and the tape decks were dead – but most importantly the FM tuner wouldn’t remember its presets if you turned it off.
I spend most of my time either listening to Radio 4, listening to vinyl via my turntables, or music/video via my computer (which plugs in to the mixer) so all I really needed was a Receiver.
I found a Sony STR-242L at a car boot sale last weekend for £2 (bargain!) and it works lovely. Thing is, it didn’t come with an FM aerial and I decided it needed something a bit better than the bit of limp wire I was using with the old system. A bit of digging on the internet and I decided to build a simple J-Pole antenna.
I don’t really have space on my windowsill to manage a 3/4 wave j-pole (which would be about 2.3m long, which is most of the hight of the room) so I went for 3/16th wave instead. The gain won’t be anywhere near as high, but it should still be reasonable.
Parts:
- 15mm Copper Pipe
- Easy solder 15mm elbows
- Jubilee hose clip.
The copper pipe was cut into 3 lengths. The shortest was 1/64th wavelength (4.8cm), the middle one is 1/16th wave (19cm) and the longest is 3/16th wave (57.4cm) These are soldered together into a J shape. I don’t have a blowtorch, so I used my camping stove…
The jubilee clip was then roughly positioned about 1/16th wave up from the bottom of the long pipe. A test clip was connected between that and the radio, the clip was then moved up and down until I got the strongest radio 4 reception – not exactly precision adjustment, but “close enough is good enough” – I then marked the position of the jubilee clip with some tape, and attached the coax cable more permanently.
I then turned my attention to the stand, and build something basic out of some scrap MDF, glued and screwed together. There are some brackets behind it which you can’t see in this picture because I don’t really trust butt joints – especially in MDF!
Using some 15mm pipe clips (and some tape to keep the cable braid from coming into contact with the copper pipe) , I mounted the antenna on the stand.
It’s now sat on my windowsill and doing a *lovely* job of picking up Radio 4! I know you can buy FM antennas for very little money, and that “a piece of wire the right length” will do in a pinch – but as I had the cable, the copper pipe and the MDF just lying around, I ended up spending under £3 on plumbing bits and got myself quite a nice antenna!
It also gave me something to do with my afternoon…
Edit: I’ve just noticed a schoolboy error. I connected the driven side of the J-Pole to the center of the coax, but I haven’t connected the shield to the stub. All I’ve effectively done is built a slightly bent 1/4 wave antenna, which will still work nicely enough but isn’t a j-pole antenna. I will endeavor to fix this tomorrow!
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New Toy! New Toy!
Whirr… buzz…. ZAP! ZAP! ZAP!
At least, that’s the plan. It needs a little TLC before it’ll run. The motor doesn’t seem to run smoothly, it could do with a new belt, and I need to fabricate some new brushes out of copper sheet.
And you all thought I’d given up on my projects!
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Project Ringflash…
I’ve spent the evening modifying disposable camera flash circuits (including doing things which are probably unwise, like moving the capacitors), wrapping them in gaffa tape and taping them to the inside of a cake tin.
I’ve already decided that there’s too much that could nibble your fingers in this project, so I won’t do a full writeup, instead I’ll stick to posting the schematics/stripboard layout for the opt-isolated trigger gubbins which means that this beast is safe to use with a DSLR.
Still todo:
- Move the charge-ready lights to somewhere visible for each board
- Build the battery pack
- Add a socket for the sync cable
- box up the trigger circuitry
- Find a better way of insulating and mounting the flash circuits
The picture above is the first test firing of the circuit, triggered by my Nik0n D80. It didn’t die, and neither did I. I count that as a success.
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52 Projects Progress
I’ve had a productive weekend projects wise. I’ve made some significant progress on the following:
- Circuit Bent Toy Train
I bought a toy train in a charity shop for 75p. It’s a pretty simple bend, no glitch potential as far as I can see but you can get some odd sounds out of it by putting body contacts across the speed resistor. This will all make more sense when I’ve shot the video. This one is finished, apart from the writeup/video.
- Ring Flash built from disposable cameras (aka “Deathflash”)
Designed and built the trigger circuit so I can safely fire 5 disposable camera flashes from a DSLR (The trigger voltage of a disposable camera is in the region of 230V which would do the DSLR no good whatsoever) – I now need to mount the flash units to the test rig, wire the whole lot up and fire it. Then I need to buy something to use as the final reflector (time to start searching ebay for jelly/jello molds)
- PVC Flute
I’m building a flute out of PVC pipe. The first attempt is now playable, although the tuning leaves a bit to be desired (especially if you like your notes to follow some form of scale). I think I may just document the build and call it a day for this one. The tuning seems to be too difficult to get spot on, and I don’t have enough interest in learning to play it anyway. Still, it filled an empty couple of hours!
So none that I can cross off the list and call “done” just yet – but I thought I should post something to show I haven’t forgotten completely!
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Project 01/52 – A blackboard
I’m a fairly visual thinker, and I also like to make lists. I have a blackboard in my kitchen for things I need to buy when I next go shopping etc, but wanted a bigger one for my office – mostly to track the remaining 51 projects!
So project 01/52 was to make a blackboard.
Materials:
- Scap battening
- Blackboard paint
- Hardboard culled from the Ikea desktop that served as my desk for almost 10 years
The construction is fairly simple, the hardboard was cut to size and the battening chopped up to fit around the edge, and the chalk holder screwed to the bottom piece of battening from behind. The frame is held together with nails on each corner.
Three coats of blackboard paint on the hardboard, sanded back to get rid of some visible brush strokes, then nail it all together. Job’s a goodun!
I know the description is brief, but if you need more detail than that you have no business building one ;-)
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The Beginning?
Well, I’ve had a week off – and you know what? I miss the whole photo-a-day thing. Or at least, I miss having something to think about on the way to/from work, in the tea room, and all that.
So. I have a plan!
52 projects, in 52 weeks.
2009 is to be the year that I finish all those little things I started work on. It’s going to be the year that I build the “RS232 over tin-cans-and-string” thing, the year I build that ring flash out of disposable cameras, the year that I build a small scale AM transmitter so that I can tune the valve radio in my kitchen to the 1950s…
The rules:
- I have 52 weeks to complete 52 projects.
- Photos will be taken, build notes will be written up, software will be published.
- While I aim to average a project a week, completing two projects in a week then taking a week off is allowable
- Progress will be reported when it’s available, even if the project is as yet unfinished.
I’ll be maintaining a page which lists (and numbers) the projects, with links to the blog articles describing progress. Wish me luck!
Posted in 52 Projects, Experiments | 10 Comments »
