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Old 22nd July 2011, 07:39 PM   #11
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Yeah I'm surprised that there are so few FM kits or recent DIY articles on FM. FM is still relevant in our society.

I've been reading up on RF. Some of the more prominent ideas are to keep the circuit as tight as possible, use a ground plane (or a very low impedance ground), and to properly shield it.

I'm not sure how well it would perform because I would probably try to make it on perfboard, as I have never etched anything in my life...though I suppose I could change that.

Regarding that Somerset design...One transistor FM radio project

It calls for a 9V battery. Now I don't really know how that shunt regulator is working, but what would happen if I dropped that voltage to around 2.7-3.0V (2x AA batteries)?

Thanks for the interest.
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Old 22nd July 2011, 07:48 PM   #12
EUVL is offline EUVL  Europe
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John Linsley Hood FM tuner article/s

FM/AM Tuner
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Old 22nd July 2011, 08:11 PM   #13
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I read those before, but I didn't really get too much from it. I'm a complete newbie to RF. =/
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Old 22nd July 2011, 08:23 PM   #14
DF96 is offline DF96  England
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Perf board might not work too well at VHF. OK for an AM radio, though. For VHF FM you need either a PCB or 'dead bug' style on a plain unetched PCB sheet.

If you are an RF newbie, then don't start with FM. Try a simple AM receiver first. RF (AM) is harder than audio. VHF FM is harder still.
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Old 22nd July 2011, 08:38 PM   #15
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Quote:
Originally Posted by DF96 View Post
Perf board might not work too well at VHF. OK for an AM radio, though. For VHF FM you need either a PCB or 'dead bug' style on a plain unetched PCB sheet.

If you are an RF newbie, then don't start with FM. Try a simple AM receiver first. RF (AM) is harder than audio. VHF FM is harder still.
I made a foxhole radio when I was younger.

That's about it though. I made that on a piece of wood....sounded alright. Then again, there wasn't much to hear.
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Old 23rd July 2011, 03:32 PM   #16
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It is the VHF part which is beyond basic diy, requiring "unusual" test equipment . If you can get hold of one of the old Larsholt front end modules, that takes care of this part. The detector and stereo decoder are practical diy. My Sony STS-361 is a single sided pcb with wire links - hardly good rf practice and it works very well. One possibility is to buy an old Japanese tuner as a parts doner. Most will contain a CA3089 and MC1310 or equivalent Rohm parts and a usable tuner front end module.
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Old 23rd July 2011, 09:43 PM   #17
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Yuck...Well oh well. I might just try a TDA7000 for the hell of it, even though no one likes it.

How about FM transmitters? Do they require special layouts?
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Old 15th August 2011, 03:17 AM   #18
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Fenderbender11; "How about FM transmitters? Do they require special layouts?" Yes, if done properly. To address the original question I recall from the schematic of one of the top end Marantz receivers that its tuner had FIVE tuned stages. If I were to consider building one that's probably the one I'd attempt to emmulate. But one of the easiest best fixes for FM sound is to build your own Stereo decoder. Don't know the modern equivalent or if it's still available but I seem to recall using a National LM1800 decoder. Made a huge difference on the receiver I was using at the time. Doc
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Old 15th August 2011, 04:16 AM   #19
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A quick search revealed UA758 is pin for pin replacement and is currently on Ebay for as low as $12 shipped. but heres a link to a National App note for an entire receiver circuit. http://www.national.com/an/AN/AN-147.pdf Doc
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Last edited by thaumaturge; 15th August 2011 at 04:24 AM.
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Old 15th August 2011, 07:54 AM   #20
forr is offline forr  France
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For me, the JLH AM/FM tuner made from a kit sold by Hart Electronics in England was a failure. I never get rid of whistles in AM and always got poor stereo separation in FM. In FM, I think the sample and hold decoder had a conception problem, but previous stages were ok.
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