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 Post subject: LM386 Transmitter
PostPosted: Jan Thu 28, 2016 2:24 am 
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Please move to Homebrew. (homebrew hooch moment)

Hey Tom, I just noticed my transmitter's (built many years ago) tuning is different. My parallel L/C (toroid/v-cap) that I robbed from another project has always worked centered scale at 1,000kHz and I thought it was conventional. Plastic construction box, no hand capacitance and covers a house or two with attic antenna/copper pipes ground.
Any gain in changing to your version? Is the ant .01 cap really necessary?

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 Post subject: Re: LM386 Transmitter
PostPosted: Jan Thu 28, 2016 4:37 am 
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Geee Mike I dunno, don't remember trying your version of circuit... I can find out easy enough in the next day or so, still have one set up on breadboard...

The .01 cap is for DC blocking, without it I blew a IC when antenna accidentally grounded...


EDIT Just hit me, your version will no doubt work but is transmitting a sq wave vs a sine... I suspect it will have far less range than with load coil in series with antenna...

Do you remember the value of coil you are using?


Tom


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 Post subject: Re: LM386 Transmitter
PostPosted: Jan Thu 28, 2016 5:47 pm 
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Mike I measured carrier waveform and signal output with both setups, first is with my circuit, second yours... No settings were altered on scope, so there is a huge difference in output, plus as I stated last night, yours is transmitting a sq wave... I tried several value coils from 82 to 1000uh, no real difference in any of them...

Do you know value of you torriod??

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Tom


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 Post subject: Re: LM386 Transmitter
PostPosted: Jan Thu 28, 2016 7:00 pm 
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The toroid I used were 114-61 with about 30 turns of hookup wire.
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I just took it apart and I was wrong. This is how it's wired.
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 Post subject: Re: LM386 Transmitter
PostPosted: Jan Thu 28, 2016 11:43 pm 
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Ahhh big difference... I suspect it'll be approx same as mine but with one exception... With the body of tuning cap ungrounded, it will likely be more sensitive to hand capacitance vs being grounded...

You know I'll try it... Back in awhile...

OK, I remember why I didn't use that configuration... Produces approx same signal but has harmonics(spikes on signal peaks)...

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Last edited by 35Z5 on Jan Fri 29, 2016 12:37 am, edited 1 time in total.

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 Post subject: Re: LM386 Transmitter
PostPosted: Jan Fri 29, 2016 12:04 am 
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Location: Santa Rosa, CA
Is that toroid with 30 turns supposed to be 330 uH?

30 turns sounds low... like about 70% low... unless you really have a hi perm core.

this calculator is more like 170 turns....

http://mikeyancey.com/hamcalc/toroidcalculator.php

Rich


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 Post subject: Re: LM386 Transmitter
PostPosted: Jan Fri 29, 2016 1:30 am 
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The coil has 50 turns.
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I rewired this one to your config. Seems the same, may be a little more volume.
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 Post subject: Re: LM386 Transmitter
PostPosted: Jan Fri 29, 2016 3:42 am 
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Mike Toon wrote:
I rewired this one to your config. Seems the same, may be a little more volume.


Well you can't hear harmonics but a cleaner signal may improve audio...


BTW I did reduce scope gain on that shot to make the waveform a bit clearer, signal was virtually identical on both versions... The 330uh produces more output than does a 150uh, with a AA5 tuning cap(and likely your cap) either can be peaked...


Tom


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 Post subject: Re: LM386 Transmitter
PostPosted: Jan Fri 29, 2016 4:09 am 
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Joined: May Tue 30, 2006 4:46 pm
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Location: Santa Rosa, CA
Quote:
The toroid I used were 114-61 with about 30 turns of hookup wire.




Quote:
The coil has 50 turns.


I got confused.

Rich


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