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Author Topic: advice with new homebrew project  (Read 206 times)
M0JHA
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Posts: 647




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« on: August 12, 2008, 07:12:21 AM »

Hello,
      After making a few simple cw transmitters i want to try for a simple cw tranciever. I have a pixie 2 on its way but i have the bits to build something very similar in my box from scratch which appeals to me more.

Any way i found this design based around the pixie 2 but im unsure on a few points and wanted them clearing up before i start.

http://www.indianapolis.net/QRPp-I/pixie2_schematics.html

you may have to enlarge the image.

firstly i have everything except the L3 1.2uh inductor but i have a 1.0 uh i assume this will do.

secondly at the bottom left of the schematic you can see between the diode and C10 a 1K resistor then a symbol with a + . on checking similar schematics i assume this to be audio out, is this for a speaker?  and J2 is for headphones.

One more thing is i dont see anything to switch between rx and tx.

 all the pictures iv seen of the pixie seem to have what i expect to be a switch for this purpose or is the switch i have been seeing the RIT modification for the pixie?

cheers billy uk
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WD8AJY
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Posts: 60




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« Reply #1 on: August 12, 2008, 08:07:10 AM »

The symbol with the + sign is +V (positive voltage +9V
The Key will switch from TX to Rec good luck.
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M0JHA
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Posts: 647




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« Reply #2 on: August 12, 2008, 10:41:37 AM »

ok ,i did some more searching and found that the switch i have been seeing is the rit mod.

just one thing on the symbol with the + . what is this for? as the 9vdc supply is at the top of the schematic. in other words what does this terminate with if anything?

billy
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KA5N
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Posts: 4380




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« Reply #3 on: August 12, 2008, 12:41:25 PM »

All points with + 9 volts (or maybe just + in a simple schematic) simply means that all such points are connected together.  Just a shorthand way of drawing a schematic without having to put all the lines in.  Usually an arrow is used rather than a dot and often a large pointer with an enclosed caption is used.
Allen
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M0JHA
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Posts: 647




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« Reply #4 on: August 12, 2008, 01:08:19 PM »

Ok thanks for that. being new to electronics im still getting my head round it.

cheers billy uk
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N0NS
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Posts: 45




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« Reply #5 on: August 13, 2008, 03:05:42 PM »

You will probably get by with the 1.0uH inductor.  In the future, just change it to 1.2uH and you may see better performance.

I agree with the others, after looking at the LM386 data sheet, it looks like that +V is the supply voltage for the LM386.  I am not 100% sure why the 1N914 diode taps off the 1.5K Ohm resistor but ultimately if you hook the +V pin to 9V, you should be fine.

http://cache.national.com/ds/LM/LM386.pdf

Let us know how the rig works!

73  Joe N0NS
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