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$25 SDR receiver for the 75m AM window




 
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Author Topic: $25 SDR receiver for the 75m AM window  (Read 277 times)
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ka1tdq
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« on: October 07, 2017, 08:28:05 AM »

This is a SoftRock Lite II SDR receiver kit that I built in a soap dish.  To prevent any ground loops, it's best to build this in a non-conductive chassis.  The kit comes with a crystal for the CW portion of the band, but I got a 15.360 MHz crystal from DigiKey which centers the receiver at 3.840 MHz.  Then, if your computer has a 96KHz sound card, it will cover the 75M AM window.  

This was a real challenge to build.  There's a number of surface mount components and the two coils are really small.  The low pass filter toroid has 50 turns!  

Anyway, my USB sound card is old and can only sample at 48KHz.  I eBay'd a better one and that cost more than the whole project!

Jon


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ka1tdq
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« Reply #1 on: October 07, 2017, 10:15:51 PM »

It's nighttime and I got to test it.  It works pretty good!  I'm using my 48KHz sound card right now, but when the 96KHz one comes in I'll be able to receive the AM window.

https://youtu.be/XAMYhVvIhHY

Jon
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W3RSW
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Rick & "Roosevelt"


« Reply #2 on: October 08, 2017, 08:24:14 AM »

You'll have a lot of fun with it. Nice soap job too. Even your 40 turn winding looks neat.   Grin
Gary, once n2inr, now w2inr put I believe around 2007 / 8 posted the first experience with the original soft rock on this site. Big write up and fu comments.   I think he used it right after the First converter in his receiver.
After reading his experience, I took the plunge into sdr and got one of the first Qs1r's made br n8vb.  Seems like yesterday and seems like so long ago too. SDR's come a long way in the amateur world since then.
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RICK  *W3RSW*
ka1tdq
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« Reply #3 on: October 08, 2017, 08:47:18 AM »

It's funny.  I have this really big, mostly homebrew, transmitter stuff and the two receivers I have are the size of a soap dish.  But their performance is amazing!  It completely eliminates the desire for traditional commercial radio boxes, let alone tube receivers, in my mind.  The $21 kit price is about the eBay price of one replacement tube.  Anyway, not trying to get emotions up, but just making a point from my perspective.

I built this exact kit 5 years ago and don't remember having any difficulty whatsoever.  This time was a challenge.  I built it in several days, taking breaks, and doing everything in stages.  I don't know if it's age, patience, or what...

And yeah, the 50-turn coil... the thought crossed my mind many times, "He expects to squeeze 50 turns, single layer, on this tiny thing?"  It is possible.  The way I count the turns it is to note hashtags on a piece of paper (sort of like a prisoner counting his days on the jail cell wall).  There's basically just enough room for 50.  Not 51, but 50.

Jon  

**but now that you mention it, when I zoom in on the picture of the coil I do see one crossed turn on the top.   Roll Eyes
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