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Electronics => RF, Microwave, Ham Radio => Topic started by: vk3yedotcom on January 16, 2016, 07:04:05 pm

Title: Videos that explain the black art of RF design
Post by: vk3yedotcom on January 16, 2016, 07:04:05 pm

RF design has a reputation as a 'black art'.  Circuits don't always behave as one would expect on the diagram.  Amplifiers may oscillate.  Oscillators may not start.  And switches can act as low value capacitors that can wreck a circuit's operation. 

Mainly through describing shoddily constructed equipment a few of my videos discuss these subtleties of RF design.   Most of them are part of description of a larger project or modifications so you may need to search for the discussion.  Here's a couple of recent examples:

1. This video, which only came out this morning, discusses the modification of a cheap Chinese transceiver kit to produce more frequencies by switching in a ceramic resonator variable crystal oscillator.  You'd think it would just be a matter of inserting a switch, but not.  Two switch configurations failed until I came with an arrangement (which shorted out the unused device) that worked properly.

https://www.youtube.com/watch?v=roAc4c1a-a0 (https://www.youtube.com/watch?v=roAc4c1a-a0)

2. This video describes parasitic oscillations on a variable crystal oscillator (VXO).  Arduino builders etc intend crystals to operate at their marked frequency only.  Whereas RF people sometimes want to 'bend' its frequency a little so add series L and C.  The more reactance you add the more shift you get.  But only up to a limit when the thing breaks into drift and/or spurious oscillations as the coil and capacitor take over from the crystal as being the main frequency determining element. 

https://www.youtube.com/watch?v=UJ0-Ar7aodc (https://www.youtube.com/watch?v=UJ0-Ar7aodc)

(Note that this video is No 2 of a 3 part series which discusses the development of a superhet transceiver for 7 MHz.  Parts 1 & 3 are below:

 https://www.youtube.com/watch?v=3KgUy_MTBs8 (https://www.youtube.com/watch?v=3KgUy_MTBs8) 
https://www.youtube.com/watch?v=WN_2YBu0r7A (https://www.youtube.com/watch?v=WN_2YBu0r7A) )

3. Building very simple and terribly performing equipment and trying to improve it is a good way to learn.  Here I discuss treatments to RF breakthrough in a (too?) simple receiver. https://www.youtube.com/watch?v=C3_c_PaBXIQ (https://www.youtube.com/watch?v=C3_c_PaBXIQ)

Title: Re: Videos that explain the black art of RF design
Post by: Radio Tech on January 16, 2016, 07:45:29 pm

Peter,
Very clever way of shifting the frequency around in the pixie.
Never have thought about doing it like that.
Brilliant, thanks for posting these. I enjoy watching your videos.  :-+

Title: Re: Videos that explain the black art of RF design
Post by: miguelvp on January 16, 2016, 09:20:55 pm

Brilliant, I have very little RF knowledge and it's scary that it all made sense.
I might have to buy your book now, not for QRP application but to understand a bit better the RF world for other purposes than radio.

Title: Re: Videos that explain the black art of RF design
Post by: vk3yedotcom on January 16, 2016, 10:49:39 pm

Thanks! The book isn't really technical - only has one schematic diagram in 200+ pages. Its more about antenna selection, equipment choice & operating. So probably not quite what you want.

I suggest vk2tip's website. Also talking electronics. And get anything by drew diamond, Doug demaw, wes Hayward, pat hawker & rick Campbell. Experimental methods for rf design is the best current book.  Also arrl & rsgb handbooks.