[ARC5] Square wave oscillators

[Bruce Long]

there is a very simple way to design a three component pi or tee filter to convert a logic squar(ish) wave into a sine wave into a fifty ( or other impedance) load.  It is based upon the use of Termans Impedance matching network design method as published in radio Engineering.   I have had very very good results and will write it up for this group if there is evident interest.





On Friday, November 22, 2013 11:38 AM, Robert Nickels <ranickel at comcast.net> wrote:
 
On 11/22/2013 5:09 AM, David Stinson wrote:
> I've heard all the "it won't work for (fill in reason)."  In my 
> applications, they work just fine and are about 1/10th the cost of a 
> crystal. 

Me too, as you know Dave, as I posted last night.   In fact, I used a 
Transworld 5S channelized SSB transceiver on the air shortly after that, 
and it was heard from coast to coast.   And despite the BS someone 
posted earlier today about "digital devices don't care", putting out a 
clean signal has nothing to do with how the signal is generated.   Every 
single commercial radio on the market for the past decade or more has 
used digital frequency synthesis of one kind or another, and they all 
put out perfectly clean FCC- compliant signals.   The little oscillators 
that Dave and I use incorporate PLL technology, just like millions of 
radios in daily use do, and as I stated, existing filtering ensures a 
clean signal.  To quote Dave:  "they work just fine".

For those who want to connect the output directly to an antenna, or 
through circuitry that doesn't provide sufficient filtering, there's a 
simple solution.  It's called a Low Pass Filter....hams have been using 
them for years and they're simple and cheap to make.     The standard 
design used by QRPers dates back 30 years, and has been used by 
countless builders and commercial radios.   I use these filters on my 
Raspberry Pi to generate WSPR signals that have been heard as far away 
as Australia, with a power output of < 50 mW.

Here is the link to the design info, courtesy of GQRP: 
http://www.gqrp.com/harmonic_filters.pdf

73 and happy "digital" oscillations!

Bob W9RAN

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