And what would happen using Si5351 with analog switcher mixer (Tayloe detector). The square wave only close and open the switch.-
LU5DNM
-----Mensaje original-----
De:
[email protected] [mailto:
[email protected]] En nombre de Pavel Milanes Costa
Enviado el: lunes, 23 de octubre de 2017 07:13 p.m.
Para:
[email protected]Asunto: Re: [BITX20] Raduino question.
El 23/10/17 a las 16:53, Jerry Gaffke via Groups.Io escribi¨®:
The ARRL Handbook says square waves are better,
though does not say anything about how huge the difference is.
We are talking the same language, we are agree on the point that square
is better, but not always... I'm just making a little note to the side
of the page about a special case as per my experience...
Grab your digital copy of the ARRL handbook and keep looking at chapter
10... search for figure 10.22 on page 10.21 just in the next page of
your note. Look at the graphic at the bottom of figure 10.22 compare the
output from using a sine wave vs square wave, square wave has ALL the
harmonics (solid line), the sine one has none (dashed line)
Also the output from a sine VFO is 3dB lower than the square one. ;-)
I was only saying that if you use the Si5351 as BFO to mix with the IF
and grab the audio, and you use a low freq on it (below ~2 Mhz as per my
experience, worst on the 500 Khz range) you may get a very noisy audio
as those solid lines (harmonics) are very close each other and will mix
again and again inside the mixer/amplifiers and you will get a very
noisy reception, full of carriers here and there...
On tx there is no problem as the SSB filter wipe them away...
In deed if you use a high enough IF (as the bitx40 do, in 12 Mhz) all
the unwanted mixing are cleaned by simple filtering, but beware if you
use a low freq as 455Khz or 500 Khz... those unwanted mixing products
will haunt you...
Been there, done that, must filter it if you use a Si5351 for BFO below
~2Mhz.
--
73 CO7WT, Pavel.
