Cash Olsen, KD5SSJ
I have been looking at the ideas for PLL control and the Huff & Puff can tune
in 10 Hz steps (Wow!) So smaller steps are possible. Those step sizes compete
with digital synthesis easily.
Also I joined the HuffPuffVFO Yahoo group of Hans Summers and found out that
the concerns some have for jitter and phase noise are well addressed there and
so the matter then is very feasible and so I ordered 100 7400 IC's for a good
price of $6.95 from Jameco (see below). There are enough chips there to also
explore quadrature detection circuit ideas.
Over the course of this year I hope to learn allot. I am using DIP chips
since that is the breadboard size I have for prototyping.
I also bought some dual gate Mosfets since I want to also explore using them
as a quadrature mixers with gain.
The PLL circuit I am interested in uses a 74HC4060 CMOS Oscillator with 14
stages of binary counting or division to select a step rate from. After the
comparator section the digital counts are divided by a 64 or 128 stage shift
register to select a long or short vco voltage response delay. So, beside
being able to adjust the kHz of the varicap by a 20 pF variable ceramic cap,
you can adjust the stepping and the delay response to the VFO/VCO.
Phase noise in oscillators is reduced when using CMOS amplifiers (according
to some articles) and the VFO/VCO section is buffered by a follower stage after
the first CMOS amp in the chip. The buffer reduces loading effects which as
some have told me aids in the jitter aspect. I suspected that jitter reminded
me of bad loading and hence bad swr and so a buffer seemed to be the answer.
At the Huff & Puff group a buffer was mentioned as a means to improve the
jitter. So I wonder now about that?
Anyways there are many exploring the PLL ideas for SDR. Down the road there
will be some circuits offered up on the subject.
ka9rza
Parts Ideas from Jameco:
50 assorted crystals and oscillators $7.95 Part # 114446CK
100 assorted transistors $5.95 Part # 18171CK
100 assorted 7400, 74HC & 74LS IC's $6.95 Part # 17996CK
$20.85 total
You can order separate Texas Instruments PLL chips (non CB types) for broadband
uses for around .48 cents each and other chips. http://www.Jameco.com
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