[hpsdr] LO generation for CASMIR

[John B. Stephensen]

The one disadvatage of using the output of a divider as an LO is that the
noise floor can be quite high. Avoid ECL dividers as the noise floor is -150
to -155 dBc/Hz. CMOS dividers are supposed to be quieter, but I've haven't
seen measurements for parts made since the 1980's. Older parts had a
broadband noise floor of -165 to -170 dBc/Hz.

I don't like using the output of a DDS to drive the first mixer. A PLL can
clean up a lot of spurs. See part 1 of the ATR-2000 article in QEX.

73,

John
KD6OZH

----- Original Message ----- 
From: "Alex" <harvilchuck at yahoo.com>
To: <hpsdr at hpsdr.org>
Sent: Wednesday, June 14, 2006 01:32 UTC
Subject: [hpsdr] LO generation for CASMIR


> ***** High Performance Software Defined Radio Discussion List *****
>
> I hear two design suggestions for LO generation for the HF version of
CASMIR:
>
> (a) a modern DDC like the Analog Devices AD9958 or similar  - suggested by
N4HY
> (b) divide down a uWave VCO - suggested by VK6APH
>
> Both have technical merit.
>
> DDCs are used in a significant number of "commercial" rigs with good
results. DDCs are working quite fine for other SDRs - there are a helluva
lot of DDC-based designs by hams out on the internet.
>
> Dividing down a uWave VCO would provide a rather technically elegant
design.
>
> So before anyone flames about one design suggestion or the other, please
provide substantial technical arguments for or against, or even better yet,
post your own high-level design. Don't be shy, and no teasing.
>
> So what you say?
>
> Alex, N3NP
>
>
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