Jim: Indeed. I've a very small collection of USB instruments so far, but
it's definitely the way of the future for me. I have an older scope from
link instruments, the signal hound, and will construct one of the very
simple component bridges ( uses a dual op amp and a couple of resistors and
the sound card). As I mentioned, there's a good power meter from
Mini-circuits, and the ham radio QEX periodical has some designs for a VNA
albeit not at microwave frequenies...
All use the computer as most of the software and display. Note that a
simple EEpc used is now about $250 and can run most of this stuff. I'd
really like to have some '80's Hp stuff, but the buy it now folks have
sucked up all the bargains, and for me time is important.
Don
----- Original Message -----
From: "jimlux" <jim...@earthlink.net>
To: "Discussion of precise time and frequency measurement"
<time-nuts@febo.com>
Sent: Saturday, December 11, 2010 7:41 PM
Subject: Re: [time-nuts] Software defined spectrum analyzer
Magnus Danielson wrote:
On 12/12/2010 02:31 AM, jimlux wrote:
Two VCOs covering 1-2.2 GHz could through mixing and selecting between
sum and difference output filters (i.e. lowpass and highpass) cover that
without too much difficulty. Except for the highest end, there is a
degree of freedom in setting the oscillators to their individual
frequency which naturally could be used to avoid "bad" frequencies to
leak into the IF for instance.
C
Yeah.. but there's a whole raft of inexpensive PLL chips with multiple
VCOs on them to cover wide ranges (e.g. all cell, mobile data, and WLAN
bands).. I'll bet they're using one of them. If a chip exists with VCOs
that does the job, that's going to be cheaper and easier than any sort of
add/subtract/mix/divide scheme.
This is an example of a new class of lab instruments.. you pay for the
hard part (the RF design and performance) and software takes care of the
rest, and since software has almost zero reproduction cost....
For today, there's probably a significant "value added" in the software,
so it might not be free... but over time, that will change.
And, if it works out nicely, standardized interfaces (like 50 ohms or
resistor color codes) will evolve, so the same software will work with a
$500 inexpensive widget or a $10,000 high performance widget from Agilent.
There will always be a market for software tailored to a specific
market/need (like standards or regulatory compliance) that will cost, but
for generic functions (like a power spectrum) that will probably be free,
or close to it.
I wonder if there's an interface for this for my iPad?
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