[time-nuts] Software defined spectrum analyzer

Don Latham djl at montana.com
Sun Dec 12 06:14:06 UTC 2010


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" <jimlux at earthlink.net>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at 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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