$129 spectrum analyzer Re: [Open-graphics] PCIe know-how?

[Russell Shaw]

Dieter wrote:
>> So the question is whether you can make a good PC card digital 
>> oscilloscope for $100.00.  You need an oscillator, frequency divider, 
>> PLL, sample & hold, and DAC as well as the PCIe interface.  I seriously 
>> doubt that this is possible for $100.00 but it does depend on the 
>> maximum input frequency you wish to use, sample rate, and the accuracy 
>> (and number of bits) needed.  Actually, you can spend over $100. on a 
>> good DAC
> 
> You can get a 2.4 GHz spectrum analyzer for $129.
> 
> http://www.dunehaven.com/lcsa.html
> 
> If a 2.4 GHz spectrum analyzer can be sold for $129, why not a lower
> frequency unit?

The reason it only does 2.4GHz is because it just uses one special-purpose
mass-produced IC that can only do 2.4GHz (due to it having internal coupling
capacitors and a frequency synthesizer with limited range).

"Real" spectrum analysers only come from analog and RF designers. That 2.4GHz
thing is nothing much more than cutting and pasting circuits off the data sheet.

To cover arbitrary frequency ranges with decent performance, you'll need to
design wideband fast-sweeping frequency synthesizers and multiple intermediate
frequency amplifier and filter stages.

-- 
Russell Shaw, B.Eng, M.Eng(Research)