What is the sample rate required to digitize 18Ghz+ RF signal for decoding? - Page 1
Forum section: electronics / rf-microwave

author: mikeck
author_rank: Newbie
timestamp: April 01, 2018, 05:16:55 am
content: I'm replicatinghttps://goo.gl/QnmfSMbuild with 141T and 8555A 8552B modules and started to think I should connect the analog HW up to the hackRF SW/Audacity.I know the X and Y from the spectrum analyzer are analog so if you want to digitize a signal you need to describe it with a discrete set of its points or samples.My question is what sample rate would be required for high end of the scope which is 40GHz!!!! Even 6-18Ghz would be great.I'm trying to build my own hackRF hw in essence for reverse engineering high frequencies. I'm familiar with FGPA's like Spartan-6 which can handle up to 8 low power 3.2Gb/s serial transceivers and 800Mb/s DDR3 and this 6.4 GSPS 12 bit ADChttp://www.ti.com/lit/ds/symlink/adc12dj3200.pdfand evaluation boardhttp://www.nextwarehouse.com/item/?2757418_g10e

author: ataradov
author_rank: Super Contributor
timestamp: April 01, 2018, 05:39:04 am
content: X and Y outputs are slow, they don't carry 18 GHz signal, they just carry what's on the screen.Forget about digitizing 18 GHz, it is basically impossible in general, unless you have a lot of money and equipment already.

author: mikeck
author_rank: Newbie
timestamp: April 01, 2018, 05:45:48 am
content: Oh! Thank you very much!How do you change the scan rate for the video on the scope? Is there a knob? lol -_-

author: ataradov
author_rank: Super Contributor
timestamp: April 01, 2018, 05:56:45 am
content: If you mean the scope that is in the spectrum analyzer, then scan rate is defined by the resolution bandwidth (RBW) setting or equivalent. I'm not sure how exactly it was done on those super old analyzers.In general, there should be a setting for it, may be even a direct knob or some combination of other inputs.

author: hagster
author_rank: Frequent Contributor
timestamp: April 01, 2018, 07:02:13 am
content: A spectrum analyser isnt digitising at 18ghz. It is mixing this frequency down to baseband. For a digital system you need to pre-filter sample at lease as fast as the required resolution bandwidth.A hackRF is doing this mixing internally(up to 6GHz) and you can then set the reaolution BW by changing the sample rate and or FFT length.The main differences between a HackRF and SpecAn is the dynamic range (strongest and weakest signals it can see at the same time) and calibration and amplitude stability. You can calibrate the signal levels on a HackRF, but i suspect it will drift over time.

author: max-bit
author_rank: Frequent Contributor
timestamp: April 09, 2018, 10:32:53 am
content: The cost of such a digitizer?~ 100 k$ (200k$)You must build a preamplifier ultra fast ADC converters (you will not build one on it) probably with 10 GS / s x 4Then the data acquisition section (FPGA - very fast) and the memory section.... ultra fast DSP ....etc ...Forget about 40GHz bandwidth (ASIC)

author: ogden
author_rank: Super Contributor
timestamp: April 12, 2018, 08:23:03 pm
content: Quote from: mikeck on April 01, 2018, 05:16:55 amRight. 30GHz LabMaster 9 Zi-A scope costs around $146030And you just decided to build something like that.Here's video about such kind of scopes. You can stop dreaming right now:

author: ogden
author_rank: Super Contributor
timestamp: April 12, 2018, 11:06:27 pm
content: Quote from: mikeck on April 01, 2018, 05:16:55 amTo "reverse engineerhighmicrowave frequencies" you don't need 40GHz BW scope, nor 40GHz spectrum analyzer. Both are highly expensive & unnecessary overkill - most likely out of your reach as well. To receive signals, you don't use scope or spectrum analyzer but guess what? - Yes, radio receiver.So what you need is microwave radio receiver. Most microwave receivers just downconvert microwave frequencies to lower intermediate frequency where it is easier to sample using lower cost receiver.Let's say you want to reverse engineer 10 GHz satellite signals - then all you need isSatellite Low Noise Block downconverter, (LNB) and some receiver which can receive IF frequencies coming out of it, usually in 0..2GHz range. Some people uses RTL-SDR dongle for that.So you can reverse-engineer 10GHz microwave frequencies using satellite dish, LNB and RTL-SDR dongle(or HackRF/ADALM-PLUTO if you need wider bandwidth). No need to build 6..18GHz scope, for gods sakeSimilar approach is scaleable to other frequencies, thou getting antennas, microwave LNAs and downconverters for other than 10GHz is tricky. Most likely you shall look for surplus microwave point-point equipment and scavenge parts from it.

author: CopperCone
author_rank: Super Contributor
timestamp: April 13, 2018, 01:50:31 pm
content: :-DDDo downconverter blocks like that cause distortion and shit?What kind of electrical differences are there for this super low cost solution?Or does the fact thattheir band limited and not wideband like the oscilloscope make them pretty good?

author: ogden
author_rank: Super Contributor
timestamp: April 13, 2018, 03:27:53 pm
content: Quote from: CopperCone on April 13, 2018, 01:50:31 pmUsually you get what you pay for. Frontend of 40GHz spectrum analyzer whichused costs ~15k$, w/o doubt is better than 15$ sat LNB + crappy 15$ TV tuner.QuoteLow SNR, low dynamic range (RTL tuners have 8bit ADC), limited bandwidth of signal you can process. Indeed if you can afford R&S FSW43 with signal analysis software options - get it.

author: CopperCone
author_rank: Super Contributor
timestamp: April 13, 2018, 05:05:39 pm
content: Nah i meant the deficencies relating to using downconverter. I know the problems of the sdr itself they are very cheap.Do any of those scopes actually use downconverters like a sa or do they always handle the raw bandwidth?

author: ogden
author_rank: Super Contributor
timestamp: April 13, 2018, 05:07:48 pm
content: Quote from: CopperCone on April 13, 2018, 05:05:39 pmThis question is answered in the video.

author: DaJMasta
author_rank: Super Contributor
timestamp: April 14, 2018, 02:51:35 pm
content: The shorter answer is yes, but since the scope doesn't have the time to be able to sweep, it downconverts with a fixed LO and buffers into three bands, all to be digitized simultaneously.