KiwiSDR on Kickstarter - Page 1
Forum section: electronics / general

author: jks
author_rank: Newbie
timestamp: March 17, 2016, 08:17:44 pm
content: Well, we don't really need another new SDR. But this one is a bit different:https://www.kickstarter.com/projects/1575992013/kiwisdr-beaglebone-software-defined-radio-sdr-withI'd be happy to answer any questions.Cheers,John, ZL/KF6VONew Zealand

author: hamster_nz
author_rank: Super Contributor
timestamp: March 17, 2016, 10:22:41 pm
content: Hey John,Lots of Qns - maybe I should read the FAQWhere in NZ are you?How likely would it be to interface the design into other devices? I assume it is currently set up to DMA into the BBB...Will it also work with Beaglebone Green?I assume that I could download custom bit files into the Artix FPGA do do my own bidding? How much of the current SDR stack is implemented in the FPGA?Is there a link to a PDF of the schematic in the GitHub? I can only find Gerbers and/or CAD files...Can you recommend a suitable wide-band antenna design?I'm Backer 7 or 8 - wishing you and Mike @ValentFX a great Kickstarter...Mike

author: jks
author_rank: Newbie
timestamp: March 18, 2016, 12:23:53 am
content: Lots of Qns - maybe I should read the FAQI'm still working on a FAQ. Soon come, as they say in the Caribbean..Where in NZ are you?Tauranga. Drop by if you ever get out here.How likely would it be to interface the design into other devices? I assume it is currently set up to DMA into the BBB…Yeah, I get asked this a lot. Everyone want to pump out raw IQ and use existing client software. That's fine, but it will take a little work. Right now I just use a 48 MHz SPI to move the 8 channels of audio + spectrum baseband IQ to the Beagle. But there are 10 unused Beagle GPIO lines hooked up to the FPGA so you could implement a higher bandwidth parallel port. Some folks want a PCB spin that puts a gigabit Ethernet PHY and magnetics on board so they can do "Direct Fourier Conversion" (DFC) which is what Twente WebSDR essentially does. But that's a lot of work and is really getting away from what I wanted to do.Will it also work with Beaglebone Green?Yes. In fact the $299 reward "kit" ships with a BBG.I assume that I could download custom bit files into the Artix FPGA do do my own bidding? How much of the current SDR stack is implemented in the FPGA?The DDCs and some buffering are in the FPGA. Also a cute little embedded processor from Andrew Holme's Homemade GPS Project to help do the housekeeping. All the baseband stuff is done in the Beagle (FIR filtering, demod, FFTs). Take a quick look at some of the diagrams in the design document that show how the tasks are partitioned.Is there a link to a PDF of the schematic in the GitHub? I can only find Gerbers and/or CAD files…Sorry, I'll fix that. Until then look here:http://www.kiwisdr.com/docs/KiwiSDR/kiwi.schematic.pdfCan you recommend a suitable wide-band antenna design?I have an active antenna with bias tee in development but it's not ready. I'm going to write a whole separate article about antennas. I'm using a PA0RDT-style mini-whip on the NZ KiwiSDR right now. I soldered it together in an hour or so. What took longer was tracking down all the local noise sources.

author: vsboost
author_rank: Contributor
timestamp: March 18, 2016, 12:57:54 am
content: Just had a play with the online live ones and i'm impressed.

author: hamster_nz
author_rank: Super Contributor
timestamp: March 18, 2016, 01:05:21 am
content: Quote from: jks on March 18, 2016, 12:23:53 amSorry to be asking you somewhat trivial questions during the start of your KS campaign, but....Just had a look at the schematic, and all I can say is "Wow" - DC->30MHz into a 66MHz, 14 bit ADC, then direct into an Artix7 FPGA. Sweet! The 2-bit ADC for the GPS looks interesting too. Lots of learning to be had there... What is the tiny EEPROM for? Just presence detect and device ID?

author: jks
author_rank: Newbie
timestamp: March 18, 2016, 01:57:06 am
content: Sorry to be asking you somewhat trivial questions during the start of your KS campaign, but….No worries. When people are sending money there are never any trivial questions.Just had a look at the schematic, and all I can say is "Wow" - DC->30MHz into a 66MHz, 14 bit ADC, then direct into an Artix7 FPGA. Sweet!Yes, but some people also look at that and say that I'm seriously pushing my luck with the Nyquist limit. They are correct, but it also seems to work fine (I can hear stuff on 10 meters without any problems). And of course the project goal is to hammer the cost as low as possible while still getting acceptable "shortwave receiver" type of performance. I absolutely had to use that inexpensive 14-bit, 65 MHz LTC ADC to meet the cost target.The 2-bit ADC for the GPS looks interesting too. Lots of learning to be had there…I can't tell you how much fun I had getting Andrew Holme's GPS project to work. I knew zero about GPS signal processing when I started. His code is so clean and concise (C++ and Verilog). It was just great. If I ever get the time I have a bunch of mods I want to try (I already added decimation to speed up the acquisition of strong signals).What is the tiny EEPROM for? Just presence detect and device ID?Yes. It's required by the Beagle cape spec. Cape ID and header pin configuration information. I stash the board serial number in there for use with a dynamic DNS hack I have.

author: hamster_nz
author_rank: Super Contributor
timestamp: March 18, 2016, 03:45:33 am
content: Quote from: jks on March 18, 2016, 01:57:06 amYeah, 30MHz vs 66.666MHz sampling is pretty close.What is the response/rolloff of the 30MHz multi-pole input filter at the very front end? It looks like significant time has gone into designing it.

author: jks
author_rank: Newbie
timestamp: March 18, 2016, 09:21:19 am
content: Quote from: hamster_nz on March 18, 2016, 03:45:33 amThat 7-pole Chebyshev is from a design by EI9GQ:http://homepage.eircom.net/%7Eei9gq/lpf.htmlClaudio, IN3OTD, ran a Qucs simulation using a Q model for those chip inductors and it looked okay. When I received the first board prototypes my network analyzer hadn't been shipped to NZ yet. I still need to sweep the real circuit at some point.

author: VE7XMC
author_rank: Newbie
timestamp: March 19, 2016, 07:52:40 pm
content: Quote from: hamster_nz on March 17, 2016, 10:22:41 pmMike here from the Canadian KiwiSDR receiver.We are running the:http://dl1dbc.net/SAQ/miniwhip.htmltoo.Here are all the morse code signals it is receiving from around the world (real time) for an idea of reception you can achieve with a design like this (see attached for map):http://www.reversebeacon.net/dxsd1/dxsd1.php?f=0&c=VE7AB&t=de

author: hamster_nz
author_rank: Super Contributor
timestamp: March 19, 2016, 11:45:50 pm
content: Hi John, You wouldn't happen to have a chunk of the raw data from the GPS ADC tucked away somewhere I could have a play with?

author: jks
author_rank: Newbie
timestamp: March 19, 2016, 11:56:22 pm
content: Quote from: hamster_nz on March 19, 2016, 11:45:50 pmNot from the KiwiSDR GPS front-end. But several years ago I needed raw GPS data for testing, and after a long search found some which I archived on my site:http://kiwisdr.com/gps/gps.htmlThis data has the same IF offset (4.092 MHz), but a lower sample rate (5.456 MHz) than the 16.368 MHz rate of the KiwiSDR.

author: hamster_nz
author_rank: Super Contributor
timestamp: March 22, 2016, 02:43:15 am
content: Congratulations on making it over half way in only a few days.Fingers crossed that I can spend the next few months building and testing a few The PA0RDT Mini Whip active antenna designs. (http://dl1dbc.net/SAQ/miniwhip.html)Anybody know of a good surface mount equivalent for a 2N5109? (a RF Bipolar transistor, fT of 1.5GHz, 20V VCEO, running at about 250mW),

author: jks
author_rank: Newbie
timestamp: March 22, 2016, 03:08:39 am
content: Quote from: hamster_nz on March 22, 2016, 02:43:15 amI've been using the BFG35, mostly because it's somewhat complimentary to one of the (almost) only remaining RF PNPs in production, the BFG31. It's only a Vceo of 18V though and has fT of 4 GHz. So you have to be careful about bypassing. The Tpd is 1W which is very nice.http://www.nxp.com/documents/data_sheet/BFG35.pdf