[TangerineSDR] A few thoughts after Monday night telecon

Bob Stricklin bstrick at N5BRG.COM
Thu Jun 8 10:08:43 EDT 2023

Regarding Pulsars…

Their emissions start at about 400 MHz and continue up into the GHz falling exponentially in strength as they go up in frequency.

Pulsars are very difficult to detect and typically the signals are in the noise level and require special integrating methods sometimes called folding because you are stacking sets of successive data streams.

Having a wide bandwidth receiver is an advantage which will increase sensitivity of the system but also bring in more RFI which will have to be filtered. Wide bandwidth and make the antenna systems more difficult. The antenna system is typically a narrow beam antenna tracking the pulsars position on the sky.

Pulsars would be nice but a very difficult case.


On Jun 8, 2023, at 8:15 AM, Franco VENTURI via TangerineSDR <tangerinesdr at lists.tapr.org<mailto:tangerinesdr at lists.tapr.org>> wrote:

Thanks for the kind words Nathaniel and Jonathan.

For what I know the optimal way of using the FX3 to achieve the maximum throughput is to feed it with 32bit of data at 100MHz (it can probably be overclocked a little bit, but this is a kind of a gray area since it would be out of specs).
32 bit at 100MHz is 3.2Gb/s, or 400,000kB/s, which is in line with Cypress/Infineon application note AN86947 "Optimizing USB 3.0 Thoughput with EZ-USB FX3" (https://www.infineon.com/dgdl/Infineon-AN86947_Optimizing_USB_3.0_Throughput_with_EZ-USB_FX3-ApplicationNotes-v05_00-EN.pdf?fileId=8ac78c8c7cdc391c017d073e3a2e6243<https://url.emailprotection.link/?b9Tmm8vKSj1bLsNsbe8jEgOAHV0WRuT72ThENzaxcO3iGB5ZAoSSa8qiyax1rTAdvsNaRXw6ReHUC6VEoAp-Xm3_vw_E-cdVSz8WOOp9TiP_mSFggKWdyQ61f8Ak5nQyZmOKCfX7m0vygJSYUhpXR7F9TvLVQiyaOUzt7qrJV4Obdss5WN-RYxqFFvM2Yh7SSUUfU0YA0V0XPHNXgZ2GZJiXQGUokkmjvYAIDe8whpOO7kJBHgtTQoae1YwNnwvIA>).
This would require using the GPIF II interface, and a straight path to the FX3 DMA in 'AUTO' mode (i.e. no involvement at all of the internal MCU for the data transfer; it can be still used for the much slower SPI and I2C controls over a different USB control endpoint).

As per receiving higher frequencies it could be done via undersampling with a good external band pass filter (and assuming there are no HF low pass filters on the board or that they can be disabled); I just had a quick look at the datasheet of the AD9648, and I noticed it says 'Differential analog input with 650 MHz bandwidth'; I know 650MHz is not enough for the hydrogen line at about 1,420MHz, but I am not sure about pulsars.

Franco  K4VZ

On 06/08/2023 7:15 AM EDT Jonathan via TangerineSDR <tangerinesdr at lists.tapr.org<mailto:tangerinesdr at lists.tapr.org>> wrote:

Hi Franco,

I wanted to thank you for your input and involvement on this project! I wanted to propose the dual controller solution since the ADC has a two channel output, each data lane would be connected to each FX3. This would maintain more compatibility because you can use USB 3.0 and won't have to utilize USB 3.1 or greater speeds. With this, you can use lesser USB 3.0 SBCs and if you want more processing, connect another server or system to that multicast group. This configuration would be great for amateur pulsar astronomy too if the frontend was modified for higher frequency bands, again, maintaining more compatibility with USB 3.0.

Clocking would come from the GPSDO, of course.

Can the FX3 accept both data lanes if you wanted to run the ADC and lower sampling rates and data lengths?


On Thu, Jun 8, 2023 at 12:28 AM Dr. Nathaniel A. Frissell Ph.D. via TangerineSDR <tangerinesdr at lists.tapr.org<mailto:tangerinesdr at lists.tapr.org>> wrote:
Hi Franco,

Thank you so much for joining us and for your comments and contributions. They are much appreciated.

Dave Witten, Majid Mokhtari, and Tom McDermott are starting to discuss and plan the new USB-based interface board. I know they also appreciate your comments.

Talk to you more soon and 73,
Nathaniel W2NAF

From: TangerineSDR <tangerinesdr-bounces at lists.tapr.org<mailto:tangerinesdr-bounces at lists.tapr.org>> On Behalf Of Franco VENTURI via TangerineSDR
Sent: Wednesday, June 7, 2023 11:34 PM
To: tangerinesdr at lists.tapr.org<mailto:tangerinesdr at lists.tapr.org>
Cc: Franco VENTURI <fventuri at comcast.net<mailto:fventuri at comcast.net>>
Subject: [TangerineSDR] A few thoughts after Monday night telecon

First of all, thanks for the very interesting telecon last Monday night; I apologize I had to drop at around 10:30pm, but it was getting late here.

With this message to the list I want to try to put on 'paper' some of the points of Monday discussion (plus a few other things I found out after that) to help moving forward. Please feel free to comment and add your thoughts (and correct my errors and omissions, of course).

- the basic plan would be to have the ADC (AD9648) in the Tangerine SDR RF board somehow send the 'raw' stream of samples to the computer at 'full' speed; all the DSP processing would occur in the computer; a good approach for this would be Phil Karn's KA9Q ka9q-radio program running on the computer (fast convolution filter bank)
- by 'full' speed we mean dual 16bit streams at 122.88MHz; the 16bit number comes from 14 bit from the ADC + 1bit for overflow + 1 bit to mark the PPS sample (if I understand correctly how Tom does it); doing some quick math this means being able to transfer to the computer about 3.932Gb/s
- the USB 3.0 controller used by the RX888, Cypress/Infineon FX3, is capable of streaming about 32bit @100MHz, i.e. 3.2Gb/s
- to reach the transfer rate of almost 4Gb/s there are two approaches: scale horizontally (i.e. two FX3 controllers) as suggested by Rob Robinett, or scale vertically (USB 3.1 gen 2, USB 3.2 gen 2, or USB 4); these can offer another USB mode called SuperSpeed Plus with a signaling rate of 10GHz, i.e. probably capable of transfer rates of the order of 8Gb/s. These last couple of days I searched on the Internet, and I couldn't find a 10Gbps USB peripheral controller that could be used in a way similar to the FX3. Monday night I thought Cypress/Infineon CCG6SF and CCG6DF could do it, but looking at this document (https://new-origin.infineon.com/dgdl/Infineon-EZ-PD_CCG6DF_CCG6SF_USB_Type-C_Port_Controller-DataSheet-v11_00-EN.pdf?fileId=8ac78c8c7d0d8da4017d0ee8e2c571be<https://url.emailprotection.link/?bA86HqnWKsaV5B81l-yCL7bo8kMmmQ7rmqaAqqmE8Lz9Mbn1q_FtI7t0-EFCU8lrdRMQoxqdxmJLpoDNs2Rt0bBHwpUhclR2MEWorwgpqvvdVUZTeppkEWet4sqY-p2k38YB_-ROuwgt95hXSJTxgJ7z3L5Cx2K7e4iLgORwlGcdNdUcGJ0GBHRUcqYRkwG5tAuDp8-0ihK4zHX5j147Pww~~>), there is no mention of 10Gbps
- someone mentioned that it wouldn't be too hard to modify the design of the data engine board to use one or two FX3's instead of the FPGA, and I would be very interested to understand better this option
- also I think that someone mentioned that the FPGA could still be used to do some preprocessing of the data and reduce the amount of data that would need to be transferred via the USB 3 connection; perhaps sending the sum and the difference of the two streams could reduce the bandwidth required, since the difference would probably require less bits to be sent, similar to how the FM stereo signal is broadcast
- another option to achieve that kind of transfer rate would be via PCIe, but in this case I think the data engine board would have to be a PCIe board, and that might make the design more complicated, not sure.

I think this is all; I just wanted to start a conversation and I am looking forward to hearing your ideas.

Franco Venturi K4VZ
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