SDR (Software Defined Radio) Transceiver

Have an idea? Post it here! - Looking for developers? Ask here as well!
Post Reply
N4TLF
Posts: 7
Joined: Fri May 29, 2015 1:39 am

Re: SDR (Software Defined Radio) Transceiver

Post by N4TLF » Sat May 30, 2015 4:08 am

That was the problem, LFs turning into CR/LFs!

Thank you very much Pavel. I am listening to 40 Meters just fine now. I will be interested in your other SDR projects as you progress.
Thank you again!
Terry

pavel
Posts: 618
Joined: Sat May 23, 2015 5:22 pm

Re: SDR (Software Defined Radio) Transceiver

Post by pavel » Sat May 30, 2015 9:06 am

Hi Terry,

I'm glad to know that the Red Pitaya SDR now works for you.

It would be very interesting if you could compare this SDR with your other SDRs (for example, HiQSDR) and post the results.

Cheers,

Pavel

N4TLF
Posts: 7
Joined: Fri May 29, 2015 1:39 am

Re: SDR (Software Defined Radio) Transceiver

Post by N4TLF » Mon Jun 01, 2015 8:39 pm

Yes, Pavel, I could compare the RP SR to others, such as the HiQSR. I have a decent test bench, including a quiality signal generator, a good spectrum analyzer, and several other tools.

I ran a quick test on the RP with your receiver app, and with the RP spectrum analyzer app, and noticed some quirks with the SR app. While the sensitivity of your receiver app seems better than the RP spectrum analyxer app (minimum signal around -110dBm for SDR receiver vs about -90dBm for the RP), the SDR app seems to have some issues with signals stronger than about -80dBm. The RP spec-an app does not show the same issues. These tests were done at 7.15MHz, and at 5.0MHz.

I'm wondering if we could communicate directly, as that might save a lot of unnecessary traffic here. I also have a couple of ham buddies that just bought RPs and are also interested in SDR with them. Maybe we could create a small group to discuss this?

I just recently changed my callsign from WB4JFI to N4TLF. I'm not sure what the proper protocol is here to exchange emails or other contact methods, I have one enail address which is my new call at my old call dot com.

Congrats on the SR receiver, SDR transceiver, and your hard work.
73, Terry, N4TLF

pavel
Posts: 618
Joined: Sat May 23, 2015 5:22 pm

Re: SDR (Software Defined Radio) Transceiver

Post by pavel » Tue Jun 02, 2015 10:51 pm

N4TLF wrote:the SDR app seems to have some issues with signals stronger than about -80dBm. The RP spec-an app does not show the same issues.
Could you please provide more details about the issues that you observe?

Unfortunately, I don't have any strong enough signals at the 5-7 Mhz frequencies to reproduce this problem. Here is the closest to -80dB I can get:

Image
N4TLF wrote:I'm wondering if we could communicate directly, as that might save a lot of unnecessary traffic here.
I've sent you an e-mail.

W6MRR
Posts: 1
Joined: Sun May 31, 2015 5:04 am

Re: SDR (Software Defined Radio) Transceiver

Post by W6MRR » Wed Jun 03, 2015 12:01 am

Hi Pavel,

Thanks for the excellent project! I've been listening to ham bands and have even decoded PSK31 and JT-65 with it without much of an antenna.

It looks like you're working on a transceiver - how's that coming? We'd be very interested to give it a try.

I am a FPGA noob and have some questions about your design:
- Why go CORDIC when you have the hardware multipliers?
- How much of the PL did you use?
- Is there room for a second receive chain?

Thanks again and best regards,

Martin W6MRR

pavel
Posts: 618
Joined: Sat May 23, 2015 5:22 pm

Re: SDR (Software Defined Radio) Transceiver

Post by pavel » Wed Jun 03, 2015 1:24 am

Hi Martin,

Thank you for your feedback.
It looks like you're working on a transceiver - how's that coming?
The SDR transceiver project is progressing. I have already most of the data processing (hardware and software) in place. All the software data processing is running on the Red Pitaya board. It's based on the same library that is used in the latest version of the "PowerSDR OpenHPSDR mRX PS" program. Currently, I'm working on the user interface. Drawing and programming all the buttons and menus takes a lot of time.
Why go CORDIC when you have the hardware multipliers?
I can think of several reasons:
- In my opinion, the CORDIC algorithm fits more naturally this kind of application and is easier to use.
- For ~1 Hz tuning precision at 125 MHz, at least 27 bits should be used for the phase. The Red Pitaya FPGA does not have enough memory to store a full lookup table for this kind of phase resolution and techniques such as phase dithering should be used. I find this approach less natural.
- Some other SDR projects such as HPSDR Hermes and HiQSDR are also using CORDIC. So I'm not inventing anything new.

However, if there are strong arguments against CORDIC, then it's not difficult to switch to the DDS+Multipliers combination.
How much of the PL did you use? Is there room for a second receive chain?
For the SDR receiver, ~60% of the FPGA resources are used. There is still plenty of room for optimization and a second receiver can be easily added.

However, it's not the case for the SDR transceiver. As I'm trying to fit all the data processing to the Red Pitaya board, there is not enough resources left for a second receive chain.

Kind regards,

Pavel

Altair
Posts: 4
Joined: Fri May 08, 2015 1:40 pm

Re: SDR (Software Defined Radio) Transceiver

Post by Altair » Wed Jun 03, 2015 4:12 pm

pavel wrote: Unfortunately, I don't have any strong enough signals at the 5-7 Mhz frequencies to reproduce this problem. Here is the closest to -80dB I can get:
Pavel, you have signal source near RX input.
From RedPitaya DAC. :-)

You can use Passive Attenuator for create desired signal amplitude.

Yuri RA9MGK

dreschpe
Posts: 5
Joined: Fri May 15, 2015 8:32 pm

Re: SDR (Software Defined Radio) Transceiver

Post by dreschpe » Fri Jun 12, 2015 11:08 pm

Pavel,
thanks for the projekt.
Here is a screenshot with a magnetic loop on 41m at 500kspl .
(the upload is not working ?)

I also see the problem with signals more than 30 dBm from the floor.

I have attached a R&S SMH generator and I see a signal every ~ 1070 Hz if the signal is stronger than 30 dBm from the floor.
The first image is ~ -20dBm less than the signal, the next -25dBm and all others around -30dBm.
This is for all sample rates and for all frequency's.

I plan to add a AD8330 variable gain amplifier to the input. I think i have to reverse engineer the input schematic first, because the redpitaya guys have not answered to other questions about the inputs here.

Is somebody visiting the ham radio end of the month ?

73,de
Peter DC2PD

pavel
Posts: 618
Joined: Sat May 23, 2015 5:22 pm

Re: SDR (Software Defined Radio) Transceiver

Post by pavel » Fri Jun 12, 2015 11:13 pm

Hi Peter,

Together with Terry N4TLF, we've localized and fixed the problem of the spikes around strong signals on the spectrum display. Here is a spectrum plot to illustrate this problem:
adc-dump-32M-12M-neg30.png
The problem was in my ADC interface code.

Here is a short technical description of this problem:
  • in the default Red Pitaya configuration there are two clock sources: 125 MHz from the ADC and ~125 MHz from the FPGA;
  • in the SDR project, the ADC data is transferred from the ADC clock domain to the FPGA clock domain via a FIFO;
  • if the FPGA clock is slower than the ADC clock then some data get lost;
  • the FPGA clock is slower than the ADC clock.
To fix this problem, I did the following:
  • increased the FPGA clock frequency (it's now at ~143 MHz);
  • synchronized the phase generator with the ADC clock.
The new fixed version of the SDR receiver is incompatible with the original Red Pitaya SD card. I prepared a customized SD card image zip file and updated the instructions at

http://pavel-demin.github.io/red-pitaya ... -receiver/

Here is how to install the new fixed version:
  1. download the customized SD card image zip file
  2. copy the content of the SD card image zip file to an SD card
  3. boot Red Pitaya with the new SD card
  4. set frequency correction in the SDR program to 0 ppm
Cheers,

Pavel
You do not have the required permissions to view the files attached to this post.
Last edited by pavel on Wed Dec 28, 2016 10:15 am, edited 1 time in total.

N4TLF
Posts: 7
Joined: Fri May 29, 2015 1:39 am

Re: SDR (Software Defined Radio) Transceiver

Post by N4TLF » Sat Jun 13, 2015 7:09 pm

Thanks Pavel for this GREAT app for the RP!

After Pavel found the ADC issue, I have tested the app, and found that it can see signals on the spectrum display as low as -115dBm or better (50k sampling). The spurs are now GONE until the ADC chain is overloaded at +5dBm (!!).

I am also seeing some slight increasing of noise immediately around the main bang at above about -60dBm, which looks to me like phase noise from the master oscillator. This is not really an issue unless you ar trying to dig out a weak signal next to a strong signal. I am going to investigate using a better oscillator.

I had a similar problem with the Charleston SDR, and when I upgraded the oscillator from a programmable unit to an SI570, the phase noisee issue went away.

For the price of the unit, my initial tests show that this is potentially a great SDR. As Pavel continues to work with the RP, and finishes his transceiver, it can only get better!

Again, thanks for the work Pavel.
73, Terry, N4TLF (formally WB4JFI)

Post Reply
jadalnie klasyczne ekskluzywne meble wypoczynkowe do salonu ekskluzywne meble tapicerowane ekskluzywne meble do sypialni ekskluzywne meble włoskie

Who is online

Users browsing this forum: No registered users and 3 guests