odd results working at 250ksp/s
Hi, I've been working on a project the involves tuning VOR signals. They are narrow band signals. > 25 kHz. For that, the wide bandwidth of the RTL dongles isn't that helpful to me. (and actually a hindrance when two signals are inside the sample range but widely different strengths) Anyway, the lowest I can get my dongles (R820T) to go is 250ksps, which is fine. I've been working at that frequency for awhile, but getting some strange results. For example, if I tune in to 116.8 MHz, which should be the OAK VOR, it works fine. But if I tune to 115.8 MHz, which should be the SFO VOR I get ... the OAK VOR. That is, there is a perfect copy of the OAK signal 1 MHz shifted down. If I switch the sample rate to 1.024Msps or 900ksps, I don't get this problem. I don't understand what is happening here. 1 MHz is an even multiple of 250kHz, so maybe I'm getting an image of OAK overpowering the relatively weaker SFO signal. But should there not be filters that manage this? I guess I was expecting that if the device is set to 250ksps, then it would "close down" filters appropriately to reject signals out of that band. But maybe the filters don't work properly below a certain sample rate? Like the rtl2832 can sample down to 250ksps, but the 820T tuner was not designed for it? Or perhaps I'm doing something wrong? Can I control the filters directly? I'm glad I find this issue because I was going nuts thinking my software had some mysterious bug. But I can reproduce this issue just with SDR# or whatever. :-) Regards. Dave J
Hi,
I don't understand what is happening here. 1 MHz is an even multiple of 250kHz, so maybe I'm getting an image of OAK overpowering the relatively weaker SFO signal. But should there not be filters that manage this?
Yes most likely an image.
I guess I was expecting that if the device is set to 250ksps, then it would "close down" filters appropriately to reject signals out of that band. But maybe the filters don't work properly below a certain sample rate? Like the rtl2832 can sample down to 250ksps, but the 820T tuner was not designed for it?
The filters you'd need wouldn't be in the R820T anyway (it has filters but not that narrow). IIRC, the rtl2832 always sample at a fixed high frequency but it has an internal downconverter + FIR filter inside to convert the sample rate down. But that FIR probably can't handle such a big reduction ...
Can I control the filters directly?
If you find out, let us know, but AFAIK all attempts so far didn't succeed to get it more narrow than this. Cheers, Sylvain
The filters you'd need wouldn't be in the R820T anyway (it has filters but not that narrow). IIRC, the rtl2832 always sample at a fixed high frequency but it has an internal downconverter + FIR filter inside to convert the sample rate down. But that FIR probably can't handle such a big reduction ...
Still we must not forget that we're talking about some piece of silicon with nm structures, and therefrom no extraordinarily sharp filtering can be expected. When analog meets digital, it is important that the analog part protects the ADC from being overwhelmed by strong signals that are not in the scope of interest. All those silicon-only broadband receiver concepts drastically fail when being directly connected to a real good antenna in urban vicinity. They are good for a rubber duck style antenna sitting on your table, but that's it. There's a reason for all the solid silver and brass stuff in real world receivers :)
Cheers,
Sylvain
Ralph.
Sample rate is 28.8 MHz. That is your basic bandwidth starting point. With the E4000 delivering I and Q data for the sampler you have a starting bandwidth of 28.8 MHz. The R820T converts to around 3 MHz I only. That means the bandwidth is 0 to 14.4 MHz with the dongle slicing out up to 2.4 Msps of I/Q data. The R820T potentially has some interesting image issues if it is really delivering 3 MHz to the RTL chip and not 7 MHz. These are TV devices. That means any analog filtering they may or may not have is 6 to 8 MHz wide. So up front it has that is the bandwidth to worry about for strong signals. The RTL chip delivers as little as 250 ksps. The word I've heard from people who test the chip is that it's not very good for image (alias) rejection much below 1 Msps. So I simply live with the 2.4 Msps and learn to like it. SDRSharp more or less properly (more compromises than some) decimates this down to something usable. But there's no way to tell SDRSharp, "Really, Essdee, I'm only interested in this 200 kHz so please only show that in the FFT window." It could be done. The code would be only a little more complex. I don't worry about it. I use the zoom slider and Bob's my uncle. The fellow who posted the question indicates he's interested in VOR reception. That's a 10 MHz band between 108 MHz and 118 MHz. I have a hunch there is a small band near the FM broadcast band that's more or less useless. So 4 dongles with appropriate tuning could get all but about 400 kHz of that range all at once on a suitable computer. 5 could do it with considerable overlap. But one, really, could do the job if it knew what frequencies to tune to. One of the scanner tools would maybe make that a little easier. He'll likely want to use some 1/4 wave coax notch's since he indicated two frequencies that had huge signals were 1 MHz apart up around 106 MHz. That would make a big difference for his weak signal work. {^_^} On 2013/10/22 01:44, Ralph A. Schmid, dk5ras wrote:
The filters you'd need wouldn't be in the R820T anyway (it has filters but not that narrow). IIRC, the rtl2832 always sample at a fixed high frequency but it has an internal downconverter + FIR filter inside to convert the sample rate down. But that FIR probably can't handle such a big reduction ...
Still we must not forget that we're talking about some piece of silicon with nm structures, and therefrom no extraordinarily sharp filtering can be expected. When analog meets digital, it is important that the analog part protects the ADC from being overwhelmed by strong signals that are not in the scope of interest.
All those silicon-only broadband receiver concepts drastically fail when being directly connected to a real good antenna in urban vicinity. They are good for a rubber duck style antenna sitting on your table, but that's it.
There's a reason for all the solid silver and brass stuff in real world receivers :)
Cheers,
Sylvain
Ralph.
Thank you. You and another forum member have helped me understand the situation. I am beginning to see the attraction of SDR platforms that integrate an FPGA immediately after the ADC. You can have wide analog filtering going to an ADC running fast, and then apply digital filters in the FPGA before downsampling to a lower rate for consumption by what-have-you. I can accomplish the same completely in software; I'll set the sample rate high, then filter and decimate, probably in a few stages to keep the filters reasonable. I tried it this evening with some raw IQ recordings I made this afternoon and it works pretty well -- on a modern PC. Regards, Dave J On Tue, Oct 22, 2013 at 1:29 AM, Sylvain Munaut <246tnt@gmail.com> wrote:
Hi,
I don't understand what is happening here. 1 MHz is an even multiple of 250kHz, so maybe I'm getting an image of OAK overpowering the relatively weaker SFO signal. But should there not be filters that manage this?
Yes most likely an image.
I guess I was expecting that if the device is set to 250ksps, then it would "close down" filters appropriately to reject signals out of that band. But maybe the filters don't work properly below a certain sample rate? Like the rtl2832 can sample down to 250ksps, but the 820T tuner was not designed for it?
The filters you'd need wouldn't be in the R820T anyway (it has filters but not that narrow). IIRC, the rtl2832 always sample at a fixed high frequency but it has an internal downconverter + FIR filter inside to convert the sample rate down. But that FIR probably can't handle such a big reduction ...
Can I control the filters directly?
If you find out, let us know, but AFAIK all attempts so far didn't succeed to get it more narrow than this.
Cheers,
Sylvain
Effective filtering must occur between antenna and receiver. All the problems that a saturated preamp and ADC cause can't be repaired by software. Never. Ralph. From: osmocom-sdr-bounces@lists.osmocom.org [mailto:osmocom-sdr-bounces@lists.osmocom.org] On Behalf Of David Jacobowitz Sent: Tuesday, October 22, 2013 10:45 AM To: Sylvain Munaut Cc: osmocom-sdr@lists.osmocom.org Subject: Re: odd results working at 250ksp/s Thank you. You and another forum member have helped me understand the situation. I am beginning to see the attraction of SDR platforms that integrate an FPGA immediately after the ADC. You can have wide analog filtering going to an ADC running fast, and then apply digital filters in the FPGA before downsampling to a lower rate for consumption by what-have-you. I can accomplish the same completely in software; I'll set the sample rate high, then filter and decimate, probably in a few stages to keep the filters reasonable. I tried it this evening with some raw IQ recordings I made this afternoon and it works pretty well -- on a modern PC. Regards, Dave J
Effective filtering must occur between antenna and receiver. All the problems that a saturated preamp and ADC cause can’t be repaired by software. Never.
But his original problem is not with saturated preamps or ADC ... it's aliasing ... and that can be solved in the digital domain provided fast enough ADC. Cheers, Sylvain
But his original problem is not with saturated preamps or ADC ... it's aliasing ... and that can be solved in the digital domain provided fast enough ADC.
Yep - if this really is the problem. Aliasing-alike effects also often come from nonlinearities in the overdriven input stages...BTST, GTTS :) The RTL2832 shows this all the time, copies of strong signals show up in expected (from aliasing, proven by simply doing the maths) and not-so-expected areas of the spectrum.
Cheers,
Sylvain
Ralph.
He sent me two frequencies in private email. These were in the FM broadcast band (in the US). He probably needs to notch them out in order to get adequate response. As for wanting narrow bandwidth - I am not quite sure why he thinks that is a benefit. I use a large FFT (about 10 Hz per bin) and use the zoom control to see fine detail. (Different FFT settings suite different uses. This one seems to be a good compromise with my two needs. I'm too lazy to change it.) {^_^} On 2013/10/22 02:08, Sylvain Munaut wrote:
Effective filtering must occur between antenna and receiver. All the problems that a saturated preamp and ADC cause can’t be repaired by software. Never.
But his original problem is not with saturated preamps or ADC ... it's aliasing ... and that can be solved in the digital domain provided fast enough ADC.
Cheers,
Sylvain
I originally posted about 115.8 and 116.8 MHz, both square in the VOR band of 108 to 117.95. I might have sent something else in a PM, but if so it was a typo. :-) I am definitely only interested in the VOR band right now -- though, as you say, it is adjacent to commercial FM with its high power. My application is simple in concept: A fully auomatic VOR-based positioning system, a fallback from GPS. I want to scan the entire VOR band, looking for signals in the standard VOR format that can be demodulated. I do the initial scan with a fast sample rate and FFT, just looking for peaks. From those, I examine the signals to see if it looks like a VOR signal. From that list, I will "park" on each signal long enough (~30s) to decode the VOR's morse code station ID. From that, I will have a short list of VORs that I can currently receive. From those, if the geometry is appropriate (I know the VORs positions from a database) I can calculate a position. The software then just round-robin tunes the VORs in range and continually tries to calculate positions. If too many drop out, it returns to the initial scan mode. Not being able to receive this VOR or that VOR is not generally a problem, but obviously, the more the better. With extra VORs I have better options for choosing the closest ones or the ones with the best geometry. This is actually quite difficult to test, because VORs can generally only be received line-of-sight -- which means in the air. I'm a private pilot but I found that flying and noodling with a laptop is too much trouble.
Use a 2.4 ksps sample rate and receive both of them. In general you want to stay away from the teat in the middle of the FFT, which is zero frequency on the input. That is a noisy spot due to semi-conductor physics. You can set then up with say a 250 kHz "IF" and a 750 kHz "IF" and in principle receive both at the same time. Of course you are going to graduate from this to receiving GPS, aren't you? {^_-} Joanne On 2013/10/22 08:07, David Jacobowitz wrote:
I originally posted about 115.8 and 116.8 MHz, both square in the VOR band of 108 to 117.95. I might have sent something else in a PM, but if so it was a typo. :-) I am definitely only interested in the VOR band right now -- though, as you say, it is adjacent to commercial FM with its high power.
My application is simple in concept: A fully auomatic VOR-based positioning system, a fallback from GPS. I want to scan the entire VOR band, looking for signals in the standard VOR format that can be demodulated. I do the initial scan with a fast sample rate and FFT, just looking for peaks. From those, I examine the signals to see if it looks like a VOR signal. From that list, I will "park" on each signal long enough (~30s) to decode the VOR's morse code station ID. From that, I will have a short list of VORs that I can currently receive. From those, if the geometry is appropriate (I know the VORs positions from a database) I can calculate a position.
The software then just round-robin tunes the VORs in range and continually tries to calculate positions. If too many drop out, it returns to the initial scan mode.
Not being able to receive this VOR or that VOR is not generally a problem, but obviously, the more the better. With extra VORs I have better options for choosing the closest ones or the ones with the best geometry.
This is actually quite difficult to test, because VORs can generally only be received line-of-sight -- which means in the air. I'm a private pilot but I found that flying and noodling with a laptop is too much trouble. From my office window, on a high floor in Oakland, CA, I can receive one VOR from the Oakland airport. And I have now discovered a ridge near my home with a scenic overlook from which I can receive two.
I've tested the software enough to know that the initial scan function seems to work, and the morse decoding kind of works, but I am not confident I'll get it to work very well. (One transmitter's dit looks a lot like another's dah.) The nav signal decoding is simple. (A 30 Hz AM modulated tone is phase compared with a 30 Hz tone FM modulated at 9960 Hz. The phase obtained is the azimuth to the station.)
If I ever get this working, I looking forward to sharing it with the community. In the process of building this, I created a simple SDR toolkit of DSP functions. It's like Gnuradio in concept, but 16b fixed-point, and has no external dependencies, and C89, so is easier to build on weird and limited platforms. It also has perl bindings. Compared to GR, it looks like the work of a rank amateur just learning DSP, but I do like the concept of there being a GR-like library out there, lightweight and embedded-friendly.
Regards, Dave J
On Tue, Oct 22, 2013 at 3:06 AM, jdow <jdow@earthlink.net <mailto:jdow@earthlink.net>> wrote:
He sent me two frequencies in private email. These were in the FM broadcast band (in the US). He probably needs to notch them out in order to get adequate response.
As for wanting narrow bandwidth - I am not quite sure why he thinks that is a benefit. I use a large FFT (about 10 Hz per bin) and use the zoom control to see fine detail. (Different FFT settings suite different uses. This one seems to be a good compromise with my two needs. I'm too lazy to change it.)
{^_^}
On 2013/10/22 02:08, Sylvain Munaut wrote:
Effective filtering must occur between antenna and receiver. All the problems that a saturated preamp and ADC cause can’t be repaired by software. Never.
But his original problem is not with saturated preamps or ADC ... it's aliasing ... and that can be solved in the digital domain provided fast enough ADC.
Cheers,
Sylvain
Hi, With a lot of delay and my apologizes, as promised a while ago, I finally published some quick notes on the VOR signal today. The complete signal analysis as been posted on my blog at this page : http://www.f4gkr.org/2014/02/in-depth-study-of-the-vor-signals/ I need to save the recorded WAV signals somewhere so people interested in good SNR recordings would get it. I decided to return close to the nearby VOR transmitter (Rambouillet, south west Paris) and put the RTL SDR on my car rooftop and turn on the laptop to capture some signals... Best regards sylvain F4GKR 2013-10-22 17:07 GMT+02:00 David Jacobowitz <david.jacobowitz@gmail.com>:
I originally posted about 115.8 and 116.8 MHz, both square in the VOR band of 108 to 117.95. I might have sent something else in a PM, but if so it was a typo. :-) I am definitely only interested in the VOR band right now -- though, as you say, it is adjacent to commercial FM with its high power.
My application is simple in concept: A fully auomatic VOR-based positioning system, a fallback from GPS. I want to scan the entire VOR band, looking for signals in the standard VOR format that can be demodulated. I do the initial scan with a fast sample rate and FFT, just looking for peaks. From those, I examine the signals to see if it looks like a VOR signal. From that list, I will "park" on each signal long enough (~30s) to decode the VOR's morse code station ID. From that, I will have a short list of VORs that I can currently receive. From those, if the geometry is appropriate (I know the VORs positions from a database) I can calculate a position.
The software then just round-robin tunes the VORs in range and continually tries to calculate positions. If too many drop out, it returns to the initial scan mode.
Not being able to receive this VOR or that VOR is not generally a problem, but obviously, the more the better. With extra VORs I have better options for choosing the closest ones or the ones with the best geometry.
This is actually quite difficult to test, because VORs can generally only be received line-of-sight -- which means in the air. I'm a private pilot but I found that flying and noodling with a laptop is too much trouble. From my office window, on a high floor in Oakland, CA, I can receive one VOR from the Oakland airport. And I have now discovered a ridge near my home with a scenic overlook from which I can receive two.
I've tested the software enough to know that the initial scan function seems to work, and the morse decoding kind of works, but I am not confident I'll get it to work very well. (One transmitter's dit looks a lot like another's dah.) The nav signal decoding is simple. (A 30 Hz AM modulated tone is phase compared with a 30 Hz tone FM modulated at 9960 Hz. The phase obtained is the azimuth to the station.)
If I ever get this working, I looking forward to sharing it with the community. In the process of building this, I created a simple SDR toolkit of DSP functions. It's like Gnuradio in concept, but 16b fixed-point, and has no external dependencies, and C89, so is easier to build on weird and limited platforms. It also has perl bindings. Compared to GR, it looks like the work of a rank amateur just learning DSP, but I do like the concept of there being a GR-like library out there, lightweight and embedded-friendly.
Regards, Dave J
On Tue, Oct 22, 2013 at 3:06 AM, jdow <jdow@earthlink.net> wrote:
He sent me two frequencies in private email. These were in the FM broadcast band (in the US). He probably needs to notch them out in order to get adequate response.
As for wanting narrow bandwidth - I am not quite sure why he thinks that is a benefit. I use a large FFT (about 10 Hz per bin) and use the zoom control to see fine detail. (Different FFT settings suite different uses. This one seems to be a good compromise with my two needs. I'm too lazy to change it.)
{^_^}
On 2013/10/22 02:08, Sylvain Munaut wrote:
Effective filtering must occur between antenna and receiver. All the
problems that a saturated preamp and ADC cause can't be repaired by software. Never.
But his original problem is not with saturated preamps or ADC ... it's aliasing ... and that can be solved in the digital domain provided fast enough ADC.
Cheers,
Sylvain
Thanks a lot - very interesting! Ralph. From: Sylvain AZARIAN [mailto:sylvain.azarian@gmail.com] Sent: Sunday, February 09, 2014 8:55 PM To: David Jacobowitz Cc: jdow; Sylvain Munaut; osmocom-sdr@lists.osmocom.org; Ralph A. Schmid, dk5ras Subject: Re: odd results working at 250ksp/s Hi, With a lot of delay and my apologizes, as promised a while ago, I finally published some quick notes on the VOR signal today. The complete signal analysis as been posted on my blog at this page : http://www.f4gkr.org/2014/02/in-depth-study-of-the-vor-signals/ I need to save the recorded WAV signals somewhere so people interested in good SNR recordings would get it. I decided to return close to the nearby VOR transmitter (Rambouillet, south west Paris) and put the RTL SDR on my car rooftop and turn on the laptop to capture some signals... Best regards sylvain F4GKR 2013-10-22 17:07 GMT+02:00 David Jacobowitz <david.jacobowitz@gmail.com>: I originally posted about 115.8 and 116.8 MHz, both square in the VOR band of 108 to 117.95. I might have sent something else in a PM, but if so it was a typo. :-) I am definitely only interested in the VOR band right now -- though, as you say, it is adjacent to commercial FM with its high power. My application is simple in concept: A fully auomatic VOR-based positioning system, a fallback from GPS. I want to scan the entire VOR band, looking for signals in the standard VOR format that can be demodulated. I do the initial scan with a fast sample rate and FFT, just looking for peaks. From those, I examine the signals to see if it looks like a VOR signal. From that list, I will "park" on each signal long enough (~30s) to decode the VOR's morse code station ID. From that, I will have a short list of VORs that I can currently receive. From those, if the geometry is appropriate (I know the VORs positions from a database) I can calculate a position. The software then just round-robin tunes the VORs in range and continually tries to calculate positions. If too many drop out, it returns to the initial scan mode. Not being able to receive this VOR or that VOR is not generally a problem, but obviously, the more the better. With extra VORs I have better options for choosing the closest ones or the ones with the best geometry. This is actually quite difficult to test, because VORs can generally only be received line-of-sight -- which means in the air. I'm a private pilot but I found that flying and noodling with a laptop is too much trouble. From my office window, on a high floor in Oakland, CA, I can receive one VOR from the Oakland airport. And I have now discovered a ridge near my home with a scenic overlook from which I can receive two. I've tested the software enough to know that the initial scan function seems to work, and the morse decoding kind of works, but I am not confident I'll get it to work very well. (One transmitter's dit looks a lot like another's dah.) The nav signal decoding is simple. (A 30 Hz AM modulated tone is phase compared with a 30 Hz tone FM modulated at 9960 Hz. The phase obtained is the azimuth to the station.) If I ever get this working, I looking forward to sharing it with the community. In the process of building this, I created a simple SDR toolkit of DSP functions. It's like Gnuradio in concept, but 16b fixed-point, and has no external dependencies, and C89, so is easier to build on weird and limited platforms. It also has perl bindings. Compared to GR, it looks like the work of a rank amateur just learning DSP, but I do like the concept of there being a GR-like library out there, lightweight and embedded-friendly. Regards, Dave J On Tue, Oct 22, 2013 at 3:06 AM, jdow <jdow@earthlink.net> wrote: He sent me two frequencies in private email. These were in the FM broadcast band (in the US). He probably needs to notch them out in order to get adequate response. As for wanting narrow bandwidth - I am not quite sure why he thinks that is a benefit. I use a large FFT (about 10 Hz per bin) and use the zoom control to see fine detail. (Different FFT settings suite different uses. This one seems to be a good compromise with my two needs. I'm too lazy to change it.) {^_^} On 2013/10/22 02:08, Sylvain Munaut wrote: Effective filtering must occur between antenna and receiver. All the problems that a saturated preamp and ADC cause can't be repaired by software. Never. But his original problem is not with saturated preamps or ADC ... it's aliasing ... and that can be solved in the digital domain provided fast enough ADC. Cheers, Sylvain
I added this morning a post with links to the wav and mat files (matlab files are centered on the VOR signal, and have limited sampling rate to 30 KHz) feel free to ask further details if required sylvain 2014-02-10 11:54 GMT+01:00 Ralph A. Schmid, dk5ras <ralph@schmid.xxx>:
Thanks a lot - very interesting!
Ralph.
*From:* Sylvain AZARIAN [mailto:sylvain.azarian@gmail.com] *Sent:* Sunday, February 09, 2014 8:55 PM *To:* David Jacobowitz *Cc:* jdow; Sylvain Munaut; osmocom-sdr@lists.osmocom.org; Ralph A. Schmid, dk5ras *Subject:* Re: odd results working at 250ksp/s
Hi,
With a lot of delay and my apologizes, as promised a while ago, I finally published some quick notes on the VOR signal today.
The complete signal analysis as been posted on my blog at this page : http://www.f4gkr.org/2014/02/in-depth-study-of-the-vor-signals/
I need to save the recorded WAV signals somewhere so people interested in good SNR recordings would get it.
I decided to return close to the nearby VOR transmitter (Rambouillet, south west Paris) and put the RTL SDR on my car rooftop and turn on the laptop to capture some signals...
Best regards
sylvain F4GKR
2013-10-22 17:07 GMT+02:00 David Jacobowitz <david.jacobowitz@gmail.com>:
I originally posted about 115.8 and 116.8 MHz, both square in the VOR band of 108 to 117.95. I might have sent something else in a PM, but if so it was a typo. :-) I am definitely only interested in the VOR band right now -- though, as you say, it is adjacent to commercial FM with its high power.
My application is simple in concept: A fully auomatic VOR-based positioning system, a fallback from GPS. I want to scan the entire VOR band, looking for signals in the standard VOR format that can be demodulated. I do the initial scan with a fast sample rate and FFT, just looking for peaks. From those, I examine the signals to see if it looks like a VOR signal. From that list, I will "park" on each signal long enough (~30s) to decode the VOR's morse code station ID. From that, I will have a short list of VORs that I can currently receive. From those, if the geometry is appropriate (I know the VORs positions from a database) I can calculate a position.
The software then just round-robin tunes the VORs in range and continually tries to calculate positions. If too many drop out, it returns to the initial scan mode.
Not being able to receive this VOR or that VOR is not generally a problem, but obviously, the more the better. With extra VORs I have better options for choosing the closest ones or the ones with the best geometry.
This is actually quite difficult to test, because VORs can generally only be received line-of-sight -- which means in the air. I'm a private pilot but I found that flying and noodling with a laptop is too much trouble. From my office window, on a high floor in Oakland, CA, I can receive one VOR from the Oakland airport. And I have now discovered a ridge near my home with a scenic overlook from which I can receive two.
I've tested the software enough to know that the initial scan function seems to work, and the morse decoding kind of works, but I am not confident I'll get it to work very well. (One transmitter's dit looks a lot like another's dah.) The nav signal decoding is simple. (A 30 Hz AM modulated tone is phase compared with a 30 Hz tone FM modulated at 9960 Hz. The phase obtained is the azimuth to the station.)
If I ever get this working, I looking forward to sharing it with the community. In the process of building this, I created a simple SDR toolkit of DSP functions. It's like Gnuradio in concept, but 16b fixed-point, and has no external dependencies, and C89, so is easier to build on weird and limited platforms. It also has perl bindings. Compared to GR, it looks like the work of a rank amateur just learning DSP, but I do like the concept of there being a GR-like library out there, lightweight and embedded-friendly.
Regards,
Dave J
On Tue, Oct 22, 2013 at 3:06 AM, jdow <jdow@earthlink.net> wrote:
He sent me two frequencies in private email. These were in the FM broadcast band (in the US). He probably needs to notch them out in order to get adequate response.
As for wanting narrow bandwidth - I am not quite sure why he thinks that is a benefit. I use a large FFT (about 10 Hz per bin) and use the zoom control to see fine detail. (Different FFT settings suite different uses. This one seems to be a good compromise with my two needs. I'm too lazy to change it.)
{^_^}
On 2013/10/22 02:08, Sylvain Munaut wrote:
Effective filtering must occur between antenna and receiver. All the problems that a saturated preamp and ADC cause can't be repaired by software. Never.
But his original problem is not with saturated preamps or ADC ... it's aliasing ... and that can be solved in the digital domain provided fast enough ADC.
Cheers,
Sylvain
participants (6)
-
David Jacobowitz -
jdow -
jdowjunkmail＠earthlink.net -
Ralph A. Schmid, dk5ras -
Sylvain AZARIAN -
Sylvain Munaut