Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Hi Brady, Thank you very much for the detailed.description of the code. This was very helpful. It appears that there is no difference between 2400b and my modem except for the pulse shaping filters. I think the performance should also.be very similar. Unfortunately I no longer have the time to

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

agreed. the only way these DMR/ C4FM mod schemes fit into a channel is because they are aggressively filtered... On 7/07/2016 10:55 AM, David Rowe wrote: > Hi Jeroen, > > Pls check that gut feeling abt pulse shaping very carefully - many ideal > demods use "integrate and dump" filters - and IIRC

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Hi Jeroen, Pls check that gut feeling abt pulse shaping very carefully - many ideal demods use "integrate and dump" filters - and IIRC Brady obtained some surprisingly good Eb/No versus BER results for the 2400B modem. Indeed, the pulse shaping filters used on DMR/C4FM and friends seem to be

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Hi Adrian, On 07/06/2016 09:20 PM, Adrian Musceac wrote: > I have read your blog posts about the 2400B modem, but I would really > like to understand more, like what kind of filters do you use for > pulse shaping and how do they affect performance/bandwidth, how do you > track the carrier

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Hi David, I wish I was able to generate BER plots similar to those in your images. Unfortunately, while Gnuradio has powerful real time plotting blocks, I haven't figured out how to use them yet. For this reason, I have to use two flowgraphs, one for the analog radio and one for the USRP, get

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Nice work Adrian. A good way to present this work is plots of BER against Eb/No for the various modulation schemes you are experimenting with. See my blog posts on FSK etc for examples. It's useful to include the theoretical curves as comparisons to your real world implementations, these are

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Hi Brady, David, Thank you very much for sharing the GRC flowgraphs. This will help me a lot setting up a similar test. Regarding the performance, I was just surprised to see such a big difference between a modem which runs through analog FM and your new modem. I would have expected something in

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Hey Adrian, The gnuradio-companion pipelines I used for the test are attached. These grc pipelines are only meant to get 16-bit 48k samples in and out of the HackRF and rtlsdr for testing. The meat of the FSK is done with the C fsk modem, used in freedv_rx, freedv_tx, fsk_mod, and fsk_demod. We

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Hi Adrian, I think Brady's going to get back you with his GR code. Not sure if the FSK modem is still outboard of GR, or if he has a GR module for it. Note we are not running our modems through the analog FM modulator/demodulator, as that's how you throw perfectly good dB away. I'm looking

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Did I hear that right? Works with non linear amplifiers, competitive with SSB, replaces all your multi carrier modems? On Thu, Mar 17, 2016, 11:51 David Rowe wrote: > Hi Adrian, > > Getting the modem right can be really critical. It's good that we are > discovering this and

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Hi David, You are right, it was measurement error. With the help of Brady's GRC flowgraphs, I was able to set up a more reliable test. The chain was: gnuradio DBPSK modem on laptop -> Yaesu FT60 set on narrow deviation -> USRP B200 -> Gqrx The USRP has fine adjustable gain, between 0 and 70 dB.

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Also, for comparison purposes, here is my 2000 bit/s modem running through a Yaesu FT60 handheld radio: https://www.youtube.com/watch?v=bsmGYWxjfjU The filter in Gqrx is adjusted for wide deviation (5 kHz) but the signal is only really about 3 kHz wide. Please note how the signal is 15-16 dB

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

I think in the case of coherent vs non-coherent for 4FSK, the plot of EbN0(dB) vs BER for ideal coherent and non-coherent says it all. If we find that we really need that extra dB, It'd be easier to switch to non-coherent 8FSK than write and test coherent 4FSK (and at 8FSK, coherent and

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Hi David, Is it possible to get our hands on the Gnuradio code? I've been trying to optimize modems running at 1200 bits/second and the best I could do was 100% copy at 8 dB above analog FM for DBPSK and 12 dB above for GMSK. Your modem seems to be 16-20 dB better than that! If I could see the

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Ha, I wish it was through a radio! I'm trying to think what I have laying around here that might make a good transmitter for it. On Wed, Mar 16, 2016 at 4:02 AM, glen english wrote: > ah. good stuff. nice progress. > > > On 16/03/2016 7:50 PM, Steve wrote: > > Just using

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

ah. good stuff. nice progress. On 16/03/2016 7:50 PM, Steve wrote: Just using the script: freedv_tx 2400A ve9qrp_10s.raw modem.raw Which produces a RAW audio file sampled at 48 kHz and

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Cool. Perhaps something to put my HackRF to use for, a local FreeDV beacon. OH6ESQ expressed some interest in FreeDV, perhaps he'll be able to pick it up from across the Baltic sea /Tomas, SA2TMS On 2016-03-16 00:28, David Rowe wrote: > Hello Lists, > > We've just tested the new FreeDV 2400A

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Hi Steve Nice is that through a PA- if so, linear or linear in say 3dB compression? On 16/03/2016 7:42 PM, Steve wrote: Thought I'd upload a spectrum snapshot. You can't really see the carriers until you drop the

Re: [Freetel-codec2] new FreeDV 2400A VHF Modem

Thought I'd upload a spectrum snapshot. You can't really see the carriers until you drop the number of samples to about 256, but this shows how wide it is. I noticed that the freedv_tx was outputting +/- 1.0 signals and a couple of clips going on. Maybe need to knock it down to +/- .5 like the

[Freetel-codec2] new FreeDV 2400A VHF Modem

Hello Lists, We've just tested the new FreeDV 2400A mode designed for VHF and above. Here's the scoop: http://www.rowetel.com/blog/?p=5119 Thanks, David -- Transform Data into Opportunity. Accelerate data