Re: [Freetel-codec2] 2400A VHF modem performance

(cc-ed to list) Sure, SM1000 purchase details here: http://www.rowetel.com/?page_id=3902 The LDPC codes have much better performance (coding gain) than Hamming codes. I've found Codec 2 (especially the lower rates like 700) fall over at a few % BER. Cheers, David On 08/10/17 23:58,

Re: [Freetel-codec2] 2400A VHF modem performance

Hi David, Thanks for pointing me at the Octave code. I'll have to do some reading as I'm pretty sure my implementation is buggy. Regarding, the 700 bit/s mode, I do hope there will be no major change in the library version, as we have to use the distribution packaging, on stable. Thanks, Adrian

Re: [Freetel-codec2] 2400A VHF modem performance

Hi Adrian, There is Octave and C code for the mFSK modem we have developed in codec2-dev, that we have tested against the ideal FSK performance curves. Not sure I'd call it matched filter, but take a look at the code. It's important to check your modem implementation against theory at a

Re: [Freetel-codec2] 2400A VHF modem performance

Hi David, Thanks very much for the tips! Would you suggest that the matched filter approach is better for 4FSK as well? I am using it for 2FSK and it works well, it's just that being lazy I wanted to avoid too much complexity in the code for the 4FSK variant. Regarding PSK: I have several things

Re: [Freetel-codec2] 2400A VHF modem performance

On 10/5/17, Steve wrote: > You might also do your testing in a more remote spot. The use of ISM > in the city is probably pretty high, and interference would be an > issue. It might not break the squelch (spread spectrum, etc), but the > bits would be corrupted. > > I see

Re: [Freetel-codec2] 2400A VHF modem performance

Hi David, Thanks for the answer! I have just simulated a 2FSK modem on AWGN channel, but this time without using FM demodulation. It performs just like you said, ~2 dB worse than QPSK (at 5% frames dropped). This means that the FM demodulator I used for 2400A must be introducing some symbol

Re: [Freetel-codec2] 2400A VHF modem performance

You might also do your testing in a more remote spot. The use of ISM in the city is probably pretty high, and interference would be an issue. It might not break the squelch (spread spectrum, etc), but the bits would be corrupted. I see a lot of users on that band, with just a junkbox antenna and

Re: [Freetel-codec2] 2400A VHF modem performance

Hi Adrian, This blog post compares a bunch of different modems at the 2% BER operating point: http://www.rowetel.com/?p=4663 Given all things being equal (e.g. sync overheads, bit rate etc) PSK is about 3dB better than 4FSK at the 2% BER point. In practice real world PSK modems tend to

[Freetel-codec2] 2400A VHF modem performance

Hi, I was able to perform some field measurements on Sunday to compare the performance of the 4FSK modem and the QPSK modem in the 433 MHz ISM band. My transmitter was set to 1 mW output power into a 2 dBi gain antenna located at approx. 21 meters above ground on one of the buildings in my city.