Hello Glen, This blog post has a demo of how differences in sample clock rates at the tx and rx are handled:
http://www.rowetel.com/blog/?p=2433 The demod asks for more/less samples from the rx ADC to compensate, e.g. see freedv_rx.c IIRC the modems can handle +/-1000ppm, see tcohpsk.m for how I tested it recently. Sound card modems tend to get presented with rather large sample clock offsets. Cheers, David On 01/08/15 12:31, glen english wrote: > David > for free DV etc > How are you dealing with differences in clock speed for TX to RX ? > > Does the RX sample-rate-convert to its local domain, or does it follow > the incoming sample clock (and hence adjust its own clock ) > > ? > > On 1/08/2015 12:54 PM, David Rowe wrote: >> Sounds like you have it about right Michael! >> >> On 01/08/15 11:36, Michael Carey wrote: >>> Hi David, >>> >>> I get virtually the same results with the microphone connector as I do >>> with the ACC connector. Other things like TBW (transmit bandwidth) are >>> disabled with you enable the Data mode but I'm sure there is still >>> processing/DSP in the audio path... the IC-7100 is that kind of radio. >>> >>> It appears to be working pretty good, but I'm just not confident on the >>> output power. The only thing that seems to be consistent and may be >>> what I follow... is the PA current indication. >>> It doesn't jump around all over the place and shows a nice steady 5-6A >>> which would be about right for 20-25W RF output. >>> >>> I've tried a different RX radio (TS-140S) just to see if that would make >>> a difference... but no. >>> >>> Michael. >>> VK5ZEA >>> >>> On 1/08/2015 8:19 AM, David Rowe wrote: >>>> Hi Michael, >>>> >>>> SNR sounds similar to what I get from my IC7200. I think yr close. >>>> >>>> Only issue with using the data connector is levels. The SM1000 output >>>> is attenuated quite a lot down to typical mic levels (see SM1000 page >>>> for specs). So maybe check the levels are compatible. >>>> >>>> Cheers, >>>> >>>> David >>>> >>>> On 01/08/15 08:09, Michael Carey wrote: >>>>> Thanks for the info David, >>>>> >>>>> I'm hoping to find others who are using the SM1000 and FreeDV with the >>>>> Icom IC-7100 radio and compare what we've done. >>>>> >>>>> I am flying a bit blind with setting the power levels. I'm presuming >>>>> that both the radio power output meter and my external wattmeter don't >>>>> "like" the FDMDV modulation to give a true power output indication. I >>>>> set the radio power output at 25% (once again presuming that 100% is >>>>> 100W! :-) ), I increase drive so that ALC just indicates and I get >>>>> around 3-5 W showing on the power output meter... but it's not steady, >>>>> jumping around all over the place. >>>>> >>>>> I'm modulating via the ACC connector on the back of the transceiver, the >>>>> IC-7100 has Data mode which when selected allows you to take audio from >>>>> different places... in my case the ACC connector. This also turns off >>>>> compression and other trickery that might mess with a data transmission. >>>>> >>>>> I'm using a Kenwood TS-50, SignaLink (non USB version) and a Cmedia >>>>> sound card in my shack PC to decode the IC-7100. >>>>> >>>>> I get 0 BER, SNR of 17, but the spectrum display looks a little lumpy. >>>>> I can fiddle with the output of the SM1000 over a fair range with very >>>>> little change in the displayed signal and received audio. The scatter >>>>> diagram also doesn't look as nice as I've seen others. The dots are >>>>> most certainly grouped together, but not as tight as I would have liked. >>>>> >>>>> I'm hoping to get more time in the shack this weekend to experiment a >>>>> bit more. >>>>> >>>>> 73 >>>>> >>>>> Michael. >>>>> VK5ZEA >>>>> >>>>> On 26/07/2015 7:19 AM, David Rowe wrote: >>>>>> Hi Michael, >>>>>> >>>>>> FB on getting your SM1000 up on the air - lets have a QSO some time! >>>>>> >>>>>> Adjusting so your ALC just moves, and 20-25 watts average power for a >>>>>> 100W PEP rig is a useful rule of thumb for FreeDV 1600. The classic >>>>>> "rookie mistake" is overdriving the SSB tx, which causes clipping and a >>>>>> poor bit error rate at the receiver. Make sure any speech compression >>>>>> is off too. >>>>>> >>>>>> The best way to adjust your tx drive is monitor the SNR of the signal >>>>>> using a 2nd rx and the FreeDV GUI program. For example when I tx with >>>>>> my IC7200, I have a FT817 nearby with no antenna and the RF gain wound >>>>>> down. I feed the rx audio into my laptop and monitor the scatter >>>>>> diagram and SNR. Incidentally, with my IC7200 I can't seem to get >>>>>> better than 20dB, perhaps due to it's sharp tx filtering. >>>>>> >>>>>> I have a video that demonstrates this (and explains scatter plots): >>>>>> >>>>>> http://www.rowetel.com/blog/?p=3109 >>>>>> >>>>>> Cheers, >>>>>> >>>>>> David >>>>>> >>>>>> On 25/07/15 23:05, Michael Carey wrote: >>>>>>> Hi Everybody, >>>>>>> >>>>>>> I've been building up a set of SM1000 cables for a few of my different >>>>>>> HF radios. The main radio I use at home is an Icom IC-7100. >>>>>>> I understand you set the input level to the radio so the AGC indication >>>>>>> barely moves and make sure you don't stress the output stage too much... >>>>>>> I've settled on around 30W output. >>>>>>> >>>>>>> I find that the AGC indication on my IC-7100 tends to jump around a >>>>>>> little when transmitting the FDMDV signal. >>>>>>> Can I use the test tone to set the transmit level and be confident that >>>>>>> this is OK for FDMDV? >>>>>>> >>>>>>> 73 >>>>>>> >>>>>>> Michael. >>>>>>> VK5ZEA >>>>>>> >>>>>>> ------------------------------------------------------------------------------ >>>>>>> _______________________________________________ >>>>>>> Freetel-codec2 mailing list >>>>>>> [email protected] >>>>>>> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >>>>>>> >>>>>> ------------------------------------------------------------------------------ >>>>>> _______________________________________________ >>>>>> Freetel-codec2 mailing list >>>>>> [email protected] >>>>>> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >>>>>> >>>>> ------------------------------------------------------------------------------ >>>>> _______________________________________________ >>>>> Freetel-codec2 mailing list >>>>> [email protected] >>>>> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >>>>> >>>> ------------------------------------------------------------------------------ >>>> _______________________________________________ >>>> Freetel-codec2 mailing list >>>> [email protected] >>>> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >>>> >>> >>> ------------------------------------------------------------------------------ >>> _______________________________________________ >>> Freetel-codec2 mailing list >>> [email protected] >>> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >>> >> ------------------------------------------------------------------------------ >> _______________________________________________ >> Freetel-codec2 mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >> > ------------------------------------------------------------------------------ _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
