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Re: communication of two b200 via ax.25

From: bryan
Subject: Re: communication of two b200 via ax.25
Date: Fri, 25 Jun 2021 09:54:58 +0900

Hi Fabian,
   Thank you so much for your suggestions as well as the advice to try it without the USRPs and escape reality for a bit. Will certainly do that. :-D


On Thu, Jun 24, 2021 at 9:03 PM Fabian Schwartau <fabian@opencode.eu> wrote:
Hi Bryan,
just increase the cutoff of the LPF, not the deviation. I am just saying
that the bandwidth of a signal with 5 kHz deviation is probably more
like 10 kHz wide (single sided). But I am not sure about that. You can
use the "Qt GUI Frequency Sink" to take a look at the spectrum and see
what the bandwidth of the signal is. Just try a few different values and
see if it gets better.
You can also try to put both flow graphs into one and get rid of the
USRPs. Just to make sure that the flow graph alone works as expected
without this annoying thing called "reality" ;) Remember to add a
throttle block.

Best regards,

Am 24.06.21 um 13:39 schrieb bryan:
> Hi Fabian,
>    Thank you for the reply. Actually, I am just starting to learn the
> ins and outs of GNU Radio and SDR. I will try to increase the cutoff and
> max deviation and check the results. With regards to the Fractional BW
> at TX, I just copied it from some code I found online. Should I change
> it to a different value? *sorry, i am still trying to absorb all the
> concepts*
> Regards,
> Bryan
> On Thu, Jun 24, 2021 at 4:58 PM Fabian Schwartau <fabian@opencode.eu
> <mailto:fabian@opencode.eu>> wrote:
>     Hi Bryan,
>     I just noticed a few things I am not sure about. Maybe I got something
>     wrong, maybe they are a mistake:
>     You transmit at 70cm and receive at 2m.
>     You use a low-pass filter with 5kHz cutoff and allow a maximum deviation
>     of 5kHz of the NBFM receiver. I am not sure, but I think this is not
>     optimal. I would expect a spectrum quite a bit wider than 5kHz when
>     transmitting with 5kHz max deviation.
>     Why is the fractional BW of your Rational Resampler in the TX path 0?
>     Best regards,
>     Fabian
>     Am 24.06.21 um 08:19 schrieb bryan:
>     > Hi,
>     >    I have this flowgraph programmed in two b200 SDRs. I want to
>     > communicate via ax.25. The problem is both are not consistent in
>     > receiving data from each other. It is like for every 10  transmitted
>     > data, around 5 are received from the other end. Can anybody tell
>     me what
>     > I did wrong so that the two SDRs will communicate consistently? Note
>     > that both of them are just located very near to each other? Here is my
>     > flowgraph:
>     >
>     > RX:
>     > image.png
>     >
>     > TX:
>     >
>     > image.png
>     >
>     > Regards,
>     > Bryan

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