- Thread starter Kayos
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Kayos
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I need someone who understands them on a deep level, how they communicate with software, in particular Svxlink and Remotetrx
sako243
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Can you be more specific?
I was involved with everything from the RF front end up to the worldwide command and control side of things so covered all aspects but we didn't use stuff like the software you're describing because fundamentally our radios originated several decades before SDR became common place.
But its all just a bit of software and I've been involved in more Linux than most having ported it to different platforms and written software from drivers to Web stuff working on it.
I was involved with everything from the RF front end up to the worldwide command and control side of things so covered all aspects but we didn't use stuff like the software you're describing because fundamentally our radios originated several decades before SDR became common place.
But its all just a bit of software and I've been involved in more Linux than most having ported it to different platforms and written software from drivers to Web stuff working on it.
Kayos
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I'm getting huge distortion and noise, it must be a software issue as using something like GQRX is fine.
I've got it setup to monitor one frequency, when a CTCSS tone is detected it opens the squelch and sends it to a soundcard so it can either be transmitted (the original function of the software) or in my case listened to on headphones.
I cant work out the relationship between the preamp and the gain. I think preamp is Svxlink and gain is the sdr but even on with the gain on -50 (the most I can go) I get distortion, just quiet distortion
It doesn't matter if i read the sdr direct, from rtl_tcp or from a Remotetrx node, still the same.
Doesn't matter what antenna I use, what coax or if I use the LNB, made by nooelec, same as the sdr. It's currently connected direct to the antenna, with about 4" of coax and sending the signal uncompressed down ethernet, direct into the Pi4
I've got it setup to monitor one frequency, when a CTCSS tone is detected it opens the squelch and sends it to a soundcard so it can either be transmitted (the original function of the software) or in my case listened to on headphones.
I cant work out the relationship between the preamp and the gain. I think preamp is Svxlink and gain is the sdr but even on with the gain on -50 (the most I can go) I get distortion, just quiet distortion
It doesn't matter if i read the sdr direct, from rtl_tcp or from a Remotetrx node, still the same.
Doesn't matter what antenna I use, what coax or if I use the LNB, made by nooelec, same as the sdr. It's currently connected direct to the antenna, with about 4" of coax and sending the signal uncompressed down ethernet, direct into the Pi4
sako243
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As I'm not particularly au-fait with the open source alternatives (the SDR stuff I was involved with we did all the signal processing ourselves) any chance of a diagram (or just a text list) of what apps you've got talking to what. What are you trying to achieve because SDR is a broad spectrum of things. Doing some research on the apps you've mentioned it looks like you're trying to pick up hand-held radios?
Kayos
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About as basic as it can be, Rasbian with just what it needs to run
Rtl_sdr controlling the sdr, the dvb modules are black listed, this is opened and controlled by Svxlink the audio is then output to the soundcard through Alsa
Thought I'd cracked it when I tuned to radio 2 and heard sound and music but no amount of fiddling gets me decent sound from a handheld.
I'm thinking it might be more basic and I could be overloading the sdr input, I'm as far away as I can get from the antenna and I'm only using 1w so I'm not sure
I'm determined to get it working, one way or another
Rtl_sdr controlling the sdr, the dvb modules are black listed, this is opened and controlled by Svxlink the audio is then output to the soundcard through Alsa
Thought I'd cracked it when I tuned to radio 2 and heard sound and music but no amount of fiddling gets me decent sound from a handheld.
I'm thinking it might be more basic and I could be overloading the sdr input, I'm as far away as I can get from the antenna and I'm only using 1w so I'm not sure
I'm determined to get it working, one way or another
sako243
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Try removing the antenna from the Pi - if you can't pick up anything it sounds like you can boost the power on the handheld so you could try upping that. If you're close then you probably won't need the antenna to pick up stuff. That might test your theory.
sako243
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If it works out behaves any differently at least it'll tell us something. It it works it points out that your setup is likely introducing too much gain into the system.
As an aside, you usually can't increase gain in an SDR but what you do is add attenuation. It's a subtle difference and sometimes developers get signs cocked up. You mentioned you had -50dB of gain, have you tried knocking that towards zero?
As an aside, you usually can't increase gain in an SDR but what you do is add attenuation. It's a subtle difference and sometimes developers get signs cocked up. You mentioned you had -50dB of gain, have you tried knocking that towards zero?
mr migwire
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i use HDSDR for decoding DMR transmisions the dongle receives the signal and it is then fed via a virtual audio cable to DSD+ the decoding software the resulting audio is the patched via a virtual audio cable to the soundcard.
i have to set the hdr plus gain pretty low or it seems to overload the sds+ and starts muddling the signal,
that im afraid is as far as my knowledge streches with it but being methodical i would start at the in comming signal and see if you are picking up spurious RF,
i have to set the hdr plus gain pretty low or it seems to overload the sds+ and starts muddling the signal,
that im afraid is as far as my knowledge streches with it but being methodical i would start at the in comming signal and see if you are picking up spurious RF,
Kayos
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I do feel it is gain, tried removing the antenna and moving far away from the SDR, still exactly the same.
There are 2 adjustments, pre-amp and gain. pre-amp i believe is part of svxlink, in the config files it says its a last resort, most online examples show it at -4 or -5, I've tried everything from -10 to 10 without any difference to the problem i'm having
The other setting is gain, i believe this is sent to the SDR, most online examples have it around 20.
I've taken a screenshot of what happens if you manually start the software, the gain values are provided by the sdr, I've tried quite a few across the range, both positive and negative values, without any noticeable difference.
Other parts of the software work fine, including CTCSS and DTMF decoding, turning pre-amp below -5 causes that to stop working reliably, at -10 it cant decode the DTMF at all
Using normal SDR software GQRX I can see the signal is spot on, nothing spurious out of range on any demod.
The home directory bit is unimportant, i have set udev rules so i don't have to run a root and the temp config file is in the wrong home directory but it has no impact on how it runs
There are 2 adjustments, pre-amp and gain. pre-amp i believe is part of svxlink, in the config files it says its a last resort, most online examples show it at -4 or -5, I've tried everything from -10 to 10 without any difference to the problem i'm having
The other setting is gain, i believe this is sent to the SDR, most online examples have it around 20.
I've taken a screenshot of what happens if you manually start the software, the gain values are provided by the sdr, I've tried quite a few across the range, both positive and negative values, without any noticeable difference.
Other parts of the software work fine, including CTCSS and DTMF decoding, turning pre-amp below -5 causes that to stop working reliably, at -10 it cant decode the DTMF at all
Using normal SDR software GQRX I can see the signal is spot on, nothing spurious out of range on any demod.
The home directory bit is unimportant, i have set udev rules so i don't have to run a root and the temp config file is in the wrong home directory but it has no impact on how it runs
Kayos
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Fixed it, sort of...
No idea what the actual issue is or was but I've found a workaround that might actually simplify .
Rather than directly reading the SDR I have started rtl_tcp and told Svxlink to read it that way.
Works perfectly, I tried copying the settings it spits out (auto gain off, gain 86) into my config but still the same result
Using rtl_tcp on the remote SDR might actually be simpler than running Remotetrx and would mean other devices could access it if needed. The remote devices are on their own wired network
No idea what the actual issue is or was but I've found a workaround that might actually simplify .
Rather than directly reading the SDR I have started rtl_tcp and told Svxlink to read it that way.
Works perfectly, I tried copying the settings it spits out (auto gain off, gain 86) into my config but still the same result
Using rtl_tcp on the remote SDR might actually be simpler than running Remotetrx and would mean other devices could access it if needed. The remote devices are on their own wired network
