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Discuss RTL-SDR and cheap software defined radio
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PostPosted: Wed Feb 15, 2017 10:00 am 
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I'm using SDR# as my SDR software for my RTL-SDR dongle. However, there's one thing about SDR# that I don't like. Whenever it gets into a band of frequencies that it thinks should be using NFM or AM (or whatever modulation it's configured with) it automatically switches to that demodulation mode automatically. Is there any way in SDR# to DISABLE the auto-mode-switching? I often explore a given RF band with USB (upper sideband) mode first (because it allows you to hear even UNMODULATED carrier waves) before switching to a particular demodulation mode like AM or FM. This allows me to find a carrier wave, even if nothing is being sent at the given time, so I can know that at some point something WILL be sent on it (then I just wait to see what gets sent, when it actually starts transmitting something useful). I absolutely hate to have the program keep switching me out of USB mode to something else every time it changes bands (according to whatever modulation it thinks is most likely going to be used in a given band). Because this means I have to EVERY SINGLE TIME it switches bands while I'm tuning (when it crosses over that band boundary), end up manually switching it back to USB mode. This gets VERY tedious.

So again, my question is, is there some way to actually disable this auto-band-switching?


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PostPosted: Wed Feb 15, 2017 9:22 pm 
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I think this is related to the new 'Band Plan' plugin which is included by default. Just disable it via the left side bar menu.


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PostPosted: Wed Feb 15, 2017 10:28 pm 
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rtlsdrblog wrote:
I think this is related to the new 'Band Plan' plugin which is included by default. Just disable it via the left side bar menu.


But then it won't show me which band I'm in. I like it to show me the name of the band I'm in. I just don't like it to automatically automatically switch the demodulation mode.
Is it possible that there's a hidden/undocumented technique for disabling its auto-mode-feature?
If it is hard-coded into the plugin's DLL file, is it possible to hack the DLL file, and replace the code responsible for auto-mode-switching with NOP opcodes (in effect erasing that unwanted part of the code)?
Has anybody accomplished such a hack yet?


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PostPosted: Thu Feb 16, 2017 6:58 am 
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I see an option in that plugin "Auto update radio settings", that's probably the setting that you want to turn off.


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PostPosted: Thu Feb 16, 2017 10:34 pm 
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rtlsdrblog wrote:
I see an option in that plugin "Auto update radio settings", that's probably the setting that you want to turn off.


Thanks. That worked.


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PostPosted: Thu Feb 16, 2017 10:46 pm 
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Joined: Sat Dec 24, 2016 11:03 pm
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You then can use HDSDR . it 's far better in everything.


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PostPosted: Thu Feb 16, 2017 11:21 pm 
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on1bes wrote:
You then can use HDSDR . it 's far better in everything.


SDR# can do some things that HDSDR can't:

SDR# can tune to anything that the SDR hardware plugged into your PC can handle. Meanwhile, HDSDR can't tune above 2147.483647MHz, even on RTL-SDR dongles that support it (those that have an E4000 tuner, which can tune up to 2300MHz according to the specs on the NooElec website).
Here's why HDSDR can't tune that high. Notice that 2147.483647MHz is 2147483647Hz, and the number 2147483647 is the largest value that can be represented by a 32bit signed integer. For RF frequency, the value should be stored as an unsigned integer, but for some reason the developers chose to store it in a signed integer. The moment you try to turn 1Hz higher than this value, it wraps around to the value -2147483648, and of course a negative frequency (at least in this context) is meaningless, so it pops up an error box saying that the frequency you tuned to is invalid, and then the software resets the frequency to 0Hz.
If the frequency value was instead stored in an unsigned 32bit integer (as it should be), it would then be able to store a maximum value of 4294967295, which would mean it could handle tuning an RTL-SDR (if any RTL-SDR ever had a tuner chip that supported it) up to the the frequency 4294.967295MHz. And if it used 64bit integer (or even double precision 64bit floating point) values, whether signed or unsigned, it could tune to any imaginable radio frequency (just like SDR# does, which makes SDR# much better software).

SDR# does not have a constant signal at the 0Hz mark. HDSDR always has a signal present at 0Hz (right in the middle of the RF band that the RTL-SDR is tuned to). Again, this makes SDR# the better software. There are no other glitches (like signal from the USB leaking into the LSB, like you might get if you had a problem with proper amplitude and phase in the I/Q signal). It seems that HDSDR simply introduces its own signal right at the 0Hz mark of the currently tuned-in RF band.

SDR# supports plugins for any possible features (whether at the RF stage, the IF stage, or the AF stage), via the use of DLL files. Plugins can even add new control panels to the left side of the GUI, so you can change settings for these new features. HDSDR does not support any plugins (or if it does, nothing even close to the features that can be accessed with SDR#'s plugins). There's no way to add additional control panels to the GUI of HDSDR.

There may be certain things that HDSDR can do that SDR# can't in its "vanilla" form, but most (if not all) of these can be added to SDR via plugins.

Overall SDR#, is WAY better than HDSDR.


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