[USRP-users] B200 Broadcast FM and other signals on airband

Marcus D. Leech mleech at ripnet.com
Thu Apr 23 18:14:29 EDT 2015


On 04/23/2015 04:43 PM, Paul B via USRP-users wrote:
> Hi Marcus,
> Thank you for your advice and the explanation of the HDSDR/UHD 
> incompatability.
> Regarding the tuning, i believe that my centre frequency is 
> 122.590MHz, and i can tune to +/- 8MHz either side of that. I'm not 
> completely sure though, as i'm still rather new to the whole SDR 
> scene, and the B200 is my first major SDR since using the RTL Dongles.
> I've managed to, i think, narrow down the problem to the computer i'm 
> using. I tried the B200 on my partners laptop, plugging it in, 
> installing Balints ExtIO package, zadig driver and libusb0 and it 
> seemed to work fine. No ghost signals at all. Admittedly it was using 
> USB 2, but even when using USB 2 on my main computer, i was still 
> getting ghost signals.
> The computer i use the B200 with is running the USB 3.0 Intel 
> eXtensible host controller, which i believe is compatible with the 
> B200 series, and i've done a complete fresh install of Windows 8.1, 
> installing Balints package, and using the zadig driver only, so i 
> can't see the error being within Windows.
> I've also noticed they appear even with rather low gain, but only 
> within 110MHz -- 135MHz region. I've not seen any signals above that, 
> that shouldn't be there.
> Paul
You may, then, not be dealing with intermodulation or other 
non-linearity products at all then, but rather, spurs produced by your 
computer,
   and carried along the USB cable, or just plain radiated by your computer.


> *From:* Marcus Müllervia USRP-users <mailto:usrp-users at lists.ettus.com>
> *Sent:* Thursday, April 23, 2015 7:27 PM
> *To:* usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>
> *Subject:* Re: [USRP-users] B200 Broadcast FM and other signals on airband
> Hi Paul,
>
> sorry to hear you're still in trouble; I'll try my best to help you, 
> though HDSDR and Windows are really not my forte.
> Balint is currently not in office, so I can only give you my piece of 
> insight:
>
> first of all, I'm a bit confused; your settings say you've got a 
> sampling rate of 16MS/s, and your center frequency is 120.8MHz, so 
> your observable spectrum should be 112.8MHz - 128.8MHz. However, 
> HDSDR's waterfall shows different frequency limits -- maybe there's 
> some sweeping or caching, or is maybe my definition of tuning and LO 
> frequency different from that of HDSDR?
>
> I can, however, explain the incompatibility warning: HDSDR is linked 
> against a specific version of UHD, and can only work with exactly that 
> version of the UHD.dll, which is why Balint packages it with the whole 
> Extio framework. Installing a more modern version of UHD system-wide 
> doesn't help you, here, since HDSDR continues to use the packaged 
> UHD.dll. Thus, after installation of UHD and flashing of the images, 
> you've got "modern" FPGA and firmware on your B200, and "old" UHD 
> talking to the device -- which is what the error complains about.
>
> Regarding your ghost signals: Those are interesting, though, if I read 
> that correctly, they are at -82dB, which is relatively little, 
> considering your 27dB gain. Can you try to disable AGC? If that's not 
> enough, my first guess would be to play around with gain: Too much 
> gain leads to spectral images[1], too little gain together with AGC 
> might over-emphasize spurs.
>
> Greetings,
> Marcus
>
> [1] If you have a strong signal, and high gain, your amplifier, being 
> composed of nothing more than transistors, goes into saturation; the 
> transmission function then is no longer practically output = input * 
> gain ($y(t) = a x(t)$), but gets a quadratic term ($y(t) = ax(t) - 
> bx^2(t)$); now using the some properties of the trigonometric 
> functions, in this case $\sin \alpha \; \sin \beta = 
> \frac{1}{2}\left(\cos (\alpha-\beta) - \cos (\alpha+\beta)\right)$ 
> applied to an input signal $x(t) = \sin(f t)$, you'll notice that for 
> $x^2 = \sin^2(ft)= \sin(ft)\sin(ft) = \frac12 
> \left(\cos(ft-ft)-\cos(ft+ft)\right)$ you see a signal with twice the 
> input frequency. In fact, semiconductor mixers are usually based on 
> that principle, and thus are basically amplifiers driven out of spec :)
>
>
> On 04/23/2015 01:07 AM, Paul B via USRP-users wrote:
>> Hi guys,
>> My troubles seem to be at no end at the moment!
>> After reinstalling my Windows 8.1 due to a hard drive change, i've 
>> been having trouble with my B200 on HDSDR using Balints 
>> ExtIO_USRP+FCD+RTL2832U + BorIP-1.6 BETA 3.
>> Before re-installing Windows 8.1, i had no issues at all, but since 
>> re-installing, i've been getting what seem like ghost signals on 
>> airband. They appear from about 114MHz through to 128MHz. They appear 
>> to be broadcast FM, Trunking and MotoTRBO signals, though when i move 
>> the frequency slider, they vanish, only to reappear when i move 
>> further along the band.
>> I've included a picture of the problem, and my settings in ExtIO:
>> https://www.dropbox.com/s/o6u3oe83ch4gm9o/Signals.jpg?dl=0
>> and my settings:
>> https://www.dropbox.com/s/082d17pi0osnw36/Settings.jpg?dl=0
>> I'm running the B200 over USB 3, and it's using 003.007.001, which 
>> unfortunately, i can't seem to upgrade due to getting an 
>> incompatability warning when trying to use HDSDR after upgrading.
>> I've installed the B200 USB Driver, and in Device Manager, my device 
>> shows up as USRP B200.
>> Does anyone have any idea what could be causing this problem, and any 
>> possible solution?
>> Thanks for any help,
>> Paul
>>
>>
>> _______________________________________________
>> USRP-users mailing list
>> USRP-users at lists.ettus.com
>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>
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