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

Marcus Müller marcus.mueller at ettus.com
Thu Apr 23 14:27:15 EDT 2015

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
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.

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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