[USRP-users] USRP Input Protection

Marcus Müller marcus.mueller at ettus.com
Thu Mar 3 07:40:53 EST 2016


Dear Jan,

Well, in that case, a bandpass that only lets through your signal of
interest surely sounds the most "high quality" solution, but it would
limit your flexibility, as you would have to change that filter
depending on what frequency you want to receive.

Protection diodes for high bandwidths / Gigahertz frequencies and low
powers are inherently hard to get -- low powers imply thin semiconductor
interfaces, thin semiconductor interfaces imply small separation between
positive and negative charges, which implies high capacitance, which
implies low-pass characteristics if inserted between signal line and ground.

This quickly boils down to a matter of money: Of course you could "just"
use attenuators and a properly cooled LNA close to the antenna...

Best regards,
Marcus

On 03/03/2016 10:37 AM, Jan Safar via USRP-users wrote:
>
> Hi Marcus,
>
>  
>
> Thank you for your reply. Unfortunately a notch filter does not seem
> to be a practical proposition for our application. There are normally
> more than one frequency that could cause problems and different
> frequencies may be in use at different locations (our terminals are
> mobile).
>
>  
>
> Jan
>
>  
>
> *From:*USRP-users [mailto:usrp-users-bounces at lists.ettus.com] *On
> Behalf Of *Marcus D. Leech via USRP-users
> *Sent:* 02 March 2016 16:12
> *To:* usrp-users at lists.ettus.com
> *Subject:* Re: [USRP-users] USRP Input Protection
>
>  
>
> On 03/02/2016 05:19 AM, Jan Safar via USRP-users wrote:
>
>     Hello,
>
>      
>
>     We are looking to use the E310 for some over-the-air tests in the
>     VHF band. In our application we need to install our antennas
>     within a few meters (say 3 to 5 m) of another VHF system antenna.
>     The transmitter power of the co-located unit can be up to 25 W,
>     antennas for both systems are typically 0 dBd omnidirectional. The
>     interfering transmissions are intermittent and can be as close as
>     on the adjacent channel. The stated maximum input power for all
>     USRPs is -15 dBm; for the E310 and at VHF, the limit is probably
>     somewhat higher but Ettus haven’t been able to provide an exact
>     figure.
>
>      
>
>     I’m wondering if anyone can advise on how to protect the USRP
>     input in this scenario?
>
>      
>
>     I looked into the availability of suitable limiters. Mini Circuits
>     don’t seem to have any with output power below 0 dBm. I found the
>     following two models from Herotek and RF-LAMBDA which limit at -10
>     dBm, but they are quite costly (~£600 excl. VAT) and the lead time
>     is 6 to 10 weeks. Does anyone know of a better solution?
>
>      
>
>     http://www.herotek.com/datasheets/pdf/Pin_Diode_Very_Low_Leakage_Limiters_10MHz-18GHz_LL_Series.pdf
>
>     http://www.rflambda.com/pdf/limiter/RFAPLT01M05M.pdf
>
>      
>
>     Thanks & regards,
>
>     Jan
>
> You could install a notch filter for the other VHF frequency that is
> most likely to cause you issues.
>
>
>
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