[USRP-users] Fwd: B2x0 maximum receive power before device damage occurrs.

Urban Hakansson uhakansson at tecore.com
Thu Jul 16 15:38:02 EDT 2015


See my reply with follow up questions below. 

In case my first reply reached you, I apologize for sending my reply twice. I am never quite sure if I should 1) hit Reply button which enters "Marcus D. Leech" <mleech at ripnet.com> in the To: field or 2) hit Reply To All, which also enters "USRP-users at lists.ettus.com" <usrp-users at lists.ettus.com> in the Cc: field or swap the two addresses, so that "USRP-users at lists.ettus.com" <usrp-users at lists.ettus.com> ends up in the To: field and "Marcus D. Leech" <mleech at ripnet.com> ends up in the Cc: field or 3) just enter "USRP-users at lists.ettus.com" <usrp-users at lists.ettus.com> in the To: field and delete "Marcus D. Leech" <mleech at ripnet.com> all together from my reply. 


----- Original Message -----

From: "Urban Hakansson" <uhakansson at tecore.com> 
To: "Marcus D. Leech" <mleech at ripnet.com> 
Sent: Thursday, July 16, 2015 3:19:48 PM 
Subject: Re: [USRP-users] B2x0 maximum receive power before device damage occurrs. 


It seems to me that -15 dBm is a specific value chosen for B2x0 and is not a number specced across the entire product line where LNAs may be involved. 

Otherwise, why does the "Application Note Examples Provided with the USRP Hardware Drive" http://www.ettus.com/content/files/kb/application_note_uhd_examples.pdf state 
"care must be exercised to guarantee that the maximum input specification of the particular daughterboard is not exceeded. This level is -10 dBm for all daughterboards 
- other than BasicRX and LFRX" 

Why is not -15 dBm specced? The loopback Kit at http://www.ettus.com/product/details/LPBK-KIT contains 30 dB attenuators. Assuming max TX power is + 20 dBm, this would make sure max RX power is -10 dBm. But if the B2x0 can only handle -15 dBm the max input power level would be exceeded by 5dB (almost 3.2 times the specced max RX power) 

Here is an example of how higher received power levels could occurr. Let's say we have an indoor communication system running openBTS GSM850 MHz: A GSM MS is transmitting channel requests at +21 dBm. The BS RX gain set to 30 dB (just below the huger IIP3 15 dB drop on the B210 +8 dBm to -7dBm) to be able to detect far away mobiles throughout building(through doors, walls, floors etc.). Assume a MS is 10 meters from BS, which is not unrealistic in an indoor environment. Due to being that close to the BS I think I can assume free space loss model at frequency . At 10 meters (30 feet) the received power level would be in the range 0 to +0.23 dBm, neglecting antenna gain/attenuation, coaxial cable power loss etc. 

When I look at a data sheet I want to find out what the radio can actually handle before damage will occur, not what power level one could reasonbly be expect to receive. Are these max power ratings -10 dBm, or -15 dBm at least somewhat influenced by what Ettus thinks one could reasonbly expect to receive, rather than simply being based what the radio hardware is actually capable of handling? 

----- Original Message -----

From: "Marcus D. Leech via USRP-users" <usrp-users at lists.ettus.com> 
To: usrp-users at lists.ettus.com 
Sent: Thursday, July 16, 2015 1:17:16 PM 
Subject: Re: [USRP-users] B2x0 maximum receive power before device damage occurrs. 

On 07/16/2015 01:10 PM, Urban Hakansson via USRP-users wrote: 


RX power -15dBm max according to http://files.ettus.com/manual/page_usrp_b200.html 

Why is this the max Rx Power limit? I assume this is the max RX Power before device damage may occur. 

I looked at the schematics at http://files.ettus.com/schematics/b200/b200.pdf "B200 RF Interface", page 8 of 8. 

Following the RF path from the RX1 (J802) SMA port to the AD9361-RX here are the components I have identified, followed by the max input power ratings. 

1) U807: SKY13335−381LF, a pHEMT GaAs FET I/C switch that can handle up to +31 dBm 
2) U800: ? 
3) U801: SKY13317−373LF, a GaAs pHEMT single-pole, triple-throw (SP3T) antenna switch that can handle up to +30 dBm (1 Watts) input power. 
4) U802: BD3150L50100A00, a balanced to unbalanced transformer, that can handle up to 2 Watts ( +33 dBm ) 
5) AD9361-RX, and RFIC that can handle up to +2.5 dBm. 

When I look at the major components in the RX RF path, I cannot help but think the B2x0 should be able to handle up to +2.5 dBm ? Where does the -15 dBm max RX power limit come from? (There are a bunch of resistors, capacitors, an-15dBm is specced across the entire product line where LNAs may be involvedd inductors in between all these components, all of which I assume can handle whatever comes in.) 

Which component(s) in the RF path is it that will experience damage at this RX power level? 

Thanks for your consideration, 

Urban Hakansson 
Senior Software Engineer 
Tecore Networks 
Phone: +1 410 872 6315 
Fax: +1 410 872 6010 
Email: uhakansson at tecore.com 

-15dBm is specced across the entire product line where LNAs may be involved. Some devices may be able to tolerate much more than that, but keep in 
mind the RX chains on these devices are designed to be plugged into an antenna system, where a -15dBm power level would be considered exceedingly 

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