Hello Again, I think i know the answer to this question but I still hope i am not right. Setup N210 with SBX One of my colleagues plugged in TX/RX an external discone antenna with an RG58 cable playing around in the 3 Ghz band. Somehow he managed to get down to 400 Mhz where db increases partly because of the antenna gain and the reduced attenuation of the cable. After some experimentation the SBX stopped receiving signals. I changed antenas (LP0965) cables etc removed and reinstalled the SBX but it wont give me any signals. Usrp appears to work alright - leds flashing etc but i dont have another daughterboard to test it. SBX is flashing as well but no signal in TX/RX nor RX2. When tuning different frequencies there are no errors etc, but i receive just noise. I think that the down left corner of the SBX (as you see it- to the left of RX2) is getting hotter than it used to. That leads to the question, is the Db dead? Any way to fix it? Is there a limit in the input db when connecting an external antenna? I would guess an attenuator would be needed? Thanks alot, R.I.P SBX Jason -- View this message in context: http://old.nabble.com/SBX-Daughterboard-dead--tp33... Sent from the GnuRadio mailing list archive at Nabble.com.
on 2012-03-03 01:35
on 2012-03-03 02:25
On 03/02/2012 07:34 PM, jsrdor wrote: > receiving signals. I changed antenas (LP0965) cables etc removed and > limit in the input db when connecting an external antenna? I would guess an > attenuator would be needed? > > Thanks alot, > R.I.P SBX > > Jason There are several mechanisms that can cause a low-noise-amplifier to fail. The SBX has an LNA as its first stage. The most common are: o ESD -- a static discharge, lightning discharge close enough, etc Sometimes, you can get static build-up on antenna elements when there are high winds with very dry snow. Sometimes you can ameliorate this with an in-line gas-discharge surge arrestor. Sometimes, a large-valued carbon resistor in shunt (grounded) can bleed-off any static charges before they reach dangerous levels. This method has the disadvantage that it will negatively affect the noise figure of the LNA and reduce sensitivity somewhat. Sometimes, somebody just touching the antenna at the wrong time, after having walked across the carpet, can cause significant gate damage on the GaAsFET transistors in an LNA. It's a tradeoff between robustness, and ultimate sensitivity. o High EM levels. If you operate at a site with high-level transmitters, even ones that are out-of-band, you can get coupled EM levels "seen" at the LNA beyond its safe operating envelope. Keep in mind that the SBX, as designed is "broad as a barn door", so the LNA isn't particularly frequency-dependant. If the integrated energy from all sources within its "window" (probably from 100MHz up to 10Ghz or more) is more than about -10dBm, you run the risk of damaging the LNA. When professionals deploy sensitive receivers at sites with high RF levels, they usually place a narrowband low-loss filter in front of the LNA. This has several useful properties, including keeping the bandwidth-integrated RF levels below that which could cause damage, and also keeps the LNA within its linear operating envelope, even if levels aren't high enough to cause damage, they can be high enough to cause non-linear behaviour, leading to intermodulation products. What this means is that deploying a broadband receiver at such a site is usually not done. -- Marcus Leech Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org
on 2012-03-03 15:20
Thank you for your reply. This is what happens when software developers touch devices such as usrps. Since i have no intention to fry the tvrx daughterboard we are planning to use now , will the following setup be enought? WideBand Rx only 300-3Ghz antenna, grounded through its base surge arrestor usrp As i am at least ignorant in rf , would i need an attenuator to reduce the incoming signal? Do i need a second LNA infront of the one thats on the daughteboard? Apart from that, since its more of a computer lab than rf lab, what instrumentation would you consider as necessary in order to measure currents voltages and other signal parameters to avoid another daughterboard-fried fiasco? Thank you for your patience. Jason -- View this message in context: http://old.nabble.com/SBX-Daughterboard-dead--tp33... Sent from the GnuRadio mailing list archive at Nabble.com.