On 03/02/2012 07:34 PM, jsrdor wrote:
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
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
_______________________________________________
Discuss-gnuradio mailing list
Discuss-gnuradio@gnu.org
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
