On 01/18/2014 12:31 AM, Luke Hough wrote:
Get your tomatoes ready, I have attached a proposed block diagram and
possible component specs. I have not actually purchased the limiter or
the circulator, but I do have the power amp and antenna. The power amp
is a ZVE-8G <http://www.minicircuits.com/pdfs/ZVE-8G+.pdf>. I was
looking at the VLM-63-2W
<http://www.minicircuits.com/pdfs/VLM-63-2W+.pdf> limiter and possibly
a JCC3300T3800S10 circulator ( hoping for a sample ).
The numbers on the block diagram don't exactly match the specs shown.
The numbers are closer to the table values. I have also not taken
insertion losses into account.
Looking at the the B200 schematic
<http://files.ettus.com/schematics/b200/b200.pdf>, I was wondering if
during transmit I might set switch U807 to OUT2 while U805 is OUT1.
Then on receive switch U807 back to OUT1. Basically, during transmit
both RX1 and TX1 are set to use the TXRX1 antenna, but during receive,
RX1 is switched back to antenna RX1. Can the switch be made in less
than 1µs ?
I don't think the switch can be made in under 1us from the host. With
suitable mucking-about on the FPGA you might be able to come up with a
suitable
scheme that amounts to half-duplex switching.
In the ordinary scheme of things the ATR state machine will switch the
RX chain to the RX2 port during transmit. If this could be done fast
enough, that
would work fine, and you'd just put a terminator on the RX2 port in
half-duplex mode.
You could consider a scheme where some external machinery is helping
with switching and "scheduling" things. Such machinery would perhaps
arrange
for a high-isolation path for RX during your TX cycle.
This kind of problem is pretty standard in radar designs, so there are
probably good solutions out there that could be hybridized to interface to
an SDR approach. But radar isn't my particular expertise.
On Fri, Jan 17, 2014 at 8:45 AM, Marcus D. Leech <mle...@ripnet.com
<mailto:mle...@ripnet.com>> wrote:
On 01/17/2014 09:37 AM, Luke Hough wrote:
As a hobby project, I am developing an active radar. I
am primarily familiar with simulation and signal processing, but
not so much with RF hardware. So this is a learning opportunity.
I do need to Tx/Rx on the same frequency either through a shared
antenna or independent. I have constructed an antenna and
measured the S11 parameter to be -11dB over a 300MHz band around
the resonnant frequency.
I was hoping to avoid a GPIO controlled switch. I don't think the
B200 has any GPIO capability, so another controller device would
be required. Would it be possible to control one of the skyworks
switches on the frontend of the B200 in combination with a
circulator and a limiter? Basically open the RX1 channel and keep
the TXRX1 channel switched to the TX chain.
-Luke
Well, if this is a half-duplex application, the USRP already does
switching. Whenever the unit is transmitting, the RX is connected
to the the RX port on
the box.
Why don't you draw a diagram of what your intended setup is, and
we can through metaphoric tomatoes at it, as it were.
On Fri, Jan 17, 2014 at 1:34 AM, Ralph A. Schmid, dk5ras
<ra...@schmid.xxx <mailto:ra...@schmid.xxx>> wrote:
Hi,
> +7dBm is *very* risky.
Hmmm...3µs are not very long...but it is a risk, agreed.
> If you're feeding a common antenna, the usual approach is
to use a
> diplexer/duplexer arrangement to isolate the TX frequency
from the RX
> frequency (assuming different-frequency full-duplex).
I guess he uses the same frequency for TX and RX - usage of an
isolator/circulator makes me think so :) But this only works
for a certain
degree and requires no reflected power at all (that means,
perfect impedance
match) at the antenna port.
Depending on the needed timing it may be an option
constructing a PIN diode
RX/TX switch, operated from some GPIO.
> In fixed-purpose applications, like WiFi, where a common
antenna is used,
> there's a duplexor, usually implemented in some kind of ceramic
> resonator technology that has bandpass and band-stop
components to it,
> to keep the RX isolated very deeply.
This will not work for WiFi, as this transmits and receives
on the same
frequency, they usually apply the above mentioned diode
method to rapidly
switch between RX and TX path.
Those ceramic diplexers are common for cellphones and some
digital LMR
systems, as they have the need for full duplex on different
frequencies.
> --
> Marcus Leech
> Principal Investigator
> Shirleys Bay Radio Astronomy Consortium
> http://www.sbrac.org
Ralph.
--
Ralph A. Schmid
Mondstr. 10
90762 Fürth
+49-171-3631223 <tel:%2B49-171-3631223>
ra...@schmid.xxx <mailto:ra...@schmid.xxx>
http://www.bclog.de/
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