Luke, I am also doing a similar project in which i plan to use TR switch instead of circulator because of high TX/RX isolation (60/70 dB) as compared to isolators (20/30 dB).
Currently u are using power amplifier ZVE-8G which have output power ~=30 dBm so circulator will work as well but if u plan to go to higher power levels 60/70 dBm (kilo watts) range then T/R switch will be a better option. Otherwise if u just want a Radar test setup, then then simplest approach will be to use commonly available WiFi "Bi-Directional Amplifiers". Then have built-in limiters, power-amps, T/R-switches and LNA's etc. Limiter VLM-63-2W <http://www.minicircuits.com/pdfs/VLM-63-2W+.pdf> has Saturated output-power = +11.5 which is very w.r.t USRP max input power ( < -10 dBm ). Minicircuits ZFLM-252-1WL+ has Saturated-output power =0dBm, so in my opinion this will be a better option compared to VLM-63-2W (provided ur freq of operation is < 2.5G). Hope this helps. -Adeel On Sat, Jan 18, 2014 at 10:57 AM, Marcus D. Leech <mle...@ripnet.com> wrote: > 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>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> 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 >>> ra...@schmid.xxx >>> http://www.bclog.de/ >>> >>> >>> >>> >>> _______________________________________________ >>> USRP-users mailing list >>> usrp-us...@lists.ettus.com >>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>> >> >> >> > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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