Hi Jim, Exactly where is the hardware problem that makes it impossible to transmit and receive simultaneously? The schematic in the fourth QEX article looks like duplex is possible. There are separate QSE and QSD, TX and RX lines are separate. You would have to disconnect pins 9 and 7 on the QSE and QSD, so you could hook in your device under test (DUT). I suspect leaving the BPF on the transmitter would be necessary to insure that harmonics aren't a problem. This doesn't seem like much of a modification to the hardware. You could just lift the legs on pins 9 and 7 on U1, the QSD, to connect the input of the VNA there. You don't need two receivers like the old VNAs used because you can record the reference signal, and do the mathematics in software. Software calibration should be able to take care of the phase and magnitude response of the band pass filter etc.
What am I missing? 73, Rob Jim Lux wrote: > At 09:08 PM 5/13/2006, Rob Frohne wrote: >> Hi Everyone, >> >> It appears to me that it would be principally only a little software to >> turn the SDR-1000 into a quality Vector Network Analyzer similar to the >> N2PK VNA >> >> http://users.adelphia.net/~n2pk/VNA/VNAarch.html >> >> only using the 11 KHz IF. I have got to build my homemade SDR-1000 >> before I can try this, but some of you with one already available to >> play with should try it. It requires running the transmitter at low >> power (probably using one watt or less and a step attenuator would be a >> good idea), and receiving the signal from a reflection bridge (for S11 >> or S22) or through a network (for S12 or S21). You will need to have a >> known 50 ohm load, and a good short and open to calibrate the >> measurements. I suggest saving the magnitude and phase of the received >> signal to a file so you can massage and display it in Scilab or Octave. >> I would be happy to offer help and suggestions and Scilab or Octave help >> to anyone interested in this project. > > > The practical problem with this is that the SDR is wired up so that > you can't transmit and receive at the same time, and that it has no > good way to generate a clean transmit signal without modulation. The > audio path from DAC on the sound card through to the QSE is AC > coupled, so you can't just set I to +1, Q to zero, and feed through > the transmit LO. (and there are good reasons why you really don't want > to work with a sound card at low frequencies anyway). You CAN use the > SDR1000 as a measurement receiver, if you have another oscillator to > use as a source. For instance, you could get a DDS eval board from > Analog devices and lock it to the same oscillator. This raises some > practical problems with keeping the phase relationship of the LO in > the SDR1000 matched to your external source. In order to put the > measurement signal at 11 kHz, also, the receiver LO has to be 11 kHz > away from the signal that you are probing with. > > > All doable, not even very tricky in terms of hardware. > > > James Lux, P.E. > Spacecraft Radio Frequency Subsystems Group > Flight Communications Systems Section > Jet Propulsion Laboratory, Mail Stop 161-213 > 4800 Oak Grove Drive > Pasadena CA 91109 > tel: (818)354-2075 > fax: (818)393-6875 > > -- Rob Frohne, Ph.D., P.E. E.F. Cross School of Engineering Walla Walla College 100 SW 4th Street College Place, WA 99324 (509) 527-2075 http://www.wwc.edu/~frohro -------------- next part -------------- A non-text attachment was scrubbed... Name: frohro.vcf Type: text/x-vcard Size: 318 bytes Desc: not available Url : http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/attachments/20060514/5aeb0478/frohro.vcf _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com
