On 2 Jun 2014 18:14, "Thomas S. Knutsen" <la3...@gmail.com> wrote: > > The design of an VNA is an interesting thing. It requires quite high focus > on good RF practices and screening. > > In the range 0-3GHz there is no low cost devices avaible, not counting the > copper mountain tech boxes ( http://www.coppermountaintech.com/ ). Up to > 1.3GHz there is the DG8SAQ VNWA avaible from sdrkits, these can also be > used with mixers to extend the max frequency. The VNWA is an 2 detector VNA > that needs an S-parameter testset in order to get all the 4 S-parameters. > > An homebrew alternative would be fun to do, but its a lot of work, both in > getting reproduceable data from the hardware and in programming. Building > somthing that is connected to the PC simplifies things a lot. > Couplers and detectors are not the hardest thing to make, some small SMD > resistors, an balanced amplifier - detector and things should work to 6GHz > or higher with some care in the layout. > Signal generation is perhaps the hardest part, there is AFAIK no single > solution working from LF to high UHF, one cool alternative is to build an > generator with an YIG and mixing down, but that requires a lot of work to > get stable over the range 0-3GHz. In addition you need to keep the signal > from the generator out of the detector in order to keep the dynamic range > high. > If you are building your own VNA, I would build it with 4 detectors and the > posibility to re-configure those. It opens for several of the more advanced > calibration methods and eliminates some of the errors in the VNA. > > If I were to build something, I think I would base it on the N2PK design, > as there is documentation and programs avaible that makes for some part of > the work. > > There are some IC's avaible that do the detection of the power levels, > AD8302 comes to mind, the common denominator for these are that they don't > solve for the phase sign, and thereby are not true vector. In addition, > those I have tested don't behave to well with > > As an alternative, the HP8410 series are avaible here in the EU, sometimes > quite cheap
I assume you mean 8510. > The accuracy of the VNA is determined by the calkit used to calibrate it. > There is no way around obtaining an good calkit, learning how to use it > without destroying it, and do repeatable calibrations. The calkit is the > single most important part of the VNA. Do use an calkit for the connectors > you are going to measure, don't add adaptors or worse, coaxial cable after > the calibration plane. I had at one point an HP 8753A (3 GHz) VNA with a full S-parameter test set. It cost me about 50% of what my HP 85054B 18 GHz N calibration kit cost me and I think I got the 85054B cheap at about $3800. I do sell low cost calibration kits for N, SMA and X-band waveguide. Dave _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.