EMRFD Message Archive 9174
Message Date From Subject 9174 2013-09-27 09:06:36 Ford Peterson Vector Network Analyzer
For years I’ve had interest in working with filters of various description. My interest is once again focused on filters and this time do a roofing filter. In all previous endeavors, I have not had access to a Network Analyzer and would find one to be invaluable tool at the bench. I currently use a zener diode spanked by a 555 timer and mixed with my signal generator to form a pattern of noise I can see on my spectrum analyzer. The process works great for tuning but I’m left in the dark about things like return loss, impedance matching, etc. I think the VNA would helpful.
VNA’s are HUGE dough. State of the art can be as high as six figures. Age worn units continue to approach 5 figures. Junque status even falls into the multiple 4 figures. These babies are well outside the scope of my budget for tinkering.
N2PK did a series for QEX many years ago. http://n2pk.com/
TAPR did a design that flourished for a while. http://www.tapr.org/kits_vna.html no longer available
TAPR claims ten tec picked up the device but has since been abandoned as I don’t see it on their website.
DG8SAQ has a SDR kit http://sdr-kits.net/VNWA3_Description.html and runs $735
VE3IVM has the N2PK version boards available on his website for $36. http://www.makarov.ca/vna.htm Software availability is questionable and the project is daunting assembly of trick components, which may prove difficult to procure (unobtainium). I haven’t evaluated the cost of procuring components in Q=1 volume but I’m guessing a complete build would approach $500 quickly.
My interest is basically HF filters. Measuring the DUT for insertion loss, matching, etc., is my goal. What is a good approach to this? Characterizing crystals, comparing responses, evaluating filters is not ‘new’ by any means. I’m hoping for finding a cognac solution to my brandy ideas within reach of my beer budget.
9175 2013-09-27 09:25:44 William Carver Re: Vector Network Analyzer Windows software for the N2PK, “MyVNA” by Dave Roberts G8KBB, is great.
That software also will run the DG8SAQ.
The N2PK has somewhat more dynamic range, useful for looking at filter
stopbands below 100 dB, but without optional frequency shifting hardware
it operates only to 60 MHz. I tested mine against NIST standards at a
university laboratory and was within 1%, and at 30 MHz it happened to be
a little closer to the NIST values than a $30K hp network analyzer on
The DG8SAQ goes up to UHF frequencies, dynamic range drops as you go
higher and higher, but not dramatically so. I've had software hangups,
my own problem of not concentrating on it long enough to slog through
the software setup, so have not used my DG8SAQ unit.
9176 2013-09-27 09:46:47 Ivan Makarov Re: Vector Network Analyzer Hi Ford,There is no unobtanium parts for the N2PK VNA, the parts list is documented and all parts can be purchased from two sources: Digikey and Minicitcuits. It will probably cost you around $250, not 500.The software is also can be obtained from two sources: G8KBB (site temporary down) or DG8SAQ
9177 2013-09-27 10:16:59 Dan Rae Re: Vector Network Analyzer 9178 2013-09-27 11:13:23 Ashhar Farhan Re: Vector Network Analyzer ford,do you really need a VECTOR analyzer? A scalar analyzer is far less complicated and it could work as well. I made one last year. It is just an Si570 (as a signal source, mixed with 120 MHz crystal controlled oscillator to provide signals from DC onwards) and an AD8307 power meter. Both are controlled by an Arduino that is in turn controlled by a PC based program that does the scans.I design and measure by filters, Q of the unknown inductors, amplifier gain, etc. I can also measure the VSWR of any port/antenna using a bridge. To measure the reactive part of the an impedance, I use a little trick. I add 100 pf capacitance in series with the DUT and measure the impedance again. The two measurements can be used to extract the reactive part!I would guess, even a homebrew receiver with fixed gain can be used for your purpose. A receiver meant for such work is called an Instrumentation receiver. It is a slower but more accurate than a spectrum analyzer.- farhan 9179 2013-09-27 11:47:07 Dale Hammer Re: Vector Network Analyzer
You might want to check out the activity on the Yahoo Group, PHSNA, which stands for “Poor Ham's Scalar Network Analyzer”. The url of the group is:
The project is being designed by Jim, N5IB, and Jerry, W5JH and built around an Arduino (Funduino) controller, the cheap AD9850 signal generator board found on Ebay for $5-6, and the W7ZOI power meter. As the text on the first page of the overview found in the files section of the group says:
“The Poor Ham’s Scalar Network Analyzer
What can you do with an Italian microcomputer, a Chinese signal generator, and some ham ingenuity, for about 50 bucks?”
A pcb is being put together for around $10 to go on top of the controller to hold the AD9850 signal generator.
9180 2013-09-27 12:21:12 William Carver Re: Vector Network Analyzer A complete description of an AC signal is frequency, amplitude and
phase. A SCALAR analyzer does not measure phase.
A VECTOR analyzer has amplitude AND phase. With phase you have a more
complete understanding of impedances. For example a scalar analyzer may
say that an impedance is "71 ohms" and that's all. A vector impedance
analyzer might say "50 + j50" (which also adds up to 71 ohms). But with
the vector knowledge you know that if you insert 50 ohms of capacitive
reactance in series you will cancel the "+j50" and the impedance will
become 50+j0, a perfect match.
9181 2013-09-27 12:28:41 William Carver Re: Vector Network Analyzer And....in the case of filters....knowing phase v.s. frequency the
software will show you time delay through the filter at each frequency.
So if you want to make so-called linear phase filters, that don't ring
regardless of width, a VNA is crucial.
9182 2013-09-27 15:28:33 Dan Mills Re: Vector Network Analyzer The AD8302 is made for a poor mans vna..
Use a resistive bridge at the input of the DUT with an 8302 connected
across it, this will with trivial maths give you impedance and phase
at the input, and a second 8302 across the DUT will give you the
transfer function and phase shift.
RF source can be any sweep generator that you happen to own, or a dds
of some sort.
There will probably be some small signal relays for scale factors and
calibration test values, and control could be whatever your favorite
That log amp has only 60dB range, but if an external phase detector
was acceptable then much better log amps are available (~100dB range).
Would there be any interest in such a board (0603 size parts in all
9183 2013-09-27 15:40:16 radioaustralia123 Re: [emrfd] Vector Network Analyzer Hi Farhan.Can you please describe the method (trick) that you use to measure the reactance.Regards,Roderick, vk3yc.