IF Crystal Filters - NDK Type numbering decoded?

I wanted to know more about the crystal fitlers used in the Tait Orca handhelds ie 45E12AA and 45E15AD. 

I could not find the specifcations for these exact filters. However, after looking at some NDK datasheets I believe these crsytal filter are as follows:

 45 - denotes the nominal center frequency

E - couldn't work the meaning out. Perhazps E means 2 poles and EE means 4 poles?

12/15 - bandwidth inkHz

A  - finalises model number

A/D at the end denotes the center frequency.

 

So, 45E12AA apears to be a 45.1MHz 2 pole crystal filter (seaching for 45E12A did not return a model datasheet, perhaps a special Tait specification?)

and 45E15AD is a 45.1MHz 2 pole crystal filter (search for 45E15A to see the model datasheet)

 

Seems strange that the center frequency is not denoted by a consistent letter.  But as expected when looking for relatively old datasheets, not everything is on the web. 

Best to keep the crystal used to mix the IF down to 455kHz with the filters so you can derive the center frequency if no data can be found.

 

73's

Richard

23cm FM Receiver - Musings

 All the assemblies for a 23cm FM receiver are coming together i.e.

Once the 1296MHz signal is mixed down to a nominal 446MHz I still have not decided on my approach.

 I am leaning towards the last option, the RDA5807.

I have a number of Tait UHF Orca handheld boards which I could either use as donors for the necessary filters and IC's, or as a working IF strip. These boards probably have faults but after cutting to size I have enough boards to be able to get one working. With a bit of work I could also use the synthesizer to generate the approximate 400MHz signal needed to mix down to the 45MHz IF strip. But this all becomes a bigger project than I had contemplated and the risk is not so much technical as motivational. Will I ever get it finished?

The simplest, most expedient, lowest risk is to secure a working handheld inside the case and move forward. But that does not sit comfortably with me.

The left field final option is the RDA5807. While walking back and forth to the workshop it dawned on me that this single chip FM Receiver would be a real time saver if it worked. I have some experience with these and the risk relates to how well it will work with a narrow band FM signal. If I can get sufficient recovered audio with acceptable noise levels this will be the quickest, most expedient way forward. 

Time for some testing.

73's

Richard

Brake Cleaner used as a PCB Flux Cleaner

The usual safety disclaimers apply. Don't drink the stuff like some loopy folk do with hand sanitizer
( good one Mr President), don't inhale (didn't a past President make some claim concerning pot?) and watch the naked flames. It's your shack, your health and your life. Take it seriously because it is totally your responsibility.

In my ham projects it's ok to take shortcuts. You should never try this on a commercial product you sell. You have been warned!

I haven't been satisfied with methylated spirits as a flux cleaner for some time. And isopropyl alcohol is expensive and not that effective in my experience. I was ready buy proper flux cleaner like that I use in my own business but somewhere in my internet browsing I came across reference to using brake cleaner as a flux cleaner. Never shy of testing such claims I thought I'd give it a whirl.

Dropping into the helpful people at Repco, and being up-sold by and extra $1.20 to their premium brake cleaner costing $8.29, I came home and trialed the brake cleaner.

 

Even on my personal projects I'd only use this in a pinch. But it works out to be substantially cheaper than proper flux cleaner and is readily available. Not too many of us have an electronics outlet on our doorstep open on a weekend.  But the long term consequences on the board are unknown and it leaves more of a film on the board surface than proper flux cleaner. Other brands might be different though.

I devised a test for three flux residues :

1. Rosin from a homemade flux (rosin dissolved in methylated spirits and wiped on with a cotton wool tip or splashed on the solder reel and allowed to dry on the solder wire - why you would bother with the crap some Chinese sellers pass off as solder is beyond me, but it might make it usable)
2. residue from Multicore solder
3. the flux unused from a cheap syringe type product, again from China (works for me though)

Fluxes 1 and 3 are the result of trying to make that cheap solder flow nicely over the joint. Personally, I keep it on hand to give away to people to educate them on why saving cents can ruin your day. But enough China bashing for one day!

A quick test board was prepared using a rejected board I had to hand and is shown below:

 

The rosin flux and Mulitcore flux have proved difficult to remove in the past. The cheap eBay flux can be effective but is impossible to apply in small amounts so it is always messy.

Three brief spurts with the brake cleaner and I had this:

Rosin residue completely gone!

Multicore residue almost gone.

Cheap syringe flux partially gone.

I was starting to get excited now. A tiresome chore solved so easily. A quick dab of brake cleaner on a cotton wool bud rubbed on the remaining residues and the resulting board:

 

 

The soldermask did not appear to suffer and the result was a spotless board. 

 

In conclusion it appears brake cleaner does the job very well in the short term. The long term consequences are unknown and that needs to be considered. How comfortable are you that the construction effort today might not last?

 

73's

Richard

23CM 500mW Amplifier AH101 - duplicated with revised matching

Since I have a lot of these boards I used one to make a test fixture. OSL calibration of the VNA right at the device legs proved feasible since I have some 50ohm RF chip resistors. Fortunately, the measured S parameters were broadly consistent with the tabulated S parameters in the datasheet.

With the device soldered onto hte board I switched between the calibration at the device legs and the calibration at the SMA sockets. This allowed me to infer the electrical length and impedance of the connecting micro-strips, and any strays.The length and impedance were close to the expected value so I was able to confidently rework the matching. 

As you can see below I was able to use a single inductor at the SMA end of the board for the input. I inferred that a microstrip with slightly higher impedance would give a better match. The crazy cutter went mad and the result was just a few dB improvement to a return loss of 21dB. I overshot the mark!

Matching for the output network was placed at the device end of the output microstrip. The capacitor to ground was meant ot be 1.5pF, but I found the slightly smaller 1pF capacitor gave me a better result. Return loss of 24dB was achieved.

That makes two successful amplifier boards and a great learning exercise. I am a lot more confident with the Smith Chart now and RFSim99.  I still have a heap of the AH101 devices so one day I would like to try 4 in parallel using Wilkinson dividers.

 

 

That might have been the end of the matter but I noticed the claimed specifications in the datasheet were not supported by the S parameters. Which should be embarrassing to a manufacturer!

To be fair, this is a discontinued part and the original manufacturer has changed hands several time. So let's look at the TQP7M9102. This is Qorvo's suggested replacement. What we find is a table of S parameters in the datasheet explicitly qualified by: 

"Test Conditions: V CC  = +5 V, I CQ  = 135 mA, Temp. = +25 °C, unmatched 50 Ohm system, reference plane at device leads"

The S parameter file downloaded states:

"The data is for the unmatched device in a 50 Ohm system, 2-port file de-embedded to the device leads."

So my expectation is this should be the same dataset. The best I can say is they are broadly similar. I drew this to Qorvo's attention. The response simply acknowledged the error. With that attitude I can no longer consider Qorvo for commercial applications which means it is unlikely any of their products will ever find a way into my ham projects. Once those AH101's are gone that's it!

 

73's

23CM 500mW Amplifier AH101

 I have not determined why the SXB4089Z input matching was out. After lots of maths and component substitution I suspect the mmic itself is damaged. I will swap it out soon to confirm this.

In the meantime I tested an AH101 device. This was made awkward because the test board was set out with matching networks for the AH1, which are quite different. With some hacking I got it to work. Input return loss was initially 17db but I was able to tune that to under 30dB with a little foil gimmick capacitor. Output return loss was 17db. Gain was 13dB.

 

73's

23cm 500mW Amplifier SXB4089Z

 After calming down over JLPCB's appalling process for dealing with their errors, which is to deny everything and obfuscate to the point I gave up, I populated one of the test boards for the SXB4089Z. My earlier posts here, here and here set out the steps I took to end up with the following:

 

Expected Results

My results did not quite match this. Using the nanoVNA to measure the input and output ports, adjust for the attenuation used and then combining everything into a single file for RFSIM99 to read showed that the output matching was nearly spot on (I will need to change the 1.2pF output capacitor to 1.0pF) but the input matching was all over the place. I repeated the measurements and got the same result.

Actual Results

I am confident that once the input reflections are resolved that it will only take a small tweak to get this working well.

73's

Richard

New part - SMA3109 MMIC

Something different....

I stumble across new parts from time to time that set a price / performance benchmark. So I thought it would be worth alerting readers to these parts. Here is the inaugural post on this subject.

The new benchmark in my shack for general purpose mmics is the SMA3109. It happens to be the cheapest mmic that LCSC stock. I had wanted to use this commercially but the initial lack of S parameters meant I passed it over in favor of another device. That decision might get revisited.

Despite the low price the SMA3109 offers outstanding performance from VHF through to 4GHz. Compare it with other low cost mmics such as the BGM1013 and you will see why I rate it so highly.

When I evaluate a MMIC I consider:

1. stability
2. input and output return loss
3. noise figure at intended frequency
4. gain
5. ease of hand soldering
   

This device is ticking all my boxes but the NF of 4dB rules out demanding low noise applications.

I suspect it is useful outside these ranges but the S parameters kindly supplied by Onsemi technical only cover 100MHz to 4GHz.

Band	Gain	S11	S22
2m	23dB	-28dB	-13dB
70cm	24dB	-24dB	-16dB
23cm	24dB	-38dB	-16dB
13cm	23dB	-15dB	-14dB
9cm	21dB	-11dB	-17dB

The input match on 23cm is outstanding and I will definitely use this device in my 23cm projects where filters are connected to the input. For driving filters I would consider at least a 3-6dB pad to provide a better source termination. Being very stable across the entire frequency range matching if needed is straightforward.

Where linearity is important I would budget to get around 0dBm out of the device.

My hunch is that the feedback within the device makes it useful below 100MHz except for the output becoming a poor match to 50 ohms.

The device appears to be very useful from 2m through to 9cm and represents terrific value for signal outputs up to the Po(1dB) level of +4dBm. Definitely worth a look at US 11cents each!

73's

Chinese Solder - An update

After months of using different solders I have updated my findings. Only 2 of the Chinese sourced solders I tested are a realistic alternative to the comparatively expensive Multicore solder. Thoughts? Opinions? Comments welcome.

73's

23cm Amplifier Test Boards are almost here

As many readers will know, the current Covid19 pandemic has significantly increased the time it takes for air freight to be received. But the test boards have all been made and are presently in Singapore.

New Part - VHF Low Noise Amplifier MXDLN02C

So I was browsing for a high speed op amp and I came across this wrongly catalogued part at LCSC.COM. I am now testing it for a commercial project but it could have uses in ham projects.

But there are some caveats that go with a US$0.05 part:

1. The datasheet could be better
2. This is not a strong signal handling part
3. No details exist on how best NF is obtained

The MXDLN02C is meant to be used as a pre-amp for FM broadcast receivers. The datasheet suggests the noise figure is under 1.5dB and gain is above 20dB from 50MHz to 150MHz with good stability. I wrote to Maxscend as part of the commercial project requesting the S parameters in a table format. The response suggests Maxscend will never be one of my preferred suppliers.

So, in Ham spirit because this is a really cheap part, I simply hooked up the input to the nanoVNA and measured S11. Now I don't claim the nanoVNA is the last word in measurement, or that my test board was perfect. But the results I got suggest Maxscend was way off the mark.

From the Datasheet (2.85V) :

From measurement (also 50-150MHz) (3.3V):

I'm not dwelling on the possible reasons why there is such a disparity. What is important that based on my measured S parameters matching networks were easily calculated in RFSiim99. So, a few minutes of tweaking and I had a return loss of -30dB on the input at 6m and about 20dB of gain.

A similar story on the output port.

Summary:

It's ridiculously cheap.

Useful for 6m and 2m in non-demanding front-ends, still has +13dB of gain at 70cm.

This is not a MMIC so matching to 50 ohms, while easy, will be required

Like a MMIC no biasing calculations needed

Stability concerns limit HF applications

I always advocate using what is in your junkbox. But if you had to buy a device for low level amplification at 6m or 2m then this is what I would suggest.

73's

23cm Amplifier SBB2088Z - More Navel Gazing

It occurred to me some time after I had prepared the PCB layout that I had left out the small input "stability" resistor in the transmission line version. Since the minimum resistance needed to ensure stability was 1 ohm I wasn't too concerned. Just putting 1 ohm into the actual circuit wouldn't change much would it?

Well, it turns out it did.I started from scratch and derived a circuit with a 1 ohm resistor and transmission line matching. I found that the capacitors adjacent to the 50 ohm ports were reduced by around 50%. And the transmission lines were around 20% different in length. Now 1 ohm is a really small amount of resistance and these are significant changes.

So I inserted a 1 ohm resistor into the original transmission line version and compared the two.

While there is a small variation in gain, all versions will be substantially the same in practice. Should I be concerned that 1 ohm made such a difference?

I put the difference circuits giving almost the same result as comforting in that the matching will be smooth and relatively insensitive. I look forward to receiving the boards to find out if this is indeed the case.

73's
Richard

23cm Amplifier Musings - SBB2089Z

While I got myself organized to order PCB's for testing the SXB4089 mentioned in the last few posts, I thought it would be worth looking at some of the other devices. The first of these I turned my attention to was the SBB2089Z, a 100mW device.

What I found, if you study the large image below, was that the bare device was acceptable for 6m through 70cm. However, at 23cm the output was not as good a match to 50 ohms as I had hoped (RL= 8dB ).

As expected, matching to 50 ohms at 23cm introduces loss of gain at other frequencies. There was also some slight chance of instability hence the series resistor in the second version to prevent these.

I'm going to get two boards fabricated for testing: one for 6-70cm using just the MMIC, and one for 23cm using transmission lines.


73's
Richard

23cm Amplifier - PCB Artwork

After plugging the various parameters into a micro strip calculator I had the line length and width needed for matching. The draft of the PCB looks like this :

If you have this device and would like the artwork in PDF format just ask.

73's

23cm Amplifier Development using RFSim99 - Part 2

Following on from Part 1, here is how I plan to replace the matching netowrks with microstrip.

Step 1 : Input network

1. Remove the LC components on the input network.
2. Press Simulate and read off input impedance of 4.96R+j3.93R
   
   
3. We know that one full revolution of the Smith Chart is 23cm/2. By inspection we can see that we need a transmission line around 62 degrees (135 degrees/2)
   
   
    
4. Insert a 4cm transmission line (62degrees electrical length at 1296MHz) and press Simulate
   
5. Not quite long enough. Trial and error guesswork gives us 4.4cm. The alternative to this inspection approach is to use a program like Iowa Hills Smith Chart which I prefer. But I'll stay on-topic.
6.  Now we need to move along the arc towards the origin with a series capacitor. I started with 6pF, since it was there on the output network. There was little movement so I halved it each iteration. I found 0.82pF was the closest standard value. You can buy these!
   
   
   

Step 2 : Output network.

1.  Repeat along the lines in Step 1. It is a nice coincidence that the output transmission line is the same length as the input line. Since we hit the arc running towards the origin a littel closer to the origin than the input network did, we can use less reactacne. I guessed 1pf. Turns out 1.2pF is better.

Results

We still have stability and good matching. Gain is  unchanged at 18dB. But now we have two standard value capacitors and some PCB drafting to do.

I'll post about the artwork next.

23cm Amplifier Development using RFSim99 - Part 1

I have an assortment of MMIC's recovered from a cellular base station. Since an engineer previously selected these as suitable for a device where linearity matters I thought they would be good contenders for UHF and microwave projects. The SXB4089, a 500mW output device, looked interesting for a 23cm transmitter so I decided to document my approach. This post concerns the steps leading up to  generating PCB artwork for a test board.

Step 1 : Set up RFSim99

1. Load the S2P file into a unmatched schematic and press Simulate
2. If not auto-scaled set the lower frequency to 50MHz via the Graph Limit Setup command
3. Repeat for the upper frequency of 6.05GHz
4.  Start with 500 points and reduce until we get something close to 1296Mhz. 497 is just right

Already we note that matching will be needed on input and output where the return loss is too high (S11=-0.84dB, S22= -2.46dB)

Step 2 : Check for Instability

1. Switch to the Smith chart. S11 and S22 plots show the unstatble region is outside the smith chart boundary
2. With S11 sweep the frequency by dragging the slider. Very small possibility of instability at 630MHz noted.
3. Sweep frequency for S22 display, note large range of unstable loads at 473MHz.

Step 3 : Fix instability

1. I try a range of resistors in series with Port 2. Nothing appeals.
2. Repeat for Port 1. I quickly establish that a minimum of 1.5 ohms brings stability on input and output at all frequencies.  
   
3. Let's be a little conservative and use 2.2 ohms going forward.

Step 4 : Matching

1. Drag the slider so the frequency is 1296MHz.
2. Press Auto Match
3.  Be amazed at how clever Stuart Hyde is. I'd like to meet him to say thank-you in person.
4. A conjugate match simultaneously brings input and output to 50 ohms and updates the schematic
5. Sweeping with the slider still shows no instability

Results:

A stable amplifier with a gain of 18dB matched on input and output to 50 ohms.

You could change the values to he nearest standard value, and press Simulate to see what happens to gain, matching and stability. However, in Part 2 I will cover how I plan to replace the matching networks with micro strip.

NanoVNA - Test fixtures for measuring SMD's Summary

Well, I'm really impressed. I never expected such a low cost instrument to perform so well. Granted, as frequency increases you get some odd results, but nothing that detracts from this piece of test gear. Perhaps I'll buy a second unit and dedicate it to SMD measurements. Then I could recall calibrations like 0-30MHz, 0-100MHz, 0-300MHz and 0-900MHz with ease.

I can also recommend the test fixture I made. Simply a SMA connector onto a PCB. The track and pads allow for calibration ie

    Short - bridge the track with a piece of copper tape, perhaps like that shown in the picture which
                was there to short out some imperfections,

    Open - with nothing in place

    Load - a 50 ohm resistor bridging the gap. Could be two 100 ohm resistors soldered together but
                you can buy or recover 50R chip resistors. 

Once calibrated same your settings and if you need to recover a part or measure somehting it becomes very easy. It never appeared to be introducing errors which is a credit to the people behind the NanoVNA.

A few more pics just to whet your appetite to replicate this:

The 22nH Inductor

0201 12nH Inductor

Measured with ease

1 47nH

2 56nH

3 6.8pF

4 200 ohms

5 1.5pF

6 0 ohms

NanoVNA - Inductor Measurements

Starting with a 1.2uH inductor results were immediately satisfying. The measured L and variation with frequency matched the curve shown in the TDK datasheet. And the self resonant frequency was readily measured as 180MHz.

1.2uH Inductor

Let's try an unknown but small 0603 wire-wound chip inductor. Measured as 22nH.

How small can we go? I have some 12nH 0201 chip inductors with factory measurements (sample size, variance etc). Wow. 12nH measured.


Previously I have used a signal generator and test fixture with a measured parallel capacitance
( 112pF from memory ) to measure the resonant LC frequency, then back calculate what L was. This worked very well down to nH sized inductors. With a power detector I was also able to estimate Q by sweeping around the resonant frequency for the -3dB points.

The NanoVNA is now my preferred approach. I prefer the fixture without the 50 ohm resistor. The curves are easier to see and therefore interpret. Either fixture is fast to use and easy to see how L changes with frequency. I can't see how Q can be measured, but A/B comparisons show slight differences. The higher the inductor Q the closer to the edge of the Smith Chart. 

Go on, give it a try. 

NanoVAN Test Fixture - Capacitor results

Here I present two results: measuring a supposedly high Q 110pF capacitor with and without the 50 ohm chip resistor in series.

110pF capacitor in series with 50 ohm chip resistor

Immediately some questions are posed, and some pleasing results. VNA suggest 110pF capacitor is actually 112pF. This is true over most of the HF range but by 54MHz the effective capacitance has already fallen to 109pF. It gets progressively worse after that. Worth knowing in the design of filters and matching networks.

Overall the fixture with a 50 ohm series resistor appears useful.

110 pF capacitor with no series resistor

Keen readers will notice that the 110pF capacitor, tested in this fixture, measured 110pF, not 112pF. That could be because I lost the first capacitor in the shed floor. Sorry, but the time taken to present these results didn't warrant re-measuring the capacitor in the first fixture. ( Seconds to measure and view on the nanoVNA screen, many minutes to collate and present. )

What is interesting is that while the nanoVNA display showed a trace around the edge of the Smith Chart, the software did not. Is this evidence that at the extremes there are errors as data is transferred and manipulated to re-display the trace, or underlying accuracy issues with the NanoVNA? Loss of one too many decimal places? The S2P file I exported with "nanoVNA partner" went to 9 decimal places, however that does not mean the software worked at that level of precision. Displaying answers to 4 decimal places is meaningless without knowing the precision of the underlying calculations.



Viewed on the nanoVNA it suggested by the software the capacitor is useful up to 2m before it departs from being a 110pF capacitor.

At this point both test fixtures have, within reason, results and findings consistent with each other.

I then examined in turn capacitors of 100nF, 10nF, 1.5nF and 150pF. The nanoVNA screen clearly showed where these capacitors departed from being the stated value and confirmed my understanding of why the value and type of decoupling capacitor requires thought. Unfortunately, with no series resistor once the readings are transferred to the PC the data translation/transfer/rounding issues prevent a meaningful display of the results when the S parameter file is later opened with "nanoVNA partner".

However, all is not lost.  The exported S2P file, viewed in RFSIM99, is a close representation of what the nanoVNA screen was showing.

100nF capacitor, no series resistor

The 100nF 1206 capacitor measured 93nF at 50kHz. At 9MHz it was already a 1nH inductor. Not what I expected from a 1206 part. A trip to the workshop to check. Indeed, this seems correct. While the 50 ohm resistor fixture showed the transition was at 18MHz, the difference between the two is within the accuracy I wanted.

For decoupling purposes the series impedance at 36MHz is 0.05R+j0.65R. Above that the decoupling gets worse.

How does 10nF look? A 10nF 1206 "recovered" capacitor was tested. The series impedance at 72MHz is 0.09R+j0.63R, getting worse as frequency rose beyond that.

The 1.5nF capacitor demonstrated why two values of decoupling capacitor are sometimes shown. It would be poor at decoupling until the frequency rose to 72MHz. Above 300MHz the response was erratic so this needs checking.

The 150pF capacitor was unaffected by parasitics until the frequency rose to 234MHz.

I overlaid the results of 3 39pF capacitors of different construction, mica clad, 1206 ceramic and a SMD mica? film capacitor. There was no real difference until the frequencies rose above 300MHz. After this all displayed a similar erratic pattern though it was shifted.

3 39pF capacitors of different construction.

Advantages of 50 ohm test fixture

There is some suggestion in published papers that this fixture should have greater accuracy. I see nothing in the results to date to support this. Perhaps my test fixture for SMD parts was better than hte authors test fixture.

In any event, since you have to build one of these to calibrate the other fixture ( OSL ) then for now I put aside the "accuracy" debate. 

Advantages of the test fixture without 50 ohms

A/B comparisons of decoupling applications at spot frequencies gets easy since for the same frequency A is worse than B if it is further away from the 0+j0 point of the Smith Chart.

Conclusion to date

Either fixture appears useful at characterizing capacitors down to very small values. The lowest I tested was 1.5pF and the results gave me confidence in the value and presence of parasitics.
Accuracy appears degraded above 300MHz but for my purposes will still be adequate.

For A/B comparisons I would use the test fixture without the series resistor since the deviation is easier to spot on the small display.

NanoVNA Test Fixture - Details

Here is a picture of the fixture I am using. I had allowed for several fixture styles. At present I am using two of the fixtures, both single sided. The unused fixtures are double sided but I may never get around to trying them. The results to date suggest single sided is more than adequate.

The 50 ohm chip resistor fixture is shown on the top right hand corner. A tricky soldering job since one pad is underneath, and the other wraps around. Clearly too much solder but the OSL calibration process is hopefully negating the additional stray capacitance that blob is contributing to the measurements. Not obvious is the manual removal of the ground trace that runs under the chip resistor by scratching it off.

To calibrate the fixture I use the chip resistor version. As shown it is open circuit. I use a piece of foil squashed onto the SMA pins with my thumb as the short. The piece of foil is used to connect the pad adjacent to the ground side of the 50 ohm resistor to the untinned areas as the load calibration.

I then use the same calibration settings for both fixtures. Using the calibration for the chip resistor version with the non-chip resistor version has proven to be acceptable.

To use the same fixture without the resistor I sweat soldered a piece of tinned copper foil as shown. The SMD then is placed where the pad for the chip resistor was used to connect to the center pin of the SMA connector. That tiny chip inductor is I think 0201. It was the smallest physical and electrical value I have tested to date, with good results. But more on that later.

I hold the test device in place by clamping it with a wooden clothes peg. Sometimes  I use a piece of bare fiberglass, or other benign material like the fingernail on my thumb, and I have found no material difference in readings by doing this.

Experience with this fixture suggest I should have made the pad slightly larger to more easily accommodate some of the SMD inductors just larger than 1206 size parts. And maybe shaped the ground pad to be closer to make placing the 0201 parts a little easier.

NanaVNA - Test fixture for measuring passives

Recently I've been exploring what the NanoVNA can do. It really is an impressive piece of test equipment for such a small sum. There has been lots of discussion about measuring passives at HF but I was troubled by the lack of evidence that some commentators had actually done what they advocated. Just like fake Chinese transistors, too many online experts write on the basis of what they have read, not what they have done.

And there was very little online information I could find about using the NanoVNA to measure very small values of passive components. What information I could find was at times inconsistent. So I set out to discover for myself what worked. Over the next few weeks I'll post what I found.

But first the starting point has to be the text fixture. I had a PCB house fabricate a few boards so I could experiment. A variety of single and doubled sided layouts were contemplated, some would use a 50ohm chip resistor in series with the passive being tested, some would simply place the passive component across the SMA.

My biggest challenge was presenting the test results. Taking a picture of the screen was impossible given the screen reflections.  "nanoVNA partner" is a small download and worked well on both XP and Windows 10. I recommend it.

As far as using the NanoVNA, at least one published paper would appear to advocate a different approach to what I found. Could it be the NanoVNA was better than the equipment used in that published paper?