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On Sun, Feb 14, 2021 at 12:55 PM, Dragan Milivojevic wrote:

It has been stated, by multiple members of this group, that due to hardware
deficiencies (port 2 is not a perfect 50Ω) and lack of 12 term error
correction,
the "S21 method" can't be used to measure high impedance reliably.

Yes this is true. The "S21 series method" is a way of calculating the complex impedance (R+jX) of a device under test (DUT). Unfortunately it does not work on a NanoVNA-H or -H4 which are 2 port uni-directional analyzers for the reasons you outlined in your post.

If you try it you will find that you can calculate the magnitude of a high impedance |Z| DUT fairly well but the phase angle is not correct except at very low frequencies. You need the correct phase angle in order to convert from polar (Z&angle) to polar (R+jX) format.

Users interested in trying this should use a SMD resistor as the DUT which should have a S21 phase angle very close to zero. You will only get this at very low frequencies. A small capacitor as the DUT should have a phase angle near 90 degrees but this will be incorrect as you increase frequency. I have seen this on several test jigs that I have built.

If users want to try these measurements be very careful with parasitic capacitance on the test fixture. The capacitance across the terminals where you connect the DUT has to be well under a pF or the S21 loss in dB will be incorrect.

Roger

Even a reasonably good 10 dB attenuator makes a good dummy load as the
return loss is 20 dB - two passes through the -10 dB circuit. And 20 dB RT
amounts to an SWR of 1.02 : 1. So, you not only have a good 10 dB
attenuator, but a good dummy load as well.

Dave - W?LEV

--
*Dave - W?LEV*
*Just Let Darwin Work*

thanks

My Crystal Measuring Adapter for NanoVNA is almost finished. This will make it much easier to sort out crystals for building filters.
Will I do the faseshift calculations by hand? I think not. I'm just going to use my "FaseShift Crystal calculator" at
. Just enter the values and It does the math for you. Simple as that.

Enjoy.

V2 is open source, the later versions are not.

Hi DiSlord,

The info about updating a V2.2 to V2plus you were so kind send me recently shows a hardware change of 3 components only, one resistor and 2 capacitors.

If I do understand well, this update makes it possible to increase the scan speed? in the firmware and does not enhance the measuring results at all.

If so, this update is of less importance to me.

I also learned that there are more hardware differences between the two versions, do you know what these are and if it is possible to implement them in the V2.2 ?

I have been looking around, but sofar did not succeed to find the schematic of the V2plus.

Thanks for your time and best regards,

Jos

By the way, Ed is very well known in the VHF-UHF community. He has designed
and built some really cool solid-state amps for 144, 222 amd 432 MHz in the
200-300 watt range.

Zack W9SZ

On second thought, forget it. Those of us who have been there, done that
know better. I have a well outfitted RF lab covering to 21 GHz and know
how to use the equipment. I'm through replying to your posts. Go find
someone else to flame......

Reapectfully submetted:

Dave - W?LEV

On Mon, Feb 15, 2021 at 6:17 PM David Eckhardt <davearea51a@...>
wrote:

OK. I'm stupid and really don't know what I'm talking about. I spread
snake oil, saucery, witchcraft, and magic as applied to RF. Smith charts
are just disguised wiggie boards. And, of course, the earth is flat and
all celestial movements are determined by epicycles and epispheres. I
spent 10 years in RF design and the last 30 in EMC/RFI. Color me stupid,
dumb, incapable of handling DC Ohm's Law and don't know which end of the
soldering pen to grab.

I do not appreciate being attacked for my posts. I am working on data and
will post to this group.

Electrolytic, tantalums do NOT make good bypasses for high frequencies. I
proved that to myself decades ago in RF design and following in control of
EMC/RFI. Go build a preamp using only SMD 'electrolytics'. Control RF
emission of a ?P ringing at 3.6 GHz with only SMD 'electrolytics'. I am
taking data on that and will present it to this group. Please hold off on
flaming me further until that work is complete?

Dave - W?LEV

On Mon, Feb 15, 2021 at 2:43 AM Jim Shorney <jshorney@...>
wrote:

Drake TR7/TR4310.

73

-Jim
NU0C

On Mon, 15 Feb 2021 03:31:07 +0100
"Dragan Milivojevic" <d.milivojevic@...> wrote:

Forgot to ask, what's this legendary piece of equipment,
it has transistors so it can't be that good ?

On Mon, 15 Feb 2021 at 03:27, Jim Shorney <jshorney@...>

wrote:

Yeah, I remembered that about the one on the left after I sent the

pic.

The one on the right he called a "buzz kill".

73

-Jim
NU0C

On Mon, 15 Feb 2021 02:07:44 +0000 (UTC)
"Bob Albert via groups.io" <bob91343@...> wrote:

The left hand one is bypassed with a .01 so that doesn't count. I

am

puzzled by the other one; what's it supposed to do?

--
*Dave - W?LEV*
*Just Let Darwin Work*

--
*Dave - W?LEV*
*Just Let Darwin Work*

OK. I'm stupid and really don't know what I'm talking about. I spread
snake oil, saucery, witchcraft, and magic as applied to RF. Smith charts
are just disguised wiggie boards. And, of course, the earth is flat and
all celestial movements are determined by epicycles and epispheres. I
spent 10 years in RF design and the last 30 in EMC/RFI. Color me stupid,
dumb, incapable of handling DC Ohm's Law and don't know which end of the
soldering pen to grab.

I do not appreciate being attacked for my posts. I am working on data and
will post to this group.

Electrolytic, tantalums do NOT make good bypasses for high frequencies. I
proved that to myself decades ago in RF design and following in control of
EMC/RFI. Go build a preamp using only SMD 'electrolytics'. Control RF
emission of a ?P ringing at 3.6 GHz with only SMD 'electrolytics'. I am
taking data on that and will present it to this group. Please hold off on
flaming me further until that work is complete?

Dave - W?LEV

--
*Dave - W?LEV*
*Just Let Darwin Work*

On Mon, Feb 15, 2021 at 11:55 AM, David Eckhardt wrote:

Adam, I have to ask: Is that a vanity call to represent kTB noise?

Dave - W?LEV

Hi, Dave.

It's not a vanity call, but now that you mention it hi hi ... I am afraid the call would be lost but on a few die-hard RF engineer types! It was a random call assigned years ago. I am "0" living in "5" land, but just hadn't had a reason to change.

Adam - N0KTB

If it's of any use to anyone, here I described a simple 40 dB / 20W attenuator I once built

You can also convert a QRP Labs or QRP Guys dummyload into an attenuator that way, it may not be the "perfect" 50 Ohm IN/OUT attenuator, but surely good enough to test a QRP rig. Even with ordinary resistors, it will be useable in the HF range.

Another option is to build a "power sampler", see a link in the post mentioned above.

As for that "better" video on Youtube that Evan mentioned.
It shows the problems all right, but it does NOT explain it, the maker of that video cleary missed some points.
"... it goes up and down ... some weird filter ... " huh ?

The simple explanation is that the NanoVNA is limited to 101 points, so runs over the spectrum in too coarse steps, missing several signals if they are not on one of those 101 frequencies. Reducing the sweep range may show more signals, but still miss some.
And nothing weird about the IF filter, but the IF of the NanoVNA is at 5 kHz, so you will see an image signal at 10 kHz offset.

So the NanoVNA is not a spectrum analyzer, but yes, it can be used as a very crude signal monitor ... if you know what you're doing, and don't expect too much.

73,
Luc ON7DQ

Adam, I have to ask: Is that a vanity call to represent kTB noise?

Dave - W?LEV

--
*Dave - W?LEV*
*Just Let Darwin Work*

Measured on Fluke VOM..

On Sun, Feb 14, 2021 at 10:56 PM, Klaus W?rner wrote:

Hi,
which firmware have you used? I found out that the newest cloned firmwares for
the SAA2 has a worse quality than older. The firmwares until Sept. 2020 are
OK. Later versions are not usable. I posted it but no of the developers are
interested in it. Unfortunately only one user has answered.

Its strange, my V2 and modded V2 to V2plus work fine.

Last time i check impedance measure in 2-30Mhz range vs Agilent Impedance Analyzer E4990A (use H4 and V2Plus and V2Plus4)
Measure laboratory equivalent of HF antenna.
Exist small difference in measure small R (less 1Om) and big (bigger then 10k)
V2plus4 show best perfomance (it can correct measure 10k Om)
H4 show only 8k in this case

But all other measure good (phase, Aplitude, Resonances)

Forgot to ask, what's this legendary piece of equipment,
it has transistors so it can't be that good ?

Remove them! :-))

Just one more graph, as an addition: A 100nF 100V, 1206-size SMD multilayer ceramic cap. Above 20MHz the performance of the 100nF ceramic and the 15?F tantalum are very much the same, while below 20MHz the ceramic one gets progressively bad, while the tantalum one stays pretty good the low end of the frequency range measured.

Ergo: A tantalum electrolytic chip cap is a better, wider bandwidth bypass than a ceramic chip cap. From 20 to 300MHz there is no significant difference between them in bypassing performance, although I would expect the ceramic cap to handle more current over a longer time.

On Wed, Feb 10, 2021 at 11:05 AM, David Eckhardt wrote:

* I have actually tried one vs. both wires in parallel with the VNA in
measuring CM attenuation.. There is a very minor difference. The largest
practical effect is to reduce resistance (not so much the ±jX portion). *

* Considering each wire of the bifilar pair contributes equal
inductance by itself, so the total connected in parallel will be half that
of each wire alone. This ignores mutual coupling. A 3 dB difference in
30 dB of total *
* attenuation, to me, is of little concern. The total
inductance of two inductors in parallel can be calculated from L(total) =
[L(1) X L(2)] / [L(1) + L(2)], just like resistors in parallel.*

Second question, what is the procedure for coax chokes? I *think* what I
have seen and understand is that you connect the *braid* only on CH0 and
CH1 (Port 1 and Port 2). This is the path that the CM would take. Is this
correct for coax chokes?


*You are correct. Connect the braid from one end to CH0 and the other end
to CH1. *

I have the NanoVNA and love it. Building and measuring CMCs is my next
adventure. Thanks to you and the group for a wonderful resource.

*Anything to encourage learning the NANOs and building your own
"whatevers". Experience is the best teacher!*

*Dave - W?LEV*

Dave, thank you again for the thoughtful reply.

And, thanks to the group for the additional insight.

Adam - N0KTB

Dave,

it's a lot of fun to reply to you! You challenge me, and move me to measuring more things! So now I have to dissect your answer;

Never........NEVER.......rely on an electrolytic as a bypass for RF
energy!!!!!!

WHY? I accept such generalized statements only when they are delivered with generally valid fundamentation. The only reason I can see is that the ESR of an electrolytic capacitor is typically higher than that of a ceramic one. Thus, when bypassing is required only over a frequency range where a sufficiently small ceramic capacitor also provides low reactance, the ceramic is fine. But when good bypassing is needed, say, from 30kHz to 300MHz, what value of ceramic capacitor would you use? In such a case an electrolytic capacitor is required. Common wisdom says that it would be wise to parallel it with a small ceramic cap, but if you look at my measurement below, it turns out that an electrolytic alone can be plenty good enough - specially if it's an SMD.

Use series resonance to your advantage.

This is common practice in the microwave range, where the inductance of any part of practical size is too high for effective bypassing without resonance. But it's always narrow banded.

It's a well known fact among (most) design
engineers that tantalum capacitors are not much good above 500 kHz to a
couple of MHz. Most electrolytics are even worse. Go measure them on
your NANOs.

I did. The graphs are below. A plain run-of-the-mill SMD tantalum cap, 15?F, turns out having an impedance below 0.2? from 50kHz to 300MHz. What's bad about that? If indeed engineers know what you say, then they know wrong. They probably never measured it, and only ever believed in hearsay. Or took data measured long ago, on long-obsolete, giant size capacitors, that simply isn't applicable to modern, small size parts. Look at my RXZ curves below for that tantalum SMD cap.

I just grabbed a 1000 ?F / 25 VDC cap from the parts bin and measured it on
a calibrated HP 8753C using the Smith Chart. Even at 1 MHz it measures 78
mΩ with a series reactance 78 nH. Sure, the DC portion is fine, but what
is 78 nH at 50 MHz?

78nH suggests that it's a large, long, axial-lead capacitor. Of course you should NOT use that for RF bypassing! I just measured a modern radial-lead 1000?F 25V electrolytic, and got 6.8nH, more than 10 times better than yours! At that level, it's not much worse at 50MHz than any typical leaded ceramic cap. You just can't beat physics, and lead length costs inductance. Only SMDs get much better.

Take a capacitor better suited as a bypass at HF, a 450 pF dip mica.

WHAT?????? HF is 3 to 30MHz. 450pF has a reactance of 118? at 3MHz! Good luck with using that as a bypass!

Same setup at 10 MHz: 0.1 ohms at 462 pF.

That's its resistance, but its reactance at 10MHz is several tens of ohm, and thus it's pretty useless as a bypass. Except in high impedance circuitry.

I think that you need to get the basics straight...

Here are some measurements on candidate bypass capacitors, from 50kHz to 300MHz. First a typical small ceramic 100nF bypass cap, then a typical cheap 47?F 25V aluminium electrolytic, then a tantalum cap of the same rating, and then a 15?F 20V SMD tantalum cap. I kept the same scaling for all four graphs, for easy comparison. Judge yourself what's best, and do away with long-standing, unfounded prejudice!

Of course these graphs only show resistance, reactance, and impedance, not their ability to handle high currents, run in hot environments, and so on. In high power circuits the need to handle high current or heat might dictate the use of a capacitor that doesn't have the lowest impedance.

Very clearly these measurements run straight against the myth that electrolytic capacitors are useless at RF.

On 2/15/21 6:58 AM, Jim Lux wrote:

On 2/14/21 10:19 PM, David McQuate wrote:

Yes.? 5W is +37 dBm.? This attenuator can handle 5W continuously, and its 41 dB attenuation will reduce the transmitter signal to -4 dBm.? The TinySA max input power is +10 dBm with its internal attenuator set to 0 dB, so you are ok.? Using more attenuation in the TinySA might be prudent. Note the qrpkit attenuator upper frequency limit? is 200 MHz. Its attenuation will probably be reduced at higher frequencies.
Dave

Cierra <dubosec@...> wrote:

they have some other attenuators that might be more suitable (and cheaper) - you might look at the single T attenuator or at the dummy load. (I worry about a switched attenuator - if you accidentally forget to switch it, poof goes your SA)

That dummy load, which has a diode detector, looks interesting. What I would do is take a 50k noninductive resistor in series with the SA input and hook it to the 50 ohm line on the input of the load (making a 1000:1 voltage divider with the input Z of the SA).? That will give you about 60 dB of attenuation, putting your 5W at -23 dBm

And now that I read this.. just get the dummy load. Put your Tiny SA with its whip antenna near the load - it won't have flat frequency response, but you'll see your signal

On 2/14/21 10:19 PM, David McQuate wrote:

Yes. 5W is +37 dBm. This attenuator can handle 5W continuously, and its 41 dB attenuation will reduce the transmitter signal to -4 dBm. The TinySA max input power is +10 dBm with its internal attenuator set to 0 dB, so you are ok. Using more attenuation in the TinySA might be prudent. Note the qrpkit attenuator upper frequency limit is 200 MHz. Its attenuation will probably be reduced at higher frequencies.
Dave

Cierra <dubosec@...> wrote:

they have some other attenuators that might be more suitable (and cheaper) - you might look at the single T attenuator or at the dummy load. (I worry about a switched attenuator - if you accidentally forget to switch it, poof goes your SA)

That dummy load, which has a diode detector, looks interesting. What I would do is take a 50k noninductive resistor in series with the SA input and hook it to the 50 ohm line on the input of the load (making a 1000:1 voltage divider with the input Z of the SA).? That will give you about 60 dB of attenuation, putting your 5W at -23 dBm