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On 9/25/21 9:07 AM, alan victor wrote:

In some calibration systems like TRL, using transmission lines, thru, reflect, line... The cal pieces actually are a PLANE sheet, the various line edges which serve as the cal junction. So not a point but a surface extending the width of the line in MICROSTRIP as one case.

In the case of waveguide, where scattering parameters and such were originally used, there is a "plane", cutting across the waveguide.? One hopes, of course, that you're using waveguide that supports only one mode, but that does make it more interesting if it does support multiple modes.? Even for coax, you're looking at a transverse electric field between the center and shield, so there's a plane that cuts across the propagation path.

I'd never have thought to use jumpers at hundreds of MHz, assuming they'd be too reflective. Though I admit, I've done little work at hundreds of MHz. Nice work!

I see what appears to be quite small ground vias along the lines. Is this a quasi copanar waveguide?

I've got to put a test structure like this on a TDR and see how it looks!

I look at the calibration plane as dividing electrical space in two with the measurement system on one side and the DUT on the other. The calibration of the measurement system occurs at the plane. Everything on the other side of the plane is what gets measured.

I might add, waveguides fall under the same class and the use of a plane across the flange of the guide is apparent.

In some calibration systems like TRL, using transmission lines, thru, reflect, line... The cal pieces actually are a PLANE sheet, the various line edges which serve as the cal junction. So not a point but a surface extending the width of the line in MICROSTRIP as one case.

As far as I can tell, calibration is done at a single point in a circuit. A plane suggests two dimensions, and that anywhere on that two dimensional object, the calibration is the same. But everyone knows that even for a solid copper plane, only one point can be considered 0 volts, and every other point on that plane has resistance, inductance, and capacitance relative to that one point.
So, why do people talk about the "plane" of calibration, rather than the point of calibration?

73 de Albert KK7XO

Success! Removal of the FM9688 and adding the jumper did the trick. The nVNA starts up every time.
I'm using an external battery pack with it.
Thanks!
--Al

You can try to remove the FM9688 first in order to confirm if it is caused by a fault in the FM9688.

On Sat, Sep 25, 2021 at 08:43 AM, Hugen wrote:

It looks like the power IC is malfunctioning, so if you are willing to work without the battery, try removing the FM9688 and shorting pin4 and pin8 of the FM9688 location on the PCB.

Hugen, thank you for your reply. Do you think it's worth trying to replace the FM9688 IC? I have some experience and equipment to work on SMD and that chip has enough spacing of its leads to make it seem reasonable to give it a try.

--Al

On Sat, Sep 25, 2021 at 07:57 AM, William Smith wrote:

Try disconnecting the battery, disconnecting the USB cable, powering it on to discharge any caps, and then boot it with just the USB as power supply? Battery might be getting soft...

Thanks for the suggestion. I tried it, but all I get is a more dramatic flickering of the display at a slower rate.

--Al

It looks like the power IC is malfunctioning, so if you are willing to work without the battery, try removing the FM9688 and shorting pin4 and pin8 of the FM9688 location on the PCB.

Try disconnecting the battery, disconnecting the USB cable, powering it on to discharge any caps, and then boot it with just the USB as power supply? Battery might be getting soft...

73, Willie N1JBJ

Hello all,
I'd had this nanoVNA-H for a few years, h/w v.3.4, and it's had this startup trouble for a long time. At power on, the screen lights up, a blank screen flickers as if trying to boot and after ~30 seconds goes dark.
For a long time I've been able to get it to boot by repeatedly flicking power switch off and on. Researching the trouble on this forum I have found I can attach external power to USB port and then after ~30 seconds pull the connector and it will boot.

Symptoms were there with the original firmware. I've updated it to v.1.0.64. Battery voltage is 4.16 volts. I've read about a troublesome IC or cap, but I can't find those on my board, a blue PCB that looks official.
When it does boot, it works well enough.

What the best course of action? I wouldn't mind a larger screen, but I'm reluctant about purchasing a -H4 model if I can get this one to reliably start.
Thanks!

--Al
WD4AH

The right/constant resistance circle is the shunt circle, and the left/constant conductance

circle is the series circle" .... or is that back-to-front??

I've read it exactly this way in another article too. And in some other article I found it the other way around. IMHO I think it's just a naming issue / point of view looking at it.
It is important that you know how it works. But, however, I'm not an expert in this area, still learning and playing with Smith charts.

SimSmith is a very powerful application. It's free and can be accessed at:

Thank you very much for this link, Dave !
I just tested this, very nice !

I can add another link:

This is an online tool, you can build your circuit and see the result. Similar, but not so powerful as the mentioned SimSmith.

Best regards / 73
Rainer, DK2ZR

Hi,
Re this article is Point 3, Page 3 correct ?? ie "The right/constant resistance circle is the shunt circle, and the left/constant conductance
circle is the series circle" .... or is that back-to-front??

Secondly, I have been following all the 'Antenna sweeping/matching' Threads and playing with a test antenna also ... (folded dipole) and reading heaps of articles etc.. But one point eludes me, and that is, a bit of overview. Most of the stuff I read goes into L/C impedance matching (as per this article) OR concentrates on Voltage transformer/Ferrite core matching of feedline to antennae. I am missing the link here. Specifically, the L/C Network approach focusses on matching reactances, whereas the Voltage/Ferrite Core matching seems to me to be focussed on the resistances eg 300ohm antenna to a 50 ohm coax ... antenna reactance?? My gut feel here is that the link I am missing is to do with the resonant frequency or bandwidth or .... ???
Can some-one expand on this or point me to a relevant article???

Thanks, Ian

--
Cheers,
Ian
Melbourne, Australia

Hi Miro,
Yes, you need 2 jumpers to engage a section, but only 1 to bypass it.
It is more convenient to keep the 2 jumpers together, this way you switch the section with a single motion of turning the pair. Not as good as a single button push, but I think it is a good tradeoff between cost, performance, and convenience.

73, Mike AF7KR

SimSmith is a very powerful application. It's free and can be accessed at:



and an excellent tutorial specifically addressing SimSmith:


<>

Dave - W?LEV

On Fri, Sep 24, 2021 at 12:35 PM chris_group_mail via groups.io
<chris_group_mail@...> wrote:

I have read it and as a complete beginner to this it looks very useful.
It's increased my understanding of the matching process.

Intriguing that for a simple single frequency all that's involved is
rotating the point about various circles so what is needed is to determine
the intersection between two circles. Somebody must have an app for that,
which starts with an impedance and generates the L and C values needed to
match it to a transmission line. Have looked but can't find anything,
maybe I'm not using the correct terms.

Chris

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

A nice document with a lot of good information.? The restrictions on impedance matching range in Figures 4 and 5 of the Abracon white paper are shown in more detail in Figures 5.57 and 5.58 of the 2021 ARRL Handbook and in similar figures in earlier editions.

Note that the restriction on the geometry of L-networks (Rs < Rl) in Figure 5.58 applies to all combinations of impedances only when the impedances on both sides are real.? The impedances on either side may be complex in practical installations, especially when electrically short antennas are to be matched.

Figure 5.58 of the Handbook shows only two L-network geometries that conform to the restriction, both of which place the parallel element across the higher of the two impedances.? For some combinations of impedances, it is possible to reverse the network, yielding four possible geometries instead of two.? In "More Octave for L-Networks," QEX, May/Jun, 2012, a GNU Octave procedure is given for determining whether or not an L-network may be reversed and, if so, what other geometries result from that reversal.? The Octave code gives values for the elements of either two or four L-networks as appropriate.

73,

Maynard Wright
W6PAP

On Thu, Sep 23, 2021 at 09:31 AM, vbifyz wrote:

For a poor ham's step attenuator design, look here:

Nicely done Mike!

Just a quick question - why do you need "dual" jumpers? Would it work if you have a single jumper per attenuator, so either you have attenuator engaged (jumper off) or shorted "jumper on"?

If I see it correctly, in your design, in order to "engage" the attenuator u must remove one "bridge" (horizontal) and put two (vertical) in, right?

THANKS for the work put in!

On Fri, Sep 24, 2021 at 07:35 AM, <chris_group_mail@...> wrote:

... Somebody must have an app for that, which starts with an impedance and generates the L and C values needed to match it
to a transmission line.

And to answer to the google search string with another - "impedance matching lc calculator" :)

Here are some



I use the first one often