NanoVNA-App v1.1.209-OD15 released

Most of the changes I have made to NanoVNA-App have been to align it with accepted standards and conventions.

This change is to the format of saved Touchstone, .s1p and .s2p, files.

Though the relevant specification is silent on the permitted decimal separator, the only one shown in examples is “.” so it is reasonable to interpret that the required separator is “.” which makes the file format locale independent (as were the first instruments using Touchstone format.

This release of NanoVNA-App writes “.” decimal separator, independent of locale.

The original reading code which was tolerant of either “.” and “,” is maintained, so it will continue to open files which might have been (incorrectly) saved using “,”.

NanoVNA-App-Setup-v1.1.209-OD15

Last update: 3rd May, 2023, 10:03 AM

Paccomm Tiny-2 Mk2 capacitor polarity problem

Many Paccomm Tiny-2 Mk2 TNCs have a polarised capacitor installed incorrectly. They become leaky and it degrades performance.

Let’s look at the datasheet for a MAX231 and review the charge pump and related filter capacitors.

Note especially the capacitor connected from pin 3 to ground, it is an electrolytic with -ve terminal to pin 3 and it develops the -ve voltage for the true RS-232 line driver. Continue reading Paccomm Tiny-2 Mk2 capacitor polarity problem

Last update: 2nd May, 2023, 5:46 AM

Derivation of the expression for the unknown impedance in an s21 series through measurement

This article presents a derivation of the expression for the unknown impedance in an s21 series through measurement.

The diagram above is from (Agilent 2009) and illustrates the configuration of a series-through impedance measurement. Continue reading Derivation of the expression for the unknown impedance in an s21 series through measurement

Last update: 25th April, 2024, 4:19 PM

Mower deck maintenance – Toro MX 4250

The deck is a fabricated deck on a Toro MX 4250 residential zero turn mower, it has 200h of service over 8 years… which is not very much.

The deck has the recycler option installed.

Deck service included:

  1. Fit new bearings to spindles;
  2. Replace both idler wheels (components are not serviceable);
  3. Clean and apply corrosion protection under deck;
  4. Procure, fit and balance new blades; and
  5. Procure spare drive and deck belts for spares.

Spindle bearings

Jiggling the blade tips showed 2-3mm vertical play in both spindles. New bearings have much less play, undetectable without instruments.

The spindles are easily serviced.

The lower bearing is one spindle had a rusted retainer / separator and collapsed when driving it from the housing. The other lower bearing was rough, but did not collapse. The top bearings were in good condition.

A set of four NSK 6203-2RS bearings was purchased ($35) to replace all the bearings.

Idler pulleys

Both idler pulleys were dry of grease. It was possible to pop the rubber seal and pack a little more grease pending arrival of replacement parts.

Replacement parts were purchased for $60 (inc shipping) and fitted.

The message is that water sprayed over the top of the deck assembly is retained in a shallow cup on the sealed bearings and some will wind up inside the bearings… don’t wash the top of the deck.

Deck clean, descale and corrosion protection

Above, the underside of the deck after washing, de-scaling with a pneumatic needle scaler, power brushing with a cup brush, and another high pressure wash ready for application of corrosion protection. Continue reading Mower deck maintenance – Toro MX 4250

Last update: 21st April, 2023, 10:49 AM

A low cost break-out board for STDC14

It is now near impossible to procure a genuine STLINKV2 or a good clone. Newer versions of STM32CubeProgrammer will not work with poor clones.

In pursuit of a small inexpensive replacement for the STLINKV2, the STLINKV3-MINIE is a candidate. That said, they can be difficult to source… mine is on 9 months wait from element14.

Above is the STLINKV3-MINIE (~$20). Continue reading A low cost break-out board for STDC14

Last update: 12th September, 2023, 10:41 AM

Programming a PIC 12F510 using the DIY-150 programmer

A correspondent asked how to program a PIC 12F510 used in one of my projects using his DIY-150 programmer.

The DIY-150 programmer is quite an old design and there has been no development for more than 10 years, meaning no new chips added, though there are lots of online sellers of the now stale design.

The 12F510 is very similar to the 12F509 which microbrn v150807 does support. The 12F510 can be programmed by selecting chip type 12F509.

Alternatively, download the archive below and extract a modified chipdata.cid file which includes a 12F510, and extract it to replace the existing installed file.

The revised chipdata.cid can be downloaded here: chipdata.7z.

Last update: 11th April, 2023, 6:43 AM

Review of mower starter motor current using Owon HDS242S and Hantek CC-650

This article documents capture of starter motor current on a Toro MX4250 mower with the Toro V-twin engine. The test is part of diagnosis of possible starter motor problems.

The current was captured with a Owon HDS242S hand held DSO and Hantek CC-650 current probe.

The motor is a permanent magnet DC motor with bendix gear.

Above is a screenshot, vertical scale is 50A/div, measurement is of battery current. Continue reading Review of mower starter motor current using Owon HDS242S and Hantek CC-650

Last update: 8th April, 2023, 9:52 AM

NanoVNA-H4.3 R44 mod

Whilst following up another matter, I came across the following commit to Hugyen’s NanoVNA-H4 repository.

Remove R44 from NanoVNA-H4 Rev4.3, this resistor may damage U2 and the battery if the NanoVNA-H4 is not used for a long time and the battery is too low.

Above is an extract from the revised schematic committed, the change highlighted by the red arrow. R44 has been changed from 5.1kΩ to not populated. Continue reading NanoVNA-H4.3 R44 mod

Last update: 31st March, 2023, 3:19 PM

NanoVNA – interpolation – part 5

NanoVNA – interpolation – part 4 and prior articles discussed the possibility of significant error when calibration data is interpolated.

This article illustrates the effects with some very simple examples.

Test scenario

The test scenario is a NanoVNA-H4 with 5m length of RG58A/U to the reference plane. It has been OSL calibrated at the reference plane using a 1-101MHz 101 point sweep.

Result without interpolation of the calibration dataset

Above is a zoomed in view of 1-5MHz of a 1-101MHz 101 point sweep, there are measurements at every whole MHz value from 1 to 101. There are only 5 measurement points on this graph. Continue reading NanoVNA – interpolation – part 5

Last update: 18th March, 2023, 1:02 PM

NanoVNA – interpolation – part 4

NanoVNA – interpolation – part 3 discussed selection of a sweep step size to provide sufficient data points for reasonably accurate interpolation.

When / where is interpolation used?

The VNA correction process uses measurements of some known conditions to create a calibration dataset, a table if you like of the sweep frequencies and calibration data. Commonly the calibration dataset is a table of the correction factors calculated from measurements of the knowns for each frequency of the calibration sweep. The correction factors are usually calculated for each frequency independently of adjacent frequencies.

When used to sweep a different range, interpolation can be used to interpolate those correction factors to the new measurement frequencies.

A common data flow is that shown above, where the correction terms are calculated for each of the frequencies in the calibration sweeps, and then those terms are interpolated to the frequencies actually used for a DUT measurement sweep. Continue reading NanoVNA – interpolation – part 4

Last update: 17th March, 2023, 5:53 PM