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Common mode choke measurement – length matters #2 discussed the effect that even quite short pigtails might have on the measurement of a high value resistor.

This article documents an experiment to measure a DUT comprising two 1206 0.1% 10kΩ resistors soldered to a 2w section of turned pin male header strip.

Above is the measurement fixture with the 5kΩ DUT, and the parts used to calibrate the fixture. The LOAD resistor measured 50.185Ω at DC, and that was entered into the NanoVNA for improved calibration accuracy. Continue reading Common mode choke measurement – length matters #4

I have used RPi over a number of years, always with the ‘official’ Raspbian distribution.

I have a single RPi 3B+ and several 2B models, I stopped buying RPi due to the RPi3B+ voltage issue. Yes, I purchased the official power supply (at uncompetitive price), and it failed in less than a year.

Came time to upgrade the 3B+ software, as much for security assurance as anything, and a quick desk study turned up this advice on https://www.raspberrypi.com/ , the Raspberry Pi Foundation website. Continue reading RPi Raspbian – are they serious?

I have had three of these SX25 chainsaws over the years. These appear to be clones of the Chinese Zenoah G2500, a single hand aborist’s saw of 25cc.

Air leaks into either fuel induction, whether in the liquid fuel lines, carburettor gaskets, intake manifold or crankcase spells early death for two stroke engines. It quickly results in lean mixture, lack of lubrication, overheating and seizure. Continue reading Quick pressure test of SX25 chainsaw intake

I bought two ISDT Q6 Plus battery chargers over some months, and they both quickly developed the same fault symptoms:

• jog wheel unreliable / skips; and
• jog switch unreliable, eventually failing totally.

The worst one was disassembled. These are build a bit like mobile phones, the manufacturer did not want them being disassembled.

Here are pics of the evidence of the problem.

Above is the component side of the PCB, the right hand side is opposite to the rotary encoder for the jog wheel. The PCB around the hand soldered terminals of the encoder has a large amount of flux residue which is usually corrosive to a greater or lesser extent. Over time with atmospheric humidity, this spreads wider and wider, and in this case has penetrated both the encoder and the switch which is to the right of the PCB opening. Continue reading ISDT – Chinese junk

Nanosaver v0.4.0 contains a graph that I have found difficult to understand, much less find application.

Above is the graph scaled R/ω and jX/ω, and an untitled X axis, though it would appear to be frequency in Hz (scaled by the M multiplier).

I had difficulty reconciling the Y values plotted for R/ω and jX/ω with the displayed R,jX values.

David F4HTQ offers the following explanation online.

I add some explanations.

I asked Rune if he could add this graphic because it is very useful.
It display curves that have exactly the same shape as the complex permittivity curves (μ’r and μ”r) of the ferrite datasheets.

The values do not match those of the constructor curve ( to have the right value the software might know the exact geometry of the inductor) , but the shape is absolutely identical.

This allow to easy identify unknown ferrite core, and to better understand how to use it in a RF device.

He says permittivity… but he is talking about permeability.

The quote seems to say the Y axis scale is worthless?

In any event, the underlying R,X data only follows µ at frequencies well below the self resonant frequency (SRF) of the inductor.

Let’s try a measurement

Continue reading Trying to make sense of Nanosaver’s R/ω and jX/ω graph

Origins

(Austin 1987) described a multiband HF antenna that is very popular with hams some thirty years later.

In his article, Austin explained the characteristic of a single wire multiband antenna with a series section matching transformer. The geometry is quite similar to the G5RV with hybrid open wire and coax feed, but Austin pursued lengths of the dipole legs, and matching section length and Zo to optimise VSWR₅₀.

The design was never an ‘all band’ antenna, but rather a multiband antenna with low feed point VSWR₅₀ on several bands. Austin tabulated the frequency relationship of the optimised bands for the case of a 400Ω matching section, and they were in the ratio of 1:1.97:2.52:3.47:4.04. If the first frequency was chosen to be 7.2MHz, the other centre frequencies would be 14.2, 18.1, 25.0 and 29.1MHz.

NEC model

To give insight into behaviour of the ZS6BKW I have built and NEC-4.2 model of a ZS6BKW with dipole 28.5m (L1) of 2mm dia copper wire at height of 10m above ‘average’ ground (σ=0.005 εr=13), and 13.44m (L2) electrical length of 400Ω lossless transmission line. L2 was tweaked to optimise alignment of the VSWR₅₀ response with the ham bands. The model assumes no feedline common mode current.

Above is the VSWR₅₀ response of the model from 3-30MHz. Minimum VSWR near the nominated five bands is quite low. Note that VSWR₅₀ at 80m is quite poor. Continue reading The ZS6BKW five band antenna – discussion of an NEC model

Recent updates to Noise Figure Y factor method calculator expose the temperature of each of the attenuators in each scenario and so allow more flexibility in application to real world problems.

The screenshot above demonstrates its use where the DUT and Att₁₂ are cryogenically cooled.

For most applications, the default value of 290K is appropriate, so though the form has a few more fields, there isn’t more data entry for most usage.

The calcs have not changed, just replacement of a global T_att with T for each instance. The input form and output form have been reformatted to suit.