NanoVNA-H4 v4.3 – initial impressions

I have owned a NanoVNA-H v3.3 for more than two years now. It required some modification to fix a power supply decoupling problem on the mixers, reinforcement of the SMA connectors, replacement of the USB socket, rework of the case so the touch screen worked properly / reliably, and some minor works (eg battery charger chip, bad patch cables, faulty USB cable).

With recent enhancement of firmware to support an SD card, the prospect of stand alone use becomes more practical, so I set about researching and purchase.

It seemed the best option was to buy a ‘genuine’ NanoVNA-H4 v4.3, and I started the search at the recommended (by Hugen) store, Zeenko… but whilst there was a listing for v4.2, there was no v4.3 listing (perhaps it is out of stock). I did find another store selling what they described as a ‘genuine’ NanoVNA-H4 v4.3, but this is a high risk transaction, experience is that Chinese sellers are not to be trusted, and Aliexpress is an unsafe buying platform.

This is one of those concerning transactions where the seller notifies shipment and gives a tracking number hours before the deadline, then a week later change the tracking number (the ‘real’ shipment).

Above, the promo image from the listing. Continue reading NanoVNA-H4 v4.3 – initial impressions

nanoVNA – measure common mode choke – it is not all that hard!

It seems that lots of hams find measuring the impedance of a common mode choke a challenge… perhaps a result of online expert’s guidance?

The example for explanation is a common and inexpensive 5943003801 (FT240-43) ferrite core.

Expectation

It helps to understand what we expect to measure.

See A method for estimating the impedance of a ferrite cored toroidal inductor at RF for an explanation.

Note that the model used is not suitable for cores of material and dimensions such that they exhibit dimensional resonance at the frequencies of interest.

Be aware that the tolerances of ferrite cores are quite wide, and characteristics are temperature sensitive, so we must not expect precision results.

Above is a plot of the uncalibrated model of the expected inductor characteristic, it shows the type of response that is to be measured. The inductor is 11t wound on a Fair-rite 5943003801 (FT240-43) core in Reisert cross over style using 0.5mm insulated copper wire. Continue reading nanoVNA – measure common mode choke – it is not all that hard!

A simple Simsmith model for exploration of a 50Ω:200Ω transformer using a 2843009902 (BN43-7051) binocular ferrite core

EFHW-2843009902-43-2020-3-6kThis article applies the Simsmith model described at A simple Simsmith model for exploration of a common EFHW transformer design – 2t:14t to a ferrite cored 50Ω:200Ω transformer.

This article models the transformer on a nominal load, being \(Z_l=n^ 2 50 \;Ω\). Keep in mind that common applications of a 50Ω:200Ω transformer are not to 200Ω transformer loads, often antennas where the feed point impedance might vary quite widely, and performance of the transformer is quite sensitive to load impedance. The transformer is discussed here in a 50Ω:200Ω context.

Above is the prototype transformer using a 2843009902 (BN43-7051) binocular #43 ferrite core, the output terminals are shorted here, and total leakage inductance measured from one twisted connection to the other. Continue reading A simple Simsmith model for exploration of a 50Ω:200Ω transformer using a 2843009902 (BN43-7051) binocular ferrite core

A simple Simsmith model for exploration of a common EFHW transformer design – 2t:14t

This article describes a Simsmith model for an EFHW transformer using a popular design as an example.

This article models the transformer on a nominal load, being \(Z_l=n^ 2 50 \;Ω\). Real EFHW antennas operated at their fundamental resonance and harmonics are not that simple, so keep in mind that this level of design is but a pre-cursor to building a prototype and measurement and tuning with a real antenna.

Above is the prototype transformer measured using a nanoVNA, the measurement is of the inductance at the primary terminals with the secondary short circuited. Continue reading A simple Simsmith model for exploration of a common EFHW transformer design – 2t:14t

A simple Simsmith model for exploration of a common EFHW transformer design – 2t:16t

This article describes a Simsmith model for an EFHW transformer using a popular design as an example.

This article models the transformer on a nominal load, being \(Z_l=n^ 2 50 \;Ω\). Real EFHW antennas operated at their fundamental resonance and harmonics are not that simple, so keep in mind that this level of design is but a pre-cursor to building a prototype and measurement and tuning with a real antenna.

The prototype transformer follows the very popular design of a 2:16 turns transformer with the 2t primary twisted over the lowest 2t of the secondary, and the winding distributed in the Reisert style cross over configuration.

Above is a plot of the equivalent series impedance of the prototype transformer with short circuit secondary calculated from s11 measured with a nanoVNA from 1-31MHz. Note that it is almost entirely reactive, and the reactance is almost proportional to frequency suggesting close to a constant inductance. Continue reading A simple Simsmith model for exploration of a common EFHW transformer design – 2t:16t

Measuring a 1/4 wave balanced line – nanoVNA

A question was asked recently online:

I am about to measure a 1/4 wave of 450 ohm windowed twinlead for the 2m band using my NanoVNA. My question is, since I will be making an unbalanced to balanced connection, should I use a common mode choke, balun or add ferrites to the coax side to make the connection, or does it really matter at 2m frequencies? The coax lead from my VNA to the twinlead will be about 6″ to 12″ long. I will probably terminate the coax in two short wires to connect to the twinlead.

It is a common enough question and includes some related issues that are worthy of discussion. Continue reading Measuring a 1/4 wave balanced line – nanoVNA

Measure transmission line Zo – nanoVNA – PVC speaker twin – loss models comparison #3

Measure transmission line Zo – nanoVNA – PVC speaker twin demonstrated measurement of transmission line parameters of a sample of line based on measurement of the input impedances of a section of line with both a short circuit and open circuit termination. From Zsc and Zoc we can calculate the Zo, and the complex propagation constant \(\gamma=\alpha + \jmath \beta\), and from that, MLL.

Above is a plot of: Continue reading Measure transmission line Zo – nanoVNA – PVC speaker twin – loss models comparison #3

Measure transmission line Zo – nanoVNA – PVC speaker twin – loss model derivation

The article Measure transmission line Zo – nanoVNA – PVC speaker twin demonstrated measurement of transmission line parameters of a sample of line based on measurement of the input impedances of a section of line with both a short circuit and open circuit termination. From Zsc and Zoc we can calculate the Zo, and the complex propagation constant \(\gamma=\alpha + \jmath \beta\), and from that, MLL.

Measurement with nanoVNA

So, let’s measure a sample of 14×0.14, 0.22mm^2, 0.5mm dia PVC insulated small speaker twin.

Above is the nanoVNA setup for measurement. Note that common mode current on the transmission line is likely to impact the measured Zin significantly at some frequencies, the transformer balun (A 1:1 RF transformer for measurements – based on noelec 1:9 balun assembly) is to minimise the risk of that. Nevertheless, it is wise to critically review the measured |s11| for signs of ‘antenna effect’ due to common mode current. Continue reading Measure transmission line Zo – nanoVNA – PVC speaker twin – loss model derivation

Return Loss Bridge – some woolly thinking – a Simsmith model of a reflection bridge

Return Loss Bridge – some woolly thinking discussed some online opinions on the practical measurement range of nanoVNA, and underlying reasons… but both were flawed.

Reflection Bridge and Return Loss Bridge are somewhat synonymous, in practice to measure Return Loss one is interested in the magnitude of the response, and to measure the complex reflection coefficient or s11, both magnitude and phase are of interest.

He derives a flawed expression for bridge response, then plots a dodged up version to demonstrate the asymmetry of the response.

Above is Oristopo’s graph. Continue reading Return Loss Bridge – some woolly thinking – a Simsmith model of a reflection bridge