nanovna-H – measure equivalent core loss resistance

A very common design of a n:1 transformer for EFHW antennas uses a 2t primary on and FT240-43 (or even smaller) ferrite core.

In a process of designing a transformer, we often start with an approximate low frequency equivalent circuit. “Low frequency” is a relative term, it means at frequencies where each winding current phase is uniform, and the effects of distributed capacitance are insignificant.

Above is a commonly used low frequency equivalent of a transformer. Z1 and Z2 represent leakage impedances (ie the effect of magnetic flux leakage) and winding conductor loss. Zm is the magnetising impedance and represents the self inductance of the primary winding and core losses (hysteresis and eddy current losses). Continue reading nanovna-H – measure equivalent core loss resistance

nanovna-H – a ferrite cored test inductor impedance measurement – s21 series vs s11 reflection

One often sees experts online insisting that s11 reflection impedance measurements of common mode chokes is inaccurate, and the ONLY way is s21 series measurement.

This one is built upside down so the connections are visible.

In this experiment using the SDR-KITS VNWA testboard (above), a series of measurements are made of an inductor, and the test setup.

The nanovna-H (modified) was calibrated using the test board and its associated OSL components. The test board is used without any additional attenuators, it is directly connected to the nanovna-H using 200mm RG174 fly leads.

s11 reflection measurement

Above is the s11 reflection measurement. It is quick, and most tools directly display R and X vs frequency (though some of the new age tools display X as pF or µH equivalents). This is nanovna MOD v3 (a derivative of nanovnasharp).

Ok, so we have 4856-j852Ω. Continue reading nanovna-H – a ferrite cored test inductor impedance measurement – s21 series vs s11 reflection

nanovna-H – Chinese junk?

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

It is not really a project as such, but a loose collection of hardware versions manufactured in variously compliant forms, and several PC and web clients competing for space. Information is partly in the public domain, partly in restricted access forums where the controller’s identity is hidden… the modern way of ham radio.

After some research, and with some residual uncertainty, I decided upon the so-called nanovna-H design by Hugen79.

Hugen79 nominates a seller on Alibaba, but I was unable to purchase there because it would not accept my suburb in an address, and unwilling to put at risk the minimal buyer protection by purchasing outside of the selling platform, I went to Aliexpress for sellers. (No listings on eBay or Amazon for AU account holders, but many listings have appears on eBay since purchase).

Above is the pic from the seller’s listing. Continue reading nanovna-H – Chinese junk?

nanovna-H – a ferrite cored test inductor – drilling down on a glitch – the fix

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

This article documents some tests using a small ferrite cored test inductor that provides a similar impedance to that of a common mode choke suited to HF antenna feed lines.

The nanovna-H has firmware NanoVNA-Q-0.4.3-20f33ba.dfu installed. The nanovna appears to be a nanovna-H v3.3 but it is hard to be sure, it is from China, the land of copyists and fraud. Indeed the nanovna-Q author asserts that genuine nanovna-H have a green overlay whereas mine is blue. Uncertainty is part of the territory!

A small fixture was OSL calibrated and impedance measured by reflection (ie s11).

The results broadly reconcile with previous measurements of the inductor, but the jitter is worth of examination.

Above is a chart showing the measured impedance components, we might expect a reasonably smooth curve for each. It has a lot of jitter on it, and you might excuse that as a result of applying the instrument and method to such a high impedance… but for two things: Continue reading nanovna-H – a ferrite cored test inductor – drilling down on a glitch – the fix

nanovna-H – a ferrite cored test inductor – drilling down on a glitch

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

I have been evaluating one for common tasks around a ham station and noticed a persistent glitch around 7.5MHz in scenarios where |s21| is high.

The nanovna-H has firmware NanoVNA-Q-0.4.3-20f33ba.dfu installed. The nanovna appears to be a nanovna-H v3.3 but it is hard to be sure, it is from China, the land of copyists and fraud. Indeed the nanovna-Q author asserts that genuine nanovna-H have a green overlay whereas mine is blue. Uncertainty is part of the territory!

Above is an example where a ferrite cored inductor similar to an antenna common mode choke is measured, and the underlying curves should be smooth with some random measurement noise. The glitch around 7.5MHz is persistent and much larger than the random noise, so I have investigated further. Continue reading nanovna-H – a ferrite cored test inductor – drilling down on a glitch

nanovna-H – standalone VHF antenna VSWR sweep

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

This article documents a task to perform a VSWR sweep of a VHF antenna stand alone, and to capture the data and screen image for download to a computer.

The nanovna-H has firmware NanoVNA-Q-0.4.3-20f33ba.dfu installed.

The instrument was OSL calibrated for reflection at Port 1 (Ch0 is nanovna speak, convention means little) for 100-500MHz.

A sweep was then performed from 143-149MHz, forcing some interpolation of the calibration data.

The nanovna was configured for VSWR and Smith chart displays, much as you would to use it stand alone.

The sweep was then “Paused”, and the nanovna carried to the computer and plugged into the USB. The power must not be disturbed, the controls must not be altered, the captured data is really just what is frozen on the paused display.

Note that if the thing is unplugged from the USB the nanovna resets and the data is lost, so plug it in properly just once.

I then connected to it using using nanovna MOD v3 and captured the screen, clicked get data once, and saved the .s1p file.

Above is the cropped screen capture. Continue reading nanovna-H – standalone VHF antenna VSWR sweep

nanovna-H – mobile UHF antenna VSWR sweep

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

This article documents a task to perform a VSWR sweep of a UHF mobile antenna.

The nanovna-H has firmware NanoVNA-H_20191018.dfu installed.

The instrument was OSL calibrated for reflection at Port 1 (Ch0 is nanovna speak, convention means little) for 100-500MHz.

A sweep was then performed from 400-470MHz, forcing some interpolation of the calibration data.

The nanovna was configured for VSWR and Smith chart displays, much as you would to use it stand alone, but I did have it attached to the computer to capure the display (it seems it cannot be saved for later playback).

Above, the captured display. The results are pretty much as expected, no surprises there. Continue reading nanovna-H – mobile UHF antenna VSWR sweep

nanovna-H – a ferrite cored test inductor

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

This article documents some tests using a small ferrite cored test inductor that provides a similar impedance to that of a common mode choke suited to HF antenna feed lines.

The nanovna-H has firmware NanoVNA-H_20191018.dfu installed.

A small fixture was OSL calibrated and impedance measured by reflection (ie s11).

The results broadly reconcile with previous measurements of the inductor, but the jitter is worth of examination.

Above is a chart from nanovna-saver showing the measured impedance components, we might expect a reasonably smooth curve for each. It has a lot of jitter on it, and you might excuse that as a result of applying the instrument and method to such a high impedance… but for two things: Continue reading nanovna-H – a ferrite cored test inductor

nanovna-H – first experience

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

It is a semi open source project, some information is published in open access places like unrestricted github and currently unrestricted acccess messages in a io.groups forum, but the wiki and files collection of that forum is by membership only and so is not publicly available.

After reviewing a lot of public information, I chose to try  purchase an Nanovna-H. There were trials along the way in that Hugen79’s preferred supplier on Alibaba could not accept my suburb in the address, so I searched eBay, Amazon and Aliexpress for items that appears to be a Nanovna-H. On the day, eBay and Amazon had no listings, but there were some on Aliexpress.

In this case, though the seller lied about material things, it does appear that I received a ‘genuine’ nanovna-H, and one of very recent manufacture as it had firmware dated two days after I placed the order.

The device was charged and needed only an hour to reach full charge, it was about 75% charged. No grief with the battery manager stuck in shutdown (yet) as some users report.

Above, the nanovna-H as received. Continue reading nanovna-H – first experience