NanoVNA – tiny palm size VNA.
Amidon is a reseller, and sells ferrite products.
They sell some products in #43 material. In recent years, they published data for their #43 material, the published characteristics are a copy of National Magnetics Group H material (though they changed the letterhead).
Above is a side by side comparison of the NMG H material datasheet and Amidon 43, the Amidon appears to be a Photoshop treatment of the NMG. Continue reading Why do I keep saying “NOT for Amidon #43?”
The design is of a 50:75Ω autotransformer using a single Fair-rite 5943003801 (FT240-43) core. Note that this data is NOT for an Amidon #43 core.
The winding is a total of 6t tapped at 5t, wound as two close wound layers. The prototype used a single conductor stripped from LAN cable. The winding configuration is an attempt to minimise leakage inductance for improved broadband performance.
This is unconventional, but then the conventional designs on Youtube etc do not usually have credible evidence of low InsertionVSWR or other performance. Continue reading A prototype 50:75 RF transformer
A reader of NanoVNA-H4 – VSWR only contended that “surely a Smith chart is superior for antenna system tuning, a universal display.”
Let’s explore that using both VSWR and Smith displays to make tuning adjustments to a real antenna system.
Above is a sweep of the antenna system showing both VSWR and Smith chart traces. Continue reading NanoVNA-H4 – Surely Smith is better?
NanoVNA-H4 – VSWR only showed how to simplify a NanoVNA to make only VSWR measurements with about the convenience of the traditional hand held scanning analyser.
This article compares measurement of a DUT similar to a common mode choke using NanoVNA and Rigexpert AA-600.
Let’s capture a measurement sweep of a small ferrite cored inductor with a response similar to what you might expect of a good common mode choke for antenna feed lines using a NanoVNA-H4.
Above is a screenshot of the measurement. The measurement was also saved as a .s1p file to view in other applications. Continue reading NanoVNA-H4 – charts in Antscope2 and Antscope(1)
Hams wanting to resolve an antenna system problem often seek the advice of the assembled experts on social media of one form or another.
They are often advised by many that “you need an NanoVNA”… no matter what they have described, no matter their own capabilities.
Now if they follow that path, it might be the beginning of wonderful things, or it might be a huge frustration.
The problem is that although the NanoVNA is relatively low cost for its capability, affordable to lots of hams, and arguably it can replace whatever they were using previously, but… the requisite knowledge does not come in the box.
There was a generation of “antenna analysers” that were effectively one port VNAs with fixed calibration that provided capability to sweep an antenna system over a frequency range of interest and give a graphical presentation of VSWR, and not a lot of learning required to exploit the thing. (Yes, some of them also provided for a custom SOL calibration).
These type of instruments are still of great utility, though considerably more expensive that the NanoVNA. I have used a Rigexpert AA-600 extensively, but cannot recommend any Rigexpert product, or more generally any current product in this category.
Is there a way to leverage to capability of the NanoVNA to replace the scanning antenna analyser?
This article describes a solution for very common NanoVNA-H4 hardware with SD card, and NanoVNA-D v1.2.40 firmware. The solution may not work for other hardware and firmware.
So, the objective is to simplify the interface to present just a VSWR curve as shown above. Continue reading NanoVNA-H4 – VSWR only
This article continues on from NanoVNA-H4 – inductor challenge – part 8, this time with an inductor that might be a candidate for a plate RF choke for a HF valve PA.
Above is the prototype DUT, it is 142t of 0.25mm enamelled copper wire close wound on an 18mm PMMA (acrylic) former, it measures 130µH well below first self resonance.
Let’s sweep it with a NanoVNA. Continue reading NanoVNA-H4 – inductor challenge – part 9
Earlier articles in this series explored measurement of a test inductor with the NanoVNA concentrating on frequencies below the first self resonance of the inductor.
Above is the prototype test inductor, enamelled wire on a PMMA (acrylic) tube. Continue reading NanoVNA-H4 – inductor challenge – part 8
Common mode current is one of the very popular topics on social media, but one does not see much quantitative discussion, mostly just a lot of hand waving without supporting measurement data.
There are a a number of commercial instruments instruments purporting to measure RF feed line common mode current (Icm), but many are specious frauds.
There are quite a few articles on the ‘net describing DIY ‘balance measurement’ techniques / instruments and again, many are specious frauds.
There are a very small number of commercial instruments and DIY designs that would appear to be soundly based, many of them are ‘uncalibrated’ in that they do not give absolute current readings, and even relative readings may be impacted by non-linear response.
Bear in mind that Icm is usually a standing wave, and ‘measurement’ means a survey at several points along the feed line.
In my experience, for HF, Icm with a 100W transmitter feeding a reasonably efficient antenna system is likely to result in Icm greater than about 10mA, and more that 100mA is poor… so the measurement range of interest is really between 10mA and 100mA. Continue reading Measuring RF feed line common mode current – relative or absolute measurement?
NanoVNA is a unidirectional two port VNA. It makes corrected measurements of S11 and S21 of a two port DUT wrt two reference planes:
The location of the reference planes is determined by the calibration process and saved data that is subsequently used to correct raw measurements. Note that the reference plane can be displaced from the calibration plane by using the e-delay feature.
The “Ports” are not connectors on the VNA (even if the labels might suggest that), they are the boundaries of the DUT.
For the purpose of this discussion about a unidirectional VNA, let’s call the VNA port that transmits signal the TX port, and the one that receives signal the RX port.
Above is the instrument setup. The instrument is reflection (SOL) calibrated using the parts shown on the upper SMA(F)-SMA(F) adapter which defines the DUT attachment as Port 1. Thru (T) calibration is done with the lower SMA(M) connected to the upper SMA(F)-SMA(F) adapter, so defining that SMA(M) DUT attachment as Port 2. Continue reading NanoVNA: where exactly are Port 1 and Port 2?
We have all had cause to deal with those cheap SMA(F)-SMA(F) adapters that do not have means to securely grip the body of the adapter to remove a properly torqued connector nut. These are commonly the type included in NanoVNA kits.
Above is a demonstration of my solution: Continue reading Undoing those dreaded SMA(F)-SMA(F) adapters