nanovna-saver – a first look

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

I have long held the view that these things are most useful when accompanied by a capable PC client that performs flexible text book presentations of data.

Considering buying one, my first step was to perform a desk evaluation of a popular PC client, which seems to be nanovna-saver.

Before downloading it, I examined the first screenshot on the github page.

It gives evidence that the author does not follow industry standard convention for transmission line terms and theory.

In the results shown above (s11) impedance is 39.105+j39.292Ω and some transformations of that value. Continue reading nanovna-saver – a first look

Update for NFM software (v1.19.0)

NFM has been updated to v1.19.0.

The update corrects an error in conversion between ENR and temperature where Tcold<>290K.

References

  • Duffy, O. 2007. Noise Figure Meter software (NFM). https://owenduffy.net/software/nfm/index.htm (accessed 01/04/2014).

Antenna analyser – what if the device under test does not have a coax plug on it?

I have written a few articles on fixtures for adapting the device under test (DUT) to an antenna analyser’s coax jack.

Antenna analysers come with a range of connectors, the UHF connector is very popular, perhaps less so are N-type, SMA and BNC.

I use a range of fixtures made to suit specific applications, but the most flexible are the two shown in the following pic.

Above are two adapters: Continue reading Antenna analyser – what if the device under test does not have a coax plug on it?

Noise Figure measurement of a converter / transverter

I recently came across an article Signal level measurement with PowerSDR and external transverters in which Carol (KP4MD) details a set of measurements of a Flex 1500 transceiver and Electraft XV144 transverter.

Carol gives the following table of measurements and calculated results.

Table 1.  Transverter Measurements
Freq
MHz
Noise
Source
ENR (dB)
Noise/10
kHz
Conversion
Gain (dB)
Noise
Figure
(db)
50 Ω expected Noise On Noise Off On-Off (Y)
144 15.2 -134 dBm -118.8 dBm -132.1 dBm 13.3 dB 26.5 2.1
432 15.3 -134 dBm -118.7 dBm -131.7 dBm 13 dB 24.1 2.5

Lets focus on the 144MHz measurements. Continue reading Noise Figure measurement of a converter / transverter

Franklin antenna – how does it work?

(Franklin 1924) described a technique to cophase sections of a long antenna by “concentrating alternating half wave length portions of the wire within a small space, by winding such portions as inductance coils or by doubling such portions back on themselves so that there is practically no radiation from these portions”.

Let’s explore his second option, as unlike the first, it does work reliably.

Above is an NEC-4.2 model with current shown (magnitude and phase). The stubs conductors are all defined from top to bottom. Continue reading Franklin antenna – how does it work?

End Fed Half Wave matching transformer – 80-20m – LO1238 variant

A reader of End Fed Half Wave matching transformer – 80-20m asked if a good transformer could be made with with a FT114-43 core.

The original transformer above comprised a 32t of 0.65mm enamelled copper winding on a FT240-43 ferrite core, tapped at 4t to be used as an autotransformer to step down a load impedance of around 3300Ω to around 50Ω. Continue reading End Fed Half Wave matching transformer – 80-20m – LO1238 variant

End Fed Half Wave matching transformer – 80-20m – 2xFT240-43 variant

A reader of End Fed Half Wave matching transformer – 80-20m asked if a better transformer could be made with a stack of 2 x FT240-43 cores and using half the turns.

The original transformer above comprised a 32t of 0.65mm enamelled copper winding on a FT240-43 ferrite core, tapped at 4t to be used as an autotransformer to step down a load impedance of around 3300Ω to around 50Ω. Continue reading End Fed Half Wave matching transformer – 80-20m – 2xFT240-43 variant

Online calculator of ferrite material permeability interpolations – more detail

The Ferrite permeability interpolations calculator performs interpolations of tables of complex permeability data.

From manufacturer’s curves

Some of the data is derived from manufacturer’s published complex permeability curves. The plot above shows the Ferroxcube’s published curve for 3C81 material, and points at which it was digitised to extract a table of µ’ and µ”. Continue reading Online calculator of ferrite material permeability interpolations – more detail

Diagnosing a possible antenna problem by comparison with a baseline

Recently I have had difficult reaching the local DMR repeater on 70cm, and needed to check that the antenna system had not deteriorated.

I took a baseline measurement with an AA-600 after some refurbishment work in Jan 2018, and was able to compare a current sweep to that baseline.

Above, a wide Return Loss sweep of the Diamond X-50N with feed line compared to the baseline (the thin blue line). Continue reading Diagnosing a possible antenna problem by comparison with a baseline

Matching a 5/8λ ground plane – a single stub tuner example

A chap seeking details for a matching inductor for his 5/8λ vertical on 20m reported “my AA54 RigExpert analyser gives the following reading (SWR 8,2). (R 81,5). (X -158) ” measured looking into a “length of rg58 about 15-20 cm” and asked “is the inductor coil going to be enough or will I need an L match to bring the real resistance to 50 ohms”. Continue reading Matching a 5/8λ ground plane – a single stub tuner example