## nanoVNA-H – continuing USB-C repair

I have reported issue with the USB-C plug / socket arrangement on the nanoVNA-H.

It is very sensitive to any jiggling of the cable or connector, causing a reset of the nanoVNA which almost always means lost work. The supplied cable was a partial cause, but sadly the jack on the PCB is also faulty.

This has progressively gotten worse to the point the nanoVNA-H is unusable. I have had a replacement socket on order for months from China where public health problems are causing chaos, it has only just shipped so could be some months yet.

I do realise that this is replacing cheap Chinese junk with cheap Chinese junk.

Anyway… it finally arrived after many months. A pack of 10 sockets cost \$2.30 incl shipping, so it gives one a fair idea of how cheap the low grade connector that was used would have come.

Above, the replacement USB-C socket soldered in to the board without removing the display. The SB1 pad lifted of the board during removal of the old socket, no connection is made to it, so no harm done. Continue reading nanoVNA-H – continuing USB-C repair

## Current regulation dynamics of Atten APS3005S

This article documents a simple test to ascertain whether the current regulation dynamics of are good enough to use for testing strings of LEDs as found in much modern lighting

The APS3005S is a linear bench top power supply 0-30VDC at 0-5A with adjustable voltage and current regulation… so called constant voltage and constant current modes.

A pair of 900mm long small gauge (0.5mm^2) hook up leads were used to apply a short circuit to the power supply, and current was set to 0.1A. The resistance and inductance of these leads will to some extent limit the peak current.

The short circuit was removed and the power supply set to 30V out.

The short was reapplied and the current captured with a current probe. The current probe calibration is 1mV/10mA.

Above, the peak current is 6680*0.1=66.8A, that is 668 times the set value. Continue reading Current regulation dynamics of Atten APS3005S

## nanoVNA-H – continuing USB-C woes #2

I have reported issue with the USB-C plug / socket arrangement on the nanoVNA-H.

It is very sensitive to any jiggling of the cable or connector, causing a reset of the nanoVNA which almost always means lost work. The supplied cable was a partial cause, but sadly the jack on the PCB is also faulty.

This has progressively gotten worse to the point the nanoVNA-H is unusable. I have had a replacement socket on order for months from China where public health problems are causing chaos, it has only just shipped so could be some months yet.

I do realise that this is replacing cheap Chinese junk with cheap Chinese junk.

Replacement of the USB-C socket will be difficult, fortunately it is the 12/16 pin version rather than the full 24 pins… but I do wonder at the wisdom of using a USB-C over the proven micro USB connector.

Above, the old socket has been removed from the board. One pad came off with the socket, but it is the unused SB1 pad. Of greater concern is whether the slight movement of the some other pads might cause conductor cracking. I do see signs that a couple of pins might not have tinned the full pad area, a hint of low quality board fabrication and a possible contribution to intermittent connection.

An alternate recovery is to cut the end off a USB cable and permanently wire it directly into the board.

So for now, the nanoVNA-H awaits parts again.

## nanoVNA – VSWR in terms of 400Ω

I was asked whether the nanoVNA can display VSWR in terms of 400Ω or some other arbitrary impedance.

Some antenna analysers and VNAs support display of results in terms of some specified impedance other than 50Ω, sometimes only a limited fixed set.

The direct answer to the question is “probably no, not directly on the ‘original’ nanoVNA today”, there are many firmware forks and many PC clients for nanovna, and now many significantly hardware versions appearing. Things may change.

However, if you can save a set of impedance measurements, they can be converted to VSWR relative to some other impedance reference.

## An example

At Implementation of G5RV inverted V using high strength aluminium MIG wire – impedance measurements a set of impedance measurements made with a Rigexpert AA600 is presented.

A similar set of measurements could be made with a standalone nanoVNA and saved, but given that it is such a clumsy device and its USB socket has become so unreliable, I will not repeat the measurement but use the data used for the article above.

So we have a table of frequency and (R,X) measured looking into a ‘real’ 450Ω feed line, so we will calculate wrt 450Ω but we could use any reference.

Above is a plot or (R,X) looking into the feed line. Continue reading nanoVNA – VSWR in terms of 400Ω

## Reinforcement of nanoVNA-H connectors – performance discussion

At Strength of reinforcement of nanoVNA-H connectors I showed a method I used to reinforce the SMA connectors to reduce the flexing of the PCB when the SMA connectors were torqued to specification for reliable measurement.

This has been commented on by online experts stating that Hugen, the designer of this board, posted notes about his efforts to keep the grounds for tx and rx port circuits isolated to some extent.

Opinion by some is that the modification I performed above which electrically bonds the two connectors through a brass bar of about 60mm length is likely to significantly degrade performance. Continue reading Reinforcement of nanoVNA-H connectors – performance discussion

## Windowed ladder line – single core CCS 21% IACS

There is some evidence that the common 1.024mm (#18) single core CCS windowed ladder line advertised as 30% IACS conductivity supplied recently may be closer to 21%. This is based solely on comparison of measured DC resistance with specification, but that is a strong hint that the copper cladding is less than specification.

## Theoretical prediction

This article presents a theoretical prediction based o A model of current distribution in copper clad steel conductors at RF of the matched line loss (MLL) at 1.8MHz.

The assumption is a 1.024mm steel cored conductor with 30.7µm copper cladding.

Above is a plot of the predicted current magnitude and phase distribution in the conductor. Continue reading Windowed ladder line – single core CCS 21% IACS

## W551 CCS windowed ladder line – a guide to low end loss

At Simsmith bimetal line type – a comparison around the first MLL minimum I reported calculated matched line loss vs cladding depth for a single core copper clad steel conductor in a feed line such as Wireman 551.

The common assumption is that as frequency is reduced, so is loss, and at low frequencies loss is roughly proportional to square root of frequency.

That model is for homogenous conductors with well developed skin effect and is not applicable to the CCS line under discussion.

Above is a plot for various cladding depth on a 1.024mm (#18) 30% IACS (67µm cladding) CCS conductor at 1.8MHz where skin depth δ is 49µm. MLL is minimum around cladding depth 100µm or 2δ. Continue reading W551 CCS windowed ladder line – a guide to low end loss

## nanoVNA-H – continuing USB-C woes

I have reported issue with the USB-C plug / socket arrangement on the nanoVNA-H.

It is very sensitive to any jiggling of the cable or connector, causing a reset of the nanoVNA which almost always means lost work.

Having tried a number of different cables that have worked reliably on other devices, I initially thought there was little difference.

I did have a good response to jetting plug and jack with IPA, but the effects are shortlived.

This brings me to consider whether the connector is degrading making debris that makes for unreliable contact, or whether this is too little spring pressure in the plug.

Above is a view into the supplied USB-C plug. The pic has been taken with care to line up the die parting marks at back and front of the connector, so the view is in line with the connector axes. Continue reading nanoVNA-H – continuing USB-C woes

## Simsmith bimetal line type – a comparison around the first MLL minimum

At Simsmith bimetal line type I reported an experiment with Simsmith’s experimental bimetal line type.

The details of the model are a little sketchy, I was interested in how it modelled the phase of the layer currents, or if you like the implied velocity of propagation of the EM wave in the conductor.

Again the model is of a copper clad steel conductor, but tweaked a little to fit the apparent limit to the number of layers modelled in Simsmith, it is 1mm diameter, 500 layers (1µm per layer).

Above is the model with cladding thickness set to 20% or 100µm. Continue reading Simsmith bimetal line type – a comparison around the first MLL minimum

## Measuring coaxial cable loss by reflection with a directional wattmeter

At Measuring coaxial cable loss by reflection with a VNA I discussed measuring terminated coax cable loss by reflection with an VNA, and you might ask the question can it be done with a scalar network analyser, return loss bridge, or directional wattmeter, all of which provide a measure of the amplitude of reflection wrt some reference impedance.

This article explores using a Bird 43 directional wattmeter to measure line loss in a similar scenario. We will use 6m of Belden 8359 (RG58A/U) @ 3.6MHz.

## Expectation

A short digression, what is the specification Matched Line Loss (MLL) at 3.6MHz? Using TLLC we get 0.171dB, that is our expectation.

## Return Loss of SC section

(Bird 2004) gives the following advice.

Line loss using open circuit calibration: The high directivity of elements can be exploited in line loss measurements, because of the equality of forward and reflected power with the load connector open or short circuited. In this state the forward and reflected waves have equal power, so that φ = 100% and ρ = ∞.
Open circuit testing is preferred to short circuit, because a high quality open circuit is easier to create than a high quality short. To measure insertion loss, use a high quality open circuit to check forward and reverse power equality, then connect an open-circuited, unknown line to the wattmeter. The measured φ is the attenuation for two passes along the line (down and back). The attenuation can then be compared with published data for line type and length (remember to halve Ndb or double the line length to account for the measurement technique).

This also contains the hoary old chestnut that a good OC termination is hard to achieve, but this author’s experience of measurement with modern VNAs is not consistent with Bird’s assertion.

So lets do a theoretical simulation of the Bird 43 applied to this problem.

Lets say we connect a source to the line section with a short circuit (SC) termination, and that the Bird 43 reads Pfwd=90W, and we read Pref=78W, we can calculate return loss $$RL=10 \cdot log_{10}\frac{P_{fwd}}{P_{ref}}=0.65dB$$, so RL/2=0.65/2=0.325dB.