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.

RF transmission lines – quite old art

From time to time I see online discussion about determining matched line loss (MLL) from Return Loss.

Something like 150 years ago a self educated genius thought about the problem of ‘smearing’ of telegraph signals in submarine cables and developed a model for the behavior of transmission lines that remains a very good model today. (The guy’s day job was as a telegraphist.)

He needed to develop new mathematics and new concepts like reactance, and he did this in the face of recognised engineers of the day dismissing the ideas.

The smearing problem was different propagation speed of the fundamental and harmonic components of the telegraphy waveform, he referred to it as distortion and in terms of his RLGC transmission line model he defined the requirements for a “Distortionless Line”. Zo for a Distortionless line is a purely real number, and a Lossless Line is a special case of a Distortionless Line. Continue reading RF transmission lines – quite old art

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

Annual inspection of antenna reveals balun box issue

During annual inspection of my HF antenna system, I removed the lid from the common mode choke.

AtuBalun202

The choke is housed in a (German) Hensel PS electrical terminal box. Hairline cracks were observed radiating out from one of the terminal screws, and adjacent to both screws in the lid. The lid is obviously not strong enough to be secured by two screws in the way done. Continue reading Annual inspection of antenna reveals balun box issue

Review of W8TEE, AC8GY STL (Radcom Feb 2020)

(Purdum 2020) describes a small transmitting loop (STL) which is a little novel in that it uses an arrangement of four circular conductor loops, two in parallel in series with the other two in parallel.

The article goes on to claim some pretty extraordinary efficiency calculated from radiation resistance for a loop structure that is shown at a height of perhaps 2m above natural ground. Continue reading Review of W8TEE, AC8GY STL (Radcom Feb 2020)

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

Radcom Feb 2019 “cable balun” – comment on Radcom “The last word” letter

At Radcom Feb 2019 “cable balun” and
Radcom Feb 2019 “cable balun” – a deeper look I wrote about a novel balun by K3MT.

 

Fig 1

Above is a diagram of the so-called “cable balun”.

My evaluation essentially showed that it was not effective in an example practical scenario where one might want to use a balun, and that of itself, it was not likely to significantly reduce common mode current in most scenarios.

Radcom Mar 2020 published  a letter in “The last word” from the author defending the device citing a NEC model of one scenario, curiously though without explanation, a different topology to the diagram above from the original article. Note also that it is a structure in free space with no discussion of how that is relevant to real world antennas near ground. Continue reading Radcom Feb 2019 “cable balun” – comment on Radcom “The last word” letter

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