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

Last update: 16th March, 2020, 1:12 PM

NEC – vertical monopole ground wave study

The article NEC – vertical monopole radiation resistance study discussed ‘radiation’ in the strict sense, this article takes a look at ground wave propagation from the same antenna.

NEC insight

Let us look at an example of a quarter wave monopole with 120 shallow buried radials, soil σ=0.005  εr=13, average ground, at 3.8MHz.

 

Above is the model geometry. Continue reading NEC – vertical monopole ground wave study

Last update: 22nd March, 2020, 6:56 AM

NEC – vertical monopole radiation resistance study

A recent online discussion contained an analysis of the radiation efficiency of a vertical monopole over real ground.

The poster dismissed the values calculated by 4NEC2 and proposed his own formula \(RadiationEfficiency=\frac{35.6}{\mathbb{R}Z_f}\) where 35.6 is the radiation resistance Rr of a quarter wave monopole over a perfectly conducting earth (PCE).

The reasoning seems to depend on Rr being independent of the ground type, but that is quite flawed.

NEC insight

Let us look at an example of a quarter wave monopole with 120 shallow buried radials, average ground, at 3.8MHz.

 

 

Above is the model geometry. Continue reading NEC – vertical monopole radiation resistance study

Last update: 14th March, 2020, 1:48 PM

Milton Moore’s power supply test

When I was a student at TAFE in 1970, a teacher, Milton Moore, explained why the lab power supplies that were used, Perini & Scott 30V 2A, were the largest power supplies given their modest capability.

He explained that they were almost student proof. He went on the classify students in three categories, the average students constituted the bulk, then there were the quite inept who damaged the best equipment by doing things that no one could have anticipated, and the very bright who sought to understand equipment and expose their weakness.

Milton explained that they tested these power supplies using the rat tail file and hacksaw blade test. One output terminal was attached to the rat tail file and the other to a hacksaw blade, the voltage and current were set to max and the rat tail file and hacksaw blade were rubbed together yielding a shower of sparks… and possibly smoke from the DUT.

At the time I was very interested in overcurrent protection of linear regulators, so this was especially interesting.

ua723 – the darling of power supply designers of the time

Lets look at the issue with the ua723, recently released at that time and appearing in lots of designs.

Above is a schematic from the ua723 datasheet. Rsc is the current sense resistor and it is chosen to develop 0.6V at the current limit, so for instance in a 20A power supply it would have a value of 0.6/20=0.03Ω. So, the current sense circuit presents a Thevenin equivalent circuit of Vth=Rsc*I and Rth=Rsc. Continue reading Milton Moore’s power supply test

Last update: 12th March, 2020, 10:52 AM

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

Atten-hcctl00

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

Last update: 11th March, 2020, 6:09 AM

4NEC2 – summary statistics discussion

I am a frequent user of 4NEC2 despite its many defects. It is a great work of software, in need of improvement that I suspect will never happen. Its author explained some time ago that it was developed in VB6 and with Windows upgrades, he no longer has a working VB6 development platform.

So, despite its defects, it is a very useful tool.

This article set about explaining interpretation of the summary statistics shown on 4NEC2’s main form.

I will sometimes substitute _ for – in some 4NEC2 quantity labels for clarity in mathematical expressions. Continue reading 4NEC2 – summary statistics discussion

Last update: 11th September, 2021, 10:04 AM

Programming a certain type of Chinese 315/433MHz EV1527 compatible remote relay

This article describes the programming sequences for a common Chinese 315/433MHz remote relay which works with the common EV1527 transmitter.

The EV1527 should not be confused with high security protocols, the transmitter has burned into it four fixed supposedly relatively unique codes (in a space of 1 million code possibilities) and sends the burned in code associated with the transmitter key each time it is operated. This should not be confused with rolling code systems such as KeeLoq. This information is not usually disclosed by sellers.

These are usually supplied with little or no instructions, or bad online translations that are quite misleading. I dare say sellers have refunded money in lots of cases due to user confusion about programming them or compatible transmitters. This information might assist owners to find a working solution.

Above is an example remote relay (~$3 on eBay), they are available with a number of channels and may look physically different but use the same or similar firmware. Note that though the relay on this one is rated at 10A AC, that rating is for resistive load and it is rated at 5A AC for an inductive load (PF=0.4). Continue reading Programming a certain type of Chinese 315/433MHz EV1527 compatible remote relay

Last update: 5th March, 2020, 7:46 AM

FT240-43 matching transformer for an EFHW – NEC model at 3.6MHz

The article End Fed Half Wave matching transformer – 80-20m laid out a design for a EFHW transformer based on the readily available FT240-43.

This article builds an NEC model for an EFHW antenna at 3.6MHz incorporating a realistic model of the above transformer.

NEC provides for a NT card characterising a two port network using Y parameters.

Y parameter model for the transformer

The Y parameter model is based on measured input impedance with port 2 open circuit, and short circuit, and the observed turns ratio.

Impedance was measured with the transformer at 3.6MHz using an AA-600.

Above, the calculated Y parameter model including a prototype NT card. This model captures the various loss components of the transformer, mainly magnetising loss, at 3.6MHz. Continue reading FT240-43 matching transformer for an EFHW – NEC model at 3.6MHz

Last update: 14th April, 2024, 1:35 PM

Small efficient matching transformer for an EFHW – NEC model at 3.6MHz

The article Small efficient matching transformer for an EFHW laid out a design for a small EFHW transformer.

This article builds an NEC model for an EFHW antenna at 3.6MHz incorporating a realistic model of the above transformer.

NEC provides for a NT card characterising a two port network using Y parameters.

Y parameter model for the transformer

The Y parameter model is based on measured input impedance with port 2 open circuit, and short circuit, and the observed turns ratio.

Impedance was measured with the uncompensated transformer at 3.6MHz using an AA-600, the compensation in the reference article has little effect at 3.6MHz.

Above, the calculated Y parameter model including a prototype NT card. This model captures the various loss components of the transformer, mainly magnetising loss, at 3.6MHz. Continue reading Small efficient matching transformer for an EFHW – NEC model at 3.6MHz

Last update: 14th April, 2024, 1:35 PM