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

Exploration of feasibility of ground wave comms on 80m VK2OMD-VK1EA

This article is a desk study of the likelihood of ground wave communications over the path VK2OMD-VK1EA, about 150km.

To be useful, S/N needs to exceed 10dB.

Ham mythology has it that ground wave is good for 100km on 80m without much qualification.

Ambient noise

Ambient noise is very important, it is one factor of the Signal / Noise ratio which sets the limit for communication.

Using ITU-R P.368-9 we find that expected median noise figure in a residential precinct at 3.6MHz is 57dB. Continue reading Exploration of feasibility of ground wave comms on 80m VK2OMD-VK1EA

Last update: 31st March, 2020, 7:46 AM

LDF4-50A shield prep with simple hand tools

Commscope makes a range of prep tools that have good productivity but are quite expensive for the hobbyist.

There are different forms of connectors for LDF4-50A, this article discusses a modern type that uses a collet to clamp the cable to the connector body.

There are many ways to prepare the shield end. This article describes one using a fine tooth pull saw which makes for good results for a novice.

Above, an Excel thin kerf razor saw #55001 which has a K5 handle and 30490 46tpi pull saw (~$20 on eBay).

Above, a 3.6mm (0.14″) zip tie is pulled quite firmly into the valley of the corrugated shield to serve as a saw guide. Note the partial cut. The width of the zip tie is critical, and this width is common. The objective is to trim the shield just a little towards the end from the middle of the crest. (Normally you might have the jacket trimmed further back to accommodate the o ring and back of the connector, but it can be trimmed when the cut is complete.) Continue reading LDF4-50A shield prep with simple hand tools

Last update: 29th February, 2020, 2:43 AM

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.

Last update: 27th February, 2020, 6:17 AM