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Making sense of LED output figures

Browsing eBay for some high power LEDs for a current project created frustration in trying to wade through the stated performance figures (to they extent that they can be relied upon).

LEDs are often headlined as having some luminous intensity in candelas, but while that might seem to be a good measure of the ‘brightness’ of the LED viewed on-axis, it gives no information about the spatial distribution off-axis and the total luminous flux output or flux density.

I wrote a little online calculator that can be of assistance in finding the total luminous flux and flux density give luminous intensity and apex angle, Calculate luminous flux (lm) from luminous intensity (cd) and apex angle (°). (Note that specified luminous intensity is usually on axis and should be discounted by perhaps 20% to provide an average luminous intensity over the cone angle.)

Example 1

An example, an eBay seller advertises:

Specifications:
Source Material: InGaN !
Emitting Colour: 0.5W 10MM HI POWER White 0.5W LED
LENS Type: Water clear
Luminous Intensity-MCD: Typ: 290,000 mcd
Reverse Voltage: 5.0 V
DC Forward Voltage: 3.2 ~ 3.4V
DC Forward Current: 100mA
Viewing Angle: 40 degree
Lead Soldering Temp: 260¡ãC for 5 seconds
Power Dissipation: 500mW

Does it appear rational? Lets calculate average luminous intensity at 80% of 290cd, 232cd. Lets assume the viewing angle is the half power beamwidth.

Above is a calculation from the specifications. Of concern is the calculated luminous efficiency of 266lm/W, it is perhaps three times or more the expected value, so it questions the accuracy of the claims. Even at 0.5W input, the luminous efficiency is unrealistically high. Continue reading Making sense of LED output figures

Last update: 15th April, 2016, 2:20 PM

A tale of three tuners

At HC-500 I showed some VNA plots of the HC-500 matching a 50+j0Ω load at 3.5MHz.

The following commentary is on a single load scenario, a 50+j0Ω load at 3.5MHz, and while the results are not simply extensible to other loads and frequencies, it does provide some interesting insight into the devices.

THP HC-500 (Ultimate Transmatch (McCoy 1970))

Above is the behaviour of the unmodified HC-500 (an Ultimate Transmatch).

Losses at match are 12% of input power. At its rated 500W maximum power, that is 60W (which might seem high but heat tolerant insulation materials are used). On modification to a T match, losses at match were reduced to 8% or 40W at rated maximum power.
Continue reading A tale of three tuners

Last update: 6th November, 2020, 8:10 AM

HC-500

In the early 1970s I purchased a Tokyo High Power Labs HC-500 ATU based on recommendation of other hams and the seller’s representations (Dick Smith Electronics) that it was a T match with 200pF capacitors.

The circuit configuration is of the so-called Ultimate Transmatch, an invention of (McCoy 1970) that claimed a bunch of advantages over the ordinary T match.

The HC-2500 would appear to use the same circuit.

It wasn’t long before several authors waded into the Ultimate Transmatch over its poorer efficiency. With an ambitious name like Ultimate Transmatch, it had a lot to live up to… but it failed.

Within months, a reconfigured topology appeared entitles the SPC Transmatch, but it also had issues.

The reality is that none of these designs is ‘ultimate’, they all have advantages and disadvantages and are mostly used in ignorance of those.

So, I have had this HC-500 which worked well enough I suppose, but was quite difficult to tune on some loads that ordinary T matches handled with ease. It has always been my intention to reconfigure it to a T match be rewiring the grounded stator of the input cap to parallel it with the other stator… a minimal modification to get rid of the shunt capacitor and use it to help to keep coil voltage down on some loads.

Before performing the modification, I measured transmission loss when matched to a 50+j0Ω load at 3.5MHz using a two port VNA.

Above, transmission loss is 0.54dB, efficiency is 88.3%. Continue reading HC-500

Last update: 7th October, 2018, 9:02 AM

A generic run on timer using an ATTINY25

At Improved cooling for the MFJ-949E I described a modification to the ATU to improve its cooling using a fan and run on timer.

The run on timer described was based on a Chinese STC15F104E DIP8 8051 like microcontroller.

Because the programming tools for the STC chips work so poorly, and the lack of documentation of their protocol, there is no simple way to update only the calibration data in EEPROM. I have ported the algorithm to an ATTINY25 which doesn’t cost a lot more but had a much better development environment and a range of tools to allow EEPROM update without overwriting the FLASH image, and as well it will run my bootloader, ATB.

This article describes a generic run on timer based on an Atmel AVR chip, a ATTINY25 though the code will also run in ATTINY45 and ATTINY85.

The circuit is very simple, the DC output from the forward power detector is connected to the input pin which turns the BC548C transistor on at input voltage greater than about 0.7V. The high value of base resistor ensures very light loading of the forward power detector.
Continue reading A generic run on timer using an ATTINY25

Last update: 14th April, 2016, 7:32 AM

Design / build project: Guanella 1:1 ‘tuner balun for HF’ – #6

Sixth part in the series documenting the design and build of a Guanella 1:1 (current) balun for use on HF with wire antennas and an ATU.

This article documents measurement of impedance.

Impedance measurement

The antenna system is a G5RV with tuned feeders (9m of home made 450Ω open wire). The tuned feeders terminate on the balun described in this series, and it is located on the outside of the antenna feed entrance panel shown above. Continue reading Design / build project: Guanella 1:1 ‘tuner balun for HF’ – #6

Last update: 13th February, 2017, 4:34 AM

Precision GPS experiment #1

This article reports an experiment to evaluate the usefulness of precision GPS for the purpose of location data for automated antenna field strength surveys.

The experiment was conducted with the rover located in a fixed location 13km North of the reference station at Symonston and with very wide view of the sky, about 7:00 am 07/04/2016.

Only GPS satellites were used for the rover.

The software was RTKLIB v2.4.3b8.

The GPS was a UBLOX LEA-6T with a small patch antenna (as sold for small UAVs). The LEA-6T provides binary data as used by RTK for carrier phase measurements. Above is the GPS and a USB-RS232 adapter. Continue reading Precision GPS experiment #1

Last update: 8th April, 2016, 1:16 PM

Design / build project: Guanella 1:1 ‘tuner balun for HF’ – #5

Fifth part in the series documenting the design and build of a Guanella 1:1 (current) balun for use on HF with wire antennas and an ATU.

Installation / testing

The balun packaged in a non-conductive housing was designed to have minimal stray capacitance to ground to minimise common mode current with asymmetric loads.

Above, the balun is attached to the exterior side of the antenna feed entrance panel using a male to male N adapter, done up very tight. The feed line connections are liberally coated with marine grease to prevent ingress of water and oxygen, a measure to reduce corrosion. Continue reading Design / build project: Guanella 1:1 ‘tuner balun for HF’ – #5

Last update: 13th February, 2017, 7:46 AM

Improved cooling for the MFJ-949E

At A look at internal losses in a typical ATU I demonstrated that it is quite easy to raise the temperature of the coil in the MFJ-949E to an unsafe level, even with quite modest power.

The most heat sensitive component in this ATU is the coil, specifically the coil supports which are probably polystyrene, and the melting temperature of polystyrene is around 100°.

This article documents modification of my MFJ-949E to reduce the risk of damage under some operating conditions. Continue reading Improved cooling for the MFJ-949E

Last update: 25th April, 2020, 6:55 AM

CH340, CH341 USB to RS-232 chip compatibility

One of the several sources of chips for USB to RS-232 converters is WCH, a Chinese firm offering their CH340 and CH341 chipsets.

Information is scarce as their website is mostly in Chinese language.

CH34x chips have become more common, perhaps as consumers have fled the Chinese Prolific product line (for good reason).

In true Chinese style, downgrade knock offs of Arduino boards (eg the Arduino nano) have appeared, the downgrade is achieved by use of CH340 USB to RS-232 converters instead of the FTDI chips on the genuine nano. Continue reading CH340, CH341 USB to RS-232 chip compatibility

Last update: 31st March, 2016, 9:17 AM

Some thoughts on a two turn small transmitting loop

Small transmitting loops (STL) are very popular with hams, and a fashion is developing for N turn loops. This article lays out some thoughts on a 2 turn STL.

Firstly, to the meaning of “small transmitting loop’. There are a range of definitions used, and they mostly centre around the concept of a size sufficiently small that current is approximately uniform. The issue is about the meaning of sufficiently. Accuracy of estimation of radiation resistance of small transmitting loops sets out a rationale for a single turn loop for criteria that perimeter<λ/10.

This article will compare NEC-4.2 models of loops with the following key parameters:

1m diameter (the loop perimeter is 0.07λ);
20mm copper conductor;
frequency is nominally 7.1MHz;
16 segments per turn
when not specified as in free space, the loop centre is 1m above ‘average’ ground (σ=0.005, εr=13);
the loop is directly fed in the middle, opposite to the tuning capacitor position, cap down;
pitch is 0.15m.

The model is sensitive to all these parameters. Continue reading Some thoughts on a two turn small transmitting loop

Last update: 7th March, 2017, 8:26 AM