I have recently purchased or attempted purchase of several nominally 18W LED circular plates and associated 230VAC drivers.
The circular LED plates all had 36 x 5730 nominally half watt white LEDs arranged as 18 parallel pairs in series.
It is difficult to find datasheets from reputable manufacturers of 5730 LED. Cree makes 5630 which are similar size (though different footprint) and also rated at nominally 0.5W.
Above is the V/I characteristic from Cree’s J series datasheet with an approximation of the 0.5W line superimposed in red. The V/I combination for 0.5W is at the intersection of the two lines, about 162mA and 3.08V. Continue reading Chinese LED ratings – LED plate drivers
This article describes the internals and basic test of a no-name Chinese 4′ T8 LED replacement.
The lamp is a Type B DEP (double ended power) configuration, cool white, it requires rewiring of a traditional magnetic ballast fitting or e-ballast fitting. Don’t attempt this unless you have the needed competencies.
It has no rating label, no information about its configuration on the lamp, no warnings about compatibility… so very Chinese.
The lamp is rated at 18W 1750lm, claimed life is 50,000h but you should take that with a grain of salt. The lamps cost $6.40 ea in a pack of 10, including delivery. They were well packed and the pins had a small plastic protector.
Above, the powered end of the LED strip and the LED driver partially withdrawn from the hollow aluminium extrusion. Continue reading Chinese T8 LED 4′ tube teardown
Having seen some recent discussion where the online experts opined that an example given of a VSWR plot that contained a fairly consistent ripple was
quite normal, this article suggests there is an obvious possible explanation and that to treat it as quite normal may be to ignore the information presented.
Above is a partial simulation of a scenario using Rigexpert’s Antscope. It starts with an actual measurement of a Diamond X-50N around 146MHz with the actual feed line de-embedded. Then a 100m lossless feed line of VF=0.66 is simulated to produce the plot that contains a ripple apparently superimposed on an expected V shaped VSWR curve.
This is the type of ripple that the expert’s opine is
quite normal. Continue reading VSWR ripple
The popularity of the nanovna with new users has led to a lot of ‘beginners’ seeking advice of the online experts.
A recent question and the responses exposes some common misunderstanding / woolly thinking.
A beginner in search of wisdom asked if
there an easy way to measure balun loss?
One of the responses was…
Measure the return loss of the balun with the balun shorted. The return loss should be about twice the balun loss. This is similar to measuring the loss of a shorted or open piece of cable.
This was expanded by others, basically supporting the concept. Continue reading Transformer loss from half return loss
I have a nanoVNA-H which has had many hardware problems, some designed in,but mostly sub-standard / faulty components.
Above, the latest repair. A new battery socket to replace the original that crumbled apart… sub-standard plastic from all appearances. This was from a reputable supplier, so it is probably a genuine JST part rather than some cheap Chinese knock off.
The blue wire is part of a mod to invoke the bootloader on power up, R5 was also changed to something small, 1k IIRC.
Some months ago I purchased a TKDMR TD2B LED tester.
Above is the tester. It comes with a 3 month warranty, FWIW. Continue reading TKDMR TD2B LED tester review
Three recent articles developed an explanation of the YouLoop-2T at MF/lowHF:
The first and third articles explained the concept of signal/noise degradation (SND) statistic, and gave graphs of the behavior of the subject antennas.
This article draws together those SND plots for two antennas, and some variations to the configurations.
Simple loop with transformer
Above, the “simple loop” with 0.5:1 ideal transformer. It could be implemented as a shielded loop (with transformer) with similar behavior (but improved common mode suppression). Continue reading SND implications of variations on the untuned small loop at MF/lowHF
I recently purchased two packs of 2x Osram Substitube LED replacements for a T8 36W florescent tube. The price per tube was about double that of a T8 fluorescent, and claimed life was 30,000 hours.
Note that LED life is usually an estimate of the time for 50% failure. Curiously, Osram individual LEDs have lower lifetime estimates for single LEDs, strings of LEDs will have lower lifetime, and lifetime for say 5% failures would be even lower. On the basis of experience with LED lighting, it might be optimistic to think that most of these lamps will last at least 5,000h.
In the event, three of four tubes had broken glass (yes, they use a glass tube much like the T8 fluorescent tube… though not sealed at the ends), and the other was DOA, no light output.
The LED driver is attached to pins at one end of the lamp, and covered by a label over the glass. Note that there are several incompatible schemes used in T8 fluorescent replacement LEDs, the other scheme bonds the adjacent pins at each end of the lamp and connects line and neutral to opposite ends. Osram calls this a “Type A” connection, and as the name suggests if can be fitted to an ordinary magnetic ballast luminaire PROVIDED the original starter is replaced with Osram’s “LED starter” which is actually a HRC fuse of around 1A rating.
Above is the top view of the electronics. Continue reading Osram Substitube tear down
Small untuned loop for receiving – simple model with transformer gave a simple model for analysing a loop. If you haven’t already read it, you should. It provides a step towards understanding the YouLoop-2T at frequencies where is is a small loop (perimeter<λ/10).
Above is the Airspy Youloup-2T. Try to put the two turns thing out of your mind, it is misleading, panders to some common misunderstanding, and so does not help understanding.
This is somewhat similar to the simple loop, but now the transformer primary is connected to the loop gap terminals by two parallel sections of 50Ω transmission line, the combination being effectively a 100Ω with similar parameters to the component coax sections. Because of the series connection at the transformer and parallel connection at the loop gap, there is a 1:4 impedance transformation additional to that of the coax sections themselves. Continue reading Towards understanding the YouLoop-2T at MF/lowHF
This article explains the operation of a simple nominally 1:4 impedance transformer using transmission line (TL) elements.
Above is a diagram of the device. The currents shown are differential currents in the coax (ie wholly inside the coax), the current on the outside of the shield is not shown on the diagram.
At very low frequencies it may be intuitive that \(V_1\approx V_2\) and \(I_1\approx I_2\), but as frequency increases, a more exact solution is needed. Continue reading A transmission line 1:4 impedance transformer