At nanoVNA-H – de-embedding the feed line in remote measurement I recently wrote on a procedure that can be very useful to refer measurements made at the transmitter end of a feed line to the antenna feed point.
A correspondent recently shared an AIM 4170 scan file of his 40m half wave dipole antenna system taken from the transmitter end of the coax and maintaining the common mode current path by bonding the shield of the coax connector to normal connection point on the transmitter.
Above is his graphic of the measurement looking into around 23m of RG58 feed line.
It shows the VSWR curve is quite classic in shape, the frequency of minimum VSWR is a little low, and the minimum VSWR is 1.478 which is quite within expectations of such an antenna. Continue reading AIM4170 – de-embedding the feed line in remote measurement
This article is about an inexpensive GU10 230V 7W LED lamp.
Like so much inexpensive Chinese lamp product, it has not markings on the exterior or the lamp (eg voltage, current, power), but the product was sold as 7W and the box had that printed on it.
The lamp failed after less than 100h service, switching on and off intermittently symptomatic of a heat related problem.
Above is the dismantled lamp. Interestingly the LED driver PCB has “Q-3-5*1W” etched into the board, so presumably it is actually a driver for 5 series 1W white LEDs. So much for the claimed 7W, LED product performance claims are often a fraud, more so when the Chinese are involved. Continue reading LED lamp failure analysis – GU10 230VAC 7W
I was sent a pic of a balun and asked to explain how it works.
With no other detail than the pic, it is difficult to supply a complete answer.
Nevertheless, an analysis of what is presented follows. Continue reading (How) does this balun work?
At nanoVNA-H – measure ferrite transformer I gave an example of using a nanovna to measure loss of a ferrite cored transformer.
Noelec makes a small transformer, the Balun One Nine, pictured above and they offer a set of |s11| and |s12| curves in a back to back test. (Note: back to back tests are not a very reliable test.) Continue reading nanoVNA-H – measure ferrite transformer – Noelec balun
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 Molex Picoblade 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.
PS: a word of warning… always check polarity when fitting a battery, there is not rigid standardisation of connectors on LIPO batteries.
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