I have a 24W LED oyster in service. The luminaire was purchased complete on eBay for about $45.
It regularly fails, usually the LED driver fails, usually due to failure of the output filter capacitor. Continue reading LED plate driver failure – 24W round plate
RF compensation of power relays referred to a video I have recently posted RF compensation of power relays.
Above, the example relay.
So, does this technique work for bigger relays?
Firstly, small is beautiful… it is easier to get good compensation of smaller relays over a wider frequency range.
Above is an example relay by K5UJ for discussion. I do not have measurement data for this relay box, but experience tells me that at HF, the compensation technique discussed above is likely to give good results for its intended purpose as a HF T/R relay. Continue reading RF compensation of power relays – bigger relays
Oscilloscopes have always had some dead time after completing a trace when they were not able to be retriggered.
I noticed a hand held DSO that I was evaluating to produce a different result on a train of pulses that repeated every 10m, different to a budget Tek TDS2024C DSO.
So, I have conducted an experiment comparing 7 DSOs that I can put my hands on.
The test waveform is a burst of 1MHz 50% square wave of adjustable number of cycles n, and the burst repeated every 100ms.
Setting the DSO timebase to 1µs/div and NORMAL trigger, and with zero time at mid display, the initial display with n=10 is a flat line up to mid screen, then pulses (5 or 6 depending on the display width) to edge of screen. This is rewritten every 100ms with every new burst. Continue reading DSO – dead time after a trace
I have recently posted a video on RF compensation of power relays.
Above, the example relay. Continue reading RF compensation of power relays
We have around 25 MR16 LED lamps, half of which are almost never used, the other half probably average 4 hours per day, or ~1500 hours per annum.
Remember that greens touted this ‘green technology’ to have a life of 100,000 hours. More recently, claims have been moderated to 10,000 to 25,000 hours… but that is a single LED element alone, not a set of them, and it does not include failures of the internal and external drivers. IOW it continues the fraud of green lighting.
Above, the MR16 50mm LED lamp. Continue reading Ongoing MR16 LED failures & purchasing frustrations
I rode my motorcycle over to visit Ray, VK2COX, and we rode our bikes across to Canowindra (pronounced /kəˈnaʊndrə/ kə-NOWN-drə) for a burger at the famous Garden of Roses Cafe.
Over lunch, Ray described his new cigarette packet sized CW rig build that he would take up onto the local hill on his block for a little play, and told me he was going to jam his favorite 3xNE555 CW keyer into it.
I offered to design him an accurate keyer based on an 8 legged DIP chip and less than a dozen parts overall. I designed the logic in my head on the way home to Canberra, and started programming it that night in May 2001.
The PIK is described at PIK – PIC Iambic Keyer. Above is the generic circuit diagram of the PIK. Continue reading Origins of the PIK (PIC Iambic Keyer)
A recent online posting provides content for learning. K3EUI posted a NanoVNA-Saver screenshot of his antenna described as:
Set out a horizontal loop wire antenna for possible NVIS paths
Wire is about 140 ft length with an outside CLC tuner, fed with 50 ft RG213. …Here were the Nano VNA graphs of this new loop antenna, measured from inside the shack (50 ft RG213)…
Can we learn something from this? Continue reading Antenna assessment using NanoVNA – learning from a user example
This article documents a second failure of a 24W LED oyster. The luminaire was purchased complete on eBay for about $45.
After about two years use, the light became sensitive to switching transients on the mains, visibly blinking when other appliances were turn off or on. After some time, this progressed to oscillating on and off for a few seconds on a cold startup, but on hot startup it was stable.
These are exactly the same symptoms as the first failure… no surprises, it is the same driver board that had a faulty capacitor replaced… and worked fine for a couple of years.
Above is the failed driver board with the replaced 105° 6.8µF input filter capacitor (at the right). The capacitor should have an ESR around 5Ω, but now cannot be measured by my ESR meters (both upper limit ~100Ω). The other capacitor also has excessive ESR. Continue reading LED plate driver failure #2- 24W round plate
I was chatting with a chap the other day, and he said “pity you cannot weld star pickets anymore” wanting to raise an existing fence 600mm to try and keep kangaroos out (exclusion fencing).
You can buy a section of star picket with a socket to put on top of an existing picket, but they are quite expensive.
So, the problem arises because a lot of star pickets sold in Australia in the last 20 years or so are made in China from “rail steel”, a higher carbon steel (~0.6%) that allows thinner section, less weight, lower transport cost etc.
If you arc weld these with ordinary general purpose electrodes (E6013 in Australia), they are likely to crack and fail under load.
I have used two options:
To extend an existing picket in situ, you can lap the extension and do two vertical welds, or but the sections (see jig below) and do horizontal three welds.
Above is a jig using a short piece of water pipe and two locking chain clamps. Of course you would straddle the join to clamp the pieces and remove the jig after two welds are completed. Continue reading Welding modern star pickets
A ham consulting the experts on QRZ asked:
On 30 meters, my SWR reads 3:1 to my antenna (an EndFed 53 feet long wire up about 25 feet). Reading a chart I have, I see that at 80 watts output, my reflected power should be 20 watts. I verified this by looking at my Diamond SX-200 Meter which also indicates the reflected power is 20 watts. My questions are these: does the 20 watts reduce my 80 watts output to 60 watts at the antenna? I have a choke on my feed line in my shack (near my transceiver) & the SX-200 Meter is between the choke & transceiver….
The OP later explained that the transceiver is a IC-7300 and it appears that the internal tuner is in use above… so let’s proceed on that basis.
Analysing the OP’s report, his SX-200 indicates VSWR=3 Pf=80, therefore Pr=20, and P=60W. Note that \(P=P_f-P_r\) is valid because Zref is real, so the answer to his question about power to the antenna is 60W, he is quite correct.
He went on to ask where the 20W reflected goes to… but I will leave that to Walt Maxwell devotees to discuss energy sloshing around and re-re-re reflections… the stuff of ham lore.
As an example of what might be expected of the IC-7300 with a mismatched load, I did a series of measurements at 7MHz with a sample variably mismatched load.
Above is a plot of power output vs VSWR for a sample mismatched load. Also plotted is the measured reflected power and the calculated power output based on the ham lore \(P=P_f (1-\rho^2)\). Continue reading IC-7300 VSWR protection