RF compensation of power relays – bigger relays

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

DSO – dead time after a trace

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

Ongoing MR16 LED failures & purchasing frustrations

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

Origins of the PIK (PIC Iambic Keyer)

I rode my motorcycle over to visit Ray, VK2COX, and we rode our bikes across to Canowindra  (pronounced /kəˈnndrə/ 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.

Screenshot - 18_04_16 , 19_47_22

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)

Antenna assessment using NanoVNA – learning from a user example

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

LED plate driver failure #2- 24W round plate

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