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 /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.

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)

Last update: 8th October, 2023, 3:41 PM

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

Last update: 19th December, 2023, 8:04 AM

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

Last update: 27th October, 2023, 12:48 PM

Welding modern star pickets

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:

  • stick weld with E7018 2.5mm electrodes; or
  • MIG weld with AWS A5.20 E71T-GS 0.9mm flux cored wire.

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

Last update: 21st December, 2023, 8:05 AM

IC-7300 VSWR protection

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.

Understanding the IC-7300

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

Last update: 3rd October, 2023, 7:12 AM

Designing a Gamma Match – Simsmith design tool and confirmation of as-built antenna – comparison with Healey

A correspondent reading Designing a Gamma Match – Simsmith design tool and confirmation of as-built antenna referred me to (Healey 1969) and questioned my method.

I have tried several times to reconcile built and tuned antennas and NEC models with Healey and failed, leading me to think of the problem and devise a good approximation that did reconcile (for me).

This article attempts to reconcile the example given at Designing a Gamma Match – Simsmith design tool and confirmation of as-built antenna, an example where the two built antennas reconcile well with the ARRL published design article and NEC model.

Example for reconciliation

The example antennas are 4 element 144MHz Yagis built around 1970. They were originally designed with a 50Ω split dipole feed, or the option of a folded dipole with 4:1 half wave coax balun. Continue reading Designing a Gamma Match – Simsmith design tool and confirmation of as-built antenna – comparison with Healey

Last update: 19th September, 2023, 8:37 AM

Transmission lines – forward and reflected phasors and the reflection coefficient

Let’s consider the following transmission line scenario:

  • Lossless;
  • Characteristic Impedance Zo=1+j0Ω; and
  • load impedance other than 1+j0Ω, and such that Vf=1∠0 and Vr=0.447∠-63.4° at this point.

The ratio Vr/Vf is known as the reflection coefficient, Γ. (It is also synonymous with S parameters S11, S22… Snn at the respective network ports.)

Above is a  phasor diagram of the forward and reflected voltages at the load. Continue reading Transmission lines – forward and reflected phasors and the reflection coefficient

Last update: 17th September, 2023, 7:45 AM

Design / build project: Guanella 1:1 ‘tuner balun for HF’ – #7

Seventh 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 describes a measurment of common mode impedance Zcm of the packaged balun.

Packaging

The prototype fits in a range of standard electrical boxes. The one featured here has a gasket seal (a PTFE membrane vent was added later).

AtuBalun201

Above, the exterior of the package with M4 brass screw terminals each side for the open wire feed line, and an N(F) connector for the coax connection. N type is chosen as it is waterproof when mated. Continue reading Design / build project: Guanella 1:1 ‘tuner balun for HF’ – #7

Last update: 9th September, 2023, 2:23 PM

Overheating balun cores – how much power does it take?

Overheating balun cores – an explanation discussed a scenario where an operator reports unstable VSWR after 30s of ATU adjustment.

Where the antenna system incorporates ferrite elements, a possible / likely explanation is that loss in a ferrite core has been extreme and raised core temperature to the Curie temperature at which it quickly loses its magnetic properties.

In that scenario, theoretically, the complete temperature curve would look like this.

The initial rate of temperature increase here is 5°/s, and we can safely assume that almost all of the power absorbed by the core is stored as heat energy, little energy is lost the the air when the temperature difference is very small. Continue reading Overheating balun cores – how much power does it take?

Last update: 9th September, 2023, 2:47 PM