RFPM2 – current probe – #4 – TinySA Ultra

I have been asked about compatibility of the RFPM2 current probe with the TinySA and variants.

The current probe was intended for use with a broadband 50Ω RF power meter, but could also be used with a Spectrum Analyser with 50Ω input or an oscilloscope with 50Ω input.

RFPM2 – current probe described a current probe for use with a power meter calibrated in dBm (eg RFPM1 and RFPM2). RFPM2 – current probe – #2 exposed some of the build details. RFPM2 – current probe – #3 showed the implementation.

Above the current probe with RFPM2. Whilst this is not of a clamp-on design, the aperture in the core is sufficient to pass a DIN 7/16 connector through. Continue reading RFPM2 – current probe – #4 – TinySA Ultra

Initial review of ECO-LFP210 LiFePo4 (LiFe) battery

A ECO-LFP210 10Ah 4S LiFePo4 battery was purchased on eBay for a solar powered project, cost about $65 delivered.

Above, the battery (the Anderson Power Pole connector is an addition). The battery incorporates a battery management system (BMS), so protected against over voltage, undervoltage, over current, and cell balance is preserved. Continue reading Initial review of ECO-LFP210 LiFePo4 (LiFe) battery

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)

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

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

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

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