Another small efficient matching transformer for an EFHW – 2 x 5943000601 (FT82-43) – VK4JJ build and measurement

The transformer is an autotransformer of 3+21 turns single layer close wound on a ‘stack’ of two Fair-rite 5943000601 cores (FT82-43?). Note that these were genuine Fair-rite stock, other #43 mix products in the market place may be significantly different (see Ferrite cored RF chokes in Class-E RF power amplifiers – core material issues for more discussion).

There are a plethora of designs using FT82-43 published on the ‘net, most of them have appalling loss.

Above is a Simsmith model and measurement of the transformer for reconciliation. The blue VSWR curve is the measurement and the magenta curve is the calibrated model, they agree well considering the tolerance of ferrite materials. Continue reading Another small efficient matching transformer for an EFHW – 2 x 5943000601 (FT82-43) – VK4JJ build and measurement

Last update: 14th April, 2024, 1:34 PM

Another small efficient matching transformer for an EFHW – LO1238 – VK3PY, VK3TU build and measurement

This article documents the process of design, prototyping, measurement and final build of a 1:49 impedance ratio (1:7 turns ratio) EFHW transformer, exploring some alternative designs along the way, a collaboration between VK3PY and VK3TU with a little guidance.

The transformer is wound on a Jaycar LO1238 35x21x13mm toroid of L15 material (L15 appears to be a NiZn ferrite based on its very high resistivity), they sell at $7 for a pack of two.

2:14 winding

The first test was of a 2:14 turn winding terminated in a 2450Ω load. The transformer is an autotransformer of 2+12t with 91pF compensation capacitor installed in shunt with the 2t winding.

As expected, |s11| is pretty poor at the low end, corresponding to an InsertionVSWR=1.7 @ 3.5MHz.

Design rejected due to high InsertionLoss, magnetising admittance too high.

3:21 turn windings

The transformer is an autotransformer of 3+18t with 91pF compensation capacitor installed in shunt with the 3t winding. Continue reading Another small efficient matching transformer for an EFHW – LO1238 – VK3PY, VK3TU build and measurement

Last update: 14th April, 2024, 1:34 PM

An improved simple Simsmith model for exploration of a common EFHW transformer designs (v1.03)

The article A simple Simsmith model for exploration of a common EFHW transformer design – 2t:14t proposed a simple model.

The previous proposal

Above is the equivalent circuit used to model the transformer. The transformer is replaced with an ideal 1:n transformer, and all secondary side values are referred to the primary side.

The model works quite well for low leakage inductance / low ratio transformers but falls down for the higher leakage inductance / higher ratio transformers.

An improved model

The improved model is similar, but Cse in the model above is distributed to the outer sides of the lumped constant model.

Above is the equivalent circuit used to model the transformer. The transformer is replaced with an ideal 1:n transformer, and all secondary side values are referred to the primary side. Continue reading An improved simple Simsmith model for exploration of a common EFHW transformer designs (v1.03)

Last update: 14th April, 2024, 1:34 PM

Modelling an antenna as a simple two terminal resistance is often naive

in the article A simple transformer model of the Guanella 1:4 balun – some further observations I stated:

Note that a two terminal impedance is a naive representation of many if not most antennas, popular, but a naive over simplification that does not facilitate evaluation of current balance.

An example was a recent posting above that used the model to make assertions about the behaviour of a Guanella 1:4 balun.

This article reports results of two experiments with NEC to model an ‘imperfect’ half wave dipole. It is not exactly resonant, but the main issue is that it is tilted from one end to the other, it is not parallel to the ground surface. Continue reading Modelling an antenna as a simple two terminal resistance is often naive

Last update: 12th November, 2022, 7:52 AM

Garden environmental telemetry project – part 4

Garden environmental telemetry project – part 1 laid out plans for a simple maker / DIY IoT garden environmental telemetry system.

This article documents a change to the sensor configuration and payload formatter in preparation for another RS485-LN.

The sensors are now:

  • ID=1 air temperature and humidity;
  • ID=2 soil temperature and humidity.

The payload  contains a 8bit payload version number then four 16bit values for the four sensors. This is parsed by the TNN uplink formatter.

function decodeUplink(input) {
  var payver=input.bytes[0];
  switch(payver){
    case 1:
      return {
        data: {
          field3: ((input.bytes[3]<< 8)|input.bytes[4])/10,
          field4: ((input.bytes[1]<< 8)|input.bytes[2])/10,
          field5: ((input.bytes[7]<< 8)|input.bytes[8])/10,
          field6: ((input.bytes[5]<< 8)|input.bytes[6])/10
        },
      warnings: [], // optional
      errors: [] // optional (if set, the decoding failed)
      };
    case 2:
      break;
    }
  }

Above, is the Custom Javascript formatter which writes the measured values into variables fields3-field6 of the data object.

To be continued…

Last update: 9th November, 2022, 8:09 AM

A simple transformer model of the Guanella 1:4 balun – some further observations

A simple transformer model of the Guanella 1:4 balun discussed a simple model for the operation of the device, but a model that is too simple for most RF baluns. Notwithstanding that, it does expose some interesting issues that are not only valid at lower frequencies, but will also be manifest in an RF balun.

Isolated load

Consider the effect of breaking the connection at the red X, so that we now have  what is often referred to as an “isolated load”. Continue reading A simple transformer model of the Guanella 1:4 balun – some further observations

Last update: 8th November, 2022, 4:50 AM

A simple transformer model of the Guanella 1:4 balun

(Guanella 1944) described a 1:4 balun, of a type often known as a current balun.

From Definition: Current Balun, Voltage Balun:

An ideal current balun delivers currents that are equal in magnitude and opposite in phase.

A good current balun will approach the ideal condition. It will deliver approximately equal currents with approximately opposite phase, irrespective of the load impedance (including symmetry).

Common mode current will be small.

If the load impedance is not symmetric, then the voltages at each output terminal will not be equal in magnitude and opposite in phase. (Note that for a truly ‘isolated’ load, one well represented as a two terminal load, the currents MUST be equal in magnitude and opposite in phase, but the voltages may not be equal in magnitude and opposite in phase.)

A simplified model

 

Above is a schematic of the Guanella 1:4 balun as often presented, this is an edited graphic from the ARRL manual, so may be familiar to readers. Continue reading A simple transformer model of the Guanella 1:4 balun

Last update: 7th November, 2022, 1:31 PM

An experimental propagation beacon on 144.385MHz – part 2

An experimental propagation beacon on 144.385MHz laid out plans and some first test results.

This article explores a possible deployment scenario and likely paths over which it may be ‘heard’ using Spectrum Lab or the like to dig the signal out of the noise.

Path

Transmit end

Tx power is 10W with on-off keying (OOK or A1 CW).

Tx antenna system gain ~17dBi.

Receive end

Rx antenna gain is 9dBi.

Rx NF specification is 12dB (4236K).

Above are the results of an ambient noise test. In this case, the noise floor at the antenna is some 7000K, it is probably ~7dB higher than a modest weak signal station. Continue reading An experimental propagation beacon on 144.385MHz – part 2

Last update: 7th November, 2022, 9:34 AM

An experimental propagation beacon on 144.385MHz

An experimental beacon on 144MHz has been deployed for evaluation. The beacon is designed to permit observation of aircraft enhancement propagation by way of a 200+s unmodulated carrier in each 300s cycle. Ident is by very slow Morse code. Necessary bandwidth (ITU-R SM.1138-3) is just under 5Hz, requiring 5Hz receiver bandwidth for ‘crisp’ decoding under weak signal conditions, but 1Hz receiver bandwidth is better for observing aircraft reflections.

There has been long running argument about whether such propagation paths are reflection from hot gasses behind the aircraft, or reflection from conducting skin on the aircraft. With increasing use of reinforced plastic skins, we may observe different response from similarly sized aircraft, depending on the skin, and these differences may be frequency dependent.

An interesting topic for study.

Details:

  • frequency: 144.385MHz, 144.384Hz USB dial freq, 144.385MHZ dial frequency in CW mode on modern transceivers (accuracy should be within 200Hz);
  • power: 20W EIRP (current details: https://vkspotter.com/?action=beacon-item&bid=355), ACT, horizontally polarised, antenna is 20m AGL;
  • modulation: ~5 minute cycle uses A1 Morse modulation (OOK) QRSS1 (1s dits) callsign (VK1OD) followed by key down for the rest of the cycle;
  • location is QF44op.

Continue reading An experimental propagation beacon on 144.385MHz

Last update: 3rd November, 2022, 6:23 AM

KB0YH’s STLcalc v2.05

In the light of Small transmitting loop calculators – a comparison a reader asked my thoughts on yet another small transmitting loop calculator, KB0YH’s STLcalc v2.05.

There are lots of small loop calculators published, and yes, I have added to the number. Most are some form of elaboration of formulas published by (Hart 1986), and given ‘imprimatur’ by ARRL (Straw 2007). These formulas are deeply flawed, see Reconciling W5QJR’s loop formulas.

For that reason, my first step in reviewing any small loop calculator is to look for hints of Hart. Continue reading KB0YH’s STLcalc v2.05

Last update: 29th December, 2022, 5:28 AM