Small efficient matching transformer for an EFHW

At FT82-43 matching transformer for an EFHW I wrote about the likely losses at 3.6MHz of a common design using a FT82-43 ferrite core with a 3t primary. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz.

I have been offered input VSWR curves for such a configuration, and they are impressive… but VSWR curves do not address the question of loss / efficiency.

Note that building loss into antenna system components is a legitimate and common method of taming VSWR excursions, eg TTFD, CHA250, many EFHW transformers, but in some applications, users may prioritise radiated power over VSWR.

Design context / objectives

Objectives are:

  • used with a load such that the input impedance Zin is approximately 50+j0Ω, Gin=0.02S;
  • broadband operation from 3.5-30MHz;
  • VSWR < 2 with nominal 3200Ω load; and
  • transformer efficiency > 90% at 3.6MHz.

The following describes such a transformer using a Fair-rite 2643625002 core (16.25×7.29×14.3mm #43).

I mentioned in the reference article that the metric ΣA/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. ΣA/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass.

The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. Continue reading Small efficient matching transformer for an EFHW

FT82-43 matching transformer for an EFHW

A published design for an EFHW matching device from 80-10m uses the following circuit.

Like almost all such ‘designs’, they are published without supporting measurements or simulations.

The transformer is intended to be used with a load such that the input impedance Zin is approximately 50+j0Ω, Gin=0.02S.

Analysis of a simple model of the transformer with a load such that input impedance is 50+j0Ω gives insight into likely core losses.
Continue reading FT82-43 matching transformer for an EFHW

Surecom SW-102 VSWR meter review – v2.6

At Surecom SW-102 VSWR meter review I wrote a review of a meter which I had purchased a little over a year ago, it was at v4.5.

One of the many problems identified was inconsistency of displayed values.

v2.6

Surecom’s versions are confusing, the highest number is not necessarily the latest version. It appears a partial version history from their current page advertising the SW-102 is:

OLD VERSION : V3.3 ,V3.8 ,V4.5,V4.9 ,V5.0,V5.1
2017-8 NEW VERSION : V2.02 ,V2.03

The following image is from Surecom’s current page advertising the SW-102, and I assume that the version shown here (v2.6) is the latest at time of writing.

The image captures the outputs of two tests with poor and good dummy loads.

Let’s check the displayed values for internal consistency. Continue reading Surecom SW-102 VSWR meter review – v2.6

Finding velocity factor of coaxial transmission line using the velocity factor solver

This article is a tutorial in use of Velocity factor solver to find the velocity factor of a sample coaxial transmission line using an antenna analyser.

Example 1: Youkits FG-01

we have two lengths of H&S RG223 terminated in identical BNC connectors at both ends. Let’s connect each in turn to a Youkits FG-01 antenna analyser and find the quarter wave resonance of each (ie the lowest frequency at which measured X passes through zero).

Above, the line sections are connected to the Youkits, and the length overall is measured from the case of the analyser to the of the cable.
Continue reading Finding velocity factor of coaxial transmission line using the velocity factor solver

Finding velocity factor of coaxial transmission line – a challenge

An upcoming article works through an approach to finding the velocity factor of a sample of coaxial cable using an antenna analyser.

As a precursor, this article poses a challenge that will identify the issues relevant to the problem.

Case 1:

A Rigexpert has been used to measure the first quarter wave resonance of a length of ‘unknown’ semi air dielectric RG6.

The length of RG6 Dual Shield is terminated in an F connectors at one end, the other end cut cleanly square. It is connected via  N(M)-BNC(F) and BNC(M)-F(F) adapters to a Rigexpert AA-600 antenna analyser and the quarter wave resonance noted (ie the lowest frequency at which measured X passes through zero).

Above, the line section is connected to the Rigexpert via adapters, and the length overall is measured from the case of the AA-600 to the of the cable. The measured length is 1.077m, make any adjustment to that length that you think is justified on the information presented here.
Continue reading Finding velocity factor of coaxial transmission line – a challenge

AIM system – AIM912 initial checkout

Given that most versions of the AIM software that I have tried have had serious defects, I approach the latest release, AIM912, with caution.

An interesting opportunity presented when a correspondent sent me some .scn files captured from an AIM4170B using AIM912.

Above is the correspondents .scn file opened in AIM912. Continue reading AIM system – AIM912 initial checkout

On winding configuration of EFHW matching transformers

The net abounds with articles on broadband transformers (ie untuned) for matching End Fed Half Wave (EFHW) antennas to 50Ω. One of the aspects that is common to most designs is that the turns of the primary winding are wound ‘bifilar’ with the start of the secondary winding, indeed the twist pitch is often very short and articles often go into detail on how to make this magic thing.

The magic is that it is supposed to give closer to ideal behaviour of the transformers by way of minimising flux leakage.

The transformer above is styled on the common design, and it consists of a 2t primary and 16t secondary where the primary is wound bifilar, and a third 2t winding wound over the primary end of the transformer between the other turns. Continue reading On winding configuration of EFHW matching transformers

Ellington 3 x FT240-52 matching transformer for an EFHW

Ellington describes in a Youtube video his high power matching transformer for an EFHW, he rates it suited to 500W CW.

Like almost all such ‘designs’, they are published without supporting measurements or simulations.

The transformer is intended to be used with a load such that the input impedance Zin is approximately 50+j0Ω, Gin=0.02S.

Analysis of a simple model of the transformer with a load such that input impedance is 50+j0Ω gives insight into likely core losses.
Continue reading Ellington 3 x FT240-52 matching transformer for an EFHW

A low cost 50Ω termination for measurement purposes

This article shows just how easy it is to make an inexpensive low VSWR load for antenna analyser validation / measurements.

Above is an AA-600 sweep of the prototype from 10kHz to 100MHz. VSWR reads 1.02 in ‘All’ mode at 100MHz… better than the inherent accuracy of the instrument.

How expensive?

It is made from two 100Ω 1% 1206 SM resistors purchased on eBay for about $2/100, so about $0.04 for the resistors, and 40mm of bare copper wire (0.5mm phone / data wire in this case).

In use, it is held in contact with the coax socket (in this case an N type) with a pair of disposable plastic first aid tweezers (yep, you can buy them on ebay for about $0.20/pair).

While you are at it, make a good short circuit termination by scrunching up a bit of (clean) kitchen aluminium foil and press that against the coax socket conductors.

Try both of these on your antenna analyser and see how it stacks up.

Review of Hantek DSO8102E hand held oscilloscope

This article is a brief review of some issues that were found with initial testing of a Hantek DSO8102E two channel 100MHz hand held oscilloscope.

The DSO8102E is a member of the DSO8000 series (DSO8060, DSO8070E, DSO8100E, DSO8150E, DSO8200E), and shares most specifications across the series.

The specifications are very impressive, and price at just under $1000 for a Chinese brand seemed reasonable (hand held oscilloscopes are expensive compared to bench oscilloscopes).

The test scenario was a practical application, observation of the data traffic to/from a DHT22 temperature and humidity sensor in the project ESP8266 IoT DHT22 temperature and humidity – evolution 2. Continue reading Review of Hantek DSO8102E hand held oscilloscope