Month: September 2018

Australian amateur radio licensing reform (2018)

It has become clear that ACMA intends to progress the WIA’s initial actions to partially integrate the qualifications requirement for issue of an amateur radio licence into the Australian Qualifications Framework (AQF).

The AQF is the national policy for regulated qualifications in  Australian education and training. It incorporates the qualifications from each education and training sector into a single comprehensive national qualifications framework. The AQF was introduced in 1995 to underpin the national system of qualifications in Australia encompassing higher education, vocational education and training and schools.

That push on integration includes the use of Registered Training Organisations (RTO) for assessments, RTOs are an element of the Vocational Education and Training Sector (VETS).

The definition of Vocational Education and Training can be taken from australia.gov.au:

Vocational education and training

Designed to deliver workplace-specific skills and knowledge, vocational education and training (VET) covers a wide range of careers and industries, including trade and office work, retail, hospitality and technology.

So, the WIA and ACMA have over a couple of decades acted to integrate amateur radio qualifications in the AQF to some extent, and current actions are intended to perform assessments within the VETS (ie by VETS qualified assessors under an RTO). Continue reading Australian amateur radio licensing reform (2018)

Last update: 18th October, 2018, 8:07 AM

Measuring ambient noise level using a spectrum analyser #2

The article Measuring ambient noise level using a spectrum analyser was a walk through of measuring ambient noise using a spectrum analyser.

This article details a method that uses an online calculator to conveniently perform the calcs that permit more accurate answers by factoring the internal noise of the spectrum analyser into the calcs.

Step 1: measure instrument noise figure

Measure the noise floor of the instrument with 50Ω input termination using an average power (RMS) detector.

Now calculate the Noise Figure (Field Strength Noise Figure on output report). Continue reading Measuring ambient noise level using a spectrum analyser #2

Last update: 27th September, 2018, 7:04 AM

AE7PD’s transmitting loop measurements

AE7PD documented his measurements of a 3.16m perimeter circular transmitting loop, 1.8m centre height above ground, that he made using 16mm copper tube and a split stator tuning capacitor:

AE7PD gives the radiation efficiency on 20m as 30.5% or -5.2dB.

I present here an alternative analysis of the antenna as measured on 20m.

Assuming the measurements were made with the antenna clear of disturbing conductors etc, and that 5/8″ tube means 16mm OD.

The key measurements were:

  • centre frequency 14.165MHz, VSWRmin=1.0;
  • VSWR=2.62 bandwidth 22kHz.

A NEC-4.2 model of the antenna at 14MHz was built and calibrated to the measured half power bandwidth (22kHz). Model assumptions include:

  • ‘average’ ground (σ=0.005, εr=13);
  • Q of the tuning capacitor = 2000;
  • conductivity of the loop conductor adjusted to calibrate the model half power bandwidth to measurement.

Note that the model may depart from the actual test scenario in other ways.

Above is the VSWR scan of the calibrated model, the load is matched at centre frequency and half power bandwidth is taken as the range between ReturnLoss=6.99dB points. Continue reading AE7PD’s transmitting loop measurements

Last update: 22nd September, 2018, 8:28 AM

Findling & Siwiak 2012 measurements of an Alexloop – discussion

I mentioned in Findling & Siwiak 2012 measurements of an Alexloop issues with their efficiency calculation.

Above is an extract from (Findling & Siwiak 2012).

(Siwiak & Quick 2018) give an equivalent circuit of lossless loop structure in free space.

When tuned to resonance, the response is simply that of a series RLC circuit where R=Rr (the radiation resistance) which is dependent on frequency, but varies very slowly with frequency compared to the net reactance X.

Above is a NEC simulation of such a loop. Continue reading Findling & Siwiak 2012 measurements of an Alexloop – discussion

Last update: 18th September, 2018, 2:42 PM

G3CWI 2018 measurements of an Alexloop Walkham

Richard, G3CWI, measured the impedance and bandwidth of a Alexloop Walkham, a popular small transmitting loop (STL). The antenna was situated in the clear at 1.65m centre height above natural ground.

The key measurements were:

  • centre frequency 7.014MHz, |Z|=51Ω, VSWR=1.1;
  • VSWR=3 bandwidth 16.2kHz.

The step size of the analyser prevented measurement exactly at resonance, but R changes very closely with frequency near resonance so we can estimate it quite well. The above figures can be used to find R close to resonance.

Within the limits of measurement error, we can say that R at resonance should be very close to 51Ω, and VSWRmin close to 1.02. Continue reading G3CWI 2018 measurements of an Alexloop Walkham

Last update: 14th September, 2018, 5:38 PM

Findling & Siwiak 2012 measurements of an Alexloop

(Findling, A & Siwiak 2012) documented measurements they made of a popular small transmitting loop (STL), an Alexloop Walkham.

Now Alexloops seem to have undergone some evolution, and there does not seem to be a clear list of model names or numbers with features or specifications, so to some extent the antenna is a little non descript.

The article did not document the environment of the test antenna, but Findling explained in correspondence that it was relatively clear of conducting structures and about 1.2m above natural ground.

A NEC-4.2 model of the antenna at 7MHz was built and calibrated to their measured half power bandwidth (19kHz). Model assumptions include:

  • ‘average’ ground (σ=0.005, εr=13);
  • Q of the tuning capacitor = 1000;
  • conductivity of the loop conductor adjusted to calibrate the model half power bandwidth to measurement.

Note that the model may depart from the actual test scenario in other ways, it is challenging to glean all the data that one would like from the article.

Above is an extract from (Findling, A & Siwiak 2012).

Above is the VSWR scan of the calibrated model, the load is matched at centre frequency and half power bandwidth is taken as the range between ReturnLoss=6.99dB points. Continue reading Findling & Siwiak 2012 measurements of an Alexloop

Last update: 13th September, 2018, 8:41 PM

Single turn coaxial loop resonator analysis

Recent discussion online of a purported commercial HF small transmitting loop (STL) was challenged in analysing the structure, questioning whether such a connection was ‘correct’.

The STL used a main loop resonator and a separate small auxiliary loop for the 50Ω feed, a very common arrangement.

The main loop is a coaxial cable with, in this case, a tuning capacitor inserted between the inner conductors at each end. Above is a diagram of the main loop. Continue reading Single turn coaxial loop resonator analysis

Last update: 13th September, 2018, 7:20 AM

WW1WW’s matching transformer for an EFHW

At PD7MAA’s BN43-202 matching transformer for an EFHW I gave an estimate of the core loss in PD7MAA’s transformer.

An online expert questioned the analysis and later measurements, and proposed his own transformer design as evidence.

Notably, his transformer uses #61 material and a larger binocular core, a Fair-rite 2861006802 with 2t for a nominal 50Ω primary, giving loss measurements at 7MHz of 0.08dB. Note that the confidence limits of that loss measurement because of the way in which it was obtained (eg a 1% error in the 1120Ω load resistor contributes 0.043dB error to the result), but the measurements do suggest that the loss is probably very low.

Though the loss is low and Return Loss is high at 7MHz, the limits for ReturnLoss>14dB (VSWR<1.5) is 5-18MHz. With compensation, that range may be changed.

Prediction

Lets apply the method laid out at PD7MAA’s BN43-202 matching transformer for an EFHW.

The best Fair-rite data I can find quickly is a chart of the impedance of a one turn winding.

Scaling from this graph, Xs is close of 35Ω at 7MHz, so lets used that to derive some basic parameters for the core. Continue reading WW1WW’s matching transformer for an EFHW

Last update: 14th April, 2024, 1:35 PM