End fed half wave – NEC models for 20m

Introduction

End Fed Half Wave antennas are again very fashionable with hams, accompanied by extraordinary claims and somewhat sparse understanding (the way of modern ham radio).

To add some light I have created a set of NEC 4.2 models of a half wave antenna on 20m to give some insight into the behaviour of a bottom fed vertical half wave over real ground.

This analysis does not consider harmonic operation, antennas are a half wave at 14.2MHz.

Four models are used:

  1. 20mHW-VEP – bottom fed vertical above perfect ground;
  2. 20mHW-VEA – bottom fed vertical above real ground;
  3. 20mHW-VCA – centre fed vertical above real ground (ie ground independent feed);
  4. 20mHW-HCA – centre fed horizontal at 5m height above ground;

NEC 4.2 model description:

  • 14.2MHz;
  • no conductor loss;
  • real ground assumed to have conductivity=0.005S, εr=13, of course results are dependent on these values;
  • conductors are ~10m long, 20mm diameter;
  • bottom fed vertical half wave uses a 10m x 20mm vertical driven ground electrode;
  • centre fed vertical is raised 200mm above ground;
  • feed line and feed line common mode current are excluded;
  • the centre of all antennas is ~5m above ground (real or perfect).

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Above are the patterns from the models for discussion. Continue reading End fed half wave – NEC models for 20m

Mandarin & Lime Marmalade

I couldn’t help myself, Mandarins are falling and I had to try a marmalade of Mandarins and Limes. I made a small batch of marmalade using 50% Tahitian Lime and 50% Imperial Mandarin. Raw sugar was one third the added sugar to impart a darker colour.

MandarinLimeMarmalade

The marmalade is light coloured, sweet and tangy. Continue reading Mandarin & Lime Marmalade

Accuracy of AIMuhf system – AIM910B vs several recent versions on a ferrite cored inductor

AIMuhf

At Accuracy of AIMuhf system – AIM910A vs several recent versions on a ferrite cored inductor I reported significant problems reconciling several recent versions of AIM software measuring the same inductor. Continue reading Accuracy of AIMuhf system – AIM910B vs several recent versions on a ferrite cored inductor

Another chapter in the NBN debacle – Jul 2016

I mentioned that NBN is coming….

NBN201607-01

This NBN cabinet has been in place for about eight months, no electronics in it… but an important showpiece in the government’s desire to show that Malcolm Turnbull’s copper based NBN was on track. Empty cabinets probably persuaded some naive voters at the federal election earlier this month.

The deception worked, Malcolm was returned, albeit with barely the majority to allow majority coalition government.

NBN is a wholly government owned ‘enterprise’ operating on a ‘commercial’ basis. Who else could afford to spend capital on infrastructure that delivers no service.
Continue reading Another chapter in the NBN debacle – Jul 2016

Tahitian Lime Marmalade

We had a small excess of Tahitian Limes ripen, so I tried a test batch of Tahitian Lime Marmalade.

TahitianLimeMarmalade

The marmalade is light coloured, sweet and tangy.

The downside is that the fruit is full of seeds, not just in the equatorial plane but distributed right through it, so scooping seeds out is quite a task.

Screenshot - 26_07_16 , 10_37_42

 

It is the first time I have made jam from these, and essentially I used the 40:60 mix from FAO’s Generic Jam Recipe, though being limes no acid was needed, in fact about 6g of Sodium Bicarbonate per kg of fruit to achieve the ideal pH of 3.2-3.3. The limes were cooked to release some Pectin, but a little Pectin 10g/kg) was added as the cooked fruit gave a slightly weak reaction in Methylated Spirits.

Endpoint was assessed by measuring Brix using a refractometer, confirmed by setting a drop of jam on a cold plate.

InsertionVSWR of Grebenkemper’s Tandem Match

The findings at InsertionVSWR of Revex W560 on HF and the suggestion that the low frequency problem is characteristic of poorly designed Sontheimer couplers (Sontheimer, C & Frederick 1966).

These couplers were popularised by (Grebenkemper 1987)  in his Tandem Match – An Accurate Directional Wattmeter and have appeared in ARRL handbooks over the decades, and may have inspired the many commercial implementations of the coupler.

Grebenkemper claims his meter is ‘good’ down to 1.8MHz, but does not clearly claim any particular InsertionVSWR. There is limited value in an instrument that can measure down to 1.05 when it causes significantly higher VSWR itself.

Screenshot - 24_07_16 , 15_31_41

Lets drill down on Gebenkember’s article, specifically the coupler design.
Continue reading InsertionVSWR of Grebenkemper’s Tandem Match

Fan controlled by humidity sensor – design technique

This article gives an outline of the process used in designing the Fan controlled by humidity sensor to use my Generic heating / cooling controller design (hcctl).

Arduino thermistor thermometer – a tutorial gave a method for designing a thermometer based on a formula predicting the behaviour of the sensor. This article explains a different approach where that is not possible.

HDS10-02

Above is a characteristic from the manufacturer’s data.

The curves to no lend themselves to simple curve fits, so a cubic spine interpolation will be made based on key points from the curve.

Four our purposes, the mean curve (green) is sufficient for design.

Screenshot - 24_07_16 , 08_16_07

 

Above, the mean curve was digitised to capture the shape of the curve, 17 points were used.
Continue reading Fan controlled by humidity sensor – design technique