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The magic of the End Fed Half Wave antenna / EFHW

I have noted recently the increasing popularity of the so-called End Fed Half Wave antenna, though the term often includes harmonic operation of the antenna.

It seems that at the heart of common ham understanding of this antenna system is that some kind of two terminal feed device creates a scenario with current on the nominal radiator, and zero common mode current on the feed line. If that feed device is small, its contents bears little influence on the current distribution on the feed line and radiator (the device behaviour approaches that of a simple circuit node).

Above is the kind of current distribution envisaged by many. The equivalent source is shown at the end fed feed point The red curve is the magnitude of current, the horizontal line represents the nominal radiator, and the vertical line represents the common mode conductor formed by the feed line. The feed line is often of arbitrary length, arbitrary route, and it may connect to real ground via an arbitrary impedance. Pretty much everything about this antenna system is random save the length of the nominal radiator. Continue reading The magic of the End Fed Half Wave antenna / EFHW

Last update: 28th January, 2022, 8:08 AM

Exploiting your antenna analyser #21

A correspondent wrote about the apparent conflict between Exploiting your antenna analyser #11 and Alan, K0BG’s discussion of The SWR vs. Resonance Myth. Essentially the correspondent was concerned that Alan’s VSWR curve was difficult to understand.

K0BG’s pitch

For convenience, here is the relevant explanation.

By definition, an antenna’s resonant point will be when the reactive component (j) is equal to zero (X=Ø, or +jØ). At that point in our example shown at left, the R value reads 23 ohms, and the SWR readout will be 2.1:1 (actually 2.17:1). If we raise the analyzer’s frequency slightly, the reactive component will increase (inductively) along with an increase in the resistive component, hence the VSWR will decrease, perhaps to 1.4:1. In this case, the MFJ-259B is connected to an unmatched, screwdriver antenna mounted on the left quarter panel, and measured through a 12 inch long piece of coax. This fact is shown graphically in the image at right (below).

Note that the graph is unscaled, and that frustrates interpretation. The text is also not very clear, a further frustration. It is easy to draw a graph… but is the graph inspired by a proposition or is it supporting evidence. Continue reading Exploiting your antenna analyser #21

Last update: 19th June, 2016, 7:12 PM

Chinese AD8307 power measurement module #4

Desk study of opportunity to improve linearity.

At Chinese AD8307 power measurement module #2 I showed measurement of the linearity of an AD8307 based RF power meter.

The specification linearity is +/-1dB, which is poorer than one might like in a power measuring instrument.

The diagram above from the AD8307 datasheet shows the internal architecture, including 9 stages of cascaded log detector cells that attempt to give a log response over around 100dB range. The issue is that in the transition region between detector cells, error is worse than well inside an individual detector cell’s range.

Above is a sweep from -65 to -6dBm at 10MHz after calibration of slope and offset. The linear fit to the blue curve shows slope is 20mV/dB and intercept 1.8015 for 0dBm means the offset is -1.8015/0.02=-90.08dBm. Log conformance is 0.2dB (well within spec at this frequency, temperature etc).
Continue reading Chinese AD8307 power measurement module #4

Last update: 19th June, 2016, 10:27 AM

UV cure adhesive for temperature sensors

Seeing the promotion of a clear adhesive with cure initiated by ~400nm UV light from a LED source, one’s mind wondered to its application for attaching temperature sensors to heatsinks etc.

A sample of Kafuter K-300 was tested.

Above is the test jig, a 1N4004 diode is attached to the corner of a scrap of 1.6mm thick aluminium sheet using the adhesive which was cured with UV light and then allowed 10 hours further to strengthen (if that helps). Continue reading UV cure adhesive for temperature sensors

Last update: 17th June, 2016, 8:41 AM

W2AU 1:1 voltage balun

A very long time ago, I purchased a W2AU 1:1 balun on the maker’s claims that it was good from 1.8 to 30MHz.

These were very popular at the time, but as voltage baluns they achieve good current balance ONLY on very symmetric loads and so are not well suited to most wire antennas.

Above is W2AU’s illustration of the internals.

Mine barely saw service before it became obvious that it had an intermittent connection to the inner pin of the coax connector. That turned out to be a poor soldered joint, a problem that is apparently quite common and perhaps the result of not properly removing the wire enamel before soldering.

Having cut the enclosure to get at the innards and fix it (they were not intended to be repaired), I rebuilt it in a similar enclosure made from plumbing PVC pipe and caps, and took the opportunity to fit some different output terminals and an N type coax connector.

W2auBalun01 Above is the rebuilt balun which since that day has been reserved for test kit for evaluating the performance of a voltage balun in some scenario or another. Continue reading W2AU 1:1 voltage balun

Last update: 26th June, 2016, 11:49 AM

PAROT with transformerless power supply and 230V AC relay

This article documents an implementation of PAROT (Power Amplifier Run On Timer) using Transformerless power supply for PAROT.

This PAROT uses a 230V AC relay for 230V mains switching and includes PTT switching using an FOD852 opto coupler.

The intended application is to control power to a valve PA, providing programmable heater delay, and cool down delay of power off.

Above is the electronics built on a small piece of Veroboard. This one uses a 0.47µF cap as the power supply current requirements are a little lower than for the SSR. Continue reading PAROT with transformerless power supply and 230V AC relay

Last update: 16th June, 2016, 3:43 PM

Australian Lime Marmalade

Winter has arrived, but so has the citrus fruit matured.

I picked a bucket of Australian Limes which had ripened to the point of mostly yellow skin.

Being a bit partial to Lime Marmalade, I have cooked up a couple of 4kg batches of high fruit content marmalade and bottled it.

It is the first time I have made jam from these, and essentially I used the 45:55 mix from FAO’s Generic Jam Recipe, though being limes no acid was needed, in fact about 2.5g 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 6g/kg) was added as the cooked fruit gave a slightly weak reaction in Methylated Spirits.

Endpoint was assessed by weighing the pot from time to time until the jam had cooked down to the target 4kg of product.

Last update: 26th July, 2016, 10:46 AM

Expected ambient noise – in practice

This posts shows a measurement of ambient noise and comparison with the data given at Expected ambient noise and its more detailed references.

The test scenario is my 40m station, a G5RV inverted V dipole with tuned feeders, a balun and ATR-30 ATU. Antenna system losses are less than 1dB.

The chart above gives a range for expected ambient noise at 40m.

Above is a screen shot from a spectrum analyser measuring power in 1kHz bandwidth from 7.0 to 7.1MHz. The band is mostly unoccupied, and the mean noise power is about -99dBm, it would be 3dB higher in 2KHz bandwidth (ie -96dBm). Continue reading Expected ambient noise – in practice

Last update: 8th June, 2016, 8:39 PM

Expected ambient noise

One of the casualties of the cessation of VK1OD.net was an article on expected ambient noise.

The original work was based on ITU-R P.372-8 which has been updated to -10, -12 and now -13, but the updates do not alter the basis for the original article.

Since the work was a reference cited on my FSM pages, it has been updated and copied to Expected ambient noise level. The graphics and tables in the article and the PDF file all refer to ITU-R P.372-8 but remain correct wrt ITU-R P.372-13 (2016).

Last update: 14th January, 2018, 4:18 PM

PAROT with transformerless power supply and 10A SSR

This article documents an implementation of PAROT (Power Amplifier Run On Timer) using Transformerless power supply for PAROT.

This PAROT uses a 10A SSR for 230V mains switching and does not include PTT switching, but space exists for a FOD852 opto coupler for PTT switching.

The immediate application is to control my main station power supply so that if it has been in use, is hot and fans are running, the PAROT provides in this instance a 5min cool down before powering down.

Above is the electronics built on a small piece of Veroboard.

Above is the copper side of the Veroboard. The layout is designed to accomodate another implementation using a small Triac to switch a 230V AC relay. The board has been given a heavy coat of acrylic PCB lacquer to improve voltage withstand.

The PAROT is assembled inside a small die cast aluminium box with stick-on rubber feet.

Above is a view of the interior of the box. A 430V MOV is connected across the SSR output terminals, it is not clear whether the device has internal protection (Chinese product, very brief data). The LED / momentary switch on the right is the only control and indicator for PAROT operation. Note that because of the transformerless power supply, everything inside the box is potentially at mains voltage… a fact that must be kept in mind when working on it. An isolation transformer is a worthwhile tool for working on these type of things. Continue reading PAROT with transformerless power supply and 10A SSR

Last update: 2nd June, 2016, 9:14 AM