Radcom review of Alpha Antenna microtune magnetic loop

Alpha antenna refers to the Radcom review of their microtune magnetic loop.

(Nichols 2014) describes the loop as 12.7×3.2mm aluminium flat section formed into an ellipse with average diameter 0.84m. The pictures show that it is close to circular and I will take it to be a circle of perimeter 2.64m.

The review offers some measurements of VSWR=3 bandwidth at the feed point on various bands, and an estimate of efficiency based on RJELOOP1. Continue reading Radcom review of Alpha Antenna microtune magnetic loop

LM386 audio power amplifiers

I tested a couple of LM386 audio power amplifier modules.

LM386tThe larger one was a kit using the DIP package, the smaller came assembled and used a SO package. Both cost less than $2 each posted on eBay.


They both deliver close to 3Vpk into an 8Ω load at 1kHz when powered from 12.0V. That is close to 0.5W out, but the SO chip cannot withstand the associated dissipation of 0.5W continuous output.

Both handle broadcast program quite happily at 0.5W peak, the chip temperature rise is 15° and 25° respectively.

Another Osram e-ballast bites the dust

I wrote in the fraud of energy efficient lighting – e-ballasts of frustration with green measures forced on us, measures that have replaced tried and true reliable lighting solutions with high tech low reliability solutions in a false promise of net energy saving.

Typically, the cost of repair and replacement of this unreliable technology is much greater than their direct energy saving, indeed much greater than their energy consumption of the life of the equipment.


Above is a ballast removed from a light this morning after 4 years during which it was hardly ever used… perhaps 10 hours at most… so the original capital cost of $80 for luminaire and fitting for 10 hours service gives an average cost of $8/hr for capital and about $0.01/hr for energy. Continue reading Another Osram e-ballast bites the dust

Inexpensive utility rechargeable 9V battery pack for test instruments

There is often a need for a 9V battery for portable test equipment (NNA, Noise Bridge, Low R meter, Power Meter etc). A solution is a 8 cell NiMH pack.

BatteryPack9VAbove, a battery pack made from two Hobbyking 4 low self discharge AA cells. The packs come with JR servo connectors, and the pins are rewired to use the -ve from one pack and +ve from the other pack to one of the JR connectors. The other wires are connected via a 3A Polyswitch for s/c protection. A short JR to 2.1mm DC connector is made from a JR extension cable and 2.1mm connector. Continue reading Inexpensive utility rechargeable 9V battery pack for test instruments

Baluns – show me the numbers

Hams talk at length about baluns but rarely in quantitative terms.

A quotation from Lord Kelvin is most appropriate: When you can measure what you are speaking about, and express it in numbers, you know something about it. But when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. It may be the beginning of knowledge but you have scarcely in your thoughts advanced to the state of science. Continue reading Baluns – show me the numbers

ashim at shell servo

The message “ashim at shell servo” must be an important one.

I have heard VK2UBQ-9 sending this message to VK2XSO-5 for many months, a couple of hundred times a day when VK2UBQ-9 has his radio switched on.

The intended recipient was last reported on aprs.fi in May 2014, seven months ago, yet the APRS system is still wasting bandwidth trying to deliver this message, presumably waiting for a delivery acknowledgement. Continue reading ashim at shell servo

Near-field field strength measurements using a diode detector

My recent article Near-field field strength measurements using the RFPM1 described a technique using VK3AQZ’s RF Power Meter which is based on the AD8307 log detector.

There are many ways to measure low level RF power or voltage, and this article describes methods that I have used using a simple diode detector attached to the HF loop, and measuring the DC output voltage using a small digital panel meter with 9V battery for a self contained measurement system with little risk of significant common mode current. Such a system can be hauled to some height and read remotely with a telescope.
Continue reading Near-field field strength measurements using a diode detector