Amateur Radio – Page 43

BNC 75/50 compatibility

One sees perennial discussion in ham circles of compatibility of ordinary 50Ω and 75Ω versions of the BNC (Bayonet Neill–Concelman) connector, in particular the risk of damage in mating a 50Ω and 75Ω pair.

But are there incompatible connectors commonly in circulation.

These discussions often seize on the different dimensions 0.7mm and 0.9mm.

Above shows measurement of the centre pin diameter of a Kings BNC connector (for RG58), it is 1.339mm… nothing like 0.7mm or 0.9mm. (Amphenol Connex 2001) gives the centre pin diameter as 1.32-1.37mm. Continue reading BNC 75/50 compatibility

Last update: 14th January, 2015, 8:00 AM

Low power Guanella 1:1 tuner balun using a pair of Fair-rite 2643625102 suppression sleeves

A reader of Low power Guanella 1:1 tuner balun using a pair of Jaycar LF1260 suppression sleeves asked whether there is an equivalent Fair-rite core for the project.

Fair-rite part 2643625102 (~$4 each from Element14) is of similar size and also medium µ, but slightly different characteristic to the LF1260. Continue reading Low power Guanella 1:1 tuner balun using a pair of Fair-rite 2643625102 suppression sleeves

Last update: 13th January, 2015, 11:49 AM

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

Last update: 11th November, 2015, 4:56 PM

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.

Above, 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

Last update: 5th January, 2015, 10:41 AM

On Witt’s calculation of Matched Line Loss from Return Loss

It is a common practice that a Return Loss (RL) measurement of a s/c or o/c line section is used to calculate the Matched Line Loss (MLL) where MLL=RL/2.

This technique might work with low error in lots of cases, but not all… it is flawed. Continue reading On Witt’s calculation of Matched Line Loss from Return Loss

Last update: 2nd January, 2015, 6:04 PM

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

Last update: 19th October, 2017, 5:30 PM

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

Last update: 26th December, 2014, 8:34 AM

QRP2000 synthesiser build

I mentioned in Solder cream has a use-by date that a current project is another QRP2000 synthesiser.

Above, the topside of the synthesiser board. The optional output transformer can be seen at lower left. Continue reading QRP2000 synthesiser build

Last update: 25th December, 2014, 6:54 PM

Solder cream has a use-by date

A current project is another QRP2000 synthesiser.

It has about 15 surface mount parts on the board underside, and it was tempting to use solder paste / cream and hot air to solder the parts on… less risk of flicking them on the floor and the self align due to surface tension in the molten solder. Continue reading Solder cream has a use-by date

Last update: 24th December, 2014, 8:10 PM

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

Last update: 11th November, 2015, 4:56 PM