AIM 882 produces internally inconsistent results

 

AIMuhfI have had cause to validate the output produced by an AIMuhf measurement using AIM882 (current version, released about three months ago).

The test scenario is a pair of nominal 50+j0Ω loads on a Tee piece, connected to the AIMuhf by about 1m of RG58 coax and swept from 10 to 50MHz.

Screenshot - 16_01_2015 , 15_40_27

It is mental arithmetic that the VSWR should be very close to 2:1, and since the loss of the cable is quite low, VSWR should be almost uniform with frequency. Continue reading AIM 882 produces internally inconsistent results

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.

BncPinAbove 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

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

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

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