For some years I have used Ceramica muffin fans for low noise and long life. They use ceramic bearing which are quieter than ball bearings, but longer life than sintered bronze bearings which dry out.
That said, I was annoyed to find the fan I have replaced in a one year old computer power supply fail after another three years. The original was a bronze bushed fan which dried up. Continue reading Fan frustrations
This article explores the radiation efficiency of KP4MD’s (Milazzo 2012) small transmitting loop (STL) using a set of NEC-4 models of the loop at varying heights above ‘average’ ground. Continue reading Ground effects on KP4MD’s 0.9m loop on 28MHz
A ham posted online:
I spent several happy hours this weekend building the DE of the 6M Quad described in the June 2014 QST, p 30. When I got it completed, I put the antenna analyzer on it, expecting to find a nice resonance in the 50-51Mhz region and an impedance of 120 ohms or thereabouts. To my surprise, the radiation resistance in the couple of dozen ohm range, and resonance, if that is what I can call it, depends on how am I holding the loop.
After a bit of QST bashing in the thread, he later reveals:
The trial with the analyzer was about 2′ of RG-8X with PL-259s on each end, to BNC jacks on both antenna and analyzer with adaptors.
Much as the chap expressed his lack of confidence in modelling tools, NEC reveals what is happening. Continue reading Analysers – help or hindrance
I thought it interesting to compare EMR calc with NEC-4 on my lossless octagonal loop (top tuned), 1m across on 40m in free space radiating 1W. Continue reading Small transmitting loop EMR safety – EMR Calc predictions
This article explores the radiation efficiency of a small transmitting loop (STL) using a set of NEC-4 models of a 3.14m perimeter loop on 7MHz at varying heights above ‘average’ ground. Continue reading Ground effects on small transmitting loop efficiency
Small transmitting loops (STL) are often recommended for use inside buildings, on balconies and even hand held, but are they EMR safe?
Continue reading Small transmitting loops and EMR safety
A common method of feeding a small transmitting loop is to use a small auxiliary input loop. This is sometimes referred to as the “Faraday feed”, implying a shielded feed loop though many so-called shielded loops are not effective (Duffy 2007), but the loop does not need to be shielded nor does there need to be a metallic connection to the main loop.
This article looks at an equivalent circuit. Continue reading Equivalent circuit of small transmitting loop with auxiliary loop feed
One of the feed arrangements used for small transmitting loops (STL) is the so-called gamma match, though it is questionable if these are quite the same as matches of the same name on a linear dipole. Continue reading Small transmitting loop – gamma match
The concept of “additional loss due to VSWR” is so engrained in Ham mythology.
Here it is detailed in the latest version of TLW announced in QST June 2014. On the second last line TLW lists “additional loss due to SWR” as 0.003dB, which seems ok in relative terms as the cable is nominally matched (VSWR=1.03). Continue reading Additional loss due to VSWR – a quite flawed concept
This article describes a linear circuit model for a small transmitting loop with auxiliary loop feed. Continue reading Small transmitting loop – linear circuit analysis