In a QST column in 2008, a correspondent asked the question
… I have the ladder line terminated to double coaxes that run about 12′ (4m) inside the house to an antenna tuner. Should this pair of coaxes be grounded at one end or both ends?
The Doctor gave a detailed diagram (above) and his advice was… Continue reading Spoiling balun action with ‘shielded twin’
Martin Ehrenfried (G8JNJ) conducted some interesting experiments on a small transmitting loop.
The loop above is 3.45m perimeter of LDF4-50A Heliax, and uses the full length of the Heliax as a stub for tuning the loop to 5MHz. Continue reading Thermograph of small transmitting loop
The Double Bazooka seems to have popped up on several fora recently, QRZ, eHam and VKLOGGER.
The Double Bazooka employs a pair of coax stubs as a device for compensation of feed point impedance, extending the VSWR bandwidth, principally to reducing loss in the feed line. Continue reading Double Bazooka magic
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