An opportunity presented to measure the loss of a sample of JSC windowed ladder line. The line uses single core #18 CCS conductors and is equivalent to products sold under various proprietary names. JSC Wire & Cable is now known as Seminole Wire & Cable, and this is their 1318 product. Continue reading Loss of JSC ladder line at 160m
Category: Transmission lines
Spoiling balun action with ‘shielded twin’
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’
Double Bazooka magic
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
Analysers – help or hindrance
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.
Analysis
Much as the chap expressed his lack of confidence in modelling tools, NEC reveals what is happening. Continue reading Analysers – help or hindrance
Small transmitting loop – gamma match
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
Additional loss due to VSWR – a quite flawed concept
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
Small transmitting loop – linear circuit analysis
This article describes a linear circuit model for a small transmitting loop with auxiliary loop feed. Continue reading Small transmitting loop – linear circuit analysis
Small transmitting loop – NEC-4 analysis
This article describes a NEC-4 model for a small transmitting loop with auxiliary loop feed. Continue reading Small transmitting loop – NEC-4 analysis
Simple resonators might not appear as such initially
I have spoken in several recent articles about antennas that exhibit a simple series resonance with constant or near constant R near resonance.
Sometimes the impedance transformation used may hide that simplicity. Continue reading Simple resonators might not appear as such initially
VSWR curve of a simple series resonant antenna
This article explores a generic VSWR curve for simple series resonant matched antennas. Continue reading VSWR curve of a simple series resonant antenna