The so-called End Fed Half Wave (EFHW) has become very fashionable amongst hams. The idea of end feeding a half wave antenna is hardly new, and there is widespread use of the broad concept… but from online ham discussion, it can be observed that the things are not well understood and indeed, there is magic … Continue reading EFHW exploration – Part 1: basic EFHW
The net abounds with articles on broadband transformers (ie untuned) for matching End Fed Half Wave (EFHW) antennas to 50Ω. One of the aspects that is common to most designs is that the turns of the primary winding are wound ‘bifilar’ with the start of the secondary winding, indeed the twist pitch is often very … Continue reading On winding configuration of EFHW matching transformers
End Fed Half Waves have certainly captured the minds of QRP aficionados, and there is a steady stream of ‘designs’ appearing on the ‘net. A recent article by PD7MAA describes such a transformer using a BN43-202 balun core for up to 20W PEP from 7-29MHz. Above is PD7MAA’s graphic for his transformer. It is a … Continue reading PD7MAA’s BN43-202 matching transformer for an EFHW
There seems to have been a revival in use of the so-called End Fed Half Wave antenna. The prospect that a small radio such as the FT817, a magic match box and 10m of wire makes a good 20m field station appeals to many a SOTA enthusiast. Let us model a scenario with a FT817 … Continue reading Thinking about SOTA, EFHW and EMR safety
This article has been copied by request from my VK1OD.net web site which is no longer online. The article may contain links to articles on that site and which are no longer available. (Tester 2013) described a coaxial collinear array for VHF/UHF. Tester describes the antenna a collinear is a vertical antenna whose resonant elements … Continue reading Silicon Chip Collinear
Barry, K3EUI, posted some interesting measurements of his MyAntennas EFHW which he described with some useful detail: I have been experimenting with a “MYANTENNA” 130 foot long “end-fed” with the 49:1 UNUN* I replaced their 130 ft antenna wire with a heavier gauge #12 stranded insulated wire (I had a few hundred feet).* This is … Continue reading K3EUI’s MyAntennas EFHW on 80m
Reworked for average ground type (σ=0.005, εr=3) … A common scheme for narrow band match of an end fed high Z antenna discussed discussed the kind of matching network in the following figure. A common variant shows no capacitor… but for most loads, the capacitance is essential to its operation, even if it is incidental … Continue reading A desk study of a matching scheme for a cap hat loaded Marconi on 137kHz
A common task is an overall assessment of an antenna system, this article looks at NanoVNA display configuration that will often suit stand alone: measurement at any point on the feed line; and measurement with the reference plane, either by direct connection, fixture calibration or approximate calibration using e-delay. Caution When measuring an antenna system … Continue reading NanoVNA setup for common antenna system measurement tasks
At Where is the best place to measure feed point VSWR I discussed location of the VSWR meter and projection of its reading to another point on a known transmission line. One of the conclusions drawn in that article is: Feed point VSWR can be estimated from measurements made at another place if the transmission line parameters … Continue reading Where is the best place to measure feed point VSWR – error in Zo
Several readers have asked my thoughts on the ARRL EFHW kit. I have not built and measured the thing, but have done the first step in a feasibility study. The transformer design is not novel, it is widely copied and this may be one of the copies. The design is usually published without any meaningful … Continue reading Thoughts on the ARRL EFHW antenna kit transformer