Over a long time I have voiced concern at the likely performance at MF / low HF of the very popular windowed ladder lines that use CCS conductors.
A very popular form of commercial ladder line is that using #18 wire, comprised of 19 strands of #31 30% IACS conductivity copper clad steel. The copper cladding on such a conductor is about 14µm in thickness.
This article reports and analyses measurements of a length of Wireman 553 windowed ladder line. Continue reading Loss of Wireman 553 windowed ladder line at MF/HF
I 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.
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
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
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
My recent article Near-field field strength measurements using the RFPM1 described a technique using VK3AQZ’s RF Power Meter which is based on the AD8307 log detector.
There are many ways to measure low level RF power or voltage, and this article describes methods that I have used using a simple diode detector attached to the HF loop, and measuring the DC output voltage using a small digital panel meter with 9V battery for a self contained measurement system with little risk of significant common mode current. Such a system can be hauled to some height and read remotely with a telescope.
Continue reading Near-field field strength measurements using a diode detector
Review of Boswell et al paper “Performance of a small loop antenna in the 3-10 MHz band” discussed measurement of near-field field strength for measurement of performance of a small transmitting loop (STL).
This article describes a method of performing near-field field strength measurements using a portable RF power meter (RFPM1) and a small untuned square loop. Continue reading Near-field field strength measurements using the RFPM1
(Boswell et al 2005) discussed a small transmitting loop (STL) and offered predictions and measurements of performance.
This article is a review of the discussion at 7MHz.
The STL is a 1m diameter circular loop of 22mm diameter copper conductor at 1,5m height over ground with parameters δ=0.005 and ε=10.
Performance is assessed by prediction and measurement of near-field strength.
Above, Figure 6 from (Boswell et al 2005) shows their predictions and measurements of field strength in the near-field at a range of distances at ground level. Continue reading Review of Boswell et al paper “Performance of a small loop antenna in the 3-10 MHz band”
This article documents a series of NEC-4 models at 7MHz inspired by Paul Casper’s (K4HKX) small transmitting loop using 3″ conductor described on his web page at http://qrz.com/db/K4HKX .
The basic loop dimensions derive from 3″ (76.2mm) OD copper tube, with octagon side lengths of 27″ (685.8mm).
This series explores the effect of antenna height. (Note the models have not been calibrated to Paul’s scenario, they are stand alone models of a somewhat similar scenario for the purpose of studying the effect of height.) Continue reading Analysis of a series of NEC-4 models of a low loss small transmitting loop at 7MHz at varying height
Gamma match is not a broadband impedance transformer, so it must be classed as a narrowband match.
But, does that mean that ham folk-lore that it necessarily degrades antenna VSWR bandwidth is soundly based? Continue reading Do gamma matches necessarily degrade bandwidth
The ARRL and other publications refer to the Army Loop or Patterson match.
Patterson described his antenna system at (Patterson 1967). Hams seem to call any configuration that uses only capacitors in the matching circuit a Patterson or Army loop, though they are incorrect.
The ARRL Antenna Book 21 has a nonsense circuit that cannot work.
Another ARRL example, one that does work
Above is a diagram from a much earlier ARRL and as far as I can ascertain, this is McCoy’s version the so-called ARMY Loop. (McCoy 1968) gives the middle capacitor as 500pF variable which would reduce the matching range. Continue reading The Army Loop (Patterson match)