Loss of Wireman 553 windowed ladder line at MF/HF – does it matter

Loss of Wireman 553 windowed ladder line at MF/HF discussed the matched line loss of a windowed ladder line with 19 strand CCS conductors.

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Above, the loss curves from the article

You might look at this and ask “does it matter”, if 10m of this line is used in a G5RV, 0.0075dB/m at 3.6MHz gives 0.075dB loss… that is just 2%, so what.

That ‘back of the envelope’ calculation is incorrect, that feed line section operates with standing waves and the loss under standing waves must be evaluated. If we took the feed point impedance of the popular G5RV to be around 10-j340Ω at 3.6MHz, the expected loss in 10m of Wireman 553 with that load based on the above MLL is 3.3dB or 53%. By way of contrast, my own G5RV uses 10m of home made open wire line using 2mm copper wires spaced 50mm and the loss is 0.9dB, 2.4dB less. Continue reading Loss of Wireman 553 windowed ladder line at MF/HF – does it matter

Comparison of two small transmitting loops

At Efficiency and gain of Small Transmitting Loops (STL) I discussed the use of bandwidth measurement of a small transmitting loop (STL) for estimation of efficiency.

Paul Casper (K4HKX) has built a series of STL which he describes on his K4HKX QRZ page. Continue reading Comparison of two small transmitting loops

Loss of Wireman 553 windowed ladder line at MF/HF

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

AIM 882 produces internally inconsistent results

 

AIMuhfI 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.

Screenshot - 16_01_2015 , 15_40_27

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

Radcom review of Alpha Antenna microtune magnetic loop

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

Baluns – show me the numbers

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

Near-field field strength measurements using a diode detector

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

Near-field field strength measurements using the RFPM1

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