Antennas – Page 44 – owenduffy.net

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

Last update: 6th August, 2018, 5:54 AM

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

Last update: 26th December, 2015, 9:03 AM

Review of Boswell et al paper “Performance of a small loop antenna in the 3-10 MHz band”

(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”

Last update: 20th April, 2017, 7:20 AM

Analysis of a series of NEC-4 models of a low loss small transmitting loop at 7MHz at varying height

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

Last update: 23rd July, 2015, 7:47 AM

Do gamma matches necessarily degrade bandwidth

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

Last update: 12th December, 2014, 7:30 AM

The Army Loop (Patterson match)

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)

Last update: 11th November, 2015, 4:56 PM

An example of Eb/N0 design with the Field strength / receive power converter

I have been asked whether the Field strength / receive power converter can be used to solve a Eb/N0 (E_b/N₀) design problem.

Eb/N0 is a method often used for specifying the relationship of signal and noise that will give adequate bit error rate in a data demodulator.

Whilst the calculator was not specifically designed for that purpose, and you cannot directly enter the desired Eb/N0, with the help of a hand calculator for simple calculations, a solution can be found. Continue reading An example of Eb/N0 design with the Field strength / receive power converter

Last update: 9th December, 2014, 8:50 AM

Exploitation of NEC’s GM card

NEC-2 and NEC-4 support a GM card to translate and rotate a structure in three dimensions.

This article gives a simple but practical example of exploitation of this often overlooked facility. Continue reading Exploitation of NEC’s GM card

Last update: 5th December, 2014, 2:44 PM

Chameleon CHA M-LOOP

Chameleon has announced a small transmitting loop, the Chameleon CHA M-LOOP. Continue reading Chameleon CHA M-LOOP

Last update: 17th April, 2015, 7:07 AM

Diamond X-50N #2 at VK2OMD

I have a bit of a soft spot for the Diamond X-50N. It is a fairly rugged vertical for 2m/70cm. Though I live in a rural setting, I resist the temptation of high gain antennas of this type as they tend to suffer fatigue problems resulting in noise in quick time, whereas the rigid one piece X-50 seems to last and last (I have another that must have had 25 years outdoor service).

The X-50N is mounted on a telescopic steel mast at 11m at its base, and fed with 10m of LDF4-50A to the antenna entrance panel, and 2m of LMR-400 to the radio. The XN50N has three short radials which are visible in the pic above, but somewhat obscured by a fan of four upwards pointing wires to discourage birds perching on the gibbert for the G5RV. Continue reading Diamond X-50N #2 at VK2OMD

Last update: 27th November, 2014, 8:03 AM