Category: Amateur Radio

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.

Boswell-Fig06

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

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

Screenshot - 01_12_2014 , 13_51_37Above 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 (Eb/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

Packet loss by digi collision

It has been apparent to me that the two local digipeaters often collide.

One uses UIDIGI and therefore is conformant with the p-persistence channel access algorithm.

The other is a Argent Data T3-135 which does its own thing.

To discover how many packets are detected with bad CRC, I installed 6PACK on a TNC. 6PACK reports receive CRC failures which are logged by the Linux kernel. Data was collected for seven hours through the middle of the day to ensure that there was traffic, but that channel utilisation was low. Continue reading Packet loss by digi collision

Last update: 1st December, 2014, 4:16 PM

Another Argent Data T3 incompatibility

I have written on incompatibility of Argent Data TNCs with other devices.

In pursuing apparent packet loss, I have run up a Paccomm Tiny-2 MK-2 TNC with 6PACK firmware, and my aprx server using Linux AX25 kernel support and 6PACK driver.

It has become apparent that although the system reliably decodes packets from a multi-packet burst from VK2AMW-1, it only ever decodes the first packet of a multi-packet burst from VK2RHR-1. Frame check errors are logged. Continue reading Another Argent Data T3 incompatibility

Last update: 1st December, 2014, 4:17 PM