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

VK3AQZ RF power meter (RFPM1) – filter response example

This article shows use of Lou Destefano’s (VK3AQZ) VK3AQZ RF power meter (RFPM1) to plot the response of a 144MHz filter.

RFPM00

Above, the RFPM1 as used.

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Above, the test setup. The filter (DUT) is connected between a standard signal generator (SSG), and the RFPM1 connected to the filter output. A DVM recorded the DC voltage on the ‘CAL’ terminals of the RFPM1. A series of measurements was made from 140 to 148MHz and the results calculated and plotted in Excel. Continue reading VK3AQZ RF power meter (RFPM1) – filter response example

Where is the best place to measure feed point VSWR

The subject question is often asked, and the usual responses are mindless recitals of Rules of Thumb (RoT).

In the light of the discussion at Feed line length affect on VSWR and The half waves of coax rule for measuring VSWR accurately, lets consider the subject question and develop a rational answer. Continue reading Where is the best place to measure feed point VSWR

Exploring VK2XSO’s transmission line example

VK2XSO posted a sweep of “Return Loss (SWR) (the lower plot) from 500 to 2500MHz of a 50Ω load through ~5m of RG59” apparently to demonstrate his knowledge of transmission line basics. As he says “here are also many other things we can deduce from looking at these two lines.”

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For students of transmission lines, some deductions… Continue reading Exploring VK2XSO’s transmission line example

Signalink USB PTT disable

Many years ago I bought a Tigertronics Signalink USB, principally for measurements using FSM and NFM.

A nuisance with the device is the lack of a simple means of disabling PTT. This is particularly important if the system is being used for noise figure measurement with an expensive calibrated noise source which will not withstand transmitter output.

This note describes the fitting of a front panel PTT disable switch. Continue reading Signalink USB PTT disable

Analysers – help or hindrance

A ham posted online:

I spent several happy hours this weekend building the DE of the 6M Quad described in the June 2014 QST, p 30. When I got it completed, I put the antenna analyzer on it, expecting to find a nice resonance in the 50-51Mhz region and an impedance of 120 ohms or thereabouts. To my surprise, the radiation resistance in the couple of dozen ohm range, and resonance, if that is what I can call it, depends on how am I holding the loop.

After a bit of QST bashing in the thread, he later reveals:

The trial with the analyzer was about 2′ of RG-8X with PL-259s on each end, to BNC jacks on both antenna and analyzer with adaptors.

Analysis

Much as the chap expressed his lack of confidence in modelling tools, NEC reveals what is happening. Continue reading Analysers – help or hindrance