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
There is often a need for a 9V battery for portable test equipment (NNA, Noise Bridge, Low R meter, Power Meter etc). A solution is a 8 cell NiMH pack.
Above, a battery pack made from two Hobbyking 4 low self discharge AA cells. The packs come with JR servo connectors, and the pins are rewired to use the -ve from one pack and +ve from the other pack to one of the JR connectors. The other wires are connected via a 3A Polyswitch for s/c protection. A short JR to 2.1mm DC connector is made from a JR extension cable and 2.1mm connector. Continue reading Inexpensive utility rechargeable 9V battery pack for test instruments
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
This article shows use of Lou Destefano’s (VK3AQZ) VK3AQZ RF power meter (RFPM1) to adjust the output power of a low power transmitter.
Above, the test setup used. Continue reading VK3AQZ RF power meter (RFPM1) – adjust Tx power example
This article shows use of Lou Destefano’s (VK3AQZ) VK3AQZ RF power meter (RFPM1) to plot the response of a 144MHz filter.
Above, the RFPM1 as used.
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
This article documents my build of Lou Destefano’s (VK3AQZ) RF Power Meter kit.
The power meter is based on probes using an AD8307 logarithmic detector.
Above, the RF Power meter with two probes. (The ferrite sleeves were not part of the kit.) Continue reading VK3AQZ RF power meter (RFPM1)
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
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.”
For students of transmission lines, some deductions… Continue reading Exploring VK2XSO’s transmission line example
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