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)
A short test drive was conducted to evaluation APRS effectiveness in capturing a motor vehicle journey of about 10km.
This journey is a regular one (the run to the local shops) and due to its familiarity is a good benchmark for performance. Continue reading APRS test drive – 20141114
This morning I have been observing a weak APRS signal from a digipeater located on a prominent hill about 200km away, VK1RGI-1.
VK1RGI-1 is characterised by having a pre-emphasised transmission, but about 1.5KHz deviation, about 6dB low.
Nevertheless, VK1RGI-1 packets can be fairly reliably decoded at a strength that does not show any segments on the IC2200H S meter, less than -115dBm (by measurement). Continue reading APRS: does pre-emphasis make much difference
APRS has evolved to be all things to all men.
It inventor, Bob Bruniga, generalised the original meaning Amateur Position Reporting System to Amateur Packet Reporting System as he extended APRS to include all manner of generalised broadcast and point to point messages.
Perhaps in doing that,it was recognition of the inability for many reasons of APRS to provide reliably good position reporting performance in practice.
Any thinking person understands that there is conflict between use for timely reporting of position and loading the radio channel up with generalised message traffic, or even extending the RF coverage of a position report by repeating it many times into adjacent precincts. But simple minds muttering “use it or lose it” ruin APRS for position reporting by sending repeating traffic without a demonstrated demand.
Attempts to emphasise position reporting performance tend to be opposed in my experience mostly by owners of Kenwood trackers (eg DM-710), and the weather propagators. Many Kenwood owners like to see position reports from a very wide area repeated into the local area so that they can be displayed on their radio. There are other features that generate traffic that appeal to Kenwood owners.
This article looks at how significant the Kenwood users are in terms of unique packets reaching APRS-IS, the basis of mapping for most users these days. Continue reading APRS: how popular are Kenwood trackers
An indicator of the state of the art of APRS is the systems used for iGates contributing to APRS-IS.
The following is a recent snapshot of two Australian Tier 2 servers, 98 iGates systems in all. Continue reading APRS: popularity of iGate system software
I have been doing some research on APRS recently and acquired a used Paccomm Tiny-2 MK-II TNC, a TNC-2 clone.
Above, a top view of the PCB. Continue reading Paccomm Tiny-2 MK-II TNC review
My friend Richard found himself located on the margins of coverage of the local 2m repeater where multi path reception was the main problem, a but a little lift in signal would also help.
This begs a small Yagi solution. Continue reading A compact 3 element Yagi for 2m
A reader of my article Are gamma matches as bad as all that asked whether the W5VJB dipole was a gamma match given the hint in the article that the traditional gamma tuning capacitor
is not essential to a gamma matched antenna.
Above (Britain 2006) is the subject dipole which Britain describes as a
partial folded element having a J shape which is grounded at the midpoint of the longest portion of the element. ((Duffy2010b) refers to it as a half folded half wave dipole.)
Continue reading Is the W5VJB J dipole novel
Seeing the comment recent online comment about a gamma match
as I have noted from research online, NEC does not support modelling of the match component reminds one of the unreliability of online sources. This appeal to non-authority is fallacious, this writer writes as if it is fact that NEC does not support modelling a gamma match, and that is quite wrong.
NEC has limitations on geometry elements relative to each other and to wavelength, and those apply not just to the gamma match, but the entire model. It is the modeller’s challenge to stay within those limitations.
This article documents an NEC model of a real antenna and the model reconciles with the real antenna. Continue reading Are gamma matches as bad as all that