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).

XN50N01

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

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.

Screenshot - 24_11_2014 , 10_29_43

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

When governments tinker in telecommunications carriage…

I had cause to document Internet access performance recently, an interesting exercise.

Background

When I moved into this house about five years ago, we enjoyed an excellent broadband service delivered on an ADSL1 link of about 800m to the RIM/DSLAM. The downstream rate was capped at 8Mb/s and most of the time, most of that speed was available to the end user.

For years I have run a test file transfer every half hour to document access performance, and when asked about recent performance that was an ideal source. I needed to go back to the previous week as last week started with an outage, the RIM batteries seem to have gone flat and Telstra had not been proactive in responding to the condition that left it running on batteries. Continue reading

APRS: does pre-emphasis make much difference

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: how popular are Kenwood trackers

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

Mostly electronics…