Articles

Technical articles written for - or by - Wellington VHF Group members and friends.

Accurate Transmitting Antenna Locations Using Global Positioning System (GPS) Satellites

Introduction

Accurate transmitting antenna locations are required when applying for RSM Radio Licences.

The aim should be to achieve a location accuracy of 5 metres, or better. Several people have consistently achieved accuracies of 1 to 2 metres, by using the procedure described below.

Civilian GPS receivers are small and cheap, and can be found embedded in a wide range of electronic devices. Unfortunately, their apparent ease of use, and claimed accuracy, can lead the unwary user into a false sense of security, and location errors of more than 10 metres.

Do not use Google Earth. Location errors of more than 100 metres have been noted, because of the way the mosaic of satellite photos is stitched together.

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Tactical Amateur Radio Digital Internet Solution

Using the Spark free WiFi zones for Internet access

Need a digital radio hotspot for an AREC operation, a demonstration at a branch meeting, or something like the recent VHF Convention?

Telecom, now Spark, operate a network of more than 1,000 WiFi access points conveniently located on many public telephone call boxes around the country.  The commercial terms of the service are essentially free WiFi for Spark on-account mobile customers subject to a 1GB limit per day for up to five devices per account.

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Dick Greenbank, ZL2TGQ. 1943-08-21 to 2015-01-08

Dick Greenbank ZL2TGQDick was educated at Stratford Technical High School, Taranaki, then joined the Royal New Zealand Air Force at Blenheim as a Boy Entrant. Later after two years study at the RNZAF Electrical and Wireless School, Wigram, Christchurch, coupled with service at Defence Main Signal Centre, Wellington, he graduated RNZAF Communications Fitter.

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Duplexer Overhaul for 7075

For more than 25 years, first analog then P25, the 147.075 MHz (+600 kHz split) repeater has covered the north of Wellington, New Zealand.  The original machine was a home made crystal controlled 10W design by Peter ZL2ARW but the site now features a 100W capable Motorola Quantar.

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Digital Television tests - Bulletin No 10

Members of the DATV Project Team recently met with representatives of several Government agencies to
discuss the final series of adjacent-channel spectrum compatibility tests.

Following the extensive series of field tests that have been carried out, and laboratory simulations using an output filter
consisting of a 6-pole cross-coupled bandpass filter plus a 6-notch filter, we expect a successful
outcome from the tests.

We are grateful to one of our corporate sponsors for the bandpass filter, and also to our member Steve ZL2ASF,
for the notch filter.

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Digital Television Tests – Bulletin No 9

The 502 to 510 MHz Digital TV Transmitter is being prepared for the final series of spectrum compatibility tests, to be witnessed by users of the adjacent spectrum.

Ever mindful of the cost of these tests to the users of the adjacent spectrum, we want to ensure the tests are successful at the first attempt. Accordingly, we have performed an extensive series of field tests and laboratory simulations to determine the performance margins of the transmitter system.

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Digital Television Tests – Bulletin No.8

The unmodulated CW carrier on 506 MHz has been turned off, on the completion of coverage testing. Our thanks go to everyone who provided a reception report.

A prototype 2-way splitter, being one third of the 4-way drive splitter, has successfully passed all tests. A similar prototype, a 2-way combiner designed for higher power operation, is now under construction.

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Digital Television Tests – Bulletin No.7

Transmission of the unmodulated CW carrier continues on 506 MHz, with horizontal polarisation. Reception reports are welcome.

Four power amplifier modules have been constructed and tested one-at-a-time with the digital exciter. Their gain and linearity match within half a dB. The four modules will operate in parallel to achieve the licensed power.

A 4-way drive splitter and 4-way output combiner have been designed and are under construction.

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Digital Television Tests – Bulletin No.6

Transmission of the unmodulated CW carrier continues on 506 MHz, with horizontal polarisation. Reception reports are welcome.

Adjustment and testing of the digital modulator is complete.

The prototype power amplifier module has been constructed and is now undergoing quality testing. Once testing is complete another three modules will be constructed. The four modules will operate in parallel to achieve the licensed power.

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Digital Television Tests – Bulletin No.5

Transmission of the unmodulated CW carrier continues on 506 MHz, with horizontal polarisation. The maximum EIRP is +20 dBW (100 Watts) towards the North East.

Calibrated coverage measurements, at more than twelve locations, confirm that the transmit antenna is performing as expected. Additional reception reports are welcome.

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