Friday, 17 May 2013

Adventures on 4 Metres (70 MHz) Part 1

In my 20 years of being a radio ham, I have never used 4 metres/70MHz. So I purchased a Wouxun KG-UVD1P 4m/2m dualband 5 watt handheld transceiver from . It has a frequency coverage of 66-88 MHz and 136-174 MHz which makes it ideal for 4m portable work as well as 2 metre (145 MHz) band use, listening to the boats on VHF marine band and it has a FM broadcast receiver as well. So at least if I got nowhere with 4m, I can use it on 2m where most local amateur activity is to be found.

The radio itself is well made for the price, very sensitive on receive with clear audio. Programming the memories is a bit of a pig, but once you understand the designer's logic is quite straight forward. The supplied rubber duck antenna is 29cm (11.5") in length and gives reasonable performance on 2m, but not so well on 4m. This is because a 1/4 wave antenna on 2m is 49cm in length, and 4m is around 105cm in length, compared to the convenience of the rubber duck - a shortened inefficient antenna.

For handportable work, I decided to build a bigger antenna but it needed to work on both bands. The simplest solution was an 100cm telescopic whip mounted on a PL259 plug with a small matching coil inside. A 4-turn coil was made from a piece of enamelled wire which was wound along a 4mm diameter screwdriver. The coil was soldered into the pin of the PL259 and the other end to the telescopic whip. I clamped the whip carefully into a bench vice and filled the PL259 with Aradite epoxy resin and allowed it to set. The antenna at 100 cms in length was good for 4m. Reducing the length to 45cm on 2m, and it even works on 70cm (433 MHz) and PMR-446 MHz with a low SWR when precisely adjusted. On this years May Bank Holiday Weekend I had the opportunately to use the Wouxun and the telescopic antenna from Cox Tor on Dartmoor to the Redruth area in Cornwall speaking to Norman G4USB and Brian G4KAW, which is approximately 60miles on groundwave propagation.

For a homebase antenna, I have stuck up a 1/2 wave "Bazooka" which details of its construction is discussed here on the Charlie Tango DX Group Radio Forum:

That's it for now. More Adventures on 4 Metres to come........

73 de Dave G7OPC

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