Thursday, 10 March 2011

G3WPO GDO

Today I started to build a kit for a grid dip oscillator or more accurately a Fet dip oscillator.This kit was produced in the early 80's by Ambit International which later became Cirkit.Purchased by myself at the Donnington Park radio rally about ten years ago :-)
It came without instructions but I managed to get a reprint of the original 1981 article by G3WPO from the RSGB about eight years ago.Only now have I started to build it as it should be usefull for testing tuned circuits in the future, also makes a nice signal generator.

G3WPO GDO

Monday, 7 March 2011

4 Metre Aerial MkII

Another nice day here so I decided to have a go at  putting up a half wave endfed dipole for 70Mhz.
Construction consists of 2 metres of fishing whip, one outdoor electrical box (IP64 B&Q £3.50) and a loft mount for a TV aerial.
Using the tuned circuit from the last version with the addition of a 30pf beehive trimmer.See below.


70Mhz Matching unit


The radiating element is 2 metres of insulated wire attached to the fishing whip with black tape.
The box was sealed and attached to the fishing pole with hot melt glue, where it passes through. Below the aerial is a choke balun consisting of 3 turns of RG58 80mm in diameter.The Aerial is attached to the gutter board with a B&Q loft TV aerial mount.This is not the strongest mount in the world but the whole aerial is very light and flexible at the top so should not be affected by wind too much..





Wednesday, 2 March 2011

85ft Doublet(20m Double Zepp) at MW0IAN



I had a day off work today so since we had some early spring weather my mind turned towards a new aerial.
My previous installation was 64ft of wire fed to a SGC smartuner outside the shack window.This was tuned against an insulated counterpoise arrangement.I don't use a real earth here due to a PME mains supply.
This arrangement worked quite well with good reports on transmit but receive noise was high especially on 80m.
Having purchased some 300ohm ladder and dipole centre I decided a Doublet was the way to go.
The smartuner is now in the loft which is connected to the doublet via the 300ohm ladder which fits nicely through the soffit vents to the outside.The total length is 85ft of insulated wire as the top which should work as an extended double zepp on 20m(3dB over a dipole).The feedline has 8 nevada clip on chokes to stop feeder radiation.
One element goes over the apex of the house so balance may be compromised but I only have a small garden and this is my biggest aerial yet!
It tunes on all bands via the smartuner and sounds a little quieter on 80m.
see link for an alternative balanced smartuner arrangement .
http://www.g3ynh.info/atu/sgc230.html