Saturday, 6 September 2014

144MHz antenna




After my recent changes to the YU7EF 9 element 144MHz long yagi feed point I changed over the 6/4m yagi for the 144MHz one.
I wanted to check out the new preamp on the 2m antenna.
The first thing I noticed was how quiet the YU7EF yagi is. As long as I don't beam towards the house ( approx 10 to 20T) the back ground noise is extremely low, although punctuated by the usual pulse noise from a nearby electric fence and some computer/data equipment carriers.

The plot above shows the return loss ( match of the yagi directly at the feed point. This was achieved by the usual calibration procedure at the yagi, using short,open, term.
A across the range 144 to 145MHz the return loss is around 20dB. I'm not so happy about the way the match starts to deteriorate rapidly above 145MHz.
The original 6/4m feeder is Ecoflex 10. There is now a short length of RG213 beteen the EF10 and the yagi feed point. This will be replaced with something of lower loss once the masthead preamp is installed.


The feed line loss is 1.9dB. Measured as half the two way loss from the shack to the yagi with a cal short circuit replacing the yagi. This is a great way to check installed cable.

Sam



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