12 April 2014

End Fed Halfwave SWR test

In preparation for our up coming trip to Kruger National Park over the Easter weekend, I performed some more tests on my EFHW Granadilla tin tuner to see if I could improve the SWR from the previously measured 1.7:1. The plan for this trip is to take along the Norcal 40A 2Watt 40m rig with a minimalist station with all station components stored in a plastic food container. The 40 A was used for these tests.

Based on further reading on the EFHW I removed the grounded link between the secondary and link turns. This to reduce the chances of common mode RF flowing along the coax cable. The BNC connector was replaced with an insulated version.

I depoyed the EFHW just behind our apartment in the park area with an 8.5ft counterpoise lying under the antenna. I found that 3 Turns on the primary is ideal and results in a perfect 1:1 match. The Tx was connected via a 1 foot coax to the LED SWR meter which was connected to the tuner via a barrel connector.

Interestingly the tuner tuned to resonance indicating some capacitive reactance (about 13pF) at the wire feed point. After reducing the length of the wire by about 2 feet no change in the feed point reactance was noted. Could this reactance be predominantly the effects of stray capacitance? The tuner may exhibit less capacitive reactance if housed in a wood or plastic enclosure as opposed to the steel food tin?

Reports received from Monk ZS4SF were 549 at 1:15pm. The antenna was deployed as an almost horizontal wire about 10 feet - 8 feet above the ground.

The end of the antenna was then raised to about 20 feet and sloping down to about 8 feet to a branch above the operating position. Now I received a consistent 559 report from ZS4SF clearly showing the benefit of height.

Many thanks to ZS4SF for hanging in there as usual during this field test.

No comments:

Post a Comment