6 Meter Five Eigths Wave Vertical Antenna
Although I have been a ham for many years, I have never considered operating on the 50-54Mhz band (6 meters).
Some local interest in 6 meters started up when the emergency group was looking for a frequency to connect
2 sites that are just out of VHF range and did not have equipment or space for HF antennas. In order to test the link
for an ARDOP data link, several antennas were built and several surplus Kenwood and Motorola Maxtrac radios were modified for
6 meters. This antenna was one of the experimental antennas built to test the suitablity of 6M for the data link.
This antenna was built from scrap aluminum parts.
Tuning turned out to be a multi-day (week?) project.
Intially I tried a coil wound on the lower piece of 1" PVC pipe and could not get anything
close to working. It was determined the coil was just too big.
Next I tried a coil wound on a 1/2" diameter form. This came close to working
when I used the tap at 2.5 turns from ground and the antenna at 5.5 turns from ground.
Tap location and coil size was very critical and confusing. Finally, I decided to measure the raw
antenna impedance using my VNA (another project on this site) and I ran a wire from the vertical to the so-239
feedpoint and measured the raw impedances with the vertical 155" long from tip to feedpoint
and 4 50" radials..
Finished Vertical on Tripod
|Raw Vertical Mesurements|
Plotting these in linsmith, I played with the coil inductances and determined
that something like 49nH for the top coil and 110nH for the bottom coil would
give a reasonable match.
Raw and Matched Solution in Linsmith
Details: Base of Antenna
Details: Radial Mounting(note reinforcing tube inside radials)
Using this coil setup, and stretching the coils a bit I was able to get 1:1 SWR at
53.08MHz. To bring it down in frequency I extended the antenna length from
155" up to 160" and had an SWR of 1.02:1 at 51.84MHz.
Details: Final Loading Coil Configuration
|Antenna Performance After Matching|
Impedance Measured in the Shack