Real World Measurements of a Multi-Band End Fed Antenna using a 9:1 Un-Un
Real World Measurements of a Multi-Band End Fed Antenna
using a 9:1 Un-Un
Excited as I was to get on the air with my new antenna, I didn’t take record any data regarding its SWR, radiation resistance (RR) and resonant point (X) with my antenna analyzer. Satisfied that the antenna worked by making QRP contacts in the WAE this weekend, I pulled out the analyzer and recorded some data for bands 40 through 10.
SWR should be 1.0 RR should be 50 X should be 0
This is the ideal but is not often the case in real life set ups especially in the field when operating portable!
I found one strange thing on 40 meters. The readings were markedly different if I held the analyzer in my hand or set it on a table by itself. The readings were better if I held the instrument in my hand. Holding the analyzer or setting it down made very little difference on the other bands with 17 Meters the exception, so I didn’t post those here.
MHz SWR RR X
7.030 4.3 104 101 Not touching
7.030 2.4 66 50 Touching
10.116 2.0 27 10
14.062 1.8 30 16
14.280 1.7 39 25
18.085 2.1 35 31 Not Touching
18.085 1.7 35 19 Touching
21.058 1.5 45 21
21.430 2.3 20 3
24.905 4.2 41 75
28.062 2.2 30 30
28.560 2.5 38 42
My antenna wire is 35 feet long and 30 feet above the ground and its orientation is horizontal, (perpendicular to the ground!)
Building the 9:1 UnUn was fun and I was eager to have a multi-band antenna!
This antenna got a lot of bad press among the ‘Antenna Guru’ crowd on E-Ham. They said their (facts) were from computer modeling programs, but there was a lot of opinion written their too and a lot of disparaging remarks toward anyone who would stupid enough to actually use one of these antennas. Their facts and data in no way came close to my real world measurements!
I plan to take this antenna into the field and test it as a sloper, both with the analyzer and on the air. I’ll post the results here.
I hooked up a tuner and took readings on 20 meters. I was able to get the SWR down to 1:1 and the RR to 57 using the tuner which is very close indeed to the ideal. The readings are sensitive to whether I held the analyzer in my hand when looking through a tuner. That bothers me. There seems to be some (not a lot) but some, RFI in the shack here too.
All antennas have trade off’s!
I am not totally surprised by the difference. Try adding some more wire to make the length closer to 50-55 ft and see if it becomes more stable. Also you did not say how much coax you used. The shield is sort of a counterpoise for the matchbox. I have found over the past years (almost 10 yrs I guess) that it really never mattered since I have always used a ATU. Be it a LDG Z-11 or Z100PLUS, Elecraft T-1 or not the internal KX3 ATU. The design just plane worked every time no matter how I strung it up and worked a lot of DX using 5 watts or less and even 100 watts… It just loaded and I made contacts.
Hope my rambling will help with your great experiment…HI
You said: “My antenna wire is 35 feet long and 30 feet above the ground and its orientation is horizontal, (perpendicular to the ground!)”
I think you meant parallel to the ground, no? Perpendicular would make it a vertical.
Don’t understand all the bad press either about this as well. Built a G5RV jr a year before this. Even though it will cover roughly the same bands as this antenna…the noise (compared to this End-Fed) doesn’t even compare. Perhaps the best thing is that unlike all the other wire antennas…if you’re in a place where you can’t run one…except for being stealth…this is one of the best you can run.
Even funnier…I’ve got an MP-1 screwdriver with the legs I cut for the 40-6 M bands. Am going to use the 33 ft leg to run with this box. If I have no complaining neighbors after that…I’ve got 100 ft of 18 ga speaker wire still in the package and will get on 80 M by running it along my floor boards.
LOL, yes Chuck, Parallel to the ground.
End feed antennas like this commonly cause current to flow on the outside of the shield. Some designs even count on this. Such currents will cause erroneous readings on most SWR bridges and antenna analyzers. The effect from your hand is a good indication that the common mode current exists. If shortening or lengthening the coax changes the SWR reading, this is another strong indicator.
You may have some success by putting a choking balun just before the measurement point. Ferrite beads, coiled coax, etc. may help. If you cannot get rid of the external shield currents, the measurements are not meaningful.
– Glenn W9IQ