Wednesday, July 29, 2020

Tweaking the Endfed antenna.

I have been doing some reading regarding Endfed antennas and the length of 44 feet kept coming up as the length for a short Endfed antenna in small lots. My Endfed was just extended from 34 feet to 41 feet which I spoke about in my last post.   My plan now was to try the 44-foot length of wire and see what the results were both using a counterpoise and not using one. This was going to be a trial project so the extra 3 feet of wire I am to add is not at this point going to be permanent. 
I cut a 3-foot piece of wire and placed soldered terminal ring connectors at each end. My plan was to remove the antenna wire from the balun end which already had a terminal ring connector on it. Then bolt antenna ring connector to the 3-foot piece and the other end of the 3-foot extension that was to be connected to the balun connector. This would give me the extra 3 feet needed to extend things to 44 feet. Once the 44 feet was stretch out I found out very quickly that 44 feet is the maximum length I can use between my shed and tree.
Three feet of wire

With the counterpoise attached, I went into the shack and ran through the bands using my MFJ 259B antenna analyzer and recorded the results and then once again with the counterpose removed. As a side note, one of the best purchases I made was the antenna analyzer, it makes short work of most antenna testing tasks. I do have a second antenna analyzer which is the Funk FA-VA4  its a nice unit but because its menu-driven I find it to be a bit cumbersome.  With the MFJ unit, you select the band range with one knob and with the other knob spin to your desired frequency and then read the LED readout. 
Well back to the Endfed experiment and below are the results with the added 3 feet of wire.

Results without a counterpoise:           CLICK HERE FOR CORRECTED SWR CHARTS
     Band              Freq               SWR

  1. 80.              4.000.             7.5
  2. 80.              3.500.             6.7
  3. 40.              7.001.            3.2
    40.              7.070.            3.3
    30.              10.100.          5.0
    30.              10.150.          5.0
    20.              14.001.          1.8
    20.              14.070.         1.7
    17.              18.068.         1.6
    17.              18.168.         1.6
    21.              21.001.         2.6
    21.              21.070.         2.6

Results with a counterpoise:
         Band              Freq           SWR

  1. 80.              4.000.            9.1
  2. 80.              3.500.            9.6            
  3. 40.              7.001.            4.4
    40.              7.070.            4.4
    30.             10.100.           5.0
    30.             10.150.           5.0
    20.              14.001.          2.4
    20.              14.070.          2.3
    17.             18.068.           2.0
    17.             18.168.           2.0
    21.             21.001.           2.6
    21.             21.070.           2.7
As you can see from the above results (not sure where the 1,2,3 numbers came from but I just can't seem to remove them without screwing up the chart) the counterpoise only made things worse again. The results without the counterpoise were decent on some bands (80m and 20m) but overall when the Endfed was at 41 feet it was not that different from 44 feet. The one deciding factor for going back to 41 feet was when at 44 the wire was directly connected to the tree. I was not able to add my bungee cord to allow the antenna to have some flex in it when the winds picked up and the tree started to sway. I was not able to add a bungee cord either as this made the antenna wire hang really low. 
bungee allowing for flex when 41 feet long. 
As you can see in the picture the bungee cord allows the tree to sway in the wind but not affect the antenna with the stress of stretching. The red parachute cord you see is there as a backup if the bungee snaps. It was a nice experiment trying the 44 foot but the results were not drastic enough for me to keep with the 44-foot length. The antenna is not back to 41 feet and my curiosity has been solved. 


Unknown said...

With these SWR-numbers I suppose there is also an UNUN. If yes, 4:1 or 9:1 or other ratio? 73 Klas OZ1DTF

VE9KK said...

Good morning Klas thanks for taking the time to leave a comment, yes there is an UNUN and it's 9:1.