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Unipole Vertical 160 m

The first thing a noticed when I finished the cage was a 2 S uni’s drop in the noise captured by my EWE antenna 20 m far from the tower. It was amazing to see my EWE working again. t

After that lucky discovery I faced the difficulty to tune the skirt, the SWR was very high. I read a nice paper I found about broad band vertical with 105 -115 degree, the impedance was 200 +J800 if I remember it right, Well why not use a 4:1 balun?

Bingo, the SWR dropped on 1890 to 1:1.8, still not good. Making the tower a little longer using the hat and a 1000pf in series between the balun and the skirt gave me a almost perfect match. Unbelievable! it is very flat..

 

The relay disconnects the coax form the skirt, and it connects the detuning cap during receiving time. I’m using a 24 Vdc vacuum relay with a 40 Vdc limiting the current with a resistor to speed up the closing time.

 

For 80 and 40m I’m sing a relay to ground the cage but I still need to find the best position, I like to use the 4:1 balun because it keeps the coax DC permanently .grounded. i i l t

Detuning the tower

I was not able to measure any thing on my Vertical antenna, my MFJ259B got bananas, and my old Bridge is limited by 1000 ohms. I did not build a current probe to try the current method. I 100% agree with you about the current method.

The way I detune the tower was empirical. I plot the Waller Flag diagram several times from same 1700 KHz signal (1700 KHz BC 20 miles south of me) using different capacitors until I found the best diagram with both back lobes looking like the same. Without this capacitor I got one back lobe 10 dB enlarged. I got almost a perfect pattern using 75pf. My vertical is north of the WF but not exactly in line with the BC station. Then I to extrapolate the value for 1700 to 1830. But I'm not sure if it is the best value. What I know is that the TX Vertical is no longer affecting my RX antenna, My RX antenna is ony60ft from my TX antenna.

I'm using W8JI circuit to speed up a vacuum relay to detune the tower during RX by removing the TX feed line, so when I transmit the vacuum relay close first than my amplifier.

When I remove or close the relay connecting my TX feed line to the skirt, the noise floor on my RX antenna increase 2 S units. Without the Skirt or removing is effect by using a jumper to ground it, the RX antenna becomes useless.