Inv-L for 160m/80m finished


After a pretty long “off-station” preparation the day finally has come to complete the antenna. All I needed to do is include the trap and tune for 1830KHz. Actually I tested the 80m part last year in the ARRL-CW contest with pretty good result. I managed to log 171 NA QSO in the first 6 hours without special RX antenna. This was promising and I had great hopes for the 160m version as well. The last year 80m configuration had 30 ground radials (10m long) and the performance was satisfying. I planned to double this number up to 60 to see what will be the change. Unfortunately the property is 18m wide and the supporting tower is not centered therefore I have this 10m length compromise.

Of course, as each and every real ham antenna activity is finishing in the dark and cold I lived up to this standard. Actually I was lucky because the WX was very gentle compared to what it might have been in January. I had sunshine and +8 C on the peak. This was the result when I finished the matching network:

It was great to see how the ground loss is decreasing with adding more and more radials into the system. I really like when I can see the theory comes to reality.

It’s interesting the only big drop in impedance came with the first 10 radials. After doubling the radial number couple of Ohms the decrease only, which means a portion of a dB in gain. Only for reference this is what I measured in Feb/2015 for the stand alone 80m Inv-L:

The reason might be the soil was much more humid now than last year or maybe the trap causes the difference. But anyway, it does not matter too much now.

I was very curious about the end result compared to ON4UN’s book. I was satisfied when I could conclude that the “real” version in my garden knows the physics and acts very similarly to the “official” version in the LBDX. This is what I wanted and got:

Probably my SWR curve a bit more steep but I guess this is pretty close what the system can provide in band width wise. I was able to try it out before the CQ160m contest. I logged my first JA on top band. JA7NI had real s8 signal on the Inv-L (have no RX antenna yet) and he came back to me for the second call. Amazing. My smile was pretty long on my face. Finally, I have an antenna for 160m which is “not only radiating somehow”. I heard a bunch of other JAs with great signals as well, so the job was done.

 

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