Creation of an inverted L antenna on 160m

Finally I am able to construct an almost perfect inverted L antenna for 160m, taking into account my preferences :

1. Have resonance nearto the FT8 frequency (1840 Khz)

2. Keep the vertical part at about 15m in order to survive winter storms.  I don't want to pull up and down the tower depending the weather forecast

3. Foresee around 30 radials of 1/8 wavelength

This is the final result : 

and in real the base looks like this :

But before the final result, there are some intermediate - sometimes frustrating - steps.

For all beginners, this is a quick manual :-)

Step 1 :  Cut the wire to the preferred length via the trial and error method.  

Because this is an inverted L, it is quite easy to shorten the horizontal part of the wire.

Once this is ok, the result seems very fine.  Resistance close to 50 Ohm, SWR 1,7, clear dip nearto the FT8 freq.

But ! The efficiency of the antenna is very low when you use it like this.  Without radials, ground losses are far too high.  In my starting years, I would have stopped at this point,  focussing on good SWR and not too much labour.

Step 2 : Add radials

There are many articles on the internet about the installation of radials on vertical antennas.  It seems that up to 24 radials, you can place 1/8 lamba radials in stead of 1/4.   I have 32 x 21m radials.  The only reason is that I had the radials ready in the box, used for my 80m vertical.

As predicable, but not making happy, the resistance of the antenna gets down to about 15 Ohm.  SWR raising up to 3.5, too high to connect to a linear amplifier.

Step 3 : Add a coil between to hot side and ground.  

This is also known as the hairpin method.  I used a coil from my Butternut vertical.  It's also a bit trial and error, the result is not perfect at all, but it lowers the SWR to 3.  

The resistance stays low, creating possible (too) high currents.   It this point it must be possible to use the antenna with a tuner inside the shack.  Remark also the BALun used to avoid unwanted radiation on the coax.

But this is not the correct use.  There is a better solution

Step 4 : add a 1:2 UNUN

Final step : I contacted Hugo, ON7FU, a real specialist in transformers.  He was capable to make a UNUN within 1 day.  Fantastic job, I could use it during the CQ WW CW contest.

Replacing the Balun by the Unun, resistance goes up to 49,5 Ohm !!  :-)   SWR 1,07, no tuner needed, no EMC risk and high power available at the antenna.

The dip is on 1831 Khz, nearto 1840 Khz for FT8 and perfectly usuable for running in the CW contest.  

Most important (see my blog about the windom antenna on 160m, with changing SWR depending on the weather)  : This antenna stays tuned.  No changes in impedance due to rain or other influences.

  

 

But the proof of the pudding in is the eating...