TOP LOADED 160M VERTICAL

Hams are never satisfied with an antenna-if it works, perhaps it can be made to work better!  After reading much about vertical antennas and looking at posts on the Topband Reflector, over the past couple of years, I concluded that improvements could be made on my linear-loaded 71 foot vertical.  In December, 2002, I removed the top mast and small hat from the vertical and installed in its place a 16 foot mast with three 38 foot top hat wires.  One wire slopes at about 15 degrees to a 56 ft tower some 70 ft away; one slopes at about 30 degrees to a 22 ft mast located some 60 ft away while the third slopes at 45 degrees to a 20 ft mast about 50 ft away..

On 160M this resulted in natural resonance at 1822 khz. To obtain a 50 ohm match I used the existing base matching coil but needed only six turns to ground.  The result is an antenna which has a 2:1 SWR bandwidth of 95 khz on 160M with perfectly flat response 15 khz either side of centre.  The matching circuit for 80M  had to be reconfigured, and the antenna was deemed to be too long for effective operation on 40M.

Modelling on ELNEC showed that the efficiency of this antenna on 160M was now about 74% compared to a full-sized 1/4 wave vertical, a considerable improvement over the linear-loaded antenna.


                                                                     

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                                                           Fig.1-reconfigured toploaded vertical

The most obvious question concerning this renovation is "How well does it work?"

First of all, I now have a wider 2:1 SWR bandwidth than before (approximately 90 khz) and the antenna is flat across about 30 khz rather than 5 khz with the linear-loaded vertical.  Secondly, I find that QSOs with 100 watts to various DX locations are more numerous and occur more often.  Also, with this new antenna I have enjoyed my first QRP contacts  with EU, something which I believe may not have been possible with the linear-loaded vertical.  Thirdly, in a recent 160 meter contest running as a low-power entry, it seemed easier to hold a run frequency and QSOs seemed easier to come by from all quarters.  Finally, operation on 80M does not seem to have been compromised

Over the intervening 6 years since I modified this vertical in 2002, I have seen my country total climb from 145 to 215 (as of July, 2009), and most of the new ones have been of the more rare variety.  Power into the antenna has generally been between 650 and 850 watts.

Based on the results obtained with this vertical, I constructed a similar antenna at our summer home to replace a 50 ft toploaded three-band antenna employing a capacity hat.  Due to space restrictions I was not able to make it as high as the antenna at the home QTH; however, with 40 ft of lattice tower topped by a 21 ft aluminum mast and three 43 ft top-loading wires sloping at about 40 degrees this antenna has a 2:1 SWR bandwidth of just over 120 khz and it also works well on 80M.  The radial field comprises 43 wires varying in length from about 35 ft to 130 ft.  ELNEC analysis shows the efficiency to be on the order of 68% compared to a full 1/4 wave vertical.  As with the longer vertical, operation on 40M was deemed to be too inefficient for effective DX work and the 40M tuning network was removed.

This second antenna has allowed me to work DX while away from the home QTH; while it appears to be slightly less effective than the taller antenna, nevertheless with 750 watts I have been able to work pretty well everything I can hear.


Last modified on July 15, 2008