As an experiment I decided “after reading several article on spiral coils” 
to build a full wave loop on 40 meters in the configuration of a compact 
spiral loop to see just how well it would work.  As a form I went with 
treated 1’X 2”s that I cut notches in ½” spacing “this took about 2 hours” 
Next I measured the wire using the standard formula for a full wave loop 1005/f  
then proceeded to wind the coil on the form and attached the feed point. Then 
after checking resonance with the analyzer I found the first issue. I had 
calculated the frequency for 7.050 Mhz but the analyzer showed the resonant 
frequency above the band so I started adding wire to bring the frequency until 
I got the resonant frequency down to around 7.070. What I suspect is this 
configuration becomes capacitive and raises the frequency so instead of 1005/f 
the formula was closer to 1090/f . 

 
 
 
  




Performance of the loop. 
The loop was mounted on a roof tripod at aproxamitly 25 ft up. The first thing 
about this antenna is it seamed to be noticeably nosier this I attributed to the 
vertical polarization. Next I found as one would expect that the signals were 
around two or three S units below my main antenna (150 ft double extended zepp 
with the apex at 35 ft). The band width of the antenna was very narrow 2:1 B.W. 
was some were around 20 KHz  this may have been better if I had used larger wire 
what was used was #24 gage wire. As you can see from the far field plots there is 
some degree of directivity


















 
 
 
 

So in conclusion I think this antenna may work out ok as 
compact portable antenna more experamenting and testing 
would be needed.

Loop log
Date        Time       Call          RST sent   RST rcevd.  Freq.  Mode   Pwr  Name          QTH
07-25-08    05:45z     KC2GKU        599        579           7     CW    30   James         Wharton  NJ
08-09-08    01:27z     VO2A          599        599          10     CW    30   DXpedition Labrador
08-10-08    00:59z     CO8LY         599        599          10     CW    30   Ed            Santiago de Cuba
08-14-08    01:11z     F2LY          599        599          10     CW    30   PAUL
08-14-08    01:18z     VP2/IK2RZP    599        599          10     CW    30   Angelo