[Hi-zreceivingarraydiscussions] DIRECTIVITIY 8 CIRCLE

[John Kaufmann]

I came up with a compromise solution that allows a single Hi-Z 8-circle to
work well on both 160m and 80m.   There are two parts to the solution: 

 

1.       Use a 140-foot diameter circle instead of 200 feet for 160m or 100
feet for 80m.  140 feet seems to be the "sweet" spot for dual-band
operation.  If you go much smaller, 160m performance suffers.  If you go
much larger, the 80m forward lobe gets really narrow and the sidelobes get
big.  At 140 feet, the RDF is 12.6 dB on 160m (down less than 1 dB from the
200-foot version) and is 13.7 dB on 80m.  

2.       Use separate switchable delay lines for 160m and 80m.  These are
the same delay lines you would use for single-band operation.  I do the
switching with relays external to the controller box.

 

On 160m I get excellent F/B and F/S, 20 dB or more.  The pattern is very
clean with low sidelobes.  On 80m the pattern gets really sharp because the
forward lobe is only about 45 degrees wide, although the sidelobes are also
starting to creep up.  The F/B on 80 is often 30 dB.   The array hears
really well on both bands.

 

73, John W1FV