NVIS

Dave, VE7BX, has been doing some very interesting work lately on NVIS (Near Vertical Incident Skywave) antennas.

Here is some info cut and pasted from a note from Dave to our Emergency Communicators after our Monday night meeting.

Hi all,

Re: our Monday night discussions on making NVIS and dipole antennas:

A little 40 and 80 metre table for I made showing length for legs on dipoles and the different in inches for each 10khz.

Examples:

80 mtr. - if analyzer shows resonant freq. is 3.620 (64 feet and 7.7 inches) and desired resonant freq. is 3.760 (62 feet and 2.8 inches) = shorten 2 feet and 4.9 inches

40 mtr. - if analyzer shows resonant freq. is 7.010 (33 feet and 4.6 inches) and desired resonant freq. is 7.060 (33 feet and 1.7 inches) = shorten 2.9 inches

The actual length may be different depending on other factors, but this shows an estimated change in length.

Remember to leave enough extra wire to go through the insulators and to wrap around itself.

Also, if you have a tuner, make the length resonant to match your favorite frequency and let the tuner do the rest.

Dave G.

80 Metre	468/freq/2			40 Metre	468/freq/2
Freq	Feet	Inches	Diff.	Freq	Feet	Inches	Diff.
3.500	66	10.3		7.000	33	5.1
3.510	66	8.0	2.3	7.010	33	4.6	0.6
3.520	66	5.7	2.3	7.020	33	4.0	0.6
3.530	66	3.5	2.3	7.030	33	3.4	0.6
3.540	66	1.2	2.2	7.040	33	2.9	0.6
3.550	65	11.0	2.2	7.050	33	2.3	0.6
3.560	65	8.8	2.2	7.060	33	1.7	0.6
3.570	65	6.6	2.2	7.070	33	1.2	0.6
3.580	65	4.4	2.2	7.080	33	0.6	0.6
3.590	65	2.2	2.2	7.090	33	0.1	0.6
3.600	65	0.0	2.2	7.100	32	11.5	0.6
3.610	64	9.8	2.2	7.110	32	10.9	0.6
3.620	64	7.7	2.1	7.120	32	10.4	0.6
3.630	64	5.6	2.1	7.130	32	9.8	0.6
3.640	64	3.4	2.1	7.140	32	9.3	0.6
3.650	64	1.3	2.1	7.150	32	8.7	0.6
3.660	63	11.2	2.1	7.160	32	8.2	0.5
3.670	63	9.1	2.1	7.170	32	7.6	0.5
3.680	63	7.0	2.1	7.180	32	7.1	0.5
3.690	63	5.0	2.1	7.190	32	6.5	0.5
3.700	63	2.9	2.1	7.200	32	6.0	0.5
3.710	63	0.9	2.0	7.210	32	5.5	0.5
3.720	62	10.8	2.0	7.220	32	4.9	0.5
3.730	62	8.8	2.0	7.230	32	4.4	0.5
3.740	62	6.8	2.0	7.240	32	3.8	0.5
3.750	62	4.8	2.0	7.250	32	3.3	0.5
3.760	62	2.8	2.0	7.260	32	2.8	0.5
3.770	62	0.8	2.0	7.270	32	2.2	0.5
3.780	61	10.9	2.0	7.280	32	1.7	0.5
3.790	61	8.9	2.0	7.290	32	1.2	0.5
3.800	61	6.9	1.9	7.300	32	0.7	0.5
3.810	61	5.0	1.9
3.820	61	3.1	1.9
3.830	61	1.2	1.9
3.840	60	11.3	1.9
3.850	60	9.4	1.9
3.860	60	7.5	1.9
3.870	60	5.6	1.9
3.880	60	3.7	1.9
3.890	60	1.9	1.9
3.900	60	0.0	1.9
3.910	59	10.2	1.8
3.920	59	8.3	1.8
3.930	59	6.5	1.8
3.940	59	4.7	1.8
3.950	59	2.9	1.8
3.960	59	1.1	1.8
3.970	58	11.3	1.8
3.980	58	9.5	1.8
3.990	58	7.8	1.8
4.000	58	6.0	1.8