IJXX antenna projects

Many thanks for this page to VE7BQH, Lionel H. Edwards

Boom spacing formulas

Data sent by VE7BQH, formula by G3SEK, measures by DL6WU

Boom correction for through the boom insulated elements on 2 meters & 70cm.
Proven accurate for boom diameters smaller than .055 wavelengths.

Formula: C = 12.5975*B - 114.5*B^2

Correction for 2 meters G3SEK
Boom diameter Correction Add
Inches mm Percent Inches mm
0.750 19.050 10.56% +0.792 +2.02
0.875 22.225 12.14% +0.1062 +2.70
1.000 25.400 13.66% +0.1366 +3.47
1.125 28.575 15.13% +0.1702 +4.32
1.250 31.750 16.54% +0.2068 +5.25
1.375 34.925 17.90% +0.2462 +6.25
1.500 38.100 19.21% +0.2882 +7.32
1.750 44.450 21.67% +0.3792 +9.63
Correction for IJXX's
2 meters antennas
Boom
diameter
Correction
mm mm
20 +1.50
22 +1.75
25 +2.50
30 +4.00
35 +5.40
40 +7.00
Correction for DJ9BV's
2 meters antennas
Boom
diameter
Correction
mm mm
20 +2.00
25 +3.00
30 +5.00
35 +6.00
Correction for 70 cm G3SEK
Boom diameter Correction Add
Inches mm Percent Inches mm
0.787 20.000 25.00% 0.1968 +5.00
1.000 25.400 20.00% 0.2362 +6.00
1.125 28.575 24.50% 0.2756 +7.00
1.250 31.750 25.20% 0.3149 +8.00
1.375 34.925 25.77% 0.3543 +9.00
Correction used by K1FO on 70 cm
Boom diameter Correction Add
Inches mm Percent Inches mm
0.875 22.225 28.98% 0.2536 +6.44
1.000 25.400 31.97% 0.3198 +8.12
1.125 28.575 33.49% 0.3769 +9.57
1.250 31.750 36.00% 0.4501 +11.43
1.375 34.925 38.00% 0.5226 +13.27
Correction used by VE7BQH on 70 cm
Boom diameter Correction Add
Inches mm Percent Inches mm
0.630 16.000 22.94% 0.1445 +3.67
0.750 19.050 25.93% 0.1945 +4.94
0.875 22.225 22.50% 0.1969 +5.00
1.000 25.400 27.56% 0.2756 +7.00
1.125 28.575 31.50% 0.3544 +9.00
1.250 31.750 33.67% 0.4210 +10.69
1.375 34.925 33.33% 0.4584 +11.64
Correction for 70 cm
IJXX antennas
Boom
diameter
Correction
mm mm
20 +5.7
22 +6.2
25 +7.7
30 +10.0
35 +12.8
40 +15.1

Correction for DJ9BV's
70 cm antennas

Boom
diameter
Correction
mm mm
20 +5.00
25 +7.00
30 +10.00
35 +12.00

Note: there is no difference in correction factor for round or square booms.


Element diameter correction on 2 meters

The following are some average element diameter corrections for 2m to scale an antenna for a different diameter element.
It is not so simple as just adding a simple linear correction as the overall taper changes depending on the diameter of element.
As a consequence the correction varies from reflector to last director. Eg: 6.25mm to 5mm diameter correction on a 10 el. DJ9BV antenna is 2 mm at the reflector and 6.91mm at director 8.
The above was calculated using the YOC 5.0 scaling feature.

Element diameter correction (2 meters)
Diameter (mm) 6.35 5.00 4.76 4.00 2.00
Add (mm) 0.00 4.50 5.00 8.00 12.00
Correction factor for Cushcraft and Cudee
style mounted elements (2 meters)
Company Inches mm
Cushcraft 0.25 6.35
Cudee 0.25 6.35

DL6WU stacking formula

Dopt = (wavelength/2) * sin(beamwidth/2)

Good results can be obtained down to 90 percent of the above formula if a smaller stacking frame is desired.
Closer stacking than 90 percent of DL6WU's formula will result in a degradation of G/T.