Diamond W721


SKU: AD23450 Categoría:



Diamond W721

7/21MHz  (40m/15m)

Length: 12.4m / Weight:1.2kg

Max.power rating:1.2kW(PEP)





  • The W-Series antennas are very easy to assemble. And, low stretch ratio, rugged and weather proof 3.5 square plastic coatea stranded wire is employed for element material.
  • Adjustment element is provided for each band to adjust each band without affecting rest of the bands.
  • Completely molded wideband balun enables perfect weather proof performance.

Calculating example of element cutting length

Since quantity of the frequency change by cutting adjustment element may change more or less depending the place where the antenna is installed, it is recommended to cut the element a bit shorter for adjustment.

Cf. If desired frequency is 7.052MHz at the 40m band and present resonant frequency when the antenna is initially installed is 7.010MHz, VSWR and reflected power is lowest in 7.010MHz:

7.052MHz (desired frequency) 7.010MHz (present frequency)=

42KHz (frequency difference)

Since frequency change per 1cm at the 40m band is 7kHz from the chart.

42(KHz) ÷ 7(KHz/cm) = 6(cm)

Since present frequency is lower than desired frequency, cutting the element for 6cm will make resonant frequency to desired 7.052MHz.

To add new band

It is possible to add 15m band to the W-735 antenna. As shown in the following figure, installing self-made 15m element to the balun will add 15m band to the antenna.


Prepare a VSWR power meter for applicable frequencies and RF power, and set the meter as shown in the following figure. Practice test transmission for the adjustment as short time and least RF power as possible. (Maximum power rating in constant wave (CW) mode is approximately 1/3 of one in SSB mode.)

Start adjustment from the highest operating frequency downward by cutting adjustment element, both sides in same length, to desired resonant frequency, least VSWR return at the frequency. Since cutting the element in excess may skip desired frequency and result in losing resonant frequency, cut the element little by little.

If VSWR cannot be better.

If VSWR can not be lowered even though resonant frequency came to be desired frequency by cutting the element, it is most |:k“lv that the antenna is being effected by earth or near by buildings, hen.it is advised to change antenna height or antenna location. Bending the element downward from the balun can also change VSWR.

Adjustment element cutting chart

Cutting adjustment element will raise resonant frequency.

The following chart shows resonant frequency change per 1cm element cut.

Frequency W-8010 W 735 W-721
80m(3.5MHz) 4KHz 4KHz
40m( 7MHz) 7KHz 7KHz 8KHz
20m(14MHz) 45KHz
15m(21MHz) 40KHz 50KHz
10m(28MHz) 70KHz

Above values may change depending on surrounding environment


Diamond W721

Diamond W721

Diamond W721

Diamond W721

W-8010 W-735 W-721
BU-50 BALUN with two screws, nuts and washers 1 1 1
80m trap 2 2
40m trap 2 2
20m trap 2
Wire element A 3.75m (12.3′) 2
Wire element B 4.2m (13.8′) 2
Wire element C 2.8m (9.2′) 2
Wire element D 2.8m (9.2′) 2
Wire element E 1.4m (4.6′) 2
Wire element F 10.95m (35.9′) 2
Wire element G 2.9m (9.5′) 2
Wire element H 3.75m (12.3′) 2
Wire element 1 3.4m (11.2′) 2
Adjustment element 0.4m (1.3′) 6 6 6
Insulator 4 4 4
Nylon rope 10m(32.8′) 2 2 2
Self-melting plastic sealing tape 0.3m (1.0′) 1 1 1
Binding wire 0.6m (2.0′) 2 2 2