hy-gain VB-25FM 5-Element 2M Beam Antenna Instruction Manual
- June 6, 2024
- Hy-Gain
Table of Contents
hy-gain VB-25FM 5-Element 2M Beam Antenna
General Description
This antenna is a 5-element, 2-meter beam optimum spaced on a 7Y boom. It features, s high forward gain and an excellent front-to-back ratio. The antenna is end mounted giving it the advantage of no mast decoupling and a broad frequency response. Thi antenna now u~ tainless steel hardware in most locations except for the U-bolts. Also, this antenna now features a NEW boom- to-mast bracket that fits up to a mast diameter of 2 1/16 inches.
SWR and Feedline
The 25FM antenna has an input impedance of 200 ohms. The supplied balun matches the input to 50 ohms. If you are using a transmission line with a characteristic impedance other than 50 ohms or 200 ohms., a matching device must be made. Refer to any current Amateur Handbook for information on constructing a matching device.
Product Instructions
Item
No. Description
2 Tube, Driven Element, aluminum, 7/16″ x 171/4″
6 Tube, Rl, aluminum, 3/16″ x 39 5/8″
7 Tube, D1, aluminum, 3/16″ x 36 7/8″
8 Tube, D2, aluminum, 3/16″ x 35 3/4″
9 Tube, D3, aluminum, 3/16″ x 35 3/8″
Overall View and Boom Detail
Tuning
NOTE : The Driven and Parasitic Elements are adjusted independently in the following manner:
Parasitic Elements: This antenna is pretuned for maximum gain and best radiation pattern at 146 MHz. This setting will give optimum performance over the entire 144-148 MHz band. If you wish to optimize the antenna for a frequency higher than 146 MHz, cut 1/4″ off of the total element lengths for each MHz higher than 146.
Driven Element: SWR can be lowered to less than 1.2:1 at a desired
frequency by carefully trimming the driven element. Keep The element
symmetrical by cutting the same amount from each side. Typical SWR curves are
shown in Figure 2A, and a cutting chart is shown in Figure 2B. Each
installation is slightly different, so cut the driven element for the lowest
SWR at your particular location. Measure the SWR as close to the antenna as
you can for accurate results.
Stacking
This antenna can be easily stacked for approximately 3 dB more gain each time
the number of yagi is doubled. Refer to Figure 3 for stacking and phasing
harness cutting inf ormation. The two phasing lines coming from the two
antennas to the ‘T’ connector can be any odd multiple of 1/4 wavelength in the
75 ohm transmission line. See Figure 4.
NOTE : When phasing two antennas, the Driven Element halves that are
connected directly to the phasing lines should be on the same side of the
array.
The feedline impedance is for 50 ohms (RG- 213/U). For detailed information on
stacking more than two yagis, please consult a current Amateur Handbook.
NOTE : The boom-to-mast bracket may be placed between the Driven Element
and D1 when stacking two antennas.
Installation
This antenna fits a 2″ mast. A 2″ O.D. pipe is recommended for a sturdy mast.
Mount the antenna in the clear. Surrounding objects -particuJarly power lines
and other objects of considerable mass or length-are detrimental to the
performance of the antenna.
WARNING: Do not allow any part of the antenna to touch power lines. This
could cause severe burns or fatal injuries. When mounting two dissimilar
antennas on the same mast, be sure they are separated by at least three feet
(1 m). The antenna can be mounted either vertically or horizontally for FM or
SSB/CW respectively. Circular polarization can be obtained by using two yagis.
For information about which polarization is best, consult local Amateurs who
use the frequencies you desire.
Step-by-Step Assembly
Remove the parts from the carton and check them against the parts list and the
illustrations. Select the boom-to-mast backup plate (Item No. 5), the boom-to-
mast clamp (Item No. 4) and the four ( 4) 1/4″-20 x 3/4″ bolts, lockwashers
and nuts (Item Nos. 16, 26, and 23).
Item
No. Description
1 Tube, Boom, aluminum, 11/4″ x 75″
4 Clamp, Boom-to-Mast
5 Backup Plate, Boom-to-Mast
13 Caplug, 11/4″
15 U-Bolt, 5/16″-18 x 3 5/8″
Item
No Description
16 Bolt, hex head, 1/4″-20 x 3/4″
21 Nut, hex, 5/16”-18
23 Nut, hex, 1/4″-20
24 Lockwasher, split, 5/16″
26 Lockwasher, internal, 1/4″
Item
No. Description
1 Tube, Boom, aluminum, 11/4″ x 75″
18 Eyebolt, 5/16″, #10-24 x 11/2″
22 Nut, hex, #10-24
25 Lockwasher, internal, #10
27 Half-Washer, aluminum
Item
No. Description
3 BetaRod,3″
10 Balun Assembly
11 Insulator (Driven Element-to-Boom)
12 Beta Clip
14 Caplug, 7/16″
Item
No. Description
17 Bolt, hex head, #10-24 x 21/2″
19 Bolt, hex head, #10-24 x 11/2″
22 Nut, hex, #10-24
25 Lockwasher, internal, #10
Place the boom-to-mast clamp on the boom as shown in Figure 5. Use the l/4″-20 x 3/4″ bolts in the outside holes. Leave the inside holes for the two U-bolts, which will be used later for mounting the mast. Select either the vertical or horizontal mounting position. Adjust the boom accordingly before tightening the bolts securely. Select the 3/16″ x 39 5/8″ Rl tube (Item No. 6), use pencil to place a mark at the center of the rod (19 13/16″ from either end) and place two more marks 5/8″ from each side of the center mark.
Place a #10-24 x 11/2″ eyebolt (Item No. 18) into the Rl slot as shown in Figure 5, Detail A Slide the Rl through the holes and the eyebolt until the outer two marks on the Rl are visible on each side of the boom. Slip on an aluminum half washer, a lockwasher and a #10 nut (Item Nos.27, 25, and 22). Tighten it just enough to hold the rod securely. DO NOT OVER TIGHTEN.
Select the element-to-boom insulator (Item No. 11), two sections of the Driven
Element (7/16″ x 17 1/4″) tubing (Item No. 2) and beta rod (Item No. 3).
NOTE : If 50 ohm coaxial cable is used to feed the antenna, select the
supplied balun at this time. Use the #10-24 x 21/2″ bolt (Item No. 17) to
fasten the element-to-boom insulator to the boom. Refer to Figure 5, Detail B.
Use the two (2) #10-24 x 11/4″ bolts (Item No. 19) to assemble the Driven
Element as shown in Figure 5, Detail B. Pay particular attention to the
connections of the beta rod, balun and feedline. Waterproof the connection
with neoprene, Krylon®, or some similar substance. Install caplugs on the ends
of the boom and the Driven Element.
Use the # 10 x 3/8″ screw (Item No. 20) to fasten the beta rod shorting clip over the beta rod, as shown in Figure 5, Detail B. Select the following rods: Dl (36 7/8″ long) (Item No. 7), D2 (35 3/411 long) (Item No. 8) and D3 (35 3/8″ long) (Item No.9). Mark the center point on each rod, then make two more marks 5/8″ on either side of the center mark. Secure the elements to the boom as shown in Figure l and Figure 5, Detail A. Be sure they are oriented as shown.
Slip the two (2) U-bolts into the boom-to-mast bracket and fasten it to the mast securely. Tape the coax feedline to the boom and to the mast. Be sure to insulate any connections from the boom or the mast. This completes your installation.
PARTS LIST
Coμverting American Measurements to Metric
1 inch (l”) = 2.54 cm
1 foot (1′) = 30.48 cm
Use this scale to identify lengths of bolts, diameters of tubes, etc .. The American inch (1″) and not (1′) can be converted to centimeters in the tliliway.
Example: 42″ x 2.54 = 106.7 cm
PRINTED IN U.S.A.
CopyrightC 1993 by Telex
TELEX COMMUNICATIONS, INC.
All rights reserved.
I Sept 1993