Construction Details

4-El.-28-Ohm 0,35m

5-El.-28-Ohm 0,65m

6-El-28-Ohm 0,85m

7-El-28-Ohm 1,0m

9-El.-28-Ohm 1,5m

10-El.-28-Ohm 2,0m

 

70cm-Short-Yagis for 430-440MHz  

All Yagis in 28-Ohm-Technology, elements mounted with polyamid-clamps (Konni).

Stacking of the Yagis will give excellent contest-groups.

Picture right:

8x7-El.- built by Dirk, ON5GS

Electrical details on the pages you see above, construction with "YO 7" by K6STI and "EZNEC+5.0" by W7EL

Short Data of the Yagis:

 430-440MHz at SWR <1,8 (10 El. 430-438) , Boom 15x15mm or 20x20mm, Radiator 10mm, Elements 8mm or 6mm

Left: Collection of 70cm-28-Ohm-Yagis built by DJ8QV

Type

Boomlength

Gain (435MHz)

F/B (435MHz)

4-Element

0,35m

7,5dBd

13dB

5-Element

0,65m

9,1dBd

16dB

6-Element 0,85m 10,1dBd 20dB

7-Element

1,00m

10,5dBd

30dB

9-Element

1,50m

12,0dBd

26dB

10-Element

2,00m

13,0dBd

35dB

Mounting of elements

With these clamps the elements are mounted isolated 2-3mm above the boom. The screw has 3mm and is stainless steel. If you use other mounting methods, you must use the DL6WU-formula for boomcorrection!

The boom correction uses the DL6WU-formula:       

 C = (12.5975-114.5 * B) * B * B

C=Correction factor for one element half (for full element x2) in wavelengths

B=Boom diameter in wavelengths 

The following factors are for not-insulated mounting through the boom, if you mount the elements insulated through the boom (DJ9BV-method) or not-insulated above the boom, use the half correction factor.

Boom

10mm

15mm

20mm

Element

+3mm

+ 7mm

+ 11mm

The parallel 75-Ohm-Cables for the DK7ZB-Match (see other Webpage!)

Length Lambda/4*V

V=Velocity of propagation

e.g. for Full-PE (RG-59) is 0,67

Foam-PE 0,81-0,82,   PTFE 0,7

 

Use a good cable with a high screening effectiveness!

Lengths of the 2x75-Ohm-Lambda/4-Cables for the DK7ZB-Match

Important: Use good quality cable, because cheap TV-cables have often not 75Ohm! Measurements show a resistance of 68, 70 and 80 Ohms for such cables...

Type

Full-PE

Foam-PE, V=0,82 e.g. SATV-Cable

Teflon V=0,7 e.g.. RG-179

Length

115mm

141mm

120mm

The reflector, radiator and director 1 with the mounting box. The cable must be mounted symmetrically between the two element-halfs!

Another box with RG-179 PTFE-cable  for the DK7ZB-Match