G0KSC SC28-6DS 4el 28Mhz/50Mhz Dual band Mini Yagi Antenna with a 2.708 Metre Length Boom
About this Antenna
This is a dual band short Yagi for both 28Mhz and 50Mhz. The antenna consists of 2 elements (reflector and driven element) for 28Mhz and 2 elements (driven parrasitic and director) for 50Mhz. With only 2 elements on each band and being very short, the gian figure is low along with that of the frotn to back ratio. However, there is still good gain over a dipole on either band and a great starter project in this antenna for the novice.
There is only one feedpoint which is at the center of the smallest 28Mhz element which should maintain it's length but have a 10mm section cut out of the centre and the feed line connected at this point.
NO Matching Device is required for this antenna as it has been designed with a 50 Ohm impedance at the feed point for both bands.
All tubing is 1/2inch diameter aluminium tube.
Sizing and spacing are as follows:
Dimensions in Metres
- Ref 28 = 0
- Driven 28 = 1.914
- Driven 6 = 2.007
- D1-6 = 2.708
Element sizes per element half:
- Ref 28 = 2.584
- Driven 28 = 2.446
- Driven 6 = 1.45
- D1-6 = 1.365
Performance figures @ 28.500Mhz:
- Froward Gain: 6.71dBi free space
- Front to Back: 9.35dB
- Radiation angle at 10 Metres above ground: 17 degrees
Performance figures @ 50.250Mhz:
- Froward Gain: 7.82dBi free space
- Front to Back: 12.72dB
- Radiation angle at 10 Metres above ground: 10 degrees
Each element is made out of single piece 1/2 inch (12.7mm) aluminum tubing Each element half length needs to be doubled in order to gain your total element size. No difference is length needs to be calculated for the 1inch or 1,1/4 inch boom as the elements sit high enough above the boom for the boom to have no influence.
You can build this antenna with 13mm diameter tubing using the same parameters above. Slightly higher front to back ratio and forward gain will be seen along with a narrower SWR curve.
For construction information see 'G0KSC insulators' and the UKSMG article from the main menu on the home page.