G0KSC SC28-6-4D 15el 28/50/70Mhz Tri-band Yagi Antenna with a 5.092 Metre Length Boom
Important notes About this Antenna
Only experienced builders should attempt to build this antenna. element lengths and spacing (in particular on 70Mhz) are critical to the antenna performing as it should so be warned!
About this antenna
This is antenna is a triband OWA interlaced Yagi beam antenna designed with only one feed point to enable the user to feed just one coax feed into the shack from the antenna/mast. A simple coaxial relay or switch can be used to switch between 28/50 (most HF rigs have 28/50 on the same socket) and 70Mhz.The antenna provides 4 elements on 28Mhz, 5 elements on 50Mhz and 6 elements on 70Mhz. However, as with any Dual or triband interlaced Yagi, this is a compromise antenna and therefore, none of the inidividual antennas will perform as well as monoband Yagis for each band of the smae number of elements. Do keep this in mind if you choose to build this one.
The design is intended for the amateur that has limited space on the tower/mast to install multiple antennas and if the indivdual prefers the above mentioned bands, this this antenna will be ideal and certainly I have not seen anything like it available on the Internet or commercially.
Read this section carefully
This time, whilst I am not a fan of tapered Yagis, this one is and uses both 1/2 inch (12.7mm) and 3/8 inch (9.6mm) tubing. The centre of each element is 1/2 inch and the 3/8 slot in each end. If the antenna is being installed permenantly, it is recommended tospot wled the joints with a TIG to ensure no resistance or issues at a later stage.
the 1/2 centre sections are positioned in the centre of the boom in order that half the 1/2 inch length of tube will protude either side of the boom. The measurements for the 3/8 section should be cut twice and slotted in each end.
The 28Mhz centre sections are 4 metre lengths of 1/2 inch tubing (2 metres either side of the boom) whilst the 50Mhz centre pieces are 2 metres (1 metre either side). The 70Mhz elements are 1/2 inch tubing ONLY and have no taper.
Download the .nec file
In order to make this easier for people to understand the design (and perhaps improve it, let me know if you do, it has take many hours so far and I am sure lots of improvements can be made, especially the 70Mhz pattern!) I have placed the .nec file upon the download section of this site. If you do not have it, download 4nec2 software (on the download page too) in order to view and edit the file.
Sizing and spacing are as follows:
Dimensions in Metres
Element spacing:
- Ref 28 = -.679
- Ref 6 = -.05
- Ref 4 = .366
- Driven 28= 1.23 (this element is feed with coax)
- Driven 6 = 1.131
- Driven 4 = 1.334
- D1-28 = 2.186
- D1-6 = 1.785
- D1-4 = 1.985
- D2-28 = 4.413
- D2-6 = 2.34
- D2-4 = 2.565
- D3-6 = 4.256
- D3-4 = 3.16
- D4-4 = 4.08
Element sizes per end tip (3/8 inch section end tips for 28/50Mhz, whole element length in 1/2inch tubing to 70Mhz. See details above):
- Ref 28 = .629
- Ref 6 = .44
- Ref 4 = 1.045
- Driven 28= .568
- Driven 6 = .445
- Driven 4 = 1.023
- D1-28 = .420
- D1-6 = .391
- D1-4 = 1.018
- D2-28 = .268
- D2-6 = .385
- D2-4 = .983
- D3-6 = .38
- D3-4 = .965
- D4-4 = .995
Performance figures @ 28.500Mhz:
- Froward Gain: 8.77dBi free space
- Front to Back: 17.41dB
- Radiation angle at 10 Metres above ground: 15 degrees
Performance figures @ 50.250Mhz:
- Froward Gain: 9.58dBi free space
- Front to Back: 16.24dB
- Radiation angle at 10 Metres above ground: 10 degrees
Performance figures @ 70.250Mhz:
- Froward Gain: 9.76dBi free space
- Front to Back: 11.1dB
- Radiation angle at 10 Metres above ground: 5 degrees
For construction information see 'G0KSC insulators' and the UKSMG article from the main menu on the home page.
Antenna performance details listed below on 28Mhz, 50Mhz and 70Mhz.Any questions please mail me, I like to hear from you!
