Home > Home Brew, VHF/UHF > 6 Metre Yagi Design Dilema

6 Metre Yagi Design Dilema

Being a standard call, I wanted to design a yagi I could use on 52 MHz. I downloaded Quick Yagi 4 (QY4) and fed the numbers required into the program. I added a folded dipole with 100mm spacing to simplify matching and ran QY4. I ran the optimised for gain option. The resulting antenna showed a good plot on QY4.

Not knowing anything about QY4 credentials, I decided to model the suggested antenna in NEC. Being a Mac man, I run CocoaNEC. The resulting plot was to say the least not impressive. I’ve checked my work for errors, removed the folded dipole in NEC, removed elements etc. Interestingly removing Director 3 which is the odd one out in terms of length progression, improves the antenna. The plot on QY4 shows very small rearward lobes but the plot on CocoaNEC shows a huge rearward lobe. Do I trust QY4 or CNEC?

Do I just build it and adjust using a FS meter?

Here is the QY4 Data
Operating Freq 52.1MHz
Reflector length 2.87849m
Fed element Length 2.71749m
Reflector spacing 1.02323m
Number Directors 4
Element Dia 13mm

Result gain 11.91
F/B 26.21
Imped. 53-2 – j0 Ohms

The plot looked excellent

Here is the CCNEC data

// My 6 element 6 meter for 52 MHz model( “simple Yagi-Uda” )
{ real height, length, separation, reflector ; element driven ;
height = 8; length = 1.365875 ;
separation = 1.02323 ;
setFrequency( 52.1 ) ;
// driven element
driven = wire( 0, -length, height, 0, length, height, 0.013, 21 ) ;
voltageFeed( driven, 1, 0 ) ;
//driven folded dipole lower
wire(0, -length, height-0.1, 0, length, height-0.1, 0.013, 21 ) ;
//driven connection to bottom
wire(0, -length, height-0.1, 0, -length, height, 0.013, 21 ) ;
//driven connection to bottom wire(0, length, height-0.1, 0, length, height, 0.013, 21 ) ;
//reflector, placed behind (negative x axis) the driven element
wire( -separation, -1.439245, height, -separation, 1.439245, height, 0.013, 21 ) ;
//Director 1
wire( .844753, -1.34225, height, .844753, 1.34225, height, 0.013, 21 ) ;
//Director 2
wire( 1.92563, -1.28019, height, 1.92563, 1.28019, height, 0.013, 21 ) ;
//Director 3
wire( 3.23865, -1.314185, height, 3.23865, 1.314185 , height, 0.013, 21 ) ;
//Director 4
wire( 4.96497, -1.25992, height, 4.96497, 1.25992 , height, 0.013, 21 ) ;
//

freespace() ;}

The resulting plot looks like this

Here is D3 removed

Advertisements
Categories: Home Brew, VHF/UHF
  1. No comments yet.
  1. No trackbacks yet.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: