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The KG4FET HYBRID 6 METER 4 ELEMENT YAGI
WITH QUAD REFLECTOR! 

Let me preface by saying this 6 meter Yagi with a quad reflector was built completely from scrap antenna parts and previously failed projects. The boom is the bottom section of a ruined Cushcraft R7000 vertical, the Yagi elements are from a scrapped Cushcraft A3S triband beam, EVERYTHING was scavenged down to the gamma parts.


The goal was a wide spaced (.25 wl spacing) 4 element parasitic Yagi with wide bandwidth (50.000-50.400mHz) and good forward gain, with a gamma match feed using ONLY what I had on hand. F/B was much less of a consideration. I had built this same beam in the past and really loved the gain and much narrower E/H plane beam width over the 3 element home brew yagi I had built.


The boom material I had on hand was only 11.5' long, safely extended, so it was a little short for the beam I had in mind. I looked at trying to add another short extension on the back but just didn't have anything that would work, same for the front. Remember I am working with the limited scrap pile and did not want to spend any money. I came across a 3 inch OD piece of PVC conduit buried in the grass under my failed quad project. I had a "ah ha" moment right then. A quad did not need to be parasitic to work! I promptly drilled 1 inch holes and installed the reflector from the old quad project on the back of the boom just slipping it on at this point shown in the circle in the picture below. 


You can clearly see the 3 inch PVC pipe with the quad mounted on it in the above picture.


The Yagi elements were already built and on the boom at this point. The driven element is 110.5 inches total length and director elements are 108.5 inches long. They are tapered from 1 inch to 11/16 inches. The quad reflector was built using the formula 1030/F (MHz)= feet over all or 1030/50.150 = 20.54 ft total wire. I used 16ga stranded/insulated wire.


I used a case from a scrap 11M amp for the gamma straps. They are about 1 inches wide. They were cut with a pair of tin snips and show it. Measurements were based on my notes from the previous 4 element project but the gamma match was based on a gamma program I found on the internet, and are 14 3/8 inch long tube, sized for a 15 inch center conductor, (outer insulation removed from coax but leave center conductor insulation on), from RG8 coax to fit inside. Spacing from the boom is 2.5 inches from the top of the tube to the boom. See pictures below.




 

The quad added a couple of problems with the SWR. I adjusted the gamma as low as I could get it using the 1/4 wave spacing I had planed for, but could not get it below 2.0:1 but moving the quad back on the boom lowered it some what. I moved the first director element toward the driven element and got the SWR to drop to 1:1. You may have to experiment a bit with yours.


Final element spacing:

Reflector to driven = 55 inches

Driven to director 1 = 47 inches

Director 1 to director 2 = 52 inches


Initial tests were done from the test bed pictured below using the MFJ analyzer as a signal source for the beam and the TS2K and an OA50 omni directional antenna 250 feet away and 30 feet higher.
The Yagi, pointed at the OA50 signal, showed S9 with the PRE off and the ATT engaged on the Kenwood and showed a fairly narrow beam width and no MAJOR lobes off the side. But the BIG surprise was the F/B rejection. With the above settings on the 2K, I could just barely tell there was a signal. When I turned the ATT off (20db) the signal was in the noise!


Initial test setup.This shot is not out of focus. It's your eyes!

On the air tests proved this out. At 35 feet using LMR400 as the feed line I did a F/B test with a 1.5KW station 25 miles away. The test station 4 element yagi is at 70 ft and pointed at me. Using the same settings on the TS2K (ATT in, PRE off) he was 20db over S9 beam to beam. Side lobes were down to S3. With the rear of the beam facing him with ATT off and PRE off he was unreadable. When I turned on the PRE his signal was there but not readable. This translates, doing the basic math, to over 30db F/B ratio. This thing is deaf as a post off the back end!


This project took me several days to complete because I would get frustrated with this and that and had to stop and walk away. Antenna building is fun and trouble shooting is even more so but if you get frustrated, walking away and rethinking what you are doing is the best plan.


Here is the final installation.

Antenna is at 35 feet off the ground to the boom. Below it is my Hentenna for 2M built from plans found on Hamuniverse.com, and the 13B2. initially the 13B2 was on top but the reflector on it was in the quad and giving me fits on the SWR and pattern. This spacing seems to work just fine and neither the 6M beam nor the 2M's patterns seem skewed in any noticeable way.


The main thing when building antennas is to HAVE FUN and experiment!!!!
73 -- Sandor-- KG4FET

Editor note: And as an added plus, if you have a pile of junk "gold" laying around, it is much easier on the bank account!

If you have questions, email Sandor - kg4fet AT bellsouth.net