RE: [amsat-bb] Anyone built K5OE Eggbeater II antennas ?

[K5OE@xxxxxxx]

Ron,
It sounds like either 1) you did not have the loops connected correctly or 2) you had a short in the coax/connections somewhere.  One of those conditions would present infinite SWR across a range of frequencies--just like you described.  You can test the coax with an Ohmeter BEFORE you connect the loops (should be open).  After the loops are connected you should show continuity, but you cannot confirm correct connections except visually.  Generally, I found the size of the loop to be very close, with an overall circumference change of 1/4"/MHz for tuning.  When you are close, you can adjust the shape of the loops slightly to fine tune the SWR.  I found the antenna comes in at about 1.5:1 reliably.  I don't bother tuning below that as the antenna is typically sitting in a vise in the garage anyway (and nowhere near its real operating location).

The loops are not connected at the top where they cross.  Leave the insulation on the wire, or at least insulate the loops from touching at the top.  The reflectors can touch, though, since that is a zero-current point.  

I found using a pair of needle-nose pliars and a pair of solid-grip pliars I could form a nice "ring" in the 10 gauge wire, bent at 90 degrees to the bottom of the loop, to wrap around the stainless bolt.  Putting a stainless washer on each side of the "ring" keeps the torque from the nut off the wire "ring."  

73,
Jerry, K5OE


Jerry:

I will look at this again in a day or two.  After working on this for a week, 
time came to walk away from it for a while.  I never could get the SWR to come 
down below 3.5 to 1. Ended up having a loop 3 times the size of what you had. 
The meter pretty much stayed pegged to the right hand side of the meter with a 
minor dip when I was trying to find the low swr point of the antenna.  I am 
beginning to suspect a bad MFJ UHF Antenna analyzer.  Will talk to them on 
monday.  Can I use a ohm meter to get the readings you are talking about since 
I am questioning the reliability of my MFJ Antenna analyzer ?

When I was doing the swr measuring, I had a test harness that is a section of 
9913F that that two lugs on the center conductor that went to one part of each 
loop and two lugs on the ground shield that went to the remaining part of the 
loops.  I make sure that the center conductor of the test cable only went to 
one side of each loop and the same for the ground shield.  

I had tried to crimp lug connectors on the 10 gauge wire to make it "easier" to 
connect it to the stainless steel bolts (I had initially used zinc bolts 
because I had that on hand - same problem - high swr).
Cant tell from the pictures how you connected the antenna elements to the 
bolts.  I tried connecting the wire directly to the bolts but had a hard time 
getting a loop small enough to firmly fit around the bolts.  How did you 
connect the wires to the bolts ?

Thanks for helping,
Ron
Ka4kyi


Ron,
The procedure is to connect your feed line to both loops in parallel... with no 
other harness.  Connect two adjacent (say, 12:00 o'clock and 3:00 o'clock) to 
the center conductor and the other two (say, 6:00 o'clock and 9:00 o'clock) to 
the shield of your feedline.  You should have two roughly-100 Ohm loops in 
parallel at this point--with a near-50 Ohm load.  The radials will have minimal 
influence on antenna feedpoint impedance due to their relatively distant 
relationship (about 1/2 wavelength) in this design.  A single loop should 
reliably give you a 2:1 SWR, by the way.  

Just to double check, here are the measurements for the loops (I have built 
several of these and my results have been  repeatable):  The 70 cm loops are 
6-3/4" (17 cm) wide by 8-1/4" (21 cm) tall; the 70 cm reflectors are 13-1/4" 
(33.5 cm) long and 13" (33 cm) below the driven elements. 

And to Bob's comments... if you want the best of both worlds, use both antennas 
with a switch:  use the Egg II up to about 30 degrees elevation then switch to 
a 3/4 wl whip antenna for the higher gain at high elevations.  

Good luck,
Jerry, K5OE

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