FROM THE PROTOTYPE TO THE EGGBEATER II VERSION I
This
antenna is described by K5OE on his web-page. However myself and
Johan ZS2I expressed the desire to provide full construction detail
that pertains to building material found in South Africa. I will
go into great detail how to build this antenna to enable new
constructors to build this antenna successfully. I will not go
into the Background and Design details as this can be found on the
web-site of K5OE.
I will describe the 70 CM - Eggbeater II Antenna.
Before
we can build any antenna we need a plan, photos and the material
to build the antenna. Let's start with the bill of materials.
For the 70CM version you need:
1. 2 x 3mm Brazing Rods (1 Meter lengths)
2. 1 x 40mm PVC End Cap
3. 1 x 40mm PVC Extension Coupling/Joint
4. 680mm x 6.5mm Aluminum Rod
5. 4 x 6mm Brass Bolts (A 10 mm spanner must fit over the head of these bolts)
6. 8 x 6mm Brass Nuts
7. 6 x Brass Lugs to just fit over the 6mm Brass Bolts
8. 60mm Heat-shrink Tubing to fit over 3mm Brazing Rods
9. 150mm of RG-62 (93 Ohm) Coaxial cable
10. 8 x Brass Washers for Bolts and Nuts
11. 1.5m of LMR400 Coaxial Cable (RG213 can also be used but be careful of signal loss)
12. 1m x 40mm PVC Pipe
13. 1 x Tube of PVC Cement (Glue)
14. 300 mm x 6mm Heat-shrink Tubing
15. 4 x 3mm x 15mm Stainless Steel Self tapping Screws
16. 1 x N-Plug Connector (PL259 can also be used but be careful of signal loss)
17. Solder to solder the connections and brazing rods with.
18. 200mm of Nylon line or 2 x 100mm Cable Ties
Now that we have all the material it is time to study the plan!!
You should now have the following material at hand as shown in the photograph below.
Construction:
The
time has now arrived to build this antenna.
Take one brazing rod and mark it with a felt-pen with the
indicated measurements. ( Start with 85.5mm then 210mm; 171mm;
210mm and end with 85.5mm) Now take a small pair of pliers and
start bending the rod in the same sequence as you marked it. This
is one of the loops and should look similar than those shown in the
above photo except that the gap at the bottom is a few millimeters. We will cut
this later to fit the PVC End Cap. Now do exactly the same with
the second brazing rod. You now have two loops which should
look exactly the same. Put the two loops aside and measure the
two reflectors. Each reflector should be 33.5cm long. Take
the 1,5m LMR400 coaxial cable and fit the N-Connector and lugs as shown
in the above photo. So far so good. The 70cm phasing line
(13.5cm) is next. Cut the RG62 about 5cm longer, leaving 2.5cm at
each end to strip the insulation, peel back the braid, strip the centre
conductor and attach the lugs. Remember the total length of the
phasing line must be 13.5 cm. The PVC pipe can be cut next into
two lengths. One 400mm and the other 600mm. Next cut
your brass bolts the required length. The PVC end cap will
determine the length of the bolts. It is important that these
bolts should not touch each other. Look at the photo showing the
gap between the four bolts.
Warm up that heavy duty soldering iron!! While you wait for the soldering iron to warm up go to your bench drill and drill a 3mm x 3mm hole on the head of each brass bolt. This hole must be absolutely centre. You should now have four bolts with 3mm holes drilled in each head. The drilling of the holes is not essential but it will strengthen the connection between the loop and the bolt when soldered to each other. Your heavy duty soldering iron should be hot by now. Take one loop and measure the distance between the end cap and the loop end. The current gap is close to each leg of the loop. This must now be cut to form a rectangle loop when the end cap is installed on the 40mm PVC pipe. Before soldering the bolts cut two pieces of heat-shrink tubing and fit them in the middle at the top of each loop. This is used to isolate the two loops from one another. The photo below show the heat-shrink installed and shrinked. Tthe time has arrived to grab that big soldering iron. Heat both the bolt and the loop end and watch the plumes of solder-smoke reaching new heights. The photo below show the bolts soldered to the loop. The loop end was cut and then inserted in the hole drilled and then soldered. If your version is undrilled you just have to solder the loop to the bolt. To ensure a good soldering joint, use solder flux and clean the loop end and bolt before soldering. Both loops must be soldered and should now look like the photo below.
The loops can now be put to one side. Take the PVC End Cap and let the open side face you. Take your felt-pen and draw four lines in a cross configuration onto the end cap. Measure half way up the end cap and make a mark with the pen. This is where you will drill the hole to fit the one end of the loop. Continue drawing until you have four marks. Ensure a straight cross so that the loops is at right angles to each other. If you go to the first page and look at the end cap with the bolts installed you can see the felt-pen marks on the end cap. The bolts will be installed in the centre of the end cap on each side after the holes have been drilled. You can now install the two loops and tighten the nuts. The Eggbeater should now look something like the photo below.
Take the 400mm PVC Pipe and mark the one end of the pipe exactly the same as you have done with the end cap. Four marks right angles to each other. Measure 6mm on both ends and mark with felt-pen. You should now have three stripes in a cross formation . Remove the middle stripe and you will have a 12mm gap on each side. Cut these "slots" with a hack-saw so that the nuts and bolts will fit into the slots. Remember the 400mm PVC pipe fits into the end cap. These slots are necessary to enable a good fit of the end cap. Fit the end cap to the 400mm pipe and measure a distance of 33 cm from the driven element. Make a mark on the one end and then again on the opposite end. The one reflector will be fitted once the two holes are drilled. Drill the a 6m hole through both sides. Now measure 3mm below these holes but on the opposite side and make a mark. Drill the other two holes. You should now have 4 holes in a cross format. Fit the reflectors to ensure that they are at right angles to each other. We are now nearly ready for final assemble of the Eggbeater 2 antenna. But first you must install the phasing line and feed line. The diagram below illustrates this very clearly and no further guidance should be necessary. I would however advise you to cover all open wires with insulation tape or heat-shrink tubing to prevent shorting. Make sure that all screws are properly tightened and bind the two loops at the top (where you placed he heat-shrink) with a cable ties to prevent movement.
Once the phasing- and feed line is installed you can put the Eggbeater 2 together for its first test run. Slide the phasing- and coax line into the 400mm PVC pipe. Add the extension coupling and shove in the 600mm PVC pipe. Test the eggbeater's SWR. This version revealed a 1:1 SWR on 435.300Mhz. You may now use the PVC cement to seal all joints. Another option would be to use stainless steel self tapping screws. This will enable you to open the "insides" if you want to work on the inside. The Eggbeater 2 Version 1 should look similar to the photo below.
Performance:
The antenna was tested extensively at the QTH of ZS1I under different conditions without a pre-amp. This antenna, mounted 2 meters above the roof, performed very well for an omni-directional design. At 10 degrees above the horizon, signals on AO-51 start to come alive. (No audible modulation but you can hear the carrier) At 20 degrees, they are strong but not clear without a pre-amp and this with a 2m feed line. The signals stay strong and at 45 degrees the audio is clear and audible. The antenna pick up about 3-to-6 dB of strength up through 90 degrees. I believe this increase is due to the improved circularity as the pattern rises.The signals of AO-51 are much harder to capture and the horizontal polarization at the horizon is a definite penalty. I found the use of a pre-amp necessary. I got good copy on the bird once it reached about 30-50 degrees elevation without a pre-amp. I intend testing the antenna with a pre-amp which has not yet been done. The antenna will work without a pre-amp and you will make contacts but it is advised to use this antenna with a pre-amp. Comparing this antenna with the "Bow and Arrow" antenna on this web-page revealed the superiority of the "Bow and Arrow" antenna above the Eggbeater 2, but remember a yagi is far superior that a omni-directional antenna. If you do not want to spend a large sum of money on rotators and tracking systems then the Eggbeater 2 will do the "job" providing you install a pre-amp.
Conclusion:
This antenna is ideal for the enthusiastic listener or the licensed amateur radio station wishing to experiment with satellite transmissions. It will appeal to those with no space for large arrays, or for those who simply wish to experiment with circular polarization for terrestrial transmissions. The antenna can still be improved and I am currently looking at the Eggbeater 2 Version 2. More information later!!
THANKS AND RECOGNITION:
Thanks and recognition must go to the following entities:
ON6WG/F5VIF - EGGBEATER ANTENNA
JOHAN ZS2I - PHOTOS OF EGGBEATER 2 VERSION 1
GERALD K5OE - EGGBEATER 2
