Polarization
Circular Polarization
I will try to explain how to create Circular Polarization when using crossed yagi antenna's or
yagis that are placed under an angle of 45 degrees. If you use a Helix antenna you don't need
this solution.
Space communication has forced the use of Circular polarization. The fundamental advantage of
circular polarization is that all reflections change the direction of polarization, precluding the
usual addition or subtraction of main and reflected signals. Therefore there is far less fading and
flutter when circular polarization is used at each end of the link.
Right Hand Circular Polarization:
Left Hand Circular Polarization:
Reporting the term "Cross-Yagis", we mean two identical Yagi-antennas where the first one is
placed in Vertical position and the second in Horizontal position. In any case the angle between
these two antennas must be always 90°, so its also possible to place these antennas on "X"
arrangement, the first one with angle of 45° and the second with angle 135° vis-a-vis to
"CrossBoom". The picture below shows a typical "X" arrangement with VHF & UHF "cross-Yagi"
antennas in order to cover the LEO Satellites.
The "X" arrangement has a small advantage for a simple reason: the metallic CrossBoom does
not affect the antenna's efficiency in contrast with the V-H arrangement (V-H = VerticalHorizontal), where the CrossBoom is between Horizontal-antenna's elements. That is unwanted !
The figure below shows what happens with the V-H arrangement: half of the horizontal
elements are "shadowed" by the CrossBoom.
But, if the CrossBoom is made from non metallic material (like Wood, PVC etc), there is no
significant effect between the CrossBoom and the Horizontal-antenna, so in that case it is
possible to mount the two antennas with Vertical and Horizontal classical arrangement. On the
other hand, the V-H arrangement offers a small advantage in case you need to have a
"switchable" antenna system in order to change polarization between Vertical (for mobiles),
Horizontal (DXing) and Circular polarization (Satellites). The V-H arrangement needs a minimal
number of coaxial Relays, in order to be able to make this system "switchable" between VerticalHorizontal-RHCP polarization, in contrast with the "X" arrangement, which needs much more
Coaxial-relays (and phase-stubs).
< identical two connect to order in used been has which circuit mentioned above the happens
what enough clearly shows picture following>
The necessary "Phasing Stub" in series with ANT-2 has been added. Thus, the feeding of this
antenna is "delayed" in phase by 90°, in order to be able to generate the wanted Circular
polarization.
Figure 4, The circuit for circular polarisation:
For this box you need separate coax cables from the horizontal and vertical plane with exact the
same length. Four options can be realized:
1. Vertical polarisation with the cable of the vertical plane of the Yagi
2. Horizontal polarisation with the cable of the horizontal plane of the Yagi
3. Right hand circular polarisation: Horizontal plane to connector 1, vertical to connector 2,
to station connector 3
4. Left hand circular polarisation: Horizontal plane to connector 2, vertical to connector 1,
to station connector 3
Physical method
This method differs in the "import-technique" of Phase's Difference. In the previous chapter was
described how in practice it's possible to feed the 2nd antenna with 90° "Difference in phase"
vis-a-vis to 1st antenna, by using a coaxial piece (50 Ohms) that works as "Phase Stub".
The "Physical Method" following a different technique in order to avoid the use of coaxial piece
for the necessary 90° phase's difference. Here the "Phase Difference" has been achieved by
"shifting" (moving) each element of the 2nd (Horizontal) antenna exactly one QuarterWavelength (λ/4) forward in space, vis-a-vis to each element of 1st (Vertical) antenna onto the
common Boom.
This page is created thanks to the information I found on the website from SV1BSX
TK5EP
After a question from TK5EP to DK7ZB, a calculation was made for an antenna according to his
28 ohms principle but with a boom length of 3 meters. If the calculations for the shortened Que
Dee are very badly we will build this design in a cross yagi setup for Satellite operation.
Below is a table showing the sizes for the construction of this antenna. The dipole diameter is 10
or 12 mm. The elements are mounted isolated from the boom.
Table of TK5EP:
Diameter
Ref
Rad
D1
D2
D3
D4
D5
908mm
915mm
890mm
8mm
1030mm
970mm
(12mm)
942mm 921mm
Position
0mm
325mm
560mm 1035mm 1665mm 2405mm 2980mm
Antenna match of 28 ohms to 50 ohms.
Here you see the construction of the dipole including the mounting of the 28 Ωto 50 Ω match.
And then finally the antenna is ready for use, TK5EP has stacked two in the vertical plane and
therefore almost 3db extra gain.
n the Ham Radio DeLuxe interface quide I found a universal schema for
connecting a transceiver to a computer RS-232, Audio Line IN and Audio Line
OUT. The interface isolates the transceiver from the computer using transformers
and optocoupler.
This example used a 6 pin mini DIN, but you can use every connector you want as long as it
meets the requirements. Read the interface guide for more details.
Tracker
Update:
Monday Aug 18, 2008 I orderd a LVB Tracker enclosure made by Ten-Tec and
sold by Amsat. Here are two pictures of the enclosure.
Friday Aug 1, 2008 I finally recieved my LVB tracker and I hope to build it the
next couple of weeks. The reason that it will take so long, is the fact that I have
been sick the last two weeks and with a fever over 40 degrees that wasn't a nice
time.
Monday Juli 21, 2008 I received a message from Jim Heck who is responsible for
the delivery of the LVB tracker he wrote me that it is on its way via air mail. So I
hope to receive it this week and start building the LVB tracker next weekend.
LVB Tracker
Today I placed an order for the complete LVB Tracker kit via the Amsat UK
online shop. I hope to receive it as soon as possible. Then I can build it and after
that, tracking the satellites will be much easier. Below some picture from the kit
that is being sold via Amsat UK.
Basic kit - This includes all components (less display) to make the basic kit,
without the usb/tcp interface daughter board. It includes the main PCB
itself. (Please note that the kit does NOT include components for the USB
daughter board)
Display Unit - This should be ordered with the Basic kit above, and includes
ONLY the display unit.
The kit as it is being send to customers.
When I receive the kit, I'll keep you posted on this page on how easy or difficult
it is. You will be able to follow me step by step.