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posticon Re: Avanti Moonraker 4


Hi 26fb010.
This antenna is certianly doing the buisness for me regardless of and gain or f/b ratios etc etc.
I have worked most of eu and3,4,10,11,23,32,41,43,44,69,74,112,151,153divisions over the past year with this antenna and the SWR is constant @1.3.

OH BTW I am selling this antenna too to make room for a 6 ele long boom.


---
Yaesu Ft 1000Mp MkvV (200 w) ,Moonraker 4,Create RC5, MFJ949E ,W2IHY 8band and eqplus , t-bone studio mic.
WKS 100 for AM day

Yaesu Ft857D - KL 400- K40 or dipole (mobile)
12/Feb/2010, 10:19 pm Link to this post Send Email to 29fb002   Send PM to 29fb002 Blog
 
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Re: Avanti Moonraker 4


food for thought????
Circular Polarization
Circular Polarization is a relatively untalked about subject on 11 Meters, perhaps this is the first time you have ever heard of such a thing. Most antennas are oriented to produce linear polarization - either horizontal or vertical polarization. Sometimes, a creative CBer will turn their beam at a 45 degree angle, half-way in between horizontal and vertical polarization. This results in a signal that is weaker than if the owner would have oriented their antenna the same (polarization) as their neighbor's antenna. This is still a "linear" polarization.

To make sure we have vertical and horizontal polarization down, lets look at some animated figures again (these also are in the "Antenna Basics" section). Do not think these animations are an actual representation of a signal, they are to merely demonstrate how the electric field is parallel to the radiating elements.

Horizontal Polarization
Vertical Polarization

It is known that if one station transmits a vertically polarized signal and the local receiving station is using a horizontally polarized antenna, this will result in a signal that is 20db weaker at the receiving station's receiver! Matching the polarization's is a good idea for maximum signal strengths between two stations. When talking "Skip" (Dxing), you might think you need to make sure you are using the same polarization as the distant station for maximum signal strength. In actuality, it might be impossible to match the polarization of the Distant station - this is because when the signal "hops" off the ionosphere - it's polarization usually gets rotated - at a random amount.

(((If you are unsure how signals "skip" great distances, check out the "Angle of Radiation" section for more insight.)))

To make matter worse, the polarization does not maintain a set polarization during a period of time. When the incoming signals polarization matches your antennas polarization, you get the strongest signal strength possible. And when it is 90 degrees different (meaning, say your listening on vertical polarization and the signal is coming in on horizontal) you get the weakest signal possible. As the polarization swaps between matching your antennas polarization and varying from it, you will hear the signal "fade" (known as "QSB" to Amateur Radio Operators). Sometimes it will fade in and out fast - sometimes is will fade out and say down in strength, This is just one condition that causes fade that you can help eliminate. Just so you know, there are a few other phenomena that cause signals to fade. The two other major things are:

The reflectiveness of the ionosphere - The ionosphere isn't a perfect reflector, and perhaps is varying the signal quality. This is one type of fading you don't have any control over!
 "Multipath" fading - As the signal travels from the distant (DX) station, the signal takes more than one path. This results in the signal arriving at the antenna at slightly different times. Does this sound familiar? If you read the section on "Yagi", you know that if signals arriving at the driven element out-of-phase results in signal cancellation, which results in signal loss. As the effect of multipath varies, it causes signal fade. There isn't too much you can do about this either! A good beam with a high Front-to-back and Front-to-side ratio can help combat this. Multipath can cause signals to fade out almost entirely!
Another situation that you might not be able to match your polarization with the receiving station is that, you are talking to more than one local station, and they have opposite polarizations (i.e. one station is using vertical and the other is using horiztonal). When you are listening, you could flip between polarizations to match the transmitting station for maximum signal, but when you transmit -- well, I hope you see the problem. Perhaps you can flip your antenna switch between horizontal and vertical about 10000000 times a second and neither station will notice.

So, what we know now is, we would like to match our antenna polarization to the station we are talking to. This is easy when we are talking to a local station, where our signal travels along the ground. If we have a beam that is capable of both horizontal and vertical polarization, then we just switch between the two. Now, how do we deal with this random polarization change of "Skipping" signals? Simple, we make our antenna receive and transmit horizontal, vertical and EVERY angle between horizontal and vertical polarization. This is known as "Circular Polarization". Once we have set our antenna up for circular polarization - it will be really effective for dealing with talking to vertical and horizontally polarized stations and for reducing signal fade when talking to distant stations!

I mentioned the two other conditions that cause signal fade to let you know, it (fade) can't easily be eliminated, so don't think you did something wrong when you still hear signal fade on "skip" signals with your new circular polarized antenna.

Now, for a crude visual representation of a circular polarized signal.

Circular Polarization
Compared to horizontal and vertical polarization, you can see, it encompassed every angle. As the signal leaves the antenna, it is actually spinning, not maintaining a set angle. This is good because no matter what polarization the receiving station is using, your signal will still come in at the same intensity. On receive, the same thing is true, no matter what polarization a signal is coming in at, it will still have the same intensity. When facing the same direction as the antenna is pointed, a signal that rotates clock-wise as it leaves the antenna is known as "Right Handed Circular polarization". As signal that rotates counter-clock wise is known as "Left Handed Circular polarization".
Suitable Antennas for C.P.

Now, lets talk about what antennas we can use to transmit and receive Circular Polarization. (I am abbreviating Circular Polarization = "CP" from here out!)

Mainly, only dual-polarity beam antennas are good for this. Either yagi, quads or hybrids that can produce two polarization's can be used. If your beam has two coax connections on it, you should be good. The Moonraker 4, Moonraker 6, Shooting Star, Comet, PDL II, are some that I can think of that will work good. It doesn't matter how many elements your beam has, by the way. Sorry to all the people reading, wanting to make their vertical radiate CP. You need two opposed polarization. I can't guarantee results from Jo-Gunn Star series. I am not entirely convinced those antennas produce two polarization's that are 90 degrees opposed to each other (exact opposites). Man, I seem to pick on that antenna! Sorry! However, I was just reading their site, the "V-Series" does NOT radiate a CP signal.

The magic, how it's done. Its quite simple - you just need to feed both polarization simultaneously - but most importantly - one polarization must be fed 90 degrees out-of-phase with the other one. What does this mean, you might be thinking, This is similar to co-phasing, in that you have to make up a special coax harness to get everything to work correctly. In the case of co-phased beams, you use equal lengths from the "T" connector so each antenna is fed in-phase. In the case of CP, you want to make one leg longer than the other, so there is a timing delay in which one polarization receives the energy first. Some operators already have switch boxes that can switch to using both horizontal and vertical polarization at the same time. This does not produce CP, as CP requires very precise lengths of 50,75 and 95 Ohm coax. Whether your SWR meter indicates it or not, SWR will double when paralleling horizontal and vertical polarization when using 50 Ohm coax. To achieve the proper 90 degree phase difference, you must make one leg of the harness 1/4 Wavelength longer than the other.
8/Mar/2010, 8:39 pm Link to this post Send Email to VC7   Send PM to VC7
 
madmark1 Profile
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Re: Avanti Moonraker 4


regarding circular [sign in to see URL]

do you use RHC or LHC ?

mark 163fb20 / 163op20

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9/Mar/2010, 7:57 pm Link to this post Send Email to madmark1   Send PM to madmark1 Blog
 
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Freebander
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Re: Avanti Moonraker 4


Hi Mark I am not sure what your abbreviations stand for?
VC7 Jon
10/Mar/2010, 4:26 pm Link to this post Send Email to VC7   Send PM to VC7
 
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Re: Avanti Moonraker 4


hi,

right hand circular or left hand circular, there is a lot of signal lost if you dont both use the same, its simulair to one staion using horizontal and the other using vertical.

mark 163fb20 / 163op20

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10/Mar/2010, 9:53 pm Link to this post Send Email to madmark1   Send PM to madmark1 Blog
 
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Re: Avanti Moonraker 4


HMMMM an interesting thought.
The topic in question that I was reading and took the extract from didnt go into that

Do you have any literature on that subject you could post?

VC7 Jon

Last edited by VC7, 11/Mar/2010, 8:41 am
10/Mar/2010, 9:56 pm Link to this post Send Email to VC7   Send PM to VC7
 
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Re: Avanti Moonraker 4


He's right - the direction of rotation has to be the same or high losses are incurred.

Maybe best to just have a crossed dipole?

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Andy - 26 FB107
10/Mar/2010, 10:59 pm Link to this post Send Email to Hot Fusion   Send PM to Hot Fusion
 
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Re: Avanti Moonraker 4


circular polarization is a great idea, but it's a bit of a non starter. For talking skip yeah it's ok, but for local comms there is a signal loss to everyone you talk to, either vertical or horizontal. To be able to do it you first need an antenna that is capable of it, either a crossed yagi or a quad, which not everybody has, and the people that do have those antennas are just quite happy to switch between vertical or horizontal, whichever is better, depending on who they are talking to.

If everyone was doing it, then everyone would want to be doing it, if that makes sense, but as noone is doing it, there are very few benefits to be had.

Last edited by simon26OD004, 11/Mar/2010, 12:35 am
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Re: Avanti Moonraker 4


But, if a couple of people were planning on a long distance ground-wave contact, it's possible that circular polarisation would allow for a lower noise floor and therefore better receive conditions, but only if both used the same direction.

I wonder if this is done commercially for fixed radio links?

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Andy - 26 FB107
11/Mar/2010, 8:54 pm Link to this post Send Email to Hot Fusion   Send PM to Hot Fusion
 
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Re: Avanti Moonraker 4


Funny you should say that Andy...


[url][sign in to see URL]
11/Mar/2010, 11:02 pm Link to this post Send Email to VC7   Send PM to VC7
 


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