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Re: Transverters with *70cm* IF's



Hi Dave

Your wrote:

>I suspect that 5.6Ghz will be a long time coming.  I am sure that
someone will
>come up with a very small antenna for that band.  Maybe even a phased
>array type FLAT antenna.  There is a huge need for that type of antenna
for
>those of us that live in areas with antenna zoning restrictions.  
>There are a lot of us that need something that can be mounted flat on
the roof.
>I wonder if anyone is working on that problem?

So far my experience has taught me that  beam width , side and back lobes
are one of the weakest links to staying away from the miseries of local
interference that can make a mess out of satellite reception.        I
currently have a wireless ISP being installed in the farming area in
which I live.     I can't get a local phone number for a telephone ISP
but now it appears I might be jumped on with 2.4 gHz Spread Spectrum
digital signal so that others can have a faster ( 250 KB ) ISP hook up
Only time will tell what all of this means.    Some of the antennas that 
I know about that do not have a narrow beam width also have greater side
and back lobe patterns. Trying to make the beam width too narrow can also
lead to this problem.   
I have had to accept that when all of the options are laid on the table, 
  parameter dealing with the antennas or their hook up is the thing we
have to do the most for.    I normally start with the beam width and
design from there.    Too narrow of a beam width can not be pointed at
the satellite with enough ease.    So I try 15 degrees as a starting
point .    When TVRO came along the industry decided that the lower F/D
would lower the side lobe and back lobe and therefore reduce the
undesired reflected signal pickup problem .     Before that the F/D of a
dish hardly ever was less than .5 .      Some of the TVRO were .39 F/D.  
  Depending on how close to the ground the dish is will help determine
what F/D should be used.      My "S" mode 2 ft dish is 40 ft about the
ground ( tall trees ) so I use a .5 F/D .
The up link 54 inch dish is about 25 ft above the ground ( radiation
safety ) and on a separate tower , rotor assembly.     Which bring us to
another problem,   Having more than one pointing assembly to control
while operating a satellite.     In my case the 54 inch is going to be up
link.     So I don't want it radiating through the down link antennas.   
  My down link antennas are higher and they are on a motorized tower so I
have some lee way since direct over heard passes are less frequent.    
As we get to transmitting 5.6 gHz,  the beam width will probably lend a
hand toward helping low power amplifiers that may be the only thing
availably.

The nice thing about all of this is ,  as smaller antennas and more
powerful amplifiers become available we can reduce the antenna farm .   
Until then the antenna will be the weak link more than likely IMHO.

I hope some of this will help in your considerations at your QTH.

73's  Joe  Murray   K0VTY

  

 
.     

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