[amsat-bb] Coax jumper lenths -- Math help please.

Tom Schuessler tjschuessler at verizon.net
Sun Mar 20 22:33:35 UTC 2016

Hello all,

I have a question for those of you much more experienced than I.  It relates
to a satellite antenna installation I am working to accomplish this Spring.

I have two cross polarity yagis, one  for 145 and the other for 435.  Each
of these antennas has two separate feeds for the H and V polarities.  The
two meter antenna has two feeds, both at about 14 inches from the end of the
antenna boom.  Jumpers from the connectors will be secured to the very end
of the boom and trail off to main feed line connectors below the AZ rotor.
The mount point of this boom is 5' 2" from the end of the boom with the
driven element.  The 70CM yagi is an end mount but the two connection points
are offset from each other.  One is 17 inches from the back end of the boom
and the other is 24.  Coax jumpers will again be attached to the boom and
will trail off to connections below my AZ rotor.  

I will be using two separate rotors, (A G5400 or G5500 is not in the
paycheck right now), an elevation rotor with a 4'2" boom to mount the two
antennas and an azimuth rotor which will have a probably 2' maximum mast
from there to the EL rotor mount.  All this will mount to an only half
extended push-up-pole, which is ground mounted but attached to the apex of
my single story house.  Total height off the ground will probably be 20 feet
when all is said and done.  I will be running 4 runs of not that flexible
9913 up to just below the AZ rotor and from there want to attach jumpers of
more flexible LMR 400 Flex to make the runs out to the antennas mentioned

My question is for your more math savvy or just plain experienced folks, is
how long should the jumpers be in total for each antenna to allow for a 360
degree rotation and 180 degree elevation shift based on the parameters I
described above???  I was guessing 10 to 11 foot jumpers from antennas to
the barrel connectors just below the AZ rotor but wanted to make sure that
that was long enough, or if they could be shorter, say maybe 9 feet.  Of
course the 70 CM antenna with it's one feed point 7 inches further up the
antenna would need to be that much longer I guess.  I also understand that
the 2 meter swing will be greater because of the more center mount rather
than the end mount on the 70 cm antenna.

Clear as mud???

This is new territory for me so I am wanting to make sure that all the
decisions are right before I need to do things over, and over, and over to
get it right.  I can take some pictures if someone needs to see what I
described.  Email me and I will give you my cell if you would rather talk or
ask questions verbally.

Thank you to the group in advance for your help and thoughts.

Tom Schuessler, N5HYP
n5hyp at arrl.net

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