[amsat-bb] Tuning M2 LEO pack antennas
Mark D. Johns
mjohns+K0JM at luther.edu
Mon Apr 20 19:02:47 UTC 2020
I just went through this with my LEO-Pack that has been up for almost
8 years. I didn't have good test equipment available when I first put
it together. When I started having trouble recently, and tested it
properly, I discovered SWRs on 2m very much as you describe. On advice
from people on this list, I went back to the assembly instructions and
discovered that I had actually not put the antenna together properly
to begin with. The diagram(s) in the instructions are somewhat
confusing, and I would say, even a little misleading. Look at the
PHOTOGRAPH in the instructions very, very, VERY closely and make sure
that the various blocks and phasing lines are placed exactly as shown
in the photo. It's difficult to see, but if you study it closely and
duplicate what's in the photo I think you'll find you have better
results. I did. Now 1.1:1 at 145.9 MHz.
You probably want to be using LMR-400 UltraFlex around the rotators.
Regular LMR-400 is awfully stiff. Bring it along the antenna boom
straight back, then keep going straight back, along the same axis, for
about a foot past the mounting clamp. Then make a nice wide loop back
to cross boom to which the antenna is mounted and fasten the coax
there at a point near the end of the reflector. Don't make a sharp
bend or kink in the coax. Good luck. 73
Mark D. Johns, KØJM
AMSAT Ambassador & News Service Editor
Brooklyn Park, MN USA EN35hd
"Heaven goes by favor; if it went by merit,
you would stay out and your dog would go in."
On Mon, Apr 20, 2020 at 12:15 PM Carl A Estey via AMSAT-BB
<amsat-bb at amsat.org> wrote:
> Recently I bought through AMSAT the LEO pack and assembled and installed it this weekend. The SWR on the 2-meter antenna is 1.4:1 from 144.1 to 146.1 with resistance of 58 ohms and 2.5:1 at 148 MHz. The 70-cm antenna has the best SWR (3.0:1 and resistance of 25 ohms) at 442.6 MHZ. Obviously neither is great.
> How should I tune the antennas? It appears that the only tuning possible is to adjust the shorting straps for distance from the inside edge of the shorting bar to there boom. ShouldI I be able to achieve 1.1:1 on both antennas? How should the coax be routed from the junction block? I have the LMR-400 feedline zip tied along the boom to the cross bar and then around the rotors.
> What suggestions do you have?
> The instructions particularly concerning the location of the 1/4-wave phasing line and the 1/2 wave balun were not very clear. Does anyone have any pictures or illustrations that show placement of the tasing line and balun?
> Carl WA0CQG
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