[amsat-bb] SatGate Antenna

Scott scott23192 at gmail.com
Wed Jul 19 05:46:45 UTC 2017

Hi Andrew!

I could have written your email... I think I match everything you listed
including the ranch style house.

I have also been searching for an antenna upgrade in hopes of improving my
145.825 iGate situation.  Since the ISS returned to 2-meters, my iGate went
from a good contributor to absolute zero.

It worked great and covered a lot of territory when the ISS digipeater was
on 70cm, but now it's rare that I receive a packet from the ISS on VHF.
Works fine if I switch to 144.39 APRS, but it's ineffective with the ISS.

So, one obvious thing to optimize is the antenna.  While I believe it's
better for horizontal distance (than in the upwards direction), I recently
spotted a 5/8 wave 2m/70cm mag mount antenna sitting around the house that
was not being used.  So, I mounted that on an old DirecTV bracket at the
edge of the roof.  However, since that antenna works best on a flat ground
plane, it didn't do all that well with my 144.39 APRS benchmark.  Feel free
to laugh but I put a pizza pan under it and left the Pi monitoring the
local APRS digipeater on 144.39 this evening and the packets rolled in
nicely.   So, I'm going to leave that on 145.825 for several days to see if
I have any luck.

FYI, previously I had tried an Arrow dual-band J-pole and my 137 MHz QFH.
Both were ok for 144.39 APRS but heard nothing from the ISS.  Should anyone
wonder, I'm not judging that by what appears on ariss.net; I could always
be sending duplicates.  But rather, I'm basing my evaluation on the
direwolf logs on the Pi that show all received packets.

Finally, I can't dedicate my 2m X-Quad on an AZ-only rotator to the iGate,
but when I have used it on selected ISS passes, I can often pick up some
packets with the huge increase in antenna gain.  No LNA on the 2m beam
(SP-70 is on the 70cm X-Quad), but even without a 2m pre-amp, it does a
pretty good job for ISS packet, 2m uplink to sats, and 2m downlink from
various cubesats.

So, I don't have any grand recommendation for you but just wanted to share
my progress since it sounds like we're in the same boat.

-Scott,  K4KDR

On Tue, Jul 18, 2017 at 4:50 PM, Andrew Northam <andrewbnortham at gmail.com>

> I would like to setup an SatGate, I have been running an iGate for a little
> while, and already have the Pi, TNC, Radio, LMR400...I have read the page (
> http://aprs.org/aprs-satellite-igate-antennas.html) about antennas, and
> they all recommend a large ground plane, however I have a ranch style
> house, and would like to put the antenna on the peak of my roof on a small
> mast.
> What kind of antenna would be best for on the peak of a roof? Would a 3/4
> wave monopole work? Or should I look for something with radiators?
> I have a great view to the North, East and South, but trees to the west
> from Michigan (EN72ef)
> Thanks for your help!
> Andrew/KE8FZT

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