[aprssig] Sgate question

Stephen H. Smith wa8lmf2 at aol.com
Sat Nov 11 14:54:16 CST 2017


On 11/11/2017 1:28 PM, Ron VE8RT wrote:
> Hi Stephen,
>
>      up until this summer I though the same about HF propagation.
> Having been asked to monitor the WSPR (1/2 W) station on board the
> CG3EXP Polar Princess expedition through the northwest passage I've
> changed my mind.  On 40M some nights, running my own 5W WSPR station I
> was being heard in VK ZL and other countries in the south pacific.
> Most days, even through some of the roughest solar conditions my
> station was tracking the Polar Princess in the high arctic.  Rather
> than being concerned whether southern stations could hear an HF Igate,
> I though it might provide a service to stations inside of the auroral
> oval.
>
>     There has been ever increasing research and recreacreational boat
> and ship traffic through the northwest passage.  I was wondering if a
> Sgate may be of use to those plying the airctic ocean who might not
> otherwise be able to use a satellie digital repeater because the
> satellite itself is out of sight of a ground Sgate.  Perhaps that
> doesn't happen, maybe with a low enough inclination on their orbit they
> never track far enough over the poles to be out of sight of Sgates.
>
>     Those were my thoughts.
>
>       Ron VE8RT
>

HF---

The only band with significant HF APRS activity is 30 meters.   40 would be 
substantially different, since it is open more of the time, and supports 
significant NVIS activity (There is next to no NVIS behavior on 30 meters.  
When mobile, I simply DON'T HEAR my home station at all, until I am around 300 
miles away due to the skip distance on 30M.)   However, you would be 
on-your-own on 40 meters, without the diversity receive capability that has 
existed on 30 meters for decades due to the two dozen or so igates around North 
America (including mine) running 24/7.

Satellite--

The most severe problem that far north will not be lack of igates, but rather 
lack of accessible satellites.   Except for the handful of polar-orbit 
satellites, most satellites are inclined orbits that don't take them anywhere 
near far enough north or south to be useful in the Arctic/Antarctic regions.

For example, consider the ISS digipeater. (By far the easiest to hear and use, 
due to it's relatively high transmit power and low orbital height.) The ISS 
orbit inclination is such that it's sub-satellite point is never more than a 
few miles north of the US-Canada border.  The farthest north it can ever be 
directly overhead (i.e. longest time) is Vancouver BC or Calgary, AB.   At your 
location, the highest it will ever be above the southern horizon is about 15 
degrees.

The image below, captured from my iPad Mini from an app called HamSatHD shows 
this.   I set the ground station location ("Home") to the 62 degs N / 114 degs 
W coords you gave me.  Then I wound the data/time back and forth to yield a 
pass nearly due south of you (i.e. nearest possible).  Note the two range 
circles (ISS footprint and the Home station's horizon at the station's 
elevation)  are distorted into asymmetric ellipses that far north due to the 
Mercator-projection word map used.   (Near the equator, you get nearly perfect 
circles...)

The most important take-away is the polar sky-view map in the upper-right 
corner that shows the satellite track in the sky as seen from your location. 
Note how short and close to the horizon it is.       At least you wouldn't need 
any exotic satellite-type antenna that elevates above the horizon.   Any common 
high-gain base station collinear that squishes the radiation pattern at the 
horizon is all you would need.    This kind of pass might be OK for 
"Hello-CALLsign-Signal Report-Goodbye" contest-type exchange, but it won't be 
long enough to exchange any useful amount of information.



-------------------------------------------------------------------------------
Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

Live Off-The-Air APRS Activity Maps
    <http://wa8lmf.net/map>

Long-Range APRS on 30 Meters HF
    <http://wa8lmf.net/aprs/HF_APRS_Notes.htm>



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