[aprssig] REF:Packet on the ISS & PK900

Steve Dimse steve at dimse.com
Sat Feb 29 12:38:11 EST 2020

I never would have thought to look on homedepot for an antenna, but there it is. By size it appears to be a knockoff of the X30, though for only $21 more I would have gone for the real thing. Assuming it is internally the same as the X30 and of the same quality, it has 3 db gain on 2 meters.

The problem is there is no free ride for antenna gain. Gain antennas work by concentrating signals into a desired direction, meaning they are reduced in other directions. In the case of the steerable beam antenna this is a feature because it lessens interference in other directions. 

In the case of an omni vertical, the signal is concentrated to the horizon from the sky. This is what you want for working terrestrial repeaters and mobiles, but is not ideal for satellite work. Ironically the bigger the vertical antenna the worse it is for working satellites.

There are plots of the X30 gain on the Diamond web site, google "X30 gain pattern". You will see by the time the ISS is over about 30 degrees the gain has gone negative. Most of the time satellites are below 30 degrees, but the slant range is greater. Also, a unique problem with ARISS is the antenna is not in the clear, so the best chance of working it is when it is much higher in the sky so that other parts of the ISS are not obstructing the signal and it is closer to you. Those times when the ISS is in the best position your antenna has gain down 26 db! So this antenna, and all gain omindirectional antennas, are not the best for satellite work.

You should look at the info available through AMSAT on antenna design for 2 meters. Although ARISS packet has been offline for 14 days, it was active regularly before that, so if you have been trying for six months the problem is in your station. Are you using high quality low loss coax? Is your TNC configured correctly? I can hit ISS on every 30+ degree pass I attempt even from my truck, it is not hard to do.

Steve K4HG

> On Feb 29, 2020, at 11:20 AM, wa4tkg at netzero.net wrote:
> Thanks for that Info:
> I recently installed a dedicated Vertical for SAT use:  
> It is readily available to order on HomeDepot . Com, and it's a GREAT deal.
> A Tram; 1481  Dual Band 144/440 Vertical. (about $75!; a copy of Diamond)
> Despite this fact, I have yet to get INTO anything that passes
> USNAP1-1*>ARISS>APOFF <UI>:T#067,724,000,000,000,670,01000100
> (for one)
> I have copied most anything in the past six months, but as you found, the ISS Station is basically DEAD....well, that explains why I haven't copied THAT one.
> I have an AEA PK-900 set up with local APRS on Port 2, and SAT Frequency; 145.825MHz set up on Port1.
> NOTHING Gates to the local Network; 144.390. Can't figure out why.
> Matt; WA4TKG / 7J6CAT
> From: MJ Inabnit <ke6sls at arrl.net>
> To: aprssig at lists.tapr.org
> Subject: [aprssig] Packet on the ISS
> Date: Thu, 27 Feb 2020 11:03:28 -0800
> I've become really interested in working the ISS on packet.  A fellow
> ham was able to get his ping returned about 2 months ago which gave me
> hope!
> The last few weeks, I've planned my days around ISS passes and haven't
> heard a peep.  Yesterday I found this:
> <https://www.ariss.org/current-status-of-iss-stations.html>
> Current Status of ISS Stations
> as of 02/20/2020
> ​Columbus Module radios:
>    Ericsson VHF-  Packet system stopped working (2/15).
>    Ericsson UHF- Stowed.
>    MarconISSta - Temp. stowed.
> Looks like my odds of working the ISS are NIL at this point, but does
> anyone have an idea how long the ISS will be down?  I've dug around here
> but I really have not found any real "radio space news"..  Hopefully
> someone here might know a little more.
> Until then, my pings will remain "GROUNDED" :)
> 73
> j
> -- 
> wishing you well
> Jaye, ke6sls--
> _
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