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Thursday, October 11, 2018

SDR: Let's Walk To The Space Station?

I had high aspirations on Wednesday to do a base-band SDR recording of a scheduled International Space Station (ISS) contact with a school in Ashford,  Connecticut. 


Burger Hill at Drayton Grant Park Rhinebeck, NY 12572

The weather was nice, so I decided to trudge up the measly 550 feet of Burger Hill for amazing views and to maybe cross paths with a passersby or two interested in what I was up to with my collection of equipment. 
What is a base-band recording?  Think of it like recording a television show with a DVR or VCR.  The only difference is a base-band recording lets you record a wide block of spectrum say from 162 to 163 MHz and be able to point and click on any activity received for later playback. This would be like recording multiple movies, news and sitcoms on different channels all at the same time.

Bummer: Well, no activity from the ISS on 145.800 MHz at 14:39 PM ET (1839 UTC). 

As it turns out, the ISS contact was cancelled at the last minute due to an experiment in the Columbus module that would have prevented the use of the functional radio in that part of the space station. 
The radio to be used was actually considered the spare radio as the main radio after years of service no longer is functional.  A replacement is supposed to be sent up before the end of 2018.
I only found out about this change of schedule on a Facebook Group that I joined once I got home which is more up to date than all my usual sources such as the official ARISS Project website, AMSAT mailing lists and various NASA pages.

Serena Auñón-Chancellor, KG5TMT preparing the
NanoRacks Cubesat Deployer-14

This just goes to show that social media is still the best spot for breaking news!

Looking on the bright side...

All was not lost though. Not many minutes later at 15:02 ET was a pass of the elderly SO-50 satellite and I quickly made a contact with Tom, K8TL in grid EM89, 500+ miles away from me in FN31 thanks to this "repeater in the sky".
All that was needed was 1 watt of transmit power & a directional antenna! 
However, the down-link for the SO-50 satellite is centered on 436.795 MHz and there was someone using digital voice on that frequency which made it hard to make more contacts as SO-50 reached its apex and started to move out of range.

I did not have a DMR capable radio with me, but I am pretty sure that is what mode it was and it was local versus coming from the satellite. 
Listen:  Do you hear a "digital sound" on 436.795 MHz?
Trespasser!!

No hot spot or repeater stations appeared listed on Brandmeister on that frequency in the satellite band, so it could be some joker or ill informed amateur about the suggested ARRL and ITU band plan just intentionally interfering. Rhinebeck is pretty much far away from any "majorly" strong out of band signals that could have interfered, so it had to be an amateur radio operator.

I knew the signal was also local because if it was somehow coming in from SO-50 by someone transmitting DMR on the VHF up-link of 145.850 MHz, it would have come from the direction of the satellite and not from another direction to my south west at a "terrestrial" elevation.

This sort of interference makes me sad because 436.795 MHz is well known for over 16 years that this is where SO-50 transmits back to earth on.
There are plenty of other frequencies that can be used for digital voice that would not interfere with those interested in satellite communications.
Lets change the subject back to base-band

While I was at the great location of Burger Hill, I decided to do a 30 second base band recording of the weather band from 162-163 though should anyone wish to test it out since every NWS channel is in use from that location.

A "Normal" Recording:

A center frequency of 162.475999 MHz with a bandwidth of 15 kHz can easily be recorded and played back using pretty much any audio player, but only just that one frequency can be heard. The file size is 1.9 MB. Play: Standard AF Recording (1.9 MB)

Play: Standard AF Recording (1.9 MB)

A "Base-band" Recording: 


Compared to the "Standard AF Recording", the base-band recording for the same 30 seconds is 60.9 MB or 3105% larger. However, you can listen to any signal of any bandwidth in any mode across the entire 162 to 163 MHz captured for 30 seconds.

SDR# will help you visualize the entire 1 MHz wide
recording without needing a radio

In order to play the base-band file, you can not use a regular audio application or otherwise the sound might sound like an Imperial Probe Droid from Star Wars.
Play/Download:  IQ Base Band File (60.9 MB)

If you are a Star Wars fan, you know the
audio I reference from Echo Base on the ice planet Hoth

Ham Solo: Return of the SDR#

Download and install the popular SDR# program and select the "IQ File" option as shown. 
Then navigate to where the "IQ Base-band File" was saved and press play in SDR#


From the Burger Hill location and its good line of site, multiple weather stations were received as well as a few other signals not related to the weather.

nws noaa 162.475
Hudson Valley National Weather Service (NWS) stations
broadcasting 24/7 on the 162 MHz spectrum

Hopefully this article gave you a taste of a few interesting things you can do with amateur radio or use equipment for a dual purpose unrelated just to ham radio.

Next time there is a planned live ISS contact receivable from the Hudson Valley, we will definitely try to get that recording, just as long as the astronauts do not get busy at the last minute! 



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