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Re: Why do so many people... -- minimal station?



On Wed, 01 August 2001, Bob Bruninga wrote:

> On Mon, 30 Jul 2001, Alex wrote:
> 
> > I do some APRS-QRP experiments and some antenna experiments every once
> > in a while. Oftentimes I don't hear my own packets digipeated and they
> > also don't get relayed to ariss.net every time....
> 
> This shows why we need more dedicated permanent IGates feeding into the
> system.  RIght now, I only know of 2 or 3 in the usa.  We need them in all
> corners of the USA too.  Just 2 or 3 feeds across the whole country will
> not guarantee 100% capture.  Steve's system can easily tolerate multiple
> feeds and it throws away all dupes, so it does not hurt to have multiple
> feeds.  It improves the reliabiilty tremendously!

[clip]
 
> THus I wont be happy until we have at least 10 Igates in the USA stretched
> from Florida to Maine and San-Diego to ALaska..
> 
> And all it takes is a whip antenna, and a 2m FM packet rig and PC...

Well, Bob, you started my mind turning again and that is never a good thing.  I was trying to come up with a concept of a minimal station for doing capture of space to ground traffic.  A used 2M rig should cost next to nothing though any HAM swap meet.  An old (486 w/ 8MB) PC should be available from yard sales for next to nothing if it's not already gathering dust in the attic.  

The worst part seems to be the TNC itself.  Under Linux, the "soundmodem" driver can replace that.  For Windows, I've been looking for something equivalent and have heard about a "packet engine" that will use a sound card.  My only concern here is if a really old PC (66Mhz or worse) could keep up with the 1200 baud AFSK encoding.

Since this is a receive only station (with transmit back through a network) the cabling from the radio to the computer is nothing more than a mono audio cable.  No need for push to talk or any other fun wiring, just run the radio speaker out to the computer mic input.  The computer will only have to decode and not worry about encoding.

One assumption that has to be made here is that the receiving station has a 24x7 Internet connection (cable modem, DSL, campus network, etc).  A second computer can piggy back off this connection over Ethernet.  The computer being used will require a NIC card.  That in itself is easy.  It's the drivers part that can be difficult here.  Where do we get the network card driver and TCP/IP stack?  Linux has them built in.  Windows has a pretty good selection.  Unfortunately, however, for a small station like this DOS might be good.  Not all NIC cards even have DOS capable drivers anymore.  I haven't seen a DOS based TCP/IP stack in some years.  Have any wound up in the public domain?  Wait, brain flash, wasn't this what KA9Q did?

Even a 24x7 connection might not be required.  A batch and forward method could work here.  Try to send real time, but if the connection is down then just back off and retry slower and slower out to a 30 minute or so delay time.  Next time someone dials up the Internet, the data will find it's way out.

If the DOS/NIC/IP problem can be solved then it should just be a matter of running stock IGate software (a DOS version?) configured for one way data passage.  If this software can be made to fit in the DOS footprint then all is good.  If it won't, then Linux or Windows may become a must.  Here I'd rather see Linux to once again save on cost.

If a full station like this can be built for under $300, it might be possible to convince some schools to put them up as projects.  Since the stations won't be transmitting I'm left wondering if the hosting location will even need a HAM license.  Once the rig is setup, it should be a matter of walk away and forget it.

Down the road, I could see some 2nd generation projects like this.  Make the machine a little more elaborate and make it respond to the data coming down from space.  Show the packets arriving along with a tracking map on the screen to make it a class project that will draw interest.  If the screen starts flashing 10 minutes before a pass is due to start, you can bet someone will walk over to see what shows up on the screen.

Last note, for people like the QRP/Antenna experimenter, I still wonder if having some range information with the packets wouldn't be good.  Two nights ago I managed to bounce the station on a 17-degree pass.  My favorite passes are the low ones to the SE (out over the Atlantic Ocean) being that a lot of people can't hit it there and the traffic drops off.  It would be really interesting to me to see where the ground stations are that picked up a return.  Just a personal desire, but not something that really seems to be a driver for people here.

Anyway, I've blathered long enough.  Flame away! :)

--KG4NMC (KG4NMC@arrl.net, http://delbert.matlock.com/kg4nmc.htm)
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