[aprssig] PCSAT2 Downlink Challenge

Stephen H. Smith wa8lmf2 at aol.com
Fri Jul 29 15:29:50 CDT 2005

aprssig at ei7ig.org wrote:

> On 28 Jul 2005, at 16:56, Robert Bruninga wrote:
>> When PCSAT2 is enabled on Monday or Wednesday,
>> (1,3 Aug) we'd like to capture as much of the
>> 1200 baud and 9600 baud telemetry on 437.975
>> MHz as possible.  See the plan on:
>> http://www.ew.usna.edu/~bruninga/pec/pc2ops.html
> Evening,
> I've a dumb question.  A couple of them actually.  EI8JA and I were  
> thinking of trying to help out, but we have no experience of  
> satellite operation (other than an odd digi through pcsat or ISS).
> He has a shiny new TS-2000 connected to a Diamond X510N
> http://www.wsplc.com/acatalog/Diamond_VHF_UHF_Antennas.html mounted  
> fairly high up at his home QTH.
> I've got a Yaesu FT-847 and a soundmodem interface (I've not tested  
> it yet at 9k6... I will after I send this email) connected to a X-300  
> (same url as above).  I'm at one of the highest points around where I  
> am and can see to the horizon from the southwest to just shy of due  
> east.
> I've got the TM-D700 in the car and a TH-D7 as well.
> We have a Yaesu 736 connected to a X-300 and a 9K6 TNC in the college  
> (Near EI8JA's QTH), but I've not got the levels right yet, its not  
> receiving packets correctly.
> Would anyone have any suggestions as to how we could make best use of  
> this kit, with the highest likelihood for generating useful results?
> Yours in experimentation,
> de John
1)   You need to replace the antennas!    These tall, super-gain 
collinears concentrate transmitted and received signals toward the 
horizon, and will pick up almost nothing when the satellite is more than 
about 10-15 degrees above the horizon (which is most of the time during 
a pass!).   The higher the claimed gain of a vertical, the worse it will 
be for satellite operations.   

For satellite ops, you need high radiation angles with fat lobes looking 
upward (the exact opposite of what you want for terrestrial DX). If you 
don't go for a steerable beam with dual rotators (azimuth and 
elevation),    a simple 1/4-wave vertical over a ground plane (i.e. a 
19-inch mobile whip on a car's roof or equivalent metallic surface such 
as an aluminum window screen or piece of sheet metal) , or a turnstile 
(crossed horizontal 1/2-wave dipoles mounted over a metallic surface ) 
will receive from "up above" far better.  

2)   For work at 9600, you must tap the receive signal off the radio's 
discriminator output (not the speaker output or equivalent).    The 
6-pin MIni-DIN "data" or "packet" connector (if it exists on this 
particular Yaesu)  provides the direct discriminator connection 
required.   Details of the pinout of this type of jack, now standardized 
on many radios is on my web site at:
On this page of assorted files and documents, look for and download the 
Acrobat PDF  file     " MiniDIN6-Packet.pdf ".  

Typically the signal level for the direct discriminator output is much 
lower than the de-emphasized audio or speaker output (usually 30-60 mV 
compared to 100-500mV or more at the RX audio outs.   You may have to 
change jumpers or straps inside the TNC to increase it's input 
sensitivity to make it work with the 9K6 discriminator output.

3)   The TS2000 appears, from studying the manual (I'm about to buy one 
myself), NOT to have the easy access to the FM discriminator for 9600 
baud operation of an external TNC. The audio outputs for the primary and 
secondary receivers provided on the 13-pin full-sized DIN "ACC2" only 
provide de-emphasized speaker-type audio suitable for PSK31, SSTV, 1200 
baud packet operation, etc but not suitable for 9K6.  The internal TNC 
of the '2000 is the same TNC-on-a-chip as in the D700 and TH-D7, but 
without the APRS-specific firmware for standalone operation.   The 
internal TNC is capable of 9K6 operation and should be useable if placed 
into KISS mode operation and used with an external application such as 

4)   For monitor-only operation and easy capture/logging,  an 
alternative would be to use the AGW Packet Engine communicating with the 
TNC in KISS mode, along with it's companion freeware applicaton AGW 
Monitor .   AGW monitor displays and optionally logs, with time stamps 
from the PC system clock,  the incoming packets from the TNC.   AGW 
Monitor is a very hassle-free essentially  zero -configuration program; 
just install and run it after installing the Packet Engine.  Monitor can 
run while other apps are connected to AGW; i.e. AGW PE can be sharing 1 
or more TNCs with UIview, while AGW monitor also captures, time stamps 
and logs data from each TNC individually or together.   [ The advantage 
of AGW Monitor is that it captures and displays everything that comes 
out of the TNC(s) before applications filter, interpret and possibily 
reject certain packets.  The view is similar to the "TERMINAL" window in 
UIview, but with a separate tabbed window for each TNC or virtual TNC 
passing through AGW PE. ]

By themselves, AGW PE and AGW Monitor paired are a very undemanding set 
of programs that will work well even on low-powered PCs. (I am assuming 
the use of AGW as a distributer of data from an external hardware TNC, 
not as a soundcard "soft TNC".) .

If you have a PC with sufficient "horsepower" (approximately Pentium II 
300 or higher) and a soundcard with a stereo line input, the AGW PE  
softmodem can be configured to act as TWO TNCs, one on the left channel 
and one on the right channel, emulating something like a Kantronics 9612 
dual-port..   You could set one to 1200 baud connected to one radio via 
the speaker output, and one to 9K6 connected to the other radio via the 
discriminator output.   Note that you MUST have a line-level input to 
get the stereo input; the mic input (often the ONLY input on laptops) is 
single-channel (MONO) and can't use this feature of AGW PE.  

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com

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