[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

RE: Full Duplex Mode in Station Program



Graham,

The FDT (Full-Doppler-Tracking) part of Station is currently  a
"technology demonstration". It works in its way, but its not yet really
sorted out user interface wise. This is simply because I need a lot more
time on a high alt bird to develop it, I coded the FDT option a few
weeks before AO-13 went off the air, and since then AO-10 has not been
good from my QTH. I tried using FDT on the LEO birds, but the passes are
too short for development work.

Having said all that let me tell you my future plans and then how
everything works now.

I'm currently writing Station 2, this is the 32 bit version, and is a
150% rewrite. Station 2 includes the SGP4/SDP4 models (as well as PLAN13
that Station 1 uses). These models will give a much better start point
for full Doppler correction.

I agree 100% that fixing at the transponder is the way forward, indeed
it may be the only way to work with 3D given the 24GHz and 10GHz
downlinks on at the same time as say 2m.

Station 1 was designed to control Icom radios, the Icom radios do not
suffer from the same CAT problems as the FT-736R. Station will read the
frequency from the radio dial, calculate Doppler, then set the
corresponding frequency pair on the radio. Essentially you use the radio
the same as HF, turn the dial, find someone to talk to, then talk
letting the program do the rest. Station gives you the option of fixing
the ground RX freq. or the ground TX freq. As currently implemented the
FDT box is a lock. First you find someone to talk to, get calibrated,
then hit the FDT lock. The moment you hit the lock, the program goes
into FDT mode and fixes the transponder freqs, then varies both up and
down ground freqs for Doppler.

As I said before this is a technology demo, it was intended as proof of
concept. In the Station 2 production version a way must be found to
allow the tuning across the passband in FDT mode, that needs some more
thinking about, but will be done.

Now all the above is with the Icom (and Kenwood) radios, with the
FT-736R and FT-847 (which is just as bad CAT wise as the FT-736R) I
provide two tuning sliders, one for the passband, and the other for fine
tune adjustment. These simply replace the calls to the radio dial. You
use Fix RX or TX to find the freq. you want, then press FDT to lock. Its
not as nice as the Icom solution, but its better than nothing.

So to use Station with an FT-736R, here is the step by step guide.

1). Make sure that the FDT box is not checked to begin with.

2). Choose either Fix RX or Fix TX, I tend to use Fix RX.

3). Find the slider that controls the passband frequency. The slider is
calibrated to the passband, not the actual band. 

4). Find a clear frequency on the transponder.

5). Clear the "adjustment" value, the auto-Doppler should put you close.

6). Use the adjustment slider and buttons to tune your link, you'll
never get a 100% auto correction in practice. Station will remember this
adjustment for next time.

7). Once calibrated use the passband tuner to find a CQ call.

8). Once you've found the CQ freq., then press FDT to lock the Station
in. You may have to come out of FDT from time to time to re-adjust. This
is the bit that needs improving in Station 2.

I should point out that the Fix RX and Fix TX methods are  fully
debugged (as is the SAREX/MIR mode as well). These have been working
since 1994 and replace the old manual methods of either keeping the RX
or TX fixed and varying the other by hand. Using these methods you will
be better off than the old manual method on day one. FDT is a refinement
of the process. FDT is only any good if the other end of the link is
using FDT as well. If you are talking to someone without computer
control then use the Fix RX or TX method. I look forward to the day the
everyone is using FDT.

Now the problems that you'll see on the air with auto-correction include
the following:

1). The calibration equations published do not always match those in
real life. The RS-10 Mode A transponder was 4.8kHz off when I was using
the bird.

2). PLAN13 is good but will suffer if you use NORAD keps, which most
people do. I guess that you guys either use SDP4 or smoothed keps from
James.

3). In most cases the op on the other end has no auto Doppler
correction, and so you have to keep re-tuning to help him out. Hopefully
this will change when we get the word out about how easy computer
Doppler correction is in practice. This particularly bad on FO-20/29
where the tendency is to leave the TX set and leave the RX to vary. This
can cause some real big sweeps across the passband.

In the tests I did on AO-13 Mode S, auto correction is very effective on
the high bands on P3 type birds. Mode S operation was great, well until
the alligators found it. The dish that I built to James's design works
brilliantly, and I look forward to lots of use from it on P3D.

I hope that explains where we are currently, ... as soon as P3D is up
then I'm going to get the whole thing sorted out, my intention is to
ditch my 2m KLM 22C as soon as possible (I live in a hurricane area, so
small antennas are good), and move to the higher bands, ... FDT is going
to be the enabling factor in this quest!

Look forward to seeing you at Surrey, I'm down to run the pub quiz, so
see you soon!

I'm copying this message to the AMSAT-bb, as it may start some good
discussion.

Cheers
Paul, VP9MU
AMSAT-BDA

P.S. the latest Station patches can always be found on the web site
below.

http://www.amsat.bm


-----Original Message-----
From: Graham Ratcliff [mailto:gratclif@senet.com.au]
Sent: Monday, June 08, 1998 6:51 AM
To: vp9mu@amsat.org
Cc: jeff@kcbbs.gen.nz; Jeff.Garrett@airnz.co.nz
Subject: Full Duplex Mode in Station Program


Hi Paul,

First, let me congratulate you on your an excellent program called
'Station' and the professional manual that you and Todd, K1TM have
provided
- well done!!!

As you are probably aware Jeff ZL1BIV has been providing me with
registration numbers for AMSAT-Australia newsletter subscribers who have
donated $20 to AMSAT-Australia. Some time ago Jeff also provided me with
a
registration number but until recently I have not been using your
software
because most of my activity of operation of late has been on the 9600
baud
digital satellites for which I use Chris G7UPN's WiSP software in
conjunction with SatTrak4 for automatic antennna and doppler control.

However, I am presenting a paper at the AMSAT-UK Colloquium next month
entitled 'Automatic doppler correction for analogue transponders' which
has
prompted me to take a serious look at your 'Station' software.

The purpose of the paper is to encourage analogue transponders users to
consider using full duplex automatic doppler correction - by that I mean
maintaining a fixed RX/TX transponder point at the satellite. I have
programmed such a mode into both the SatTrak3 and SatTrak4 firmware but
if
I am going to be successful in convincing more users to try this mode
there
needs to be a way to implement it without having to use a 'special' box
preferably using a standard PC which most have in their shacks already
runing some tracking software.

So far I have identified FODTrack by Manfred XQ2FO and your 'Station'
program as possible candidates. So, today I have spent most of the day
'learning' how to drive 'Station'. However, when I try to use your full
duplex (FDT) mode on FO-29's transponder I am having a little difficulty
understanding how you intended it to be used. Therefore, I was wondering
if
you could give me a little bit of guidance in this area?

I am runing version 1.0l Beta 20 and have setup the full duplex mode on
FO-29 as described on page 32 of your manual. I am using the FT736R
radio
and the RS232 link between 'Station' and the FT736R is functioning
perfectly.

What I am trying to achieve using 'Station' is the same as I do using
the
SatTrak4 (ST4). In the case of the ST4 I have calibrated FO-29's
transponders and know that the translation frequency using my FT736R is
581.80192MHz. I am also assuming that the station in the example below
is
also running full duplex automatic doppler tuning on the uplink and
downlink to maintain a fixed point on the transponder.

1. I hear a station calling CQ on 435.8788MHz.

2. I input this RX frequency into the ST4 (because as you know the the
FT736R does allow you to read back the displayed frequency way via the
CAT).

3. The ST4 corrects this frequency for doppler and calculates the
corresponding point on FO-29's transponder i.e. the frequency on which
FO-29 is transmitting.

4. The ST4 then subtracts that frequency from 581.80192MHz to calculate
the
frequency on which FO-29's transponder expects to hear an uplink from
the
ground.

5. The ST4 then doppler corrects that frequency and then updates the TX
frequency on the FT736R such that when you transmits on that frequency
the
downlink comes down on 'exactly' 435.8788 MHz or very close - hi!!! 

6. In practice, by the time I have completed step 2. and the ST4 is in
control the desired RX frequency may have changed slightly so I have the
ability to change the  RX frequency (which is actually the transponder
point frequency) slightly (selectable 10 or 100Hz steps) via an up or
down
button on the ST4's front panel. 

I hope all the above makes sense and that you can explain to me in a
similar fashion how you use 'Station's' FDT mode to achieve the same
goal???

Any help or suggestions on this topic would be most appreciated......

73 Graham VK5AGR



AMSAT Top AMSAT Home