During the several years waiting for P3-D, I collected some parts for my personal Mode-S receiving system after having worked AO-13 via Mode-S from '92 on with the 1.6m (5') dish of my dad (Dieter, DL3NQ). The prospects for P3-D promised smaller antennas due to higher ERP on the satellite, which was not very hard comparing to the 1W TX on AO-13. After P3-D (now AO-40) was launched, I also started with this existing 1.6m dish listening to the beacon and even with the knowledge about the better ERP, I was surprised about the strong signals coming from the bird (even stronger with the S1 TX, when operational). Very soon the idea of assembling a pure Mode-S RX system (the dish was equipped with a multiband feed for the microwaves) was born and I started construction on the Mode-S receive system of the Weinheim hamradio clubstation DL0WH.
closeup of the 13cm Helix with UEK-3000
(TNX Wolf,DF1GW for photo!)
maintenance work on the tower by DH2VA
(TNX Wolf,DF1GW for photo!)
I gained some experience with this setup which was chosen for sensitivity, robustness and commercial availability. Commercial availability because of the lack of time of building it all (sigh..) and robustness because of the location: a clubstation is a very hostile enviroment for delicate electronics because the number of users is typically much greater than at home. Also the expected windload on the tower prevented me from choosing a dish as antenna, therefore a helix was chosen. Soon it became clear that although everything else was fine and sensitive a dish would provide better performance than this helix. For this next system I chose some other important points:
Therefore, I chose the following components:
ADDITIONAL INFORMATION: The dish sold by UKW-Berichte is not listed on their homepage (only in german, sorry)! You have to contact them directly.. but the still have them (01/17//2002).
For mechanical mounting of the dish, I used a design of DJ2ANG and DH0SP,
which was tuned for my dish by DF7IT. A aluminum sheet of 330mm x 330mm
(approx. 1'x1') is bent in such a way that it holds the dish with its 4
corners and a central fixture (download construction
drawing). The converter plus receiver is then mounted on a aluminum
platform fixed perpendicular to this dish mounting. This platform also
has a 1/4"-thread for putting the whole system a camera tripod. The accuracy
of the tripod is not so important as it might seem as the 3dB beamwidth
of the dish is around 13 degrees.
|60 cm dish (front view)||RX system on camera tripod||size comparison to operator|
|detail view of feed + preamplifier||converter (left side)||mechanical dish support, see also construction drawing|
As the current drawn by the converter and the preamplifier is only around
200 mA, I took a rather small lead acid battery for power supply (black
housing on top of the FT-290R). The FT-290R has its own battery pack inside
its case. On Jan 12th, 2002 I took everything outdoors for a first quick
test. This proved to be more than that, as the whole system worked better
than expected. A coarse set-up of the direction was sufficient to acquire
the satellites signal, a fine tune resulted in a couple more dBs but didn't
improve the signal significantly.
|FT-290R with converter + battery||top view||converter (right side)|
The following stations could easily be copied (range 20000 km, squint 22 degrees):
On the following pass (Jan 13th, 2002 0650UT) I also managed to copy VK6BMT from Perth, Australia..
Therefore I chose to buy some crucial components: the patch feed and the preamplifier. The patch feed from G3RUH and ON6UG has an incredible performance, even without a dish (I witnessed a beacon reception at apogee with ONLY this patch, a RHCP version!). Together with a sensitive preamplifier (at my opinion at least NF<1dB) and a 60cm dish at minimum (which is still available very cheap here in Germany), this is the base for good AO-40 reception. Things like converter and receiver are not so critical, as system sensitivity is defined by the noise figure of the first stage as long as the gain in the following stages is high enough.
I hope this article can help to overcome the fears of many hams against Mode-S operations. Talks to fellow hams showed that a basic interest is there, but the information how-to-do is sometimes just not available. The more information we spread the more hams we can work on the bird..
Top view of the 'cappucino patch'. The location of the cut corners have been changed for a RHCP patch. The original design from Tim, K3TZ, describes a LHCP patch for dish feed use.
Side view of the 'cappucino patch'. Notice the missing 3mm spacers? I didn't had any time, the current AO-40 pass was near..
Scared of any corrosion due to rain? Try this nice acrylic dome..
A short test on March 1st, 0700UT showed only minor differences to the G3RUH patch. While noise floor is around S1 and MB signal with G3RUH patch is around S9+3 needle widths (I know, this sounds funny, but I don't have any better explanation..) the K3TZ patch delivers a signal of S9+2 needle widths of the S-meter. From ear, I would suggest that this level difference is around 1dB, as 3dB is easy to distinguish and I could hardly tell the difference. Also QSB was negligible and comparable to the G3RUH patch during 2 minutes of observation.
Further improvement should be made by adding a 1/2-1" collar to the reflector (this has been discussed in the AMSAT-BB), this is the next item on my list.
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