Satellite system

News: I will be rebuilding my satellite system to improve the 70cm antennas for EME, more info here


While I'm designing (and building) the new 7 meter dish for EME, I needed something "quick" to get on the air. I have been using satellites many years ago (Oscar 10/13 etc), and today there are plenty of amateur satellites available!

I designed the antenna system in Autodesk Inventor. Antennas are from www.antennas-amplifiers.com. I choose the "Big LEO" set:

https://antennas-amplifiers.com/product/leo-pack/big-leo-pack-2meter-70cm-antennas-cross-rhcp-satellites-leo/

This will give me plenty of gain on 2 m and 70 cm for satellite work. The antennas are highly recommended, the build quality is outstanding, these are built to last!


Preamps for VHF and UHF from SSB-Electronic:

2 m:

https://www.ssb.de/de/verstaerker/vorverstaerker/sendeumschaltung/100w/sp-200-mastvorverst-m-umsch-145-mhz

70 cm:

https://www.ssb.de/de/verstaerker/vorverstaerker/sendeumschaltung/100w/sp-70-mastvorverst-m-umsch-435-mhz


The Az/El mount is a "slewing drive" for solar panels from Coresun in China (I selected to have faster motors than the standard offered):

http://www.coresundrive.com/en/product/Solar_Tracking/2019/0729/93.html


The rotorcontroller will be my own design: URC Rotorcontroller.


The horizontal boom that holds the antennas is a 40 mm diameter, 2 meter long solid fiberglass rod from R&G in Germany: https://www.r-g.de/en/art/610001

You need to use a non-conductive boom as the antannas are in a "+" configuration. The fiberglass rod is painted with a 2 component primer and 2 component paint to shield it from UV radiation from the sun.


More info below (as parts come in from production).


Design files (PDF) for the tower and parts for the mount: ZIP file




Update: The system is up and running.

I designed the tower so that it folds over (approx 50 cm above ground). This makes it easier to work on the system when/if something needs fixing.


The lower half of the tower is buried 100 cm into the ground, hole will only be 25 cm in diameter or so (tower is 10x10 cm), concrete is poured around the lower part (170 Kg concrete was used).

Az/El drive

As I don't trust most of the commercial rotorsystems (if any?), I decided to use a "Slewing drive" designed for solar panel systems, the larger ones are very popular among EME'ers. The smaller ones (3 and 7 inch) can be had in a combined azimuth/elevation configuration. I selected a 3 inch type from Coresun in China:

https://www.coiesundrive.com/solar-tracker/pv-solar-tracker/svh3-dual-axis-solar-tracker-slewing-motor.html


If you compare the holding torque, axial/radial load with commercial rotators, it is pretty obvious that you get A LOT more for your money...


The prices are reasonably fair, even the delivery by air is manageable! 

I ordered my gear with some different DC motors as compared to the standard, I also got 3 meter cables instead of the standard 1 meter, this will help with the tower etc. The motors are 24 VDC (max 8 Amp each) and there is a incremental (2 phase) output from each axis. Below is the PDF datasheet for the specific configuration I ordered (each axis is 0.2 RPM, so 5 minutes for 360 deg. rotation). Coresun also have 3D step files for all of their drives, this makes it easy to do mechanical design around these.


The controller for the system I will do myself, I need to make a nice system anyway for my 7 meter dish as the gears for that system also uses incremental encoders (2 phase), and the motors are also 24 VDC. Info for the controller here.


Tower

The tower finally returned from construction and surface treatment. Next step is to dig a hole and getting everything setup.


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The lower part of the tower is now sitting in the concrete, waiting for it to cure :)

I made the hole approx 1 meter deep and approx 30 cm in diameter. The top portion (that is to be level with the grass so my robot lawnmower can safely drive over the concrete) is 50 x 50 cm. Cables from the shack goes thru a 50mm "sewage" tubing. I have a 18 x 0.5 mm2 shielded cable (for control, encoders etc), a 4 x 2.5mm2 (for the motors in the Az/El drive), a 3x1.5 mm2 cable for 230VAC and 3 x low-loss coax for the 2M, 70CM and a future antenna.

I ended up pouring 170 Kg of concrete into the hole. This should be plenty ;)

The sorrounding grass will be leveled out once the concrete has fully cured.


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Installation of tower

The upper part of the tower was installed, this was an easy "one man job" with the hinge system. Works absolutely perfect. The hinge point is approx 50 cm above the ground. Got the junction box (Fibox 280 x 380 mm) installed. The box contains a 12VDC supply (I will have to determine if it will emit any noise in the antennas as the powersupply is a switching mode. I have a backup plan if that is the case ;) (I ended up not needing the powersupply, the preamps are powered by the IC-9700 via the coax cables)

Also a switch/fuse is installed as well as a 230 VAC outlet (that is nice if I for some reason need to use powertools in the future, no need to run an extension cord).


Test (preliminary) of coax cables to tower

I connected my R&S ZNLE-3 VNA to each of the cables (144 and 432 MHz cables) to check return loss. The "far" end of the cable (at the preamp) was terminated with a 50 ohm load. Measured from 100 to 500 MHz for both cables. The loss of both the 144 MHz and the 432 MHz cables was also measured.
Loss on 144 MHz: 1.56 dB
Loss on 432 MHz: 3.25 dB


Az/El drive has arrived

The drive was delivered today. I used DHL Express from China to Denmark, the price was reasonably. The transport took only 3 days! I was pleasantly surpriced when I opened the box. The drive was very well packed in a wooden box, total weight around 30 Kg. I connected the drive to my "under development" Rotor controller, it spun up immediatly, the incremental encoders etc worked perfectly! I can now command both azimuth and elevation to any position (still a lot of software to do on the controller, but getting there :)


The drive uses around 350 mA at 24 VDC in "no load" for each of the axis. The gear ration is 1:62 for the slewdrives, the motor/planetary gear is 1:263, so in total the gearing is 1:14508. The incremental encoder emits 2 pulses for each rotation of the motor axle. I run the incremental encoders in "edge mode", so the 2 pulses each rotation gives me a count of 8. So in total, I get 8 x 14508 = 116064 pulses for full 360 degress, this is 322.4 pulses pr degress, should be enough......

I had originally ordered the drive with longer cables, this was due to communication problems, not done. That gave me an excuse to open the motors to install new cables and at the same time have a look at the internals. The motors are very well done, there is even an "O" ring on the end-cap. 

Just to be safe, I added self-vulcanizing rubber around most of the joints.

More info on the Rotor Controller page as things progresses, for now the drive will be sitting in the lab while I do some more software work on the controller. Once I have the basics running, the drive will be installed on the upper tower, the glassfiber horisontal boom installed and the antennas mounted!


Slideshow of different pictures of the drive:

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The system is finished

The system is now finished (with a few small cosmetic changes pending), first contacts have been made (XW-2A and ISS repeater)

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De-sensing/overload of 70 cm system

I noticed that when receiving on 70 cm and transmitting on 2 m, the radio would show "OVF" (overflow). This was the 3rd harmonic from the transmit signal on 2 m that would get into the preamp and radio. I was adviced to install a MX-72M diplexer between the 70 cm antenna and the preamp. This made the overfload / de-sense go away completely.


There is an article in AMSAT about this:

https://www.amsat.org/a-simple-desense-filter-for-mode-j-satellites/


I got the diplexer from Wimo in Germany:

https://www.wimo.com/de/mx-72n

Measurement of power at the N connectors at the antennas

I measured the (calibrated) power that reaches each of the antennas from my ICOM IC-9700. The cables are Hyperflex 10 (approx 25 meters each). The tables shows the relationship between the powersetting of the IC-9700 and the corrosponding power delivered to each of the antennas.
Cable loss was also measured:
Loss on 144 MHz: 1.56 dB
Loss on 432 MHz: 3.25 dB

Tilting tower helper

Due to the weight of antennas, rotor etc (and because I'm upgrading the system with 4 long yagis for 70 cm EME), I made a "helper tower" I can mount when I need to lower the system to work on it.