Thursday, 28 November 2013

Satellite TV, RX and positioning

Satellite TV, RX and positioning

Playing with satellites TV or radio is not too hard or expensive. I did a fair bit on it a few years ago (C and K band, ~4 GHz and ~12 GHz) and still have some of the gear. I could see my house in Brisbane on Google maps from the big white C band dish, ex Sky. It was a heavy fixed dish, jerry-rigged with a linear-actuator for position control. 

A full new C (and usable on K) band system is around $400 on eBay.   Sometimes they are available for free, migrants and expats used them to get overseas TV. I had one, disassembled, but tossed it when we moved to Gold Coast. Should/may have kept pole, as big steel is expensive.

All satellite TV use a LNB (low noise block) to receive and down convert to a standard IF range of about 1 to 2 GHz for a TV set-top box. The coax is used to carry control signals as tones (diseqc) or DC. The coax is very high performance, but cheap because of the massive use of it.

The big dishes are controlled by linear actuators and a positioner box. I have one set. I last used it to with a remote control to raise and lower a TV, (on big drawer slides) that was in front of a window (acker Heath Robinson(UK), Rube Goldberg(USA), Bruce Petty(AU)) . It worked but wasn’t pretty. Disassembled now. I will try to find photo. Linear actuators are cheap ~$75 and powerful; could be used for lots of weird purposes.

A big dish can be used with any frequency just by changing the receiver/antenna at the focal point. Dishes are only useful for higher frequencies as the receiving antennas get too big.

For lower frequencies, Yagi or similar types, often multiple,  are used.

Positioning dishes is fairly easy. One dimension is plug and play, with many receivers having built-in positioner control, or using a separate box. I have a Superjack DG-120+l and control box. I used the box for it with the TV lift.
Two dimensions is not much harder, just use two positioners bolted together at 90 degrees, as per the Yaesu G-5500. Any positioner or rotators can be used (see ARRL Antenna Handbook re satellites). With two rotators or linear actuators, quite big dishes or arrays can be controlled. One advantage of satellite antenna is that they can be on the ground, putting them higher may be necessary to clear obstacles.  

However, the control is manual with two controllers, again per Yaesu G-5500. Low orbit satellites (like Funcube or weather) are visible for about 15 minutes. It may not be too hard to track them just using signal strength and knowing their trajectory. Finding them as they come over the horizon is probably the difficult bit, but again, their position is known and the positioners can be calibrated.

It is "possible" to track satellites automatically, I suppose, but I have not seen a reasonably priced system. There may be some for the Yaesu G-5000, given that it is a standard piece of amateur hardware. A Raspberry-Pi or similar could do it, the actuators all give position feedback (reed-switch pulses as minimum) but the program would be fairly equipment dependent.
I may be able to track satellites on 2m or 70 cm. I am currently building a tilting mast (literally: yacht) and a 2 m vertical and a 70 cm crossed pair antenna. The antenna will be on a horizontal fibreglass pipe I had made ~$80, as a "T", with a rotator below. I could put a second pole-mount rotator on the fibreglass pipe to give vertical rotation. With the two rotators, I could point an antenna anywhere in the sky. It would be easy to make the 70 cm circular polarization with phasing. Then I could TX and RX! Could do same with 2m if make crossed too.

Some of the receivers (and SDR satellite programs, such as BlindScan and CrazyScan), have positioner control via diseqc, but one dimension.

Changing a TV channel with the remote can include moving the dish automatically; pretty neat really. Very common in Europe and Asia.

Given that most amateur TV is DVB-S, I might check some of this anyway, as I want to be able to receive the picture (via box or card), as well as the signal (using BladeRF) from Brisbane. I have got an old Foxtel K band dish on the roof and a 1200 mm dish in the back shed.

Awesome spook card, it has a pass-through for rtl-sdr or BladeRF SDR. Using Crazyscan/Blindscan and BladeRF with SDR-Console (or what-ever for spectrum analysis) just sounded too cool…  Little Pentium system might get used for something other than print server and scanner.

With a dish, at best, I can only use the 1200 dish with a positioner on existing Foxtel mount. I don't have space for a C band dish again. Not that there is much on C band now, most is on K.
Might drag out old Dream 800 set top box and see what still works. Dream box has pass through, so I might be able to get satellite spectrum; a first IF tap again! Bizarre if it works.
To be continued...


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