DSO as SatFinder? - Page 1
Forum section: electronics / beginners

author: outofstepper
author_rank: Contributor
timestamp: August 03, 2012, 11:36:03 am
content: greets all.the other day my satellite internet goes on the fritz. tech support sends out a guyto realign the dish. He's got a portable (what appears to be ) spectrum analyzer.Gets my dish pointed in no time. Cost me $80!(I did the original install myself, a few years ago.. by eye..took me almost 2 days!).So I'm wondering, could a DSO (w/FFT?) be used to do the same thing?OWON 6062.I think the signal is 12-14 Ghz? Something like that. Its the Ku-band.I wouldn't so much care to "see" the signal.. but maybe just some anomoly on thescope (delta voltage) that tells me I'm pointing at a satellite? I can get ballpark by eye.Also, I think the transciever on the dish needs to be powered by the modem (or TV box dependingwhich dish we're talking about).. I assume my scope wouldn't power the transciever.. any suggestions?Thanks!

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 03, 2012, 01:07:37 pm
content: Your scope won't be any good for this, just get yourself a $ 10 satfinder:The LNB (what you call transceiver) converts the original signal ~11 GHz to ~1.5 GHz, that's still too high for the scope.This satfinder just measures the RF signal on the cable from the LNB to the receiver.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 03, 2012, 02:15:07 pm
content: If you can power the LNB somehow,you can build a simple detector circuit which will give you a DC output when fed with the 1.5 GHz from the cable.You can look at this with your 'scope,& adjust the dish for maximum DC level on the display.This is what they do in the satfinder,except that they use a meter.Back in the day,we used to read the AGC on receivers for Intelsat,using an old AVO model 8 meter on the end of a long length of jumper wire & adjust the dish (big ones!) for a max reading.

author: outofstepper
author_rank: Contributor
timestamp: August 03, 2012, 02:27:31 pm
content: so going with the measuring-voltage-approach:The LNBs are powered by whatever device is attached to them of course (so TV Box or Modem, etc)..what if I just made a short length co-ax "adapter" .. M to F.. and in the middle I just leave accessto the center conductor and the shielding.. shouldn't it be straightforward to just measure the voltageacross the two while everyting is wired normally?Thanks again.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 03, 2012, 03:09:15 pm
content: You need to isolate the detector circuit from the LNB supply,or you will cook the diode,& maybe your scope input.I don't really know the particulars of your system,so I can only give general help.If the satfinder is very cheap it may be easier to go with it,as all the isolation is already done inside it.If you are doing it for fun,I would suggest you Google for information on inline RF detectors.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 03, 2012, 04:14:10 pm
content: I was assuming that your main interest was aligning your disk, and since the price of a commercial satellite finder won't even buy you the housing if you want to build it yourself I pointed to that solution. Of course, when you see it as a project it is a totally different storyAlthough taking a scope up to the roof is not something I'd recommend, it is totally possible to measure the dc from a RF detector with it.But you will just be using it as a multimeter, not much pride in that...Anyway, here's a schematic as a start, if you still feel that you want to use your scope you can always leave the meter out.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 04, 2012, 02:56:43 am
content: Quote from: PA0PBZ on August 03, 2012, 04:14:10 pmNo,you keep all this stuff at ground level & send some other dummy up on the roof!As far as using the 'scope as a multimeter,usually when I troubleshoot equipment,I basically do just that!You don't normally need the accuracy of a DMM,so you can check all the DC voltages & the signal levels (or the presence of signals) with the one instrument.The 'scope will react to adjustments quicker than a DMM (well,analogs will---I'm not sure about DSOs).