Sunday, November 19, 2017

Good oscopes finally become affordable

If I had a dollar for every time I lugged a project to my work QTH in order to test or troubleshoot it with an oscope I'd be able to buy my own oscope.

An ad in a recent issue of QST achieved its intended effect and I now have a Siglent SDS-1202X-E oscope available for use any time I need it. The specs (200 MHz, dual channel), the overwhelmingly positive reviews and the low price convinced me that It Was Time.

In the past I have tried "digital oscopes" that are essentially a set of probes and an interfacing box that connect them to a PC and provide a very general, sometimes-accurate presentation of low frequency signals. These are of limited use to the ham who needs to see what is happening at RF frequencies, especially where rise time and accurate shape of a given pulse are needed to be known.

I also like the idea of building and using a ScopeMatch to monitor antenna conditions on 630 meters in real-time. A ScopeMatch provides a way to sample both the current and the voltage in a transmission line. If they are in phase, the antenna is properly matched since no phase shift occurs from a resistive load. During mis-match, an antenna appears either inductive or capacitive, causing a phase shift - that is, current will either lag or lead voltage (remember ELI the ICE man?).

40 watt output of my G0MRF amp on 475.755 kHz. Note frequency displayed in upper-right corner.

In the week I've now had the oscope, I've begun to wonder how I ever got along without one - especially having built so many QRP kits over the years with their alignments and (sometimes) troubleshooting. The scope is proving its worth as tinkerings continue with various methods of putting a signal on the new 630 meter band.

'Measure" function displays rise time, duty cycle and a lot of other data pertaining to the displayed trace

I particularly like the 'Measure' function that displays most, if not all, of the parameters of a given signal. Variable cursors can also be placed in the X or Y axis to measure parameters manually. A usb port allows data to be saved to a thumb drive.

In the coming weeks I'll do the opposite of what I did in the past - I'll take the Siglent to work and put it up against our frequently calibrated and high-$$$$$ equipment and see how it compares.
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4 comments:

  1. John, Your new purchase of that scope sounds great. I followed the link on Amazon and it like something that I would like to have in the shack. Can you do a video demonstrating some of the practical uses of the scope, involving kit building, and home building. I am also building some fpv rc drones both fixed wing and it would come in useful for that as well. Kelly - WB0WQS.

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    1. Hi Kelly - I'm hoping to test the scope at work in the next 2 or 3 weeks on a few of our radar systems with fast pulses. I'll try to make a video of that as a way of demo'ing some of the features of the scope. In the meantime I may also hook it up to my new amp and use the dual channels to show the push-pull configuration.

      73 - John AE5X

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  2. Nice Scope John. I have an old Tek 2215 that I've had for a long time and have been considering a new scope. We have nice new Teks at work but I can't justify that kind of money. I've been looking at the Rigol DS1054Z. I'd not heard of this Siglent. Very interesting. Two less channels but better specs in most all other areas. The notion of a scopematch is very interesting as well. I'll be interested to see your demo with the other scopes. Maybe I can get one of these squeezed under the Christmas tree. : )

    73,

    Tim
    KA9EAK

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    1. I did look at the Rigols a few months ago but the price:specs ratio wasn't where I needed it to be for home use. I've never had the need for 4 channels and would gladly trade 2 of them for a better bandwidth. Going by the "X5 Rule" a 50 MHz scope begins to lose accuracy when looking at signals above 10 MHz. Both Rigol and Siglent have a US-based (and probably other regions as well) website with support, firmware updates, etc.

      Regardless of manufacturer, it's good to see the prices of decent scopes come within range of hobbyists.

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