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Author Topic: Oscilloscope Specs  (Read 7512 times)
KB1WSY
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« on: March 28, 2012, 02:47:04 AM »

Trying to figure out appropriate specs for an oscilloscope to be used in ham homebrew work, with emphasis on tube technology (both the stuff being built and tested, and the 'scope itself). No hurry to obtain this equipment, but had my eye on a vintage Eico 460 until I noticed that its frequency tops out at 4.5 MHz. Deal breaker for ham work, presumably? For instance, if you want to check the shape of your CW signal to analyze click or chirp issues on bands above 80m?

More generally, how essential is a 'scope? For a homebrew beginner like me, it seems to be "a very nice thing to have" but you can easily get away without one. On the other hand, the more I read about 'scopes, the more I get the impression that they fulfil a very valuable *educational* mission in terms of giving the budding experimenter a good "picture" of the waveforms and a practical backup to all the theory s/he is learning about sine waves, square waves, sawtooths and the various types of distortion. Have also seen very nice pics of the bandwith curves for tuned circuits.

One thing that is sometimes mentioned is the distinction between a "recurrent sweep" and a "triggered sweep" scope. Seems like the latter, more sophisticated type allows one to "zoom in" on parts of the trace more easily than the simpler type (and I presume the Eico is the simple type). Surely, however, the simple type is still plenty useful for basic work?

Usual disclaimer: I'm a total beginner so you can expect some pretty stupid questions from me!

TU ES 73 DE Martin, KB1WSY
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KA4POL
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« Reply #1 on: March 28, 2012, 04:35:04 AM »

One remark to begin with: There are no stupid questions, only possibly stupid answers.  Grin

You already have given this issue a lot of thought. If you want to get into serious homebrewing you'll be better off with a suitable scope. If you skip buying one now you'll do that later. So why not go ahead right now.
The specs are set by you. If you want to limit yourself to HF then 60 Mhz will be fine. Trigger or not to trigger, most scopes can switch to triggered display. This is useful for digital signals where you want to see the rising side of a pulse, just to name a sample.
As you did not mention it, a two channel scope is quite helpful in showing input and output signals at the same time etc.
You do not have to spend lots of money for a new digital scope. There are lots of good used scopes to be found through the web. I just recently got me a Tektronix 485 for about 400$. So I can also display 145 MHz. To get some more information download: http://socrates.berkeley.edu/~phylabs/bsc/Supplementary/Lab1/xyz_scopes.pdf
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AD4U
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« Reply #2 on: March 28, 2012, 09:17:49 AM »

I agree with the previous poster.  I bought a HP 182 50 MHz scope at a recent hamfest for $50.  It is dual trace and works perfectly.  I also have a 275 MHz HP scope, but the 182 is OK for all my boat anchor HF work.

Just "having" the proper scope is a start.  The fun parts starts knowing where to put the leads and interpreting the waveforms.  This often takes a bit of knowledge and practice.  But then, "You gotta start somewhere".

Dick  AD4U
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N3LCW
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« Reply #3 on: March 28, 2012, 11:19:35 AM »

I chose an old analog Tektronix 465 100MHz scope.  Cost was $100 including a set of probes.  All I had to do was clean the time base switch contacts with contact cleaner spray and it was good as new.

A good o'scope and signal generator are good 'nice to haves' for HF homebrewing.  You can get by without them but troubleshooting and alignment are so much easier with them.

Good luck and welcome to the homebrew crowd!

Andy
N3LCW
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WD4MTW
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« Reply #4 on: March 28, 2012, 11:51:12 AM »

I would tend to disagree for most ham usage to get an elaborate, triggered lab scope. Years ago when I got licensed, the dictum used to be that a scope for station use was good enough if it "got a green line". Times have changed though with elaborate synthesizers and microprocessor control in amateur rigs. For years, the Eico recurrent sweep scope I owned was enough for my bench qualitative work. I.E. the vfo or heterodyne oscillators were functional, you could trace drive, AF or IF signals. So what if you exceeded the -3db points of the vertical amp, you still could see the presence of RF at higher frequencies, just attenuated. Most point measurements were made with a vtvm or rf probe anyways if you needed an absolute number to compare with service manual notations . If you needed the bandwidth to see the output, you went directly to the plates of the crt which were often good beyond 30mc with a line sampler....same idea with a station monitor scope. The OP mentions that he's primarily interested in tube and vintage equipment. An old recurrent sweep TV scope would be sufficient. Unfortunately 40+ years later, many of these tube based scopes have seen better days and would probably be full of leaky paper caps and drifted resistors. For the money, a rebuild wouldn't be worth it and near the price of a more recent higher bandwidth triggered scope. There should be a number of "Station Monitor" scopes of the 70's that were solid state except for the CRT that also had general purpose vertical and horizontal inputs as well as a tuned IF input for their companion receiver and some sort of line sampler/attenuator. I did a lot of repairs on the spot with first my Heathkit SB 610 monitor scope and latter Yaesu YO-901 using the direct vertical inputs with a probe without having to drag the rig to my garage shop. It's nice to have a good lab scope if you need it, but you'd do better in learning to service your station with a simpler scope. If you could find one, Leader used to make a solid state version of their LB-310 specially set up for ham use with a coaxial sampler that would make a great first scope that would also lend itself as a good general purpose scope. Many of the service and educational vendors had some very useable 20mhz private label  triggered sweep scopes that were simplified for service or student use that would make great starter scopes for the money. A great project would be making your own coaxial line sampler to use with one of these.
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WB2WIK
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« Reply #5 on: March 28, 2012, 03:53:19 PM »

Trying to figure out appropriate specs for an oscilloscope to be used in ham homebrew work, with emphasis on tube technology (both the stuff being built and tested, and the 'scope itself). No hurry to obtain this equipment, but had my eye on a vintage Eico 460 until I noticed that its frequency tops out at 4.5 MHz. Deal breaker for ham work, presumably? For instance, if you want to check the shape of your CW signal to analyze click or chirp issues on bands above 80m?

I don't understand how anyone could see a "chirp" on an oscilloscope.  A click, yes, probably.  A chirp, I really doubt it.  A chirp isn't a change in amplitude, it's a change in frequency.  A scope won't show that, it takes a receiver or a spectrum analyzer.

Quote
One thing that is sometimes mentioned is the distinction between a "recurrent sweep" and a "triggered sweep" scope. Seems like the latter, more sophisticated type allows one to "zoom in" on parts of the trace more easily than the simpler type (and I presume the Eico is the simple type). Surely, however, the simple type is still plenty useful for basic work?

I'd say it's usually not unless you're dealing with really simple stuff like analog audio, possibly very low frequency digital circuits.  A triggered sweep scope is very handy and almost any kind of modern scope or mid-range scope even from 50 years ago will have this feature.  If you want to look at analog RF signals up to 30 MHz, probably a 30-50 MHz scope is all you need.  But for high frequency digital circuits, a lot more bandwidth is really handy to help assure what you're looking at is what the circuit is really doing.  And in such cases, you want the matching, compensated probes as well.

But none of that needs to be expensive.  The ubiquitous Tek 465 and others from that 4" family work well and although 30+ years old, most of them still work fine.  They can often be found for $100-$150 complete with real Tek probes, carrying case and manual.

I wouldn't buy one "on line" unless it was from a reputable dealer with a return policy, and not a private party.  They're just too easy to find locally.  My local "Craigslist" usually has a dozen of them at any given moment, all within driving distance so I can go check it out and pick it up.

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G3RZP
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« Reply #6 on: March 29, 2012, 03:14:53 AM »

Some of the Hameg scopes are good value, too. For HF unless it's just an occasional look, 20MHz is about the minimum. But if you want to get into building RF or serious fault finding, a 60 or100 MHz 'scope is the way to go. Plenty of  good second hand Tek scopes out there. The HP analogue ones often give switch problems when old.
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KA4POL
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« Reply #7 on: March 29, 2012, 05:51:42 AM »

By the way, since 2005 Hameg is owned by Rohde & Schwarz  Wink
And since 2010 their production is also done within the R&S organisation.
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N3QE
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« Reply #8 on: March 29, 2012, 07:56:55 AM »

The old cheap Eico and Heath scopes are very useful even when used way out of their spec range.

e.g. for monitoring shape of a CW envelope on 80M or 40M, a 4 or 5 MHz scope will work fine.

About 99% of what a scope is used for is qualitative. You aren't going to measure a 3.5 MHz frequency to a hertz using a scope. You won't even be able to measure it to the 0.1MHz unless you have a well calibrated scope. Same goes for amplitude - bigger and littler are going to be the judgements you make 99% of the time, not actual numerical voltage values.

Nothing except the most modern most high spec scope (with built in spectrum analyzer and waterfall) will be useful for finding chirp. This is where a bench receiver and your ear come into play.

All that said, a Eico or Heath scope from the 60's or 70's is not a very advanced instrument. There's a world of difference between those and say a Tek 465. But just because it's not advanced, does not mean that it isn't useful. Usefulness will depend on the user's skill. Someone who knows what waveforms should exist in the circuit is going to be able to make a lot of use out of even a cheap 40 year old scope. And a brand new $10000 scope in the hands of someone who doesn't know what to look for, is not going to help any at all.
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KB1WSY
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« Reply #9 on: March 29, 2012, 09:24:41 AM »

>>The old cheap Eico and Heath scopes are very useful even when used way out of their spec range. e.g. for monitoring shape of a CW envelope on 80M or 40M, a 4 or 5 MHz scope will work fine.<<

That is what I sorta guessed, but I would be very grateful if someone could explain the physics behind that. My (completely neophyte) reasoning was, you are looking at part of the envelope, not the whole thing. I also got the impression from my reading that quite a lot of hams owned these low-bandwidth 'scopes, and was wondering why they would have bought them if they were useless in the HF spectrum. Maybe the point is that even if the BW is only 4.5 MHz, you should still get a readable waveform at (say) 7 MHz but it will be attenuated by 3db or 9db or whatever, which doesn't matter if you aren't actually using the score to (for instance) get an accurate voltage reading from the graticule or something.

One thought I had is that, if your CW waveform is OK on 80m, then (from the same transmitter) it should be OK on the other bands right? (This is assuming vintage technology, crystal control with a frequency multiplier, which is what I will be using to start with.) To the poster who pointed out that chirp isn't visible on a 'scope, of course you are right! Maybe someone can answer another question I had: can AC hum on a CW signal be seen on a 'scope?

I enjoyed reading about CW waveforms and seeing what clicks "look" like. They are asymmetrical, i.e. they look different on the "on" end of the waveform compared to the "off" end of the waveform. You can use a 'scope to find out exactly what effect your "shaping" capacitor circuit is having, and this seems to me both useful and a great practical demonstration of electronic theory.

To further explain my interests, I am not worried about having a vintage unit that is either broken or barely working. Extensive restoration would give me a great opportunity to learn more about these old behemoths and about electronics in general. I was even thinking of trying to find one of those old training kits that were used in electronics schools in conjunction with 'scopes (I think Heathkit sold these, among others) and "playing" with that.

I thank everyone for their suggestions and comments so far. My current thinking is to go ahead with the prehistoric monster scope, knowing full well that it will "need work" and have some severe limitations as a test instrument for ham homebrew but seeing it as an "educational experience" and also lots of fun. When I run into the limitations of the old monster, I can eventually upgrade to something better. Working units from that era are available for less than $50, although I fully expect that getting it back up to "new" specs will be a lengthy process. The usual defects I see, on the functioning units, are a blurry waveform or a very thick one. The thing to avoid is any unit that has either a dead CRT or a dead PS transformer, according to the advice I have seen.

Do keep the suggestions going, especially if you think I am nuts to want to do this! (And, yes, I will make sure to treat the HV floating around these units with respect, as I work on my restoration!)

TU ES 73 DE Martin, KB1WSY

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KA5IPF
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« Reply #10 on: March 29, 2012, 12:15:45 PM »

In case you are wondering why hams bought Eico and Heathkit, MONEY. Very simple a 10 MHz Tek scope, used, in the 70-80's was over $400. Forget about a good 100 or 200MHz on a ham budget.
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K9AQ
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« Reply #11 on: March 29, 2012, 06:31:07 PM »

I have both a Heathkit SB-610 monitor scope and a Tektronix 2245a 100 mhz scope so I can speak for both.  I use the Heathkit daily and find it very benefical in making sure that I am not overdriving my homebrew solid state 600 watt amplifier.  My SB-610 CRT power supply recently failed, as most of them will, but fixing it only required replacing the two diodes in the voltage doupler, 3 filter capacitors and a resistor.  Total parts cost of less than $20.

I bought the 100 mhz Tektronix scope on Ebay for less than $200, which I would say in affortable in most ham budgets.  There are a lot of good deals on 100 mhz or higher Tektronix or HP scopes on Ebay.

Don
K9AQ
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K1ZJH
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« Reply #12 on: April 06, 2012, 08:39:32 AM »

My main scopes in the shop are a 2235A on the bench, and an older 465 on a scope cart.
A 2213 is a backup.  You can save a bit of money by looking at higher end surplus scopes
that don't have delayed sweep options (i.e. a 60 MHz 2213 for about 60 to 70 bucks with
some shopping.)  Triggered sweep is a big plus, but unless you're chasing digital signals the
delayed sweep doubles the cost.  I'd avoid the old Heathkit and Eico stuff at all costs.
Some of the HP scopes are decent, but again some have well documented problems and a
cheap bargain may bite you in the end.

At a minimum, I'd look for a brand like Leader or similar, with at LEAST a 35MHz bandwidth.
The probes should be rated for a slightly higher BW than the scope for max. performance.

Pete
« Last Edit: April 16, 2012, 05:35:48 PM by K1ZJH » Logged
W2AEW
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« Reply #13 on: April 06, 2012, 10:44:03 AM »

If you have the time to spend, and really want to dig into the operation of these old analog scopes, including a description of the differences between a recurrent sweep vs. a triggered sweep, grab yourself a cup of coffee and sit down for the 2+ hour long "Scopes for Dopes" video.  I helped to teach this class last year, and the folks said it was very helpful.  If you look at the text under the video in YouTube (expand it out), you'll see an Index that you can use to see the time-stamp for the different sections of the video - so you can zoom right to the section you want to see.  Here's the link to the class video:
http://www.youtube.com/watch?v=8ZKMrzTGxLQ&list=FLiqd3GLTluk2s_IBt7p_LjA&index=7&feature=plpp_video

If you prefer a bunch of shorter topic videos on scopes (and more), check out my YouTube channel.  I've got videos on probes, triggering, vertical controls, etc., as well as a bunch of little application videos showing how scopes (and other equipment) can be used in a variety of radio related tasks.  My YouTube channel is here:
http://www.youtube.com/user/w2aew

73 and Enjoy,
Alan W2AEW
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My YouTube channel...
...ham radio, basic electronics tutorials, etc.
http://www.youtube.com/w2aew
KB1WSY
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« Reply #14 on: April 14, 2012, 05:45:52 AM »

Thank you very, very much everyone for the oscilloscope advice. In the end, I decided to adopt a two-stage process. First, obtain a crude basic oscilloscope and spend plenty of time playing around with electronic experiments from vintage "Know Your Oscilloscope" books. This, to deepen my knowledge of scopes (and electronics) in general. Second, when I run into the limitations of the scope, obtain a much better instrument, making use of the copious suggestions you have made.

So: I found a broken-down Eico 460 from the 1950s. It powers up and there is beam, and the vertical amplifiers seem to work (I can make the trace taller or shorter) but there is no response from the horizontal controls and the calibration waveforms don't appear. So, an excellent rebuilding project! Wish me luck! I am learning a lot of stuff just through the process of acquiring ancient, broken test equipment and refurbishing it myself (so far, I have rebuilt a grid-dip meter and a VTVM; am currently working on a broken RF signal generator). It is not a very efficient way to equip my workshop, but it is immense fun and I hope to emerge from it with a much deeper knowledge of how everything works. It is all from the Eico range, not because these are the best instruments (there are extremely average!) but again, just for fun. I also got hold of an Eico electronic switch so I can pretend that I have a dual-trace scope like the big boys (again, I have no illusions that this switch will be all that useful but I still want to play with it anyway).

Later, I can reward myself with a Tektronix scope or something. Sorta like what people went through in the 1950s through the 1980s, but compressed into a few years instead of a few decades.

Many 73s from Martin, KB1WSY
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