Author Topic: New lab: Oscilloscope bandwidth  (Read 5373 times)

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Offline jnichollsTopic starter

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New lab: Oscilloscope bandwidth
« on: March 10, 2016, 05:33:22 am »
Hi all, first post here.

I'm building for the first time my very own electronics lab. I am both a ham and an antenna engineer, so I have a decent amount of theoretical experience in electronics. Now I want to go hands-on.  I plan on starting with some basic electronics projects then moving into the building of radios. My goal is to quickly get up to VHF/UHF so I can potentially start playing around with satellites.

My first big decision is what oscilloscope to get. A lot of people on this forum say to just go for a Rigol 1054Z as an entry level scope. I am also considering the Rigol 2072a as I can get it for not too much more than the 1054z (only about $100-200 more). The 1054z "hacked" is 100 MHz while the 2072 "hacked" is 300 MHz. My question is really whether I can just get away with the 100 MHz bandwidth of the 1054z or if I should get the 2072a right off the bat since it has 300 MHz bandwidth. I really have no idea if that extra bandwidth will come in handy or not.

I also am not sure if I will need the 4 channels vs. 2, although more always seems better.

What would you guys recommend based on my goals and interests? Is a higher bandwidth scope necessary or even just high priority? I'll definitely be getting a spectrum analyzer at some point, although that might not happen for a little while until I save up more money.

Thanks in advance.
 

Offline Mosaic

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Re: New lab: Oscilloscope bandwidth
« Reply #1 on: March 10, 2016, 05:58:29 am »
UHF/VHF....bandwidth for instruments is what is required.

Ideally you need a spectrum analyzer, a VNA($$$) and SOL cal kit, an precision RF power meter, the ability to fab and build FR4 SMT boards. A good capacitance/inductance meter that gives Q and ESR and so forth. Signal generator good to the frq of interest. Freq. counter also good to the frq of interest. Optionally a disciplined GPS 10Mhz ref.
Then bits an pieces such as assorted N, SMA, BNC, F connectors and adaptors. RG 58, RG400 cabling and crimp type connectors and a matched die crimper. For longer antenna line runs look at LMR 400 with N connector ends. Then Couplers, mixers, splitters, attenuators and such like. Also have a look at SDR radio options. Checkout the EMRFD yahoo forum.
Have a look at this youtube channel
https://www.youtube.com/channel/UCiqd3GLTluk2s_IBt7p_LjA

As it happens I just did this over the last few months.
I use a Rigol DSA 815 TG  with all options and  I just discovered it's got some nonlinearity bumps in the recvr that have to be cal'd out manually.
So I used my HP8753D VNA as a CW signal source, my Boonton 4210-4B precision RF power meter to map the VNA  signal amplitudes to 1.5Ghz (the SA max frq) . Enter that cal table into the SA, then sweep the SA slowly with the VNA in manual sweep mode...observe the interpolation and add more cal points to iron out the bumps. Finally got it down to around 0.1dB flatness full range, which is 8x better than the OEM spec.

 

 

Offline Wuerstchenhund

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Re: New lab: Oscilloscope bandwidth
« Reply #2 on: March 18, 2016, 06:10:15 am »
My first big decision is what oscilloscope to get. A lot of people on this forum say to just go for a Rigol 1054Z as an entry level scope. I am also considering the Rigol 2072a as I can get it for not too much more than the 1054z (only about $100-200 more). The 1054z "hacked" is 100 MHz while the 2072 "hacked" is 300 MHz. My question is really whether I can just get away with the 100 MHz bandwidth of the 1054z or if I should get the 2072a right off the bat since it has 300 MHz bandwidth. I really have no idea if that extra bandwidth will come in handy or not.

You're asking in the wrong forum. This forum is for RF related stuff, you should really ask in the Test Instruments subforum.
 

Online tggzzz

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Re: New lab: Oscilloscope bandwidth
« Reply #3 on: March 18, 2016, 08:54:23 am »
You're asking in the wrong forum. This forum is for RF related stuff, you should really ask in the Test Instruments subforum.

He's doing "building of radios. My goal is to quickly get up to VHF/UHF" and want to know about instruments for that. This is an equally reasonable forum.

Don't think of an oscilloscope as a substitute for RF test equipment, unless you have an insanely high bandwidth and sampling rate.

Have a look at the attachments to the first posts in https://www.eevblog.com/forum/projects/project-yaigol-fixing-rigol-scope-design-problems/
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
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Offline Howardlong

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Re: New lab: Oscilloscope bandwidth
« Reply #4 on: March 19, 2016, 11:15:20 am »
A radio/communications test set is at least as valuable as a scope when debugging VHF/UHF, they include an RF signal generator, power measurement, frequency counter, a sensitivity check and often much more.

Some comms test sets have a scope, but they're typically single channel and very low bandwidth, Ok for checking a few voltages and a sanity check on audio frequencies, but anything more and you need a proper scope.

Why is a scope of limited use for RF? While it's certainly a near essential piece of test gear, generally they will lack the sensitivity and bandwidth required, but perhaps more importantly they lack the filtering afforded by purpose designed RF tools. You wouldn't use a scope for testing band limited signal to noise for example, although I'm sure someone will come up and tell me a contrived way of doing it with a scope!

I would get a comms test set and scope before investing in a VNA or SA for VHF and UHF circuits. Instead of an SA, and SDR can be an invaluable bit of test equipment for tracing receivers: SAs tend to be much less sensitive than SDRs. An SA on the other hand is probably more useful than an SDR for tracing transmitters as you really need wide spans to measure harmonics and IMD products. Some comms test sets already have spectrum analysers built in, by the way.
 

Offline Nuno_pt

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Re: New lab: Oscilloscope bandwidth
« Reply #5 on: March 19, 2016, 11:24:25 am »
For the communication test set an CMU, CMT, CMTA, from R&S even an CMD80, but not shure about the last one, maybe someone could step in here, should do it, better it's the Marconi 2955, IFR 120, etc.

Nuno
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Offline jnichollsTopic starter

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Re: New lab: Oscilloscope bandwidth
« Reply #6 on: March 21, 2016, 03:14:36 pm »
You're asking in the wrong forum. This forum is for RF related stuff, you should really ask in the Test Instruments subforum.

I'm asking in this forum, as my questions pertain specifically to RF work. If I ask in the test equipment section, it's a lot less likely I'll get responses from people who actually do RF work.

Don't think of an oscilloscope as a substitute for RF test equipment, unless you have an insanely high bandwidth and sampling rate.

I'm definitely not thinking of it as a substitute. However, it will take me a while to build up a good lab (not to mention money), so I want to equip myself with an oscilloscope which *may* be able to substitute for a while. But really what I am asking is whether when doing RF work, is there ever a need for an oscilloscope above and beyond the basic oscilloscope you would use for audio frequencies? If so, I would like to invest that money now, rather than buying one oscilloscope now, and another down the road. If not, then I'll just get a basic one and start saving up probably for a spectrum analyzer.

Have a look at the attachments to the first posts in https://www.eevblog.com/forum/projects/project-yaigol-fixing-rigol-scope-design-problems/

Yes I'm aware of this thread. Sounds like a fun little project if I end up buying a 1054z ;).

I would get a comms test set and scope before investing in a VNA or SA for VHF and UHF circuits. Instead of an SA, and SDR can be an invaluable bit of test equipment for tracing receivers: SAs tend to be much less sensitive than SDRs. An SA on the other hand is probably more useful than an SDR for tracing transmitters as you really need wide spans to measure harmonics and IMD products. Some comms test sets already have spectrum analysers built in, by the way.

Good to know, thanks. I'm looking to do things as cheaply as I afford to on the first pass, so an SDR sounds like a great idea. I'll have to look into comms test sets as well. At what cost can these test sets be had for?


If I interpret correctly, it seems to me that everyone is saying I should just get a basic scope, and that extra bandwidth on the scope is *mostly* useless for RF work.
 

Online tggzzz

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Re: New lab: Oscilloscope bandwidth
« Reply #7 on: March 21, 2016, 03:35:29 pm »
Don't think of an oscilloscope as a substitute for RF test equipment, unless you have an insanely high bandwidth and sampling rate.

I'm definitely not thinking of it as a substitute. However, it will take me a while to build up a good lab (not to mention money), so I want to equip myself with an oscilloscope which *may* be able to substitute for a while. But really what I am asking is whether when doing RF work, is there ever a need for an oscilloscope above and beyond the basic oscilloscope you would use for audio frequencies? If so, I would like to invest that money now, rather than buying one oscilloscope now, and another down the road. If not, then I'll just get a basic one and start saving up probably for a spectrum analyzer.

If I interpret correctly, it seems to me that everyone is saying I should just get a basic scope, and that extra bandwidth on the scope is *mostly* useless for RF work.

Radio hams developed and used radios for decades without oscilloscopes. I suggest you contact your local society and ask their opinion, and maybe borrow some equipment.

The scope will be useful for baseband time-domain analysis. An analogue scope will also enable simple baseband IQ analysis in X-Y mode; if wanting to use a digitising scope in X-Y mode, check carefully that the specific model will work well in that mode. A scope is useful for many other things, of course, such as checking PSU ripple.

However scopes are too insensitive and too non-linear for many RF purposes, e.g. checking signal purity and harmonics, finding sources of EMI/EMC; for those a spectrum analyser or modulation domain analyser is more suitable.

Whatever you choose, you will pay to gain experience in either time or money. Given that, you might choose to pick up a working secondhand scope 10MHz or 20MHz analogue scope; they are widely available and can be very cheap since nobody repairs analogue TVs any more. That will probably be sufficient for a while, by which time you will know why you need another scope.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline Martin.M

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Re: New lab: Oscilloscope bandwidth
« Reply #8 on: May 14, 2016, 07:22:09 am »
a lower cost solution can be an old sweeper test place,
it is very useful for the most parts including antennas and not so expensive then a spectrum analyzer with tracking generator.
The study of the manuals is good for months of learnig, how to use it for anything  :)

this is my SWOBIII, it works up to 1.25GHz  (and a UHF mV Meter)


my favorite oscilloscope for very high frequencys is a well restorated Tek 7104 (analog), with 7A29 plugins and active probes.

greetings
Martin

« Last Edit: May 14, 2016, 07:27:14 am by Martin.M »
 

Offline G0HZU

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Re: New lab: Oscilloscope bandwidth
« Reply #9 on: May 17, 2016, 12:22:34 am »
When I started out the three basic items you wanted (for ham/CB servicing) were a scope a sig gen and a frequency counter.

The scope would ideally be a 100MHz model that would hopefully still  'see' 144MHz signals. My first scope was a big old Tek 585 and it was a wonderful old scope and was very useful for all kinds of ham related work as it could still display 144MHz signals quite well but at reduced amplitude. I wouldn't recommend the 585 to anyone today because it is too big and old, the display area on the CRT is very limited and it makes a LOT of fan noise but I would recommend getting a fairly decent 100MHz analogue scope for ham related stuff.

You shouldn't have to pay more than about £50 for such a scope. With luck you can probably get one for free or for much less than £50. You should also get a modern DSO (eg Rigol) for general electronics work but the old analogue scopes are still king (IMO) for any casual monitoring of old school/classic ham transmissions.



« Last Edit: May 17, 2016, 12:26:32 am by G0HZU »
 

Offline AF6LJ

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Re: New lab: Oscilloscope bandwidth
« Reply #10 on: May 17, 2016, 12:56:08 am »
I go along with the communications test set as an essential for RF work. For the money you get several pieces of test gear, some of them even have built in basic spectrum analyzers such as ones made by HP and IFR.
An RF millivolt meter is also a must especially if you can get one with all the accessories such as a 10X divider, a 50 ohm head for the probe and whatnot.
As far as scopes go, I have gotten along just fine with a 100MHZ scope (Tek 466)
Sue AF6LJ
 

Offline mojoe

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Re: New lab: Oscilloscope bandwidth
« Reply #11 on: May 17, 2016, 04:50:39 pm »
I'll second or third the recommendation of a communications analyzer, or "service monitor" to the old timers. I find one very useful for Amateur Radio and electronics hobby purposes. Among other functions, you get a spectrum analyzer with tracking generator. Not as wideband as a standalone S.A., but still very useful by itself (even more so if you add a return loss bridge).

Contact Amtronix and see if he has any HP E8285A units available. They are a bit large, but will do all the usual stuff that other C.A.'s do. He was selling them for just under $1000. I had one until recently, when I upgraded to the HP 8920B.

If you go the E8285A route, make sure to get one from Amtronix. Only early serial numbered units can cover HF. These also require a particular firmware. Amtronix also does a calibration. It's a good deal.

You might also consider the E6380A, which Amtronix also sells. See here for a comparison: http://www.amtronix.com/diff.htm

One additional comment: For radio and antenna work, I very seldom use an oscilloscope. I use the 'scope more for non-radio purposes.
« Last Edit: May 17, 2016, 04:54:34 pm by mojoe »
 


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