suitable scope to use for RF work

[vk6zgo]

Alm,

Basically I think we probably agree. Absolutely if you can have 4GS/s oscilloscope and a wideband spectrum analyser - fantastic. From where I am coming from, I just hate the idea of not trying something because you don't have the right equipment. When you have to do something and you don't have the right specialized piece of equipment - you have to be creative and that's fun.

I bet the person who designed the first spectrum analyzer would have loved to have a  .... spectrum analyzer.

Richard.

He probably has a Selective Millivoltmeter!
Seriously,though,Selective Milli (& micro)voltmeters were widely used at up to UHF frequencies,& you may be able to pick one up.
VK6ZGO

[amspire]

Seriously,though,Selective Milli (& micro)voltmeters were widely used at up to UHF frequencies,& you may be able to pick one up.
VK6ZGO

You have convinced me. I want one.

As long as you don't tell me the good ones weigh about 50 KGs and use up half the bench.

Richard.

[joelby]

Well, here you go!

Unfortunately I don't quite have all the bits available to do this properly, but I did the following:

HP 8922S in CW (signal generator) mode.

Rigol DS1102E with 10x probe and ground spring, stuck in the 8922S IF output port. Equivalent time was used, though there seems to be a bug in my Rigol where stopping acquisition (to save the waveform image) reverts to normal acquisition mode. This completely messed up the 433 MHz reading, so I took a photograph instead.

Signal generator set to -10 dBm at 100, 200, 300, and 433 MHz.

So yes! You should be able to see something, even with some pretty horrible mismatches, and as long as you use equivalent time sampling and your signal has a CW carrier.

[Mechatrommer]

thanx for the picture joelby. i wish i have that kind of generator.
but maybe a stupid question... why -10dBm? why not 0dBm?
assuming the generator is flat, you are showing around -3dB attenuation at each 100MHz interval.
and assuming the dso is speced as -3dB@100MHz, the signal coming out of the generator is somewhere 0.7Vpp.

[Zero999]

Obviously,a Spectrum Analyser would be nice,but it may be outside your budget.

He didn't say what his budget is.

I've found a cheap Chinese spectrum analyser on ebay. Whether it's any good oor not is another thing but it'll almost certainly be better than an oscilloscope of the same price. It covers 150kHz to 1050MHz. If you need to go below 150kHz then try the FFT on the Rigol or your PC sound card. If you need to go above 1GHz then you need to spend serious money.
http://www.ebay.co.uk/itm/ATTEN-AT5010-Spectrum-Analyzer-150-KHz-1G-Hz-/220847258416?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item336b85bb30
 

As far as Oscilloscopes go,I would suggest you look around for an analog 'scope,as you may be able to get a 400MHz one reasonably cheaply.
Unless your sinewave is severely mangled,the level of any harmonics above the 3rd, probably won't be too high so 400MHz BW would be fairly useful.
If you already have a DS1052e,then try it & see what happens.

If he already has the DS1052E he should hack it to 100MHz.

[Mechatrommer]

i've been eyeing on that Atten SA. since 400MHz was(is) my interest, then a 4GHz is more suitable for the job. The cheapest, if i got money, i'll get back to this USB Signal Hound SA
(i know i know, its USB. i heard ya. one should get the more proper standalone with LCD SA which cost many thousands. and there's DIY SA link here if you search and powerful enough to build one)

[joelby]

thanx for the picture joelby. i wish i have that kind of generator.
but maybe a stupid question... why -10dBm? why not 0dBm?
assuming the generator is flat, you are showing around -3dB attenuation at each 100MHz interval.
and assuming the dso is speced as -3dB@100MHz, the signal coming out of the generator is somewhere 0.7Vpp.

I didn't want to run the signal generator at higher output powers without 50 Ohm termination and I don't have a feed-through terminator.

The Atten spectrum analysers don't have very great reviews. The Signal Hounds barely have any reviews at all! If you keep an eye on eBay you should be able to get something second hand and considerably better (3 GHz) for not much more.

I actually picked up the HP 8922S at a garage sale for $500. It's a 1GHz spectrum analyser, signal generator, and frequency counter, and a GSM base station.

[Mechatrommer]

If you keep an eye on eBay you should be able to get something second hand and considerably better (3 GHz) for not much more.

even if i get it for free. shipping will cost me the same as the new atten SA or more. even the "for parts" SA is not free.

[alm]

Is the output level and purity of your generator specced for high-impedance loads? Because most have to be terminated into their characteristic impedance to meet their specs. Reflections and standing waves can screw up these kinds of measurements. I would use feed-through terminators for these measurements. 433MHz is actually approaching the limit of these feed-through terminators, the capacitive stub formed by the scope input becomes a problem. Which is why 400MHz scopes tend to have real 50 ohm inputs.

[Mechatrommer]

agree with alm. a flat generator can be seen as non flat by the dso if unterminated properly. anything longer than 17cm is enough to make a perfect reflection on this 400MHz signal. but i think joelby's point is not about accuracy.

[jason695]

thanks for your reply everyone, very interesting information thanks. i might be slightly late putting this on no but, going right back to the start of this blog .

on a suitable scope for 100mhz sinusoid LOL.

im not sure if what im about to say is wright but here goes anyway.

im just trying to observe the fundamental at 100mhz

if i had a 100mhz analogue scope, this isnt good enough to see all the harmonics on a 100mhz fundamental sinusoid.however, wouldnt its front end filters just act as a harmonic filter itself and id just be left with fundamental. obviously theres attenuation of 3db. isnt this ok with about 1 volt amplitudes.

can anyone please provide screen shots of a 100mhz scope observing a 100mhz fundamental sinusoid thats got harmonics on it.

oh yes lastly im trying to build these bjt single transistor oscillators. they all work at 100mhz easily. im trying to get one to work at 27mhz at its proving very hard. can anyone help me with a schematic for a 27 mhz bjt oscillator (preferablt colpitts type but, any will do).


regrads and thanks everyone.
jason

[alm]

Attached are some screenshots. The signal is a ~100MHz square wave (plenty of harmonics) with a specified rise time of <= 1 ns. The first screenshot is from a 500MHz/5GS/s scope, and shows a decent square wave with mainly odd harmonics, as expected for a square wave. The internal 50 ohm termination was used. The cursors indicate the ~100MHz and 1GHz point in the frequency domain.

The monochrome screenshots are from a 100MHz/1GS/s scope, with similar time base / vertical attenuation settings. An external feed-through terminator was connected to the scope's input. In the time domain, it looks pretty much like a sine to me. In the FFT, only a few harmonics are even present, and the third harmonic is at -30dB, as opposed to -10dB on the 500MHz scope. The fifth harmonic is near -20dB on the 500MHz scope (note that this is likely even a few dB down), but something like -55dB on the 100MHz scope, and only above the noise floor because I turned on averaging.

[vk6zgo]

Seriously,though,Selective Milli (& micro)voltmeters were widely used at up to UHF frequencies,& you may be able to pick one up.
VK6ZGO

You have convinced me. I want one.

As long as you don't tell me the good ones weigh about 50 KGs and use up half the bench.

Richard.

You've nailed it!
Yes they are very large !--but so was most of the test equipment of the time!

VK6ZGO

[jason695]

Alm, thanks for the screenshots.

so what do you think, on a 100mhz,1gs/s dso do you think id get the fundamental of 100mhz sine if it has harmonics it?

& similarly & probably better, dya think i'll get the 100mhz sine fundamental with 100mhz analogue scope then?

also anyone know anything on oscillators, i need a 27mhz.



lastly, to see the harmonics, cheap chinese spec analyser say ATTEN AT5010 Spectrum Analyzer 150 KHz to 1G Hz. what does anyone think to spec:-

http://www.ebay.com/itm/ATTEN-AT5010-Spectrum-Analyzer-1050MHz-/220751214997

thanks all
jason

[DaveW]

To have a point of comparison, I borrowed a 433MHz radio from shl876, and probed it using a 1.5GHz passive probe on a 4GS/s, 1GHz Agilent 7000 and on a Rigol DS1102E (not modified), both the screenshots are set to AC coupled mode, and I've set the cursors to check it's the actual signal

[amspire]

Dave,

Did you put the Rigol in Equivalent sampling mode?  If it is not, there is no way it can properly show a 433MHz waveform.

Richard.

[tinhead]

i've been eyeing on that Atten SA. since 400MHz was(is) my interest, then a 4GHz is more suitable for the job.

i consider buying one of the new ATTEN SAs, AT5010D or AT5030D.

They have 7" TFT screen and tracking generator, so it will be (well, not really) good replacement for my old HP 8590,
but it will at least not wake-up my neighborhoods nor drive power plant down while booting...

ATTEN have other nice RF equipment too, e.g. AT8010D which is actually a clone of R&S SMX/SMY?
Somethign like that, a guy from China told me this, no idea if this is truth or just misinterpretation of front panel design.

[Mechatrommer]

Did you put the Rigol in Equivalent sampling mode?  If it is not, there is no way it can properly show a 433MHz waveform.

yea, me curious. how can that signal looks nice on rigol? (even if aliasing is clearly seen, near nyquist sampling). maybe its sincx turned ON? my 433MHz is just triangle shape.
and wait. if i'm not wrong, rigol showing greater magnitude? 700mVpp @ 500mV/div vs Agilent 80mVpp @ 200mV/div? are you ok Dave?