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Author Topic: O-Scopes as Station Monitors  (Read 3076 times)
W3AGT
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« on: February 21, 2013, 11:00:18 PM »

Recommendations for NEW low dollar (sub $500.00) QUALITY oscilloscopes that could be used as a station monitor? I prefer to buy American if at all possible.
Thanks
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KA4POL
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« Reply #1 on: February 21, 2013, 11:44:13 PM »

It very much depends on frequency and power level. So please fill us in.
For starters see: http://www.eham.net/ehamforum/smf/index.php?topic=34312.0 and http://www.youtube.com/watch?v=y4Zt_LJX1Tc

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KA1BIN
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« Reply #2 on: February 21, 2013, 11:46:59 PM »

There should be a few models under $500 dollars that will indeed meet your requirements. The problem will be of finding a US made Oscilloscope. Only company I know of is Tektronix in Beaverton, but they sure don't make anything that I know of anywhere near $500.00, maybe $1500, but not $500.

The days when RCA, GE, BK Precision, and a dozen other US manufactuers made test equipment in the USA are long gone, by decades.

Steve
KA1SMC
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KA4POL
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« Reply #3 on: February 22, 2013, 12:13:56 AM »

I wouldn't go with mandatory NEW scope anyway. I got a Tek 485 which does pretty well what I need.
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NK7Z
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« Reply #4 on: February 22, 2013, 05:46:18 AM »

Recommendations for NEW low dollar (sub $500.00) QUALITY oscilloscopes that could be used as a station monitor? I prefer to buy American if at all possible.
Thanks
Hi,

I am considering the same thing...  However I am not looking at 500 buck scopes...  Anything with 50 MHz range should do, and they can be had on eBay for less than 500 bucks... 
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
WA3SKN
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« Reply #5 on: February 22, 2013, 06:17:16 AM »

There are plenty of good scopes out there in the $500 range, but not US made.
And the easiest set up is to monitor your transmitter, at least for HF use.
Right now there is probably interest in monitoring the receive IF, a little more difficult to do.  And there are plenty of other uses for a scope.  I would, however, get one with lots of bandwidth... a limitation for early scopes on the used market.
But for $500, you can go to E-Bay and get a REAL spectrum analyzer that can be even more useful.  So you need to decide just what you will be using the scope for before investing!
73s.

-Mike.
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AA4PB
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« Reply #6 on: February 22, 2013, 08:11:46 AM »

I have a scope but it's on the work bench rather than hooked up as a station monitor. Your signal has to have a whole lot of distortion in order to see it on an o-scope while operating SSB voice. Normally you check a transmitter with a scope by using a dummy load and two-tone test signal.
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W5CBO
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« Reply #7 on: February 22, 2013, 09:28:29 AM »

You can get a decent used Tektronic scope for around $120 and then check out Preciserf.com which advertises here on Eham.They make what you need to couple the radio/amp etc to the scope so you can monitor your signal.

Your other choice would be to check ebay for a Kenwood SM220 station monitor.

Have fun.
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W3AGT
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« Reply #8 on: February 22, 2013, 11:43:53 AM »

I'm running a barefoot Yaesu FT-950 (100 Watts).

I would like to monitor and check my transmitted signal on AM/FM, CW, SSB and digital modes like PSK.

I have found the Yaesu YO-101 and Kenwood SM220/230 station models for sale on EBay and QRZ.

None of the sellers can say with any certainty that they would work with my FT-950.

I suspect the Kenwood series, which also function as an O-scope, with an RF sampler would work but it seems a waste of the band monitoring features. I can use the Spectrum Labs analyzer and HRD for my limited bandscope needs.

I have received recommendations that I should look for an O-Scope with bandwidth anywhere from 50 Mhz to 300 MHz. Of course the greater bandwidth the more $$$. Any thoughts on how much bandwidth I should be looking for to monitor transmissions on 160 to 6 meters?

I understand the reality of foreign made vs domestic. I just like to buy American every chance I get.

I have watched all of w2ew's fantastic videos on YouTube and visited his site.

Thanks to all for taking the time to respond to my post. Much appreciated.

Al
W3AGT
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W2AEW
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« Reply #9 on: February 22, 2013, 01:16:38 PM »

I also posted this in response to your similar question in the QRP forum...

For a station monitor, it really is quite hard to beat an analog scope.  Most of the inexpensive digital scopes don't have the refresh rate to create a decent RF envelope display, and many will often alias the RF signal when using the lower horizontal time scales that are necessary for typical phone RF monitoring.  Some will have display modes (such as peak detection) that will help, but you wind up with a very monochromatic envelope which doesn't have the same look, feel, and "value" that the old analog display has.  I don't have access to any of the modern inexpensive DSOs, so I can't give you a first hand recommendation.

To get an idea of what a typical analog scope will give you for station monitoring, check out this quick video:
http://www.youtube.com/watch?v=2D83xp3H5Bo

I'm sorry if this doesn't directly answer your question, but unfortunately I don't have a way of evaluating the new/cheap DSOs in this application.  My 10yr old TDS2000 does an OK job, but not nearly as nice as any of my old analog scopes when used as a station monitor.
« Last Edit: February 22, 2013, 02:00:47 PM by W2AEW » Logged

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K2GWK
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« Reply #10 on: February 26, 2013, 05:16:53 PM »

IMHO an oscilloscope is not an ideal station monitor as it works in the time domain and will only show you one frequency. The lower cost scopes generally do not have a FFT option which will allow your scope to make measurements as a limited dynamic range spectrum analyzer. The spectrum analyzer will enable you to see any harmonics, intermods or spurious that you will not be able to see in the time domain with your oscilloscope. I have seen some PC RF spectrum analyzers on the market for about a $1000 and I think they would be a better investment.

Guy (K2GWK)
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W2AEW
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« Reply #11 on: February 27, 2013, 08:13:35 AM »

IMHO an oscilloscope is not an ideal station monitor as it works in the time domain and will only show you one frequency. The lower cost scopes generally do not have a FFT option which will allow your scope to make measurements as a limited dynamic range spectrum analyzer. The spectrum analyzer will enable you to see any harmonics, intermods or spurious that you will not be able to see in the time domain with your oscilloscope. I have seen some PC RF spectrum analyzers on the market for about a $1000 and I think they would be a better investment.

Guy (K2GWK)

Agreed, in general.  Just to clarify, the scope doesn't show ONE frequency as you stated, it will show the envelope of all the frequency content that is within the BW of the scope.  In this view, it's certainly true that you cannot see harmonics, distortion products, spurs, etc.  hower, it is still useful to spot gross errors in setup, examination to see if you're reaching full PEP, etc.  A scope FFT is of some limited use, but your subject to long acquisition times if you want good frequency resolution, so the result is less "lively", and you have to be careful of the limited dynamic range of the scope showing you spurs and distortion components that are the created in the scope vs the radio. Cheap DSO's FFTs are surprisingly bad with this.
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K8AXW
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« Reply #12 on: February 27, 2013, 08:58:04 AM »

Alan:  The SM-220 (which I have) is used for viewing CW and SSB signals.  On CW one can see the envelope waveform which including leading edge spikes, etc. 

On SSB, the signal waveform in the shape of horizontal "Christmas trees."  As I understand it this is a pretty good indicator of linearity and modulation level.

What circuitry would be necessary to add to the typical analog O'scope to provide this same type of monitoring?

I think this is going to be the next question asked after AGT's original question.

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W2AEW
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« Reply #13 on: February 27, 2013, 09:45:16 AM »

Alan:  The SM-220 (which I have) is used for viewing CW and SSB signals.  On CW one can see the envelope waveform which including leading edge spikes, etc. 

On SSB, the signal waveform in the shape of horizontal "Christmas trees."  As I understand it this is a pretty good indicator of linearity and modulation level.

What circuitry would be necessary to add to the typical analog O'scope to provide this same type of monitoring?

I think this is going to be the next question asked after AGT's original question.



In many cases, no additional circuitry is needed at all!  You can sometimes simply wrap a bit of hookup wire around the outside of the coax and connect it to the scope input and get enough RF pickup to see the envelope similar to what the SM220 is showing you.  In the video that I linked in my early reply (http://youtu.be/2D83xp3H5Bo), you can see a couple of examples of RF samplers you can use, or even how to use an unused port on a tuner as a "sampler" to get a small sample of the RF signal to the scope.  Easy.  Even if you have a low BW scope, it will often still have enough response at higher frequencies to show you the envelope.

Station monitors like the SM220 use a slightly different trick to get the RF coupled to the scope.  They don't use any part of the vertical input or vertical amplifier channel.  They simply use the fact that the vertical deflection plates in the CRT form a small value capacitor.  Then, they simply use a small cap to couple the RF directly to the deflection plates.  In effect, the series combination of this capacitor and the deflection plate capacitance form a simple capacitive voltage divider, whose response is largely frequency independent over the HF frequency range.  Years ago, I had an old B&K scope that had connections to the deflection plates available on the back panel, and I made a simple station monitor out of it with a single capacitor connection to the center of the coax.
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W3AGT
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« Reply #14 on: February 27, 2013, 10:33:58 AM »

I'm just sitting back and taking in all this great feedback.

I think I'm going to go for the o-scope with either direct or indirect sampler.

I just have to find one smaller than a Samsonite carry-on for sale.

The size of the older analog o-scopes would require me to build a shelf below my current operating table or design a new table entirely.

Thanks to all who have joined in with your perspectives and advice.

Allen
W3AGT
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