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 Post subject: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Wed 11, 2017 9:36 pm 
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Help Please.

Has anyone done an FM alignment using the S curve with a newer Smart Digital Storage Oscilloscope? I have an Owon DS7102V 100mHz and using an Eico 369 Sweep Generator. This is my scope with with the Eico set up in the test mode with the RF cable, Detector assembly and Demod cable used withe the Eico. Set with No sweep at 10.7mHz, Trace size Max, Marker size Max. and a 10.7mHz crystal installed in the Eico369. As you can see in the X-Y Mode the Horizontal top and bottom is just a mess of dots even when I change the Display Type to Vector instead of dots. And the only way to get a marker I can see is with Persist set to a minimum of 2 seconds. Pic shows infinity just to take a photo.

Attachment:
Marker pic.JPG
Marker pic.JPG [ 98.64 KiB | Viewed 601 times ]


All the older scopes show a nice smooth Horizontal line with nice pips for the marker. I don't know how I could ever do an alignment on a FM stage and use the S curve figure/technique let only even the visual peaking method with this scope. Ready to use this for everything else and buy a old 30mHz scope just to do alignment with.

Please any help would be appreciated and would save me some money.

Jim


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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Wed 11, 2017 10:33 pm 
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Unfortunately, there is not a lot that you are going to be able to do about that. Digital oscilloscopes do not work very well in X-Y mode. An old analog Tek is going to work much better for you in this application. Even my high-end digital oscilloscope, a Tektronix TDS-3034B, gives a display similar to what you are seeing in X-Y mode. There are a couple things you can try to make it a bit better through:

1) Decrease the bandwidth. I have never used a 'Won' oscilloscope, but at least some of the nicer Tek's have a way of reducing the bandwidth to reduce the noise.

2) Try adjusting the sampling rate. Again, I don't know how this works on a 'Won' but on at least some of the Tek scopes, in X-Y mode the sec/div knob instead adjusts the sampling rate. You can adjust it to see if you can optimize the display.

3) Add a filter. A lot of the noise you are seeing may be from high frequency noise. Try building a simple RC filter to connect between the detector in the receiver and the oscilloscope.

4) Get an analog oscilloscope. It really is the right tool for the job in this case... :(

-Matthew

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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Wed 11, 2017 10:44 pm 
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The main problem here is that there is a lot of noise in the signal. Two things to try:

1. Does your scope have built in low pass filtering? Reduce bandwidth to around 1 kHz to 10 kHz, and should take out a lot of this noise. If not, try building your own little RC filter that you add to the input of your scope. Start with something like a 100 K resistor in series, and a .01 uF capacitor across the scope input. The bigger the values of R and C, the less noise you'll see, but if they get too large, you will start filtering out the S-curve you're trying to see, or causing a time delay in it, which you also don't want.

2. What sweep speed are you using? You want to go fairly fast, like 60 Hz. If you go too slowly, you'll make the noise worse, and you may have some AC coupling somewhere in the system that kills off the amplitude of the X curve itself if you go too slowly.

Check to see if you can make your signal a little bigger -- that will also help with noise.

I see Matthew answered more quickly than I did, but you can see we're thinking similarly.

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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Thu 12, 2017 12:25 am 
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Mathew and Tom,

Thank you for the quick reply. I will try the RC network tomorrow. I have tried HF and LF reject on scope and it didn't do anything. Bandwidth with the horiz input channel which is set to to the sweep gen 60 Hz signal just changes the width of the signal or display. Off to work.

Jim


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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Thu 12, 2017 1:44 am 
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Do you have a fluorescent or LED light on you workbench?

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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Thu 12, 2017 2:15 am 
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FStephenMasek wrote:
Do you have a fluorescent or LED light on you workbench?

Yep, both, had my work area dark and everything unplugged except scope and sweep generator, no difference. I swear it's a local fm station because the scope picks up noise at around 45MHz and 90MHz. Albeit the 45 is probably the harmonic. Closest station is 90.9.


Jim


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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Thu 12, 2017 2:29 am 
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If I was going to purchase an analog scope for alignments would a 30 MHz be adequate or should I opt for the 50 MHz?


Jim


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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Thu 12, 2017 2:39 am 
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jgross wrote:
I have tried HF and LF reject on scope and it didn't do anything.


The HF and LF reject are often in the scope sync system, and do not apply to the actual displayed waveform itself. Sometimes the scope will sync better on certain kinds of pulses if the high frequencies or low frequencies are rejected by the sync system. So these don't take the place of a low pass filter on the input (if indeed your HF and LF reject are only for the sync).

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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Thu 12, 2017 2:42 am 
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Tom Albrecht wrote:
jgross wrote:
I have tried HF and LF reject on scope and it didn't do anything.


The HF and LF reject are often in the scope sync system, and do not apply to the actual displayed waveform itself. Sometimes the scope will sync better on certain kinds of pulses if the high frequencies or low frequencies are rejected by the sync system. So these don't take the place of a low pass filter on the input (if indeed your HF and LF reject are only for the sync).

Now that you mention it I do think it is only on the trigger menu popups.

Looking at a Tektronix 2225, only thing it doesn't have is time delay.

Jim


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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Thu 12, 2017 2:59 am 
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For sweep alignment, the bandwidth of the oscilloscope is of no consequence at all. 1MHz would be perfectly fine. The scope is displaying the demodulated output from the radio or TV, not the actual RF or IF frequency signal. The actual repetition rate of this demodulated signal is typically only 60Hz. What is important is that the oscilloscope you choose has an X-Y mode and that it has enough horizontal gain in X-Y mode. I generally recommend a Tektronix 465 since they are cheap, reliable, and easily repairable since they don't use custom ICs. For what it is worth, I use a 422 but it doesn't have quite enough horizontal gain in X-Y mode for some sweep generators.

Matthew

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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Thu 12, 2017 3:14 am 
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7jp4-guy wrote:
For sweep alignment, the bandwidth of the oscilloscope is of no consequence at all. 1MHz would be perfectly fine. The scope is displaying the demodulated output from the radio or TV, not the actual RF or IF frequency signal. The actual repetition rate of this demodulated signal is typically only 60Hz. What is important is that the oscilloscope you choose has an X-Y mode and that it has enough horizontal gain in X-Y mode. I generally recommend a Tektronix 465 since they are cheap, reliable, and easily repairable since they don't use custom ICs. For what it is worth, I use a 422 but it doesn't have quite enough horizontal gain in X-Y mode for some sweep generators.

Matthew

Thank you for the advice. Does clear up a lot of questions I had.

Jim


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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Thu 12, 2017 9:24 pm 
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Matthew and Tom,

Tried that RC network on both inputs of scope coming from the Eico 369. No Joy. Still there. Did some further troubleshooting. Turned off all lights and power strips one by one, until all that was plugged in was the Sweep Generator, the Owon scope can run on an internal battery. Still there. So then I used the scope on battery power connected to nothing and found three things giving interference in my work area.

1. LED light (random weird noise on trace)
2. Combination Variac-Isolation transformer (60 cycle of around 20 mV)
3. FM signal broadcast at 90.9MHz (also 20 mV on trace) Got lucky here because station had dead air for just long enough for scope to lock on frequency.

I should mention I can eliminate 1 and 2 but not 3. Could try an FM trap but I think it would reduce signal to a point it would not be usable. Even with the elimination 1 and 2 the trace still looked the same on the X-Y function. Plus when I used the RC network the signal became all distorted and the 10.7MHz marker was gone. I am just going to buy a GW Intek 6112 100MHz scope for under $100 and see what I get. That way I don't break the bank on a gamble.

Jim


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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Thu 12, 2017 10:00 pm 
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FWIR the EICO outputs a sync saw tooth that should have sufficient amplitude to trigger a horizontal event in the SDS. If that is so, then a scope demodulator probe connected to the vertical of the SDS will give the amplitude of the response of the IF's when triggered by the EICO. Set sweep rate for 60 hz.

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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Thu 12, 2017 10:22 pm 
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Jim -
As I said before this is a really common problem with digital oscilloscopes in X-Y mode. First, for reasons that I don't fully understand, the noise floor of a digital oscilloscope is typically much higher than an analog model. In Y-T mode this noise only shows up in the vertical direction but in X-Y mode it shows up in both directions. Second, a digital oscilloscope can't collect and display data continuously. The way that they work is that they collect one sweep worth of data and store it in special high-speed memory. The CPU then downloads this data to regular memory and displays it on the screen before repeating the process. This means that there is "dead time" in the acquisition system which can cause aliasing effects in X-Y mode. For comparison, an analog oscilloscope has no such problem - the horizontal and vertical position of the trace is directly proportional to the X and Y inputs. Third, an oscilloscope, digital or analog, with higher bandwidth will necessarily be more susceptible to high frequency noise. Some models allow you to reduce the bandwidth for this reason, but it appears that yours doesn't have this feature.

In short, doubt that you will do much better with your digital oscilloscope.

-Matthew

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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Thu 12, 2017 10:27 pm 
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Chas wrote:
FWIR the EICO outputs a sync saw tooth that should have sufficient amplitude to trigger a horizontal event in the SDS. If that is so, then a scope demodulator probe connected to the vertical of the SDS will give the amplitude of the response of the IF's when triggered by the EICO. Set sweep rate for 60 hz.

The picture above is with the test detector circuit and cables in the Eico manual with scope in X-Y mode. Using the horiz. output of sweep gen for 60 Hz. Perfect 60 Hz sine wave.

Jim


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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Thu 12, 2017 10:28 pm 
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7jp4-guy wrote:
Jim -
As I said before this is a really common problem with digital oscilloscopes in X-Y mode. First, for reasons that I don't fully understand, the noise floor of a digital oscilloscope is typically much higher than an analog model. In Y-T mode this noise only shows up in the vertical direction but in X-Y mode it shows up in both directions. Second, a digital oscilloscope can't collect and display data continuously. The way that they work is that they collect one sweep worth of data and store it in special high-speed memory. The CPU then downloads this data to regular memory and displays it on the screen before repeating the process. This means that there is "dead time" in the acquisition system which can cause aliasing effects in X-Y mode. For comparison, an analog oscilloscope has no such problem - the horizontal and vertical position of the trace is directly proportional to the X and Y inputs. Third, an oscilloscope, digital or analog, with higher bandwidth will necessarily be more susceptible to high frequency noise. Some models allow you to reduce the bandwidth for this reason, but it appears that yours doesn't have this feature.

In short, doubt that you will do much better with your digital oscilloscope.

-Matthew

Yep in some ways the SDS is nice but for this, not so great. Thanks.

Jim


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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Thu 12, 2017 11:30 pm 
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jgross wrote:
Chas wrote:
FWIR the EICO outputs a sync saw tooth that should have sufficient amplitude to trigger a horizontal event in the SDS. If that is so, then a scope demodulator probe connected to the vertical of the SDS will give the amplitude of the response of the IF's when triggered by the EICO. Set sweep rate for 60 hz.

The picture above is with the test detector circuit and cables in the Eico manual with scope in X-Y mode. Using the horiz. output of sweep gen for 60 Hz. Perfect 60 Hz sine wave.
Jim
Hmm, let me say this a different way. The output from the port on the EICO marked 'scope is a sawtooth wave. If this sawtooth is input into the "X" input of the scope it should sweep the scope. The trigger for this sawtooth is the leading edge, adjusting the trigger for the scope on the horizontal should keep it in step. The generators signal output follows this sawtooth which represents frequency as set on the EICO controls. The vertical input of the scope goes to a detector probe the creates a vertical pip on the scope screen. So as the rf signal goes up/down the sweep bandwidth the pip follows the gain of the circuits making the familiar pattern. The detector probe is connected to the IF of the receiver, and the RF signal at the mixer. Either connection subject to radio manufacturers recommendations.

I have used a vintage Precision sweep generator and an EICO analog scope, about 1 mhz input to do this task. I used an outboard RF generator to make a variable marker, injected via a ten turn loop simply dropped into the chassis.
I do not own a "modern" scope, I have seen modern scopes no longer have a switch position and an input for external trigger. However, they should trigger with a sawtooth, however, it could be a TTL trigger...

Sorry if I got confused...

Chas

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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Fri 13, 2017 12:10 am 
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Chas wrote:
jgross wrote:
Chas wrote:
FWIR the EICO outputs a sync saw tooth that should have sufficient amplitude to trigger a horizontal event in the SDS. If that is so, then a scope demodulator probe connected to the vertical of the SDS will give the amplitude of the response of the IF's when triggered by the EICO. Set sweep rate for 60 hz.

The picture above is with the test detector circuit and cables in the Eico manual with scope in X-Y mode. Using the horiz. output of sweep gen for 60 Hz. Perfect 60 Hz sine wave.
Jim
Hmm, let me say this a different way. The output from the port on the EICO marked 'scope is a sawtooth wave. If this sawtooth is input into the "X" input of the scope it should sweep the scope. The trigger for this sawtooth is the leading edge, adjusting the trigger for the scope on the horizontal should keep it in step. The generators signal output follows this sawtooth which represents frequency as set on the EICO controls. The vertical input of the scope goes to a detector probe the creates a vertical pip on the scope screen. So as the rf signal goes up/down the sweep bandwidth the pip follows the gain of the circuits making the familiar pattern. The detector probe is connected to the IF of the receiver, and the RF signal at the mixer. Either connection subject to radio manufacturers recommendations.

I have used a vintage Precision sweep generator and an EICO analog scope, about 1 mhz input to do this task. I used an outboard RF generator to make a variable marker, injected via a ten turn loop simply dropped into the chassis.
I do not own a "modern" scope, I have seen modern scopes no longer have a switch position and an input for external trigger. However, they should trigger with a sawtooth, however, it could be a TTL trigger...

Sorry if I got confused...

Chas

Chas,
Appreciate the response. I understand your comments completely. I probably should of been more clear about the subject. The pic is a test signal from the Eico 369 which is used for adjusting the phase control properly, on the back of the generator. The manual shows nice crisp focused horizontal traces with vert line pips for the markers across the sweep or bandwidth. My new SDS scope has nothing but a thick band of dots and a cat eye shape for the marker with the test signal. I was concerned that using this scope I would not get a good visual representation of the S curve and 10.7 MHz marker. According to Matthew and Tom this scope is actually showing noise. Do to the inherent design of the scope.

There is another post in the test equipment area of a guy who refurbished an Eico 369 and he was using an analog scope and had the nice crisp trace. And all the you tube vids I have seen with the FM alignment and sweep gen were using an analog scope.

Jim


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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Fri 13, 2017 12:42 am 
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Jim,

I am sorry that the new scope does not work out. I was thinking it was a just a matter of hookup...

Chas

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 Post subject: Re: FM Alignment with New SDS Oscilloscope Problem!!!!
PostPosted: Jan Wed 18, 2017 3:39 am 
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7jp4-guy wrote:
Jim -
As I said before this is a really common problem with digital oscilloscopes in X-Y mode. First, for reasons that I don't fully understand, the noise floor of a digital oscilloscope is typically much higher than an analog model. In Y-T mode this noise only shows up in the vertical direction but in X-Y mode it shows up in both directions. Second, a digital oscilloscope can't collect and display data continuously. The way that they work is that they collect one sweep worth of data and store it in special high-speed memory. The CPU then downloads this data to regular memory and displays it on the screen before repeating the process. This means that there is "dead time" in the acquisition system which can cause aliasing effects in X-Y mode. For comparison, an analog oscilloscope has no such problem - the horizontal and vertical position of the trace is directly proportional to the X and Y inputs. Third, an oscilloscope, digital or analog, with higher bandwidth will necessarily be more susceptible to high frequency noise. Some models allow you to reduce the bandwidth for this reason, but it appears that yours doesn't have this feature.

In short, doubt that you will do much better with your digital oscilloscope.

-Matthew

Matthew,

You were right. Found the correct menu and button to push for a reduced bandwidth on this Owon SDS scope. Reduced it to 20M bandwidth. This is the S curve with no marker. Still have the analog scope on the way, so am going to compare when it gets here.
Attachment:
S Curve no marker.JPG
S Curve no marker.JPG [ 30.4 KiB | Viewed 355 times ]


Jim


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