Tuning a bandpass filter using a signal generator and oscilloscope
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- Опубліковано 30 вер 2019
- Using a signal generator with a sweep function and the oscilloscope I show how to tune an RF circuit.
I build a "de-mod" probe detector circuit to transform the wave envelope into a voltage trace. I show how to inject a marker signal to confirm the frequency point on the scope screen.
Finally! Someone showing what you can do practically with these tools. I'd love to see more "around the house and garage" uses for these devices. Please make more of these type of videos sir. Thank you.
Marvellous video ,Back in the 70's we used a device called the Wobbulator, which I still use today on radios 73 Paul
Wow that marker trik in the end is gold
Thanks to the movie with your beautiful description, please love the schematic of the above filter design for practical testing.
I enjoyed your video, and like your teaching and reasoning. We all know what you mean when you said you used "eye in 3,4 diodes" but beginners may not. They are actually 1N34 diodes. not " i " (eye)N34. you can also use 1N914 diodes as they are redily available. not as sensitive as the 1N34 type. The 1N34 type are germanium as you said and they have a forward bias of .2 to .3 volts wheras silicon 1N914 diodes need .7 volts. I've used silicon diodes in this circuit too. 1N34 is best. I enjoy watching how others do things. So keep doing what you are doing, its great info!
Very well done .. I learned couple of new tricks from this video. Thank you for this.
Great video, thank you for teaching us.
Great video , Very informative 👍
Cool video. I would have never thought to use a AWG and a scope to tune a filter. I was looking for tips on using a VNA to tune filters and stumbled into this.
How about it: I too was looking at VNA or Spectrum Analyzer/tracker and then I came here for enlightenment. The demodulator was the missing link for me (not that I couldn't bear looking at all the HF!)
Great video
GREAT video.
Very nice video. I cannot afford the nice generator you have....But I found one for half that price from Koolertron on Amazon. I learned a lot from your video about needing a SYNC pulse to trigger the 'scope and I never knew that the signal needed to to be DEMODulated to view the bandpass. I'm aligning an old Tube transceiver and there are filters needed to be checked for bandpass.
Thanks for the video. Very interesting. 👍
Absolutely agree with @Totally Unfiltered! One of the most useful videos I've ever seen. THX, DX de HA5CST
Really useful, thanks!
Thanks
Awesome
very nice video. i bet that signal gen does noise. i often measure filters with noise input and send output to a sdr radio and the sdr software FFT lets me see the filter shape. alot of scopes now days, also have an FFT function. often found in the math menu.
That's i was looking for!!! thanks for your usefull video! i was familiar using tracking generators in addition on spectrum analizer. it could be interesting to see if you can compare your measure with a tracking generator and spectrum analizer. best regards
Nice! Great application of a signal gen and scope. Thanks for taking the time to share. Your video was easy to follow. Well done :-)
VE6WGM
Great Alan very informative as per norm. Thank you.
I wonder if you could do a video for beginners of how to use a FG safely with a scope and a breadboard where someone might be probing a project of a simple circuit that has caps restistors and diodes and the correct way to use ground connections. I Know it sounds basic but at this time when people cannot go and sit with an instructor/peer it would be good I think.
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Hi, great video.
Does the Siglent generator output the trigger signal on the "SYNC OUT" connector?
Snow in Alta already? It's still Summer in BC!
very nice video, Alan! 73! IA5IOM
Thank you very much for sharing great information I need,
Now I can do visual alignment on some 10.7 MHz IF cans,
One question for extra marker signal, could we add two different frequency into the sweep system. No Any issue to the system or signal generator, thanks again
Great video. I just got a HP3325B but apparently I can’t replicate what you do since I don’t have 2 channels on it. Any thoughts on what would be the alternative? Thanks so much.
Nice video! UA-cam stuck this into my recommendations for some reason, and I'm glad it did.
In your little rectifier / demodulator circuit, what are the values of the ".001" capacitors? They seem too physically small to be .001 F (or 1 mF).
They are .001 uF or 1 nF. You could probably use 10 or even 100nF caps. I don't think really critical depending on frequency under test.
@@ve6wz Thanks!
Hello my friend,
I'm trying to use a generator similar to yours to replicate the brands (peep) similar to Heatkit's generators, but without success.
I'm trying to do the same thing as the TS-3 generator, mixing fundamental and marker signals, but the result is not similar.
Have you tried doing something similar successfully?
Hug!
How do you do an FM radio with a sweep when the trigger square wave tops out at 10Mhz? I been trying with my Siglent DSG 1032 generator which is almost identical. My trigger square wave gets really rounded off up at 10.7 MHz. I watch the channel Electronics old and new and he seems to get a great square wave from trigger with an older model generator than ours. He uses the trigger as a 10.7 point to align his trace on the channel with his curves from radio. Excuse my novice questions, new to FM, AM is simple. I finally got results using my older Wavetek generator with a sweep out function using the scope in X-Y mode on my old Tek scope. X-Y on digital scopes is not very sharp and hard to see details.
Hm. Something is amiss here... Your trigger frequency is independent from the frequencies your sweeping from and to.
It's always 1000/(sweep-time in ms) Hz.
As far as I remember, Manuel (electronics old&new) uses a 70ms sweep time, as this works nicely with his scope as it's 14div whole screen so at 5ms/div one sweep is full screen. So 70ms per sweep results in about a 14Hz trigger.
No matter if sweeping from 440kHz to 470kHz for AM, or from 10.65MHz to 10.75MHz for FM, as the sweep is done in 70ms, the trigger frequency is always 14.28... HZ
I see no reason this trigger signal would be rounded of in any way.
On most modern signal generators, the trigger is set high at sweep start, and low at 50%. So, if you set your sweep symmetrical (which mostly is the default), trigger->low is center frequency.
As you need this to be the trigger on your scope anyway, just set this channel to visible.
For your Siglent 1035 the setup to sweep a 10.7MHz filter with +/- 500KHz would be like:
(Assuming your oscilloscope has 14div/screen, if not, change sweep time accordingly to div per screen * 5)
Channel 1:
Settings: Wavefrom Type - sine
Function Sweep, Start Freq.=10.65 - Stop Freq.=10.75 - Sweep time= 70ms - Source = Internal - Trig. Out = ON
Connect SDG1035 Channel 1 output to the input of the filter to test,
Connect your oscilloscope Channel 1 to the output of the filter to test
Connect the SDG1035 AUX (rear of device) to Channel 2 of your oscilloscope.
Set you oscilloscope to trigger from Channel 2.
Timebase 5ms/div.
Make sure your oscilloscope is in XT Mode (!) - This setup works differently as the old waveteks which needed XY mode, as you get a digital trigger out, no analog sweep-sawtooth!
Edit:
Of course: Connection to the input according to spec for this filter, this may require a cap or a loosely coupling - should be noted in the alignment instructions of the radio.
Connection from filter to scope via a demodulation probe or (if not available) with the diode-circuit mentioned in the video. A similar circuit is also often shown in alignment instructions.
Hi Stephen,
I'm in a painful situation to find the best option for an arbitrary (technically only a general) waveform generator, for nearly the same goal as you use your Siglent. I have tons of questions. Yours sincerely, 73&DX, Tamás, HA5CST
The Kenwood TS-520 service manual describes pretty much the same procedure, however they call for three frequencies to be injected. 8.295, 8.595, 8.895 with a 3 db PEP wave between them. What is the best way to get the three injected and measured?
I'm looking for the same answer, did you got find a way of doing this?
hi, good presentation on how using function generator to the scope for displaying frequencies response.. i'm using hantek dso2d10 and fy6900 signal generator., i think my sweep function doesn't have trigger out like your signal generator. i am using VCO for sweeping frequencies, and feed to VCO IN and external trigger on the scope. it works{tested with LPF) but i think it's not very stable like yours(curves move forth and backward). do you have any suggestion? thanks and 73
I've found my own answer. I've done some researchs. Now i'm able plotting frequencies response. Thank you anyway 😊
Will this same process work to sweep the IF cans at 455khz on a radio? If so I've been searching for years for a way to do this. Any suggestions would be greatly appreciated. I have a siglent SDG1032x and a Rigol DSO very similar to the scope in this video.
yes this will work wit h 455 , also with 10.7 MHZ its a good way to tune old radios
What was the step sweep frequency?
What is the model number of your signal generator?
Pls. Make a video 7MHz and 14MHz
mHz and MHz are not the same. 'm' = milli 'M' = Mega mHz = millihertz, MHz = megahertz
see this for more info: en.wikipedia.org/wiki/Hertz#SI_multiples
Also, how about posting a link to a schematic for the "de-mod' probe detector circuit that you used.
73 de N1FBZ
At 06:26 you'll see a schematic.
Tuning a BAND PASS FILTER you need to look at the BAND PASS FREQUENCY and the RETURN LOSS ( SWR), how well it looks like 50 ohms match to the FILTER, at the same time. You can do this but you need VECTOR NETWORK ANALYZER. There is a crud way to but together one, but it would take to much time to try to explain how to put one together.