Measuring HF Transmitter Harmonics with the Siglent 1204Xe
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- Опубликовано: 28 июл 2022
- Hi I’m Mario Vano. I operate amateur radio station AE0GL near Minneapolis and like to experiment with QRP hardware designs and for that, I need a way to measure spurious outputs of my radio transmitters. In an earlier video I provided a simple introduction to the use of the Siglent 1204x-e oscilloscope to measure in-band intermodulation products from an HF two tone SSB test.
In this video I’m going to use the math functions to display the HF hararmonics generated by a QRP Transmitter. I'll also compare the results with those measured by a TinySA Spectrum analyzer. 
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Thank you, I have this DSO and still learning! 73, Jim WB8ZLK
I really appreciate your video Sir👍
Glad to hear that
Thank you! Such a wonderful tutorials
Hi Mario,
I have this scope and will try this out soon! Thank you for the class!
Jim
Enjoy!
@@mariovano my Siglent is actually the 1104 but upgraded to the 1204 and performs fine. But it's my 1st DSO, lots of features I have to learn. My old Hitachi V355 was used for 30 years or so before this purchase. Look forward to more of your thorough lessons!
Jim.
FYI - you can display a table of the markers on the Siglent, and see the relative dB values without having to cursor around.
Of course, but that only works on the 4 channel models like mine.
I've been trying to show other ways to do it for the benefit of users of the very popular 1202X-e which has no tables in the FFT function.
Unfortunately, I can't test on it since I don't have a 1202Xe available.
I've been trying to show simpler ways to do things lately after being accused by a friend of doing videos about hardware no ham can afford!
Thanks for the comment, however. I love the tables myself!
M
Hi Mario, Thanks for doing this video. I've got this scope and a QCX+. Can you confirm the correct setup is output of QCX goes into a T. Dummy load attached to side connector on T and where I'm lost is where/what is the scope probe connected to? I've got a bnc breakout that goes from bnc to 2 screw terminals. Could I just use that?
Also, I'm wanting to measure power output with this scope and radio. Would the same setup be what I'm looking for? My concern is in not wanting to blow up my scope. So, I'm assuming at 10Watts or less an attenuator is not needed?
Thanks again for the video and for any insight you care to offer. 73! Fleet KC1QHE
If you think about it as a normal voltage reading with the scope probe you can see what is safe and what isn't. You're just connecting the x10 probe to the dummy load the way you would probe any normal AC signal with it if you were troubleshooting.
Here's a link to a slightly better picture of the dummy load, BNC T and 10x probe with its BNC Tip adapter plugged into the T: drive.google.com/file/d/1tcTT-pdPCHPf3pgUR9npNjJ_JjPd0het/view?usp=sharing
My scope came with 4 probe kits, and each one contained a funny looking adapter that slips over the probe tip (with the clip removed) and plugs in to a bnc/tnc connector's inner shield (It doesn't look like a BNC connector at all). Note: This is not the same thing as a terminated adapter for a scope input!
A bigger unshielded adapter might work OK with your 10x probe, but it would probably introduce errors as the frequency rises. You need to keep a short, low capacitance path to the probe and its ground return if you don't use the proper adapter for a 10x probe. If you try your adapter, consider using the short grounding clip instead of the alligator clip and going straight in to the probe tip instead of the self-holding cap.
I see no problems doing this at 10 watts which should be 62 volts peak to peak. I believe the probe and scope with probe is rated at well over 200 Volts. Just don't forget to convert from Peak-to-Peak to RMS Voltage. Note that the FFT automatically does this conversion and displays power if the units are dbm.
@@mariovano Thank you. I just gave it a try and it works well. Now, if I can just get my power on the QCX to around 5Watts I'll be happy.
Using an oscilloscope probe to measure the spectrum is far from optimum. Amplitude vary with frequency since the cable is not match to 50 ohm.
That's a common misunderstanding!
In the configurations where I show the scope connected to a load via a T it should NOT be matched to 50 ohms as the signal is already terminated properly. We are properly measuring voltage across the accurate 50 ohm load with a scope probe calibrated to do that. That is what the probe and scope were designed to do.
The supplied T and probe adapter for the high impedance probe setting work to at least the specified bandwidth of the scope when used this way. You are correct, however that this means that at 200 MHZ, the measurements can be 3Db low as that is what the 200 MHz specification of the scope actuallymeans! This bandwidth will not be improved by using a 50 home setup for the measurement - it's the limit of the scope's design. It also limits the FFT and power measurements of the 200 Mhz version of this scope to to around 160MHz.
In some videos I show how to use the scope as the destination load, but it's usually via some sort of properly calibrated power attenuator.
Thahk you for reminding us that's that it is easy to forget the scope bandwidth is only 200 MHz! This means that that using it to measure harmonics above 100 MHz can give misleading results. This is a great system for HF work up to about 30 MHZ, but 6 meters and beyond requires a better analyzer ( and I have several).
thanks again for your interest...