Thank you so much. Been thinking about getting an oscope but wasn’t too sure about connecting it and using it. This was by far the best information I’ve found. Thanx again 73
Thank you Dave. Your efforts to instruct and motivate are always appreciated but especially now during the global pandemic. BTW, I set up a small dipole antenna (~0.3m each leg), connected my scope probe to it, and used the oscilloscope (PicoScope 2204A) to measure Vpp. This would tell me if my antenna (on the balcony) was radiating or not. I believe that one could take this one step further by using a "nanoVNA" to measure the impedance of an actual antenna which is ~R if the SWR=1.0 (Z -> R). Then disconnect the nanoVNA and connect your antenna back up w/a "T" splitter into your scope. Make sure your Xceiver doesn't autotune (SWR is already 1 after all), press the PTT down, and the scope would give you Vrms (from Vpp). From here, P=E^2/R would give you the Power at your antenna. Or pretty close. Just a thought.
Hi Davide, I am an Italian radio amateur, I have an oscilloscope like yours a Rigol DZ 1054 but I have expanded it to 100Mhz of band extension. I should measure the power of a Tokio Zodiac rtx (it is the President Jackson clone with an extra 40 channel band (frequency 25.615 to 28.315Mhz) I used it 30 years ago together with a double needle Zetagi HP202 Rosmeter / wattmeter. A few days ago I took everything from the warehouse and I restored the Zodiac Tokio by replacing all the electrolytic and tantalum capacitors and I tested it: it is aligned and in frequency. But I don't get the original RF power (12 watts), at least that's what the wattmeter rosmeter indicates. I come out with max 6 watts of power foward with SWR 1: 1.1. I connected a dummy load of the MFJ 260C which in HF has a SWR of 1: 1.1 (I tested the dummy load with 2 vna: nanovna and MiniTiny vna and the smith chart shows me that the load is perfectly in the center of the circle , it has no inductive XL nor capacitive XC reactances) so I believe that the trimmers of the ZETAGI wattmeter ros meter have to be set (also the ZETAGI HP 202 rlo has 30 years of inactivity). So I measured everything by replacing the wattmeter Rosmeter with a professional Daiwa CH 901 HP 3 and in fact it detects 10.5 watts but I would like to make an even more precise measurement with the oscilloscope taking the cue from this video of yours. Should I use the original probes or for safety should I use an active differential probe (which I have in my kit)? I also have a 100x passive high attenuation probe could I also use this? Many thanks 73 51 fromMassimiliano
If your 'scope, like mine, can't automatically calculate V(rms) you can use V(peak to peak). The equation is: Power = E^2 (peak to peak) / 400. This assumes a 50 ohm load. I'll leave it as an exercise for the student to figure out where the 400 value comes from. So, using Dave's data E (peak to peak) was 52 volts. Power is then 52^2 / 400 = 6.76 watts.
I have a dual band Tektronix O Scope that is from the 60's, I have not used it in years. I lifted it up to the bench and nearly got a another Hernia ! It turned ON, but I suspect that I have some Caps that have dried up. The tubes should be OK, they don't go bad sitting idle in a good room environment. I have a similar issue with a Bell and Howell O Scope that I built years ago as part of a course that I took after leaving the Army, Caps !! But at least that scope is transistor and weighs FAR less than the TEK Beast.
You'd be much better off mounting the BNC-T directly to the scope input and run the main path on the other two ends. This way, the open stub length is minimized.
Shouldn't the T be at the cantenna side connector and use the probe @ 10x to take the measurement "accross the load" and not have a stub in the firstplace ?
Scope reading will read higher because the scope's high impedance input (10M Ohms) is not matched with the transmitter and coax impedance (50 Ohms). Some scopes have switchable Hi Z / Lo Z inputs. Otherwise, use a 50 Ohm through terminator to get accurate results.
Thank you for the good video. What else could we hams do with an oscilloscope? There are other models of Rigol scopes why that one? What about the others? How do we select?
At 2:04 until 3:06 I wish you would have made that diagram just a tad different ....... The Tap point should be in the middle point of the East to West line , that way some people, NOT familiar with schematic lines might mistake the line from the Micro BITX to the scope with the TAP off of that point to the MFJ-849 meter and Dummy Load ..... I hope I didn't misword it .... In other words the tap point to the scope , should be after the BITX on the way to the watt meter and dummy load .... I would not put any radio or XMTR directly in a scope .....It would be a OMG Oops moment .....
Enjoyed this video Dave. Haven't done a power check with an scope for twenty years. Thanks for touching on the safety issue at the end. Did you have your scope grounded to the RF ground?
Great informative video. I'm new to your channel and have enjoyed several of your episodes. I'm curious about your shirt. What meaning do you have in the initials OG? Looking forward to more videos. Thanks and 73, Alex, WD2T
Very nice tutorial! I tried it out and used my Rigol DS1054Z (same as you, with 100 MHz option) to try and measure the output power of an RFM69HCW module on 433 MHz. I wasn't expecting to see anything at all. But then I got this: * Lowest power level should be 5 dBm (3 mW). Measured 18 mV RMS (6 mW) (noise floor not taken into account, should have done that maybe) * Highest power level should be 20 dBm (100 mW). Measured 75 mV RMS (112 mW) Some steps in between showed increasing voltages, so the measurement was comprehensible. I wasn't able to measure the frequency though, it mostly showed nothing or some 50 or 100 Hz. Am I dreaming or is this a somewhat correct measurement? BTW: I have a lambda/4 monopole attached and measured at its foot. With the standard 1x probe.
Wow Dave, another great video! With that scope, can you also use the math functions to calculate & display the power output? To carry on with that, those Rigol scopes are pretty nice to have, and so could you show us how with that setup - how the signal looks in the frequency domain; i.e. poor man's spectrum scope... & comparison with different modes, cw, am, ssb, fm, digital...
Power depends on the resistance of the load. Since the scope doesn't know the value of the load, it could not calculate power, unless there was a way to tell the scope the load but that's not a feature. You are stuck with having to drag out that old slide rule!! HI
If and only if the bandwidth of the scope is appropriate for the frequency you're attempting to measure at? If you pipe a 450 MHz signal into that 54 MHz scope, you're going to need to know how the scope attenuates or mis-measures higher frequencies, if at all. (?)
Generally speaking, an o-scope's response is fairly flat, but it will be down 3 dB at the rated bandwidth. I mean that a 50 MHz-rate 'scope will be 3 dB down at 50 Mhz. If you try to pipe a 450 MHz signal into that oscilloscope you probably won't see much of anything. I think I've answered what you were asking.
Thank you Dave. Very informative video. So the question I have is with the mj voltage and SWR meter. Is there a way to calibrate it to the right voltage that the scoop gave you? Thank you. Clark KG7LOI. 73's
Hi David. I have used the peak method to calculate Tx power for some years. There was a chap on the web who used to repair Kenwood hybrid radios, he offered spares but also offered the parts and plan to build your own test load in a paint can similar to your test load. Incorporated in the parts was a diode. The diode along with a capacitor formed a peak detector capable of driving a DVM. The maths went like this, Vrms is equal to route2/2 x Vpk (note Vpk not V pk to pk, note route2/2 equals 1/route2). Power equals V squared/R. Subs in and power equals Vpk squared/50 times route 2 squared (that's 50x2). That is Vpk squared divide by 100. Now my Icom produces 99 and a bit Volts pk, add 0.6 Volts for the diode volt drop, say 100 Volts, square 10000 and divide by 100 answer 100 Watts. My 4 watt CB produces 20 Volts peak. Square 400 divide by 100, 4 Watts. Quite simply Power in Watts equals Vpk squared divided by 100 for a 50 Ohm impedance radio. Tell me if I have it wrong some where. Many thanks for your many amazing videos.
Very interesting and informative demo. Thank you Dave. I know that +/- 10% is good enough for Ham radio work, but I was wondering if by using the O Scope, which I also agree is more accurate, one could use the O Scope reading of power to calibrate the watt meter to be more accurate? If the watt meter stays linear with any corrective calibration, I would think it would be possible ? What are your thoughts Dave ?
Thank you for sharing. I did not recognize terminator at scope. Would that provide more accurate results? I mean; connect transmitter to an attenuator (for example 20db) and continue the 50 ohms cable right to the input of the scope. At the input of scope mount a 50ohm terminator and the scope will measure the voltage over the 50ohm. I have used this approach so far. What's your view?
@@davecasler thanks for the nice video! this detail put me into thinking as the scope is not directly on the dummy load. EMRFD ch7.4 shows a few methods for measuring power with the oscilloscope and i am not sure if this setup would give accurate results! i would be very interested to see the difference if it was measured exactly on the dummy load.
As David pointed out several times, if you toss in an antenna with a complex impedance, let alone adding feed line to further complicate the issues, then this process won't work easily. His entire setup depended upon a source impedance of 50 ohms, a transmission line with a matching characteristic impedance of 50 ohms, and a resistive load of 50 ohms. There's no capacitive or inductive reactance to mess things up. You can see that because (assuming the dummy load had no reactance) the VSWR was 1:1. If you can measure all the bits, like complex impedance, amplitude, and signal phase, you could calculate it out, but it gets much harder. If you want to try, I'd suggest that doing things using polar notation is easier than using Cartesian. And, let me add, you are a braver man than I, sir. -- grin
![АЛАУДИНОВ у Скабеевой: эти их ВСУ нас НЕ ДОГОНЯТ 😁 [Пародия]](http://i.ytimg.com/vi/an0anqU4WGQ/mqdefault.jpg)
Thank you so much. Been thinking about getting an oscope but wasn’t too sure about connecting it and using it. This was by far the best information I’ve found. Thanx again 73
As a returning amateur this was very useful revision. I'm grateful for this and any videos explaining what test equipment is useful and how to use it.
Always a great fundamentals session Dave!
Excellent video Dave. Thanks for posting
Thank you, Dave. You are really helping folks.
Thanks for the short demonstration Dave! I’ll be trying this myself shortly after getting my license and building my first radio. 73
Clear, concise and informative. Thank you.
Thank you Dave. Your efforts to instruct and motivate are always appreciated but especially now during the global pandemic.
BTW, I set up a small dipole antenna (~0.3m each leg), connected my scope probe to it, and used the oscilloscope (PicoScope 2204A) to measure Vpp. This would tell me if my antenna (on the balcony) was radiating or not.
I believe that one could take this one step further by using a "nanoVNA" to measure the impedance of an actual antenna which is ~R if the SWR=1.0 (Z -> R). Then disconnect the nanoVNA and connect your antenna back up w/a "T" splitter into your scope. Make sure your Xceiver doesn't autotune (SWR is already 1 after all), press the PTT down, and the scope would give you Vrms (from Vpp). From here, P=E^2/R would give you the Power at your antenna. Or pretty close.
Just a thought.
Dave thank you for this video. I would like to see more along these topics, very informative and instructional. 73
Thanks for explaining this in a way i could understand. I can'y believe how much electronics theory i have forgotten since college!!
Thank you Dave, good information!
thank you dave
Hi Davide, I am an Italian radio amateur, I have an oscilloscope like yours a Rigol DZ 1054 but I have expanded it to 100Mhz of band extension. I should measure the power of a Tokio Zodiac rtx (it is the President Jackson clone with an extra 40 channel band (frequency 25.615 to 28.315Mhz) I used it 30 years ago together with a double needle Zetagi HP202 Rosmeter / wattmeter.
A few days ago I took everything from the warehouse and I restored the Zodiac Tokio by replacing all the electrolytic and tantalum capacitors and I tested it: it is aligned and in frequency. But I don't get the original RF power (12 watts), at least that's what the wattmeter rosmeter indicates. I come out with max 6 watts of power foward with SWR 1: 1.1. I connected a dummy load of the MFJ 260C which in HF has a SWR of 1: 1.1 (I tested the dummy load with 2 vna: nanovna and MiniTiny vna and the smith chart shows me that the load is perfectly in the center of the circle , it has no inductive XL nor capacitive XC reactances) so I believe that the trimmers of the ZETAGI wattmeter ros meter have to be set (also the ZETAGI HP 202 rlo has 30 years of inactivity).
So I measured everything by replacing the wattmeter Rosmeter with a professional Daiwa CH 901 HP 3 and in fact it detects 10.5 watts but I would like to make an even more precise measurement with the oscilloscope taking the cue from this video of yours. Should I use the original probes or for safety should I use an active differential probe (which I have in my kit)? I also have a 100x passive high attenuation probe could I also use this? Many thanks 73 51 fromMassimiliano
That's for the informative video. Just bought a scope today
If your 'scope, like mine, can't automatically calculate V(rms) you can use V(peak to peak). The equation is: Power = E^2 (peak to peak) / 400. This assumes a 50 ohm load. I'll leave it as an exercise for the student to figure out where the 400 value comes from. So, using Dave's data E (peak to peak) was 52 volts. Power is then 52^2 / 400 = 6.76 watts.
I have a dual band Tektronix O Scope that is from the 60's, I have not used it in years. I lifted it up to the bench and nearly got a another Hernia ! It turned ON, but I suspect that I have some Caps that have dried up. The tubes should be OK, they don't go bad sitting idle in a good room environment. I have a similar issue with a Bell and Howell O Scope that I built years ago as part of a course that I took after leaving the Army, Caps !! But at least that scope is transistor and weighs FAR less than the TEK Beast.
You'd be much better off mounting the BNC-T directly to the scope input and run the main path on the other two ends. This way, the open stub length is minimized.
Good point
Shouldn't the T be at the cantenna side connector and use the probe @ 10x to take the measurement "accross the load" and not have a stub in the firstplace ?
you did a nice job with this one, well done.
Thanks, I needed that!
The milestone of # 290 comes next!!!!
Scope reading will read higher because the scope's high impedance input (10M Ohms) is not matched with the transmitter and coax impedance (50 Ohms). Some scopes have switchable Hi Z / Lo Z inputs. Otherwise, use a 50 Ohm through terminator to get accurate results.
The scope has Hi Z inputs. The transmitter was terminated by the dummy load.
Just what the doctor ordered! Presented with your usual crystal clarity. Very grateful Dave. 73 Howard 2E0HWO
Dave can you do a video showing now the scope was set up for this measurement?
I described the setup in the video. Next time I use the scope this way I'll be sure to add a little bit showing the exact configuration.
Thank you for the good video. What else could we hams do with an oscilloscope? There are other models of Rigol scopes why that one? What about the others? How do we select?
At 2:04 until 3:06 I wish you would have made that diagram just a tad different ....... The Tap point should be in the middle point of the East to West line , that way some people, NOT familiar with schematic lines might mistake the line from the Micro BITX to the scope with the TAP off of that point to the MFJ-849 meter and Dummy Load ..... I hope I didn't misword it .... In other words the tap point to the scope , should be after the BITX on the way to the watt meter and dummy load .... I would not put any radio or XMTR directly in a scope .....It would be a OMG Oops moment .....
Enjoyed this video Dave. Haven't done a power check with an scope for twenty years. Thanks for touching on the safety issue at the end. Did you have your scope grounded to the RF ground?
No, not grounded to my RF ground system, but grounded to the utility ground.
Great informative video. I'm new to your channel and have enjoyed several of your episodes. I'm curious about your shirt. What meaning do you have in the initials OG?
Looking forward to more videos. Thanks and 73,
Alex, WD2T
Isnt the correct formula for power in an AC circuit: E x I x COSØ so any reactance in the load would cause a phase shuft right ?
Very nice tutorial! I tried it out and used my Rigol DS1054Z (same as you, with 100 MHz option) to try and measure the output power of an RFM69HCW module on 433 MHz. I wasn't expecting to see anything at all. But then I got this:
* Lowest power level should be 5 dBm (3 mW). Measured 18 mV RMS (6 mW) (noise floor not taken into account, should have done that maybe)
* Highest power level should be 20 dBm (100 mW). Measured 75 mV RMS (112 mW)
Some steps in between showed increasing voltages, so the measurement was comprehensible. I wasn't able to measure the frequency though, it mostly showed nothing or some 50 or 100 Hz.
Am I dreaming or is this a somewhat correct measurement?
BTW: I have a lambda/4 monopole attached and measured at its foot. With the standard 1x probe.
Wow Dave, another great video!
With that scope, can you also use the math functions to calculate & display the power output?
To carry on with that, those Rigol scopes are pretty nice to have, and so could you show us how with that setup - how the signal looks in the frequency domain; i.e. poor man's spectrum scope... & comparison with different modes, cw, am, ssb, fm, digital...
Power depends on the resistance of the load. Since the scope doesn't know the value of the load, it could not calculate power, unless there was a way to tell the scope the load but that's not a feature. You are stuck with having to drag out that old slide rule!! HI
Hi Dave! Any thoughts of a video on using the digital scopes and FFT to check FM Deviation? Thx & 73, John/N6VTS
Very interesting video. I would bet not many hams have an oscilloscope, though.
I have a 27 mhz vswr meter. IS there a way to make this work with hand held? Any modifications etc? Any reply appreciated cheers from Australia
If and only if the bandwidth of the scope is appropriate for the frequency you're attempting to measure at? If you pipe a 450 MHz signal into that 54 MHz scope, you're going to need to know how the scope attenuates or mis-measures higher frequencies, if at all. (?)
Generally speaking, an o-scope's response is fairly flat, but it will be down 3 dB at the rated bandwidth. I mean that a 50 MHz-rate 'scope will be 3 dB down at 50 Mhz. If you try to pipe a 450 MHz signal into that oscilloscope you probably won't see much of anything.
I think I've answered what you were asking.
@@tfrerich Right. So where the title says 'Absolutely' it should say 'in some cases'.
Hello Dave, again a very good video, learned a lot!!! Stay healty and ...... HAM RADIO MATTERS !!!!
I was surprised you did not use a 50 ohm through terminator at the scope's input. Does the dummy load connected to the T-Connector do the same thing?
Yes
I'd love to know if there are any under $100 options out there for measuring swr and rf?
Hi Dave! What is my rig doesn't have BNC out? Just use an adapter?
Thank you Dave. Very informative video. So the question I have is with the mj voltage and SWR meter. Is there a way to calibrate it to the right voltage that the scoop gave you? Thank you. Clark KG7LOI. 73's
Not that I know of
Hi David. I have used the peak method to calculate Tx power for some years. There was a chap on the web who used to repair Kenwood hybrid radios, he offered spares but also offered the parts and plan to build your own test load in a paint can similar to your test load. Incorporated in the parts was a diode. The diode along with a capacitor formed a peak detector capable of driving a DVM. The maths went like this, Vrms is equal to route2/2 x Vpk (note Vpk not V pk to pk, note route2/2 equals 1/route2). Power equals V squared/R. Subs in and power equals Vpk squared/50 times route 2 squared (that's 50x2). That is Vpk squared divide by 100. Now my Icom produces 99 and a bit Volts pk, add 0.6 Volts for the diode volt drop, say 100 Volts, square 10000 and divide by 100 answer 100 Watts. My 4 watt CB produces 20 Volts peak. Square 400 divide by 100, 4 Watts. Quite simply Power in Watts equals Vpk squared divided by 100 for a 50 Ohm impedance radio. Tell me if I have it wrong some where. Many thanks for your many amazing videos.
Very interesting and informative demo. Thank you Dave. I know that +/- 10% is good enough for Ham radio work, but I was wondering if by using the O Scope, which I also agree is more accurate, one could use the O Scope reading of power to calibrate the watt meter to be more accurate? If the watt meter stays linear with any corrective calibration, I would think it would be possible ? What are your thoughts Dave ?
Yes, you certainly could. You'd want to do it separately for each band, though.
@@davecasler Good point Dave, frequency will certainly effect readings
Thank you for sharing. I did not recognize terminator at scope. Would that provide more accurate results? I mean; connect transmitter to an attenuator (for example 20db) and continue the 50 ohms cable right to the input of the scope. At the input of scope mount a 50ohm terminator and the scope will measure the voltage over the 50ohm. I have used this approach so far. What's your view?
The termination was provided by the dummy load.
@@davecasler thanks for the nice video! this detail put me into thinking as the scope is not directly on the dummy load. EMRFD ch7.4 shows a few methods for measuring power with the oscilloscope and i am not sure if this setup would give accurate results! i would be very interested to see the difference if it was measured exactly on the dummy load.
oh, boy! i feel like a mad scientist already!
where're my white lab coat and elbow length rubber gloves?
High impedance input of the scope and 50 Ohm coax doesn’t look good. Using standard 10x probe would give better results.
Oscilloscope will always be correct.
So my antenna and coaxial is not at 50 Ohm (as many ham shacks are) So how do I actually measure the true power then?
As David pointed out several times, if you toss in an antenna with a complex impedance, let alone adding feed line to further complicate the issues, then this process won't work easily.
His entire setup depended upon a source impedance of 50 ohms, a transmission line with a matching characteristic impedance of 50 ohms, and a resistive load of 50 ohms. There's no capacitive or inductive reactance to mess things up. You can see that because (assuming the dummy load had no reactance) the VSWR was 1:1.
If you can measure all the bits, like complex impedance, amplitude, and signal phase, you could calculate it out, but it gets much harder. If you want to try, I'd suggest that doing things using polar notation is easier than using Cartesian. And, let me add, you are a braver man than I, sir. -- grin
Why would anyone ask such a silly question?
Because they wanted to know the answer!
@@davecasler Someone who doesn't know about Ohm's law shouldn't be messing around with transmitters!