Kevin, you used the right constants, but it is the RMS voltage we use, not average. You said "average" but actually used the correct RMS values. 73, KE0OG
Yeah, at one point I said "average, or RMS". I know, they're different. I often hear them interchanged and my speech processor didn't filter it right. ;-)
I went ahead and added a note to the video description about me misspeaking "average" when we mean RMS, but I suspect I'll still get beat up over that detail in the comments. Oh well.
If you look at the formula for power from voltage P = V^2 / R, the power depends on the square of the voltage. That is why we need the average of the squares of the voltages ie RMS.
That oscillator leakage is exactly what the USN was worried about in ww2 receivers and is why they brought back the use of regen receivers. Speculation was to keep the enemy from homing in on the leakage through the antennas. Other speculation was and I feel might be more correct was to keep leakage from interfering with other equipment on board the submarine or ship.
That little bit about the SWR was a better illustration of how it reduces output power than most explanations I've seen. A followup with a precise (-ish) 50ohm load and maybe a few worse ones would be highly educational, too.
My understanding is that in the early days of AM broadcast radio, stations would drive through neighborhoods and pickup the leaking oscillators of superhet radios to determine what stations people were listening to. From what you have said this is certainly possible. 73 K9AEE
It is actually a bit frightening how much you can learn from electronic leakage. Do a web search for TEMPEST certified equipment and read some unclassified reports.
In the U.K., they required a license just to receive. I don't think they still do it, but the government used to have vans that would drive around sniffing for signals to find people with receivers that hadn't purchased a license.
@@WECB640 It was the local oscillator in a superhet that could be picked up outside a house. Of course it was about 455 kHz offset from the station frequency. I know regen receivers use oscillation to increase the amplification and Q, but I don't think they were used much for commercial broadcast listening.
Hello Kevin, I use the oscillator leakage signal to align the various home-brew and commercial DC receivers I have in the shack... quite convenient actually!
Hi Kevin, thanks for this very practical example. It would be awesome if you could walk us through an example were the end result would be the E.R.P. (i.e. effective radiated power) and E.I.R.P. (i.e. equivalent isotropically radiated power) for a given antenna with some cable loss. Not that it matters for "Cricket", but very interesting exercise due the fact that the regulatory allowed transmit power-limits are taken at the antenna. Thanks and a Happy New Year ;-)
If you peak detect the voltage across the load then for a 50 ohms load the power rms is equal to the peak voltage squared divided by 100. My test load has peak detection on it, a diode, smoothed by a capacitor that can then be measured with a DVM as a DC voltage. You are using a scope to measure the peak to peak voltage, twice the peak voltage, across a load. Hope that clarifies my previous post. The maths is on the website I previously mentioned.
Check for spectral purity. The spurious emissions must be 40 dB below the fundamental, and the amount of low pass filtering there might no be enough on the antenna output.
The leakage is at the same frequency it's receiving. It will happily pass through the filter. Any filter that would stop the leakage would also stop the incoming signals.
I’m not referring to the leakage that you demonstrated in the video. I’m referring to harmonics. The second harmonic looks like it would be around 25-30 dB below the fundamental, which can cause unwanted interference in the 20 meter area.
I'm a big proponent of accurate communication, particularly when making an educational video like this, and while the average power of an AC signal is mathematically zero, it's obvious from the context that the power arising from the negative half of the signal is still positive power. The RMS calculation is the average of the rectified signal. Connect an AC voltage to a resistor and the resistor heats just as much from the "negative power". The power is disipated regardless of which direction the current is flowing. RMS is root mean square. Mean is just another word for average. The root and square mathematically rectify the signal so all the power from either half of the AC signal is counted as positive power. From some of the comments, it would be easy to get the idea that RMS is something special and distinctly different from averaging a variable signal. RMS is the average of absolute values (all negatives converted to positive values). RMS power IS average power, because the power disipated is always positive.
I kinda doubt that your dummy load being off a smudge is the reason why the power is down a little. I bet it would more have to do with powering it from a 9 volt battery and the battery not able to supply sufficient current for the full power output.
Thanks for doing the test Kevin. I like the way the kit's coils are formed using PCB tracks. Not sure if these kits are available in the UK as I would like to build one. Wondering you have had any QSOs with it.
Nice vid for many many less technical hams. But ya have to be careful... as David C pointed out below... you used terms average and RMS synonymously and they're not. Average is 0.637 * peak. RMS 0.707 as you know.. and is 0.3535 * p-p. I've seen so many hams measure the signal with a scope then use .707 to calc RMS. To close out 2019.. even tho its now 2020.. I'll 'highlight' (lol) one comment I made here during '19: I still say that QRP is 5w at the output port... and you don't get to up it by including feedline loss, ant gain or loss, etc. Haha. Happy new year Kevin and all the subs in here. Fun vids, fun comments, fun community. 72 OMs and YLs
Yo Kevin!: Great video. I'm gonna screen grab the chart scene of the Ohm's law. Yes well worth the admission price! Keep up the great work! 73's! de seeker/Jeff WA7LFP
Hi Kevin, Oh, my, gawd....! The anti-baofeng crowd is going to go spastic; how dare there be any leakage of the oscillator, blash, blah... Now they"ll wanna ban this. Thanks for the insight into this nice little kit. How is it performing on the air? Get many qso's yet?
@11.49 you say, "point zero six three eight." This is incorrect. You should have said "zero point six three eight". It makes a big difference. Were you on the team that ground the lens aboard the Hubbell telescope?
Good video. But average is not RMS voltage. Your calculations were right but you kept saying average. It is a minor point but to be accurate I needed to comment. 73, JP, K8AG
I built the dummy load kit from web site k4eaa.com/dummy.html and this incorporates a diode, capacitor voltage peak detector. The sums on this to work out the rms power are - Power rms equals the measured V peak (measured with a DVM) add 0.4 volts for the diode volt drop, square it and divide by 100. A 4 watt FM CB gives 20 volts on a DVM, 20 squared divide by 100 equals 4 Watts My Icom transmitter gives 100 volts peak. 100 squared divide by 100 equals 100 Watts. Your transmitter gave 17 volts pk/pk or 8,5 volts plus 0.4 volts diode drop let's say 9 volts. So 9 x 9 divide by 100 equals 0.81 watts. So if I got it right around 800 mWatts. Hope that's of some help.
Well, I'm not sure how to respond. Measuring voltage with a DVM at RF frequencies is not accurate. They fall off in accuracy above around 150khz. I remember having to build an RF probe in order to use a vacuum tube volt meter to make such measurements. My dummy load is a simple resistor, no diode. Since you arrive at a value that is different from a value based on measurements made with devices designed to operate correctly at these frequencies, I'd say it's helpful in showing the errors that can result from measuring with the wrong tool? :-)
@@loughkb the diode and capacitor on his dummy load are an accessory, not part of the load. They let it read a DC value for RF voltage. However, a simple diode detector can be less than accurate when you get down to micropower. eg. www.n5ese.com/rfprobe1.htm and www.nonstopsystems.com/radio/pdf-ant/antenna-dummy-article-7.pdf (which has specific diode responses) (also, check out htis e2aew vid: th-cam.com/video/2D83xp3H5Bo/w-d-xo.html)
Ah, sorry, I misunderstood what he was saying. There's also a small amount of capacitance in a diode junction that could skew things based on frequency. But then again, we're not talking about lab grade test gear here. :-)
Before QRPp (output power at less than one watt), we used to joke about two hams trying to see how low they could go. Each turned the power down on their old Heathkit DX-20s (reduced the drive) until it was impossible to go further. Finally, one guy came back on the air incredibly weakly and the other guy asked how he did it. "I got out my GDO* OM", he replied. *Grid Dip Oscillator./grid dip meter.
Kevin, you used the right constants, but it is the RMS voltage we use, not average. You said "average" but actually used the correct RMS values. 73, KE0OG
Yeah, at one point I said "average, or RMS". I know, they're different. I often hear them interchanged and my speech processor didn't filter it right. ;-)
I went ahead and added a note to the video description about me misspeaking "average" when we mean RMS, but I suspect I'll still get beat up over that detail in the comments. Oh well.
If you look at the formula for power from voltage P = V^2 / R, the power depends on the square of the voltage. That is why we need the average of the squares of the voltages ie RMS.
@@donreid358 Don, we need the RMS value of V for the formula--the root mean square, not the average.
Don, see Section 3.2 of the 2019 ARRL Handbook.
That oscillator leakage is exactly what the USN was worried about in ww2 receivers and is why they brought back the use of regen receivers. Speculation was to keep the enemy from homing in on the leakage through the antennas. Other speculation was and I feel might be more correct was to keep leakage from interfering with other equipment on board the submarine or ship.
That chart was worth the price of admission. I had heard all these values separately, together it is slick.
That little bit about the SWR was a better illustration of how it reduces output power than most explanations I've seen. A followup with a precise (-ish) 50ohm load and maybe a few worse ones would be highly educational, too.
My understanding is that in the early days of AM broadcast radio, stations would drive through neighborhoods and pickup the leaking oscillators of superhet radios to determine what stations people were listening to. From what you have said this is certainly possible. 73 K9AEE
It is actually a bit frightening how much you can learn from electronic leakage. Do a web search for TEMPEST certified equipment and read some unclassified reports.
In the U.K., they required a license just to receive. I don't think they still do it, but the government used to have vans that would drive around sniffing for signals to find people with receivers that hadn't purchased a license.
@@WECB640 It was the local oscillator in a superhet that could be picked up outside a house. Of course it was about 455 kHz offset from the station frequency. I know regen receivers use oscillation to increase the amplification and Q, but I don't think they were used much for commercial broadcast listening.
Hello Kevin,
I use the oscillator leakage signal to align the various home-brew and commercial DC receivers I have in the shack... quite convenient actually!
Excellent video! Those 4SQRP kits are pretty nice.
Hi Kevin,
thanks for this very practical example. It would be awesome if you could walk us through an example were the end result would be the E.R.P. (i.e. effective radiated power) and E.I.R.P. (i.e. equivalent isotropically radiated power) for a given antenna with some cable loss.
Not that it matters for "Cricket", but very interesting exercise due the fact that the regulatory allowed transmit power-limits are taken at the antenna. Thanks and a Happy New Year ;-)
If you peak detect the voltage across the load then for a 50 ohms load the power rms is equal to the peak voltage squared divided by 100. My test load has peak detection on it, a diode, smoothed by a capacitor that can then be measured with a DVM as a DC voltage. You are using a scope to measure the peak to peak voltage, twice the peak voltage, across a load. Hope that clarifies my previous post. The maths is on the website I previously mentioned.
Check for spectral purity. The spurious emissions must be 40 dB below the fundamental, and the amount of low pass filtering there might no be enough on the antenna output.
The leakage is at the same frequency it's receiving. It will happily pass through the filter. Any filter that would stop the leakage would also stop the incoming signals.
I’m not referring to the leakage that you demonstrated in the video. I’m referring to harmonics. The second harmonic looks like it would be around 25-30 dB below the fundamental, which can cause unwanted interference in the 20 meter area.
@@robertcullipher3492 ah, ok. You might ask Dave about that, it's his design.
Thanks, exactly what I was looking for and very well presented 👍
I'm a big proponent of accurate communication, particularly when making an educational video like this, and while the average power of an AC signal is mathematically zero, it's obvious from the context that the power arising from the negative half of the signal is still positive power. The RMS calculation is the average of the rectified signal. Connect an AC voltage to a resistor and the resistor heats just as much from the "negative power". The power is disipated regardless of which direction the current is flowing. RMS is root mean square. Mean is just another word for average. The root and square mathematically rectify the signal so all the power from either half of the AC signal is counted as positive power. From some of the comments, it would be easy to get the idea that RMS is something special and distinctly different from averaging a variable signal. RMS is the average of absolute values (all negatives converted to positive values). RMS power IS average power, because the power disipated is always positive.
You can calculate power directly from V and R, look at the formula directly above the "P" in the chart, P = V^2 / R
Yes. But since id already mentioned it, I went the long way around to demonstrate.
A Happy New Year! :D
Another good one. Thanks for sharing
I kinda doubt that your dummy load being off a smudge is the reason why the power is down a little. I bet it would more have to do with powering it from a 9 volt battery and the battery not able to supply sufficient current for the full power output.
I mean we are talking about 3/4 of a WATT from a little battery...
The spec sheet should give the voltage needed for full power.
It's designed and speced to operate on the single 9v battery. It was a brand new battery also.
Thanks for doing the test Kevin.
I like the way the kit's coils are formed using PCB tracks. Not sure if these kits are available in the UK as I would like to build one. Wondering you have had any QSOs with it.
Nice vid for many many less technical hams. But ya have to be careful... as David C pointed out below... you used terms average and RMS synonymously and they're not. Average is 0.637 * peak. RMS 0.707 as you know.. and is 0.3535 * p-p. I've seen so many hams measure the signal with a scope then use .707 to calc RMS. To close out 2019.. even tho its now 2020.. I'll 'highlight' (lol) one comment I made here during '19: I still say that QRP is 5w at the output port... and you don't get to up it by including feedline loss, ant gain or loss, etc. Haha. Happy new year Kevin and all the subs in here. Fun vids, fun comments, fun community. 72 OMs and YLs
Yo Kevin!:
Great video. I'm gonna screen grab the chart scene of the Ohm's law. Yes well worth the admission price! Keep up the great work! 73's!
de seeker/Jeff WA7LFP
I linked the graphic in the video description. You can download it directly.
We old old timers call that leakage "backwave". (And use "e" as the voltage variable: e = ir; p = ie. So we can make pie jokes.)
Just finished the cricket 30.
Hello from K9DI
Hi Kevin,
Oh, my, gawd....!
The anti-baofeng crowd is going to go spastic; how dare there be any leakage of the oscillator, blash, blah...
Now they"ll wanna ban this.
Thanks for the insight into this nice little kit.
How is it performing on the air? Get many qso's yet?
Just tell 'em the leakage is -35 dB down on the transmitted power and they'll be okay with it. Meanwhile, HNY Kevin.
@11.49 you say, "point zero six three eight." This is incorrect. You should have said "zero point six three eight". It makes a big difference. Were you on the team that ground the lens aboard the Hubbell telescope?
Good video. But average is not RMS voltage. Your calculations were right but you kept saying average. It is a minor point but to be accurate I needed to comment. 73, JP, K8AG
See the note on the first line of the description. ;-)
I built the dummy load kit from web site k4eaa.com/dummy.html and this incorporates a diode, capacitor voltage peak detector. The sums on this to work out the rms power are - Power rms equals the measured V peak (measured with a DVM) add 0.4 volts for the diode volt drop, square it and divide by 100.
A 4 watt FM CB gives 20 volts on a DVM, 20 squared divide by 100 equals 4 Watts
My Icom transmitter gives 100 volts peak. 100 squared divide by 100 equals 100 Watts.
Your transmitter gave 17 volts pk/pk or 8,5 volts plus 0.4 volts diode drop let's say 9 volts. So 9 x 9 divide by 100 equals 0.81 watts. So if I got it right around 800 mWatts. Hope that's of some help.
Well, I'm not sure how to respond.
Measuring voltage with a DVM at RF frequencies is not accurate. They fall off in accuracy above around 150khz. I remember having to build an RF probe in order to use a vacuum tube volt meter to make such measurements.
My dummy load is a simple resistor, no diode.
Since you arrive at a value that is different from a value based on measurements made with devices designed to operate correctly at these frequencies, I'd say it's helpful in showing the errors that can result from measuring with the wrong tool? :-)
@@loughkb the diode and capacitor on his dummy load are an accessory, not part of the load. They let it read a DC value for RF voltage. However, a simple diode detector can be less than accurate when you get down to micropower. eg. www.n5ese.com/rfprobe1.htm and www.nonstopsystems.com/radio/pdf-ant/antenna-dummy-article-7.pdf (which has specific diode responses) (also, check out htis e2aew vid: th-cam.com/video/2D83xp3H5Bo/w-d-xo.html)
Ah, sorry, I misunderstood what he was saying. There's also a small amount of capacitance in a diode junction that could skew things based on frequency.
But then again, we're not talking about lab grade test gear here. :-)
The diode peak charges the capacitor so that the DVM reads a DC voltage. Take a look at k4eaa web site.
H.N.Y. from C.&D. ⚔️🇺🇸⚔️
Well, do CW at 200uW WHILE you receive 😆
Before QRPp (output power at less than one watt), we used to joke about two hams trying to see how low they could go. Each turned the power down on their old Heathkit DX-20s (reduced the drive) until it was impossible to go further. Finally, one guy came back on the air incredibly weakly and the other guy asked how he did it.
"I got out my GDO* OM", he replied.
*Grid Dip Oscillator./grid dip meter.
@@warplanner8852 Haha well yea, if you could connect a key to to the GDO and sit a coupling loop next to the GDO coil, you could use it as a CW TX.
I got almost a watt out using a lithium 9 volt. hihi
I did find itinteresting