Yeah, I forgot to add the
after asking him if it was better. I just feel like crap today, bad cold and all that goes with it. I'm not right in the head today.
I'm sure the last sentence will bring a comment or two.
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CALCULATE AVERAGE POWER TO PEAK POWER
- Thread starter TonyV225
- Start date
Yeah, I forgot to add the
after asking him if it was better. I just feel like crap today, bad cold and all that goes with it. I'm not right in the head today.
I'm sure the last sentence will bring a comment or two.
That "0.707" is for the peak of a sine wave.
Not the same thing as your AM modulation envelope.
If what you want is a peak modulated power reading, that is NOT the same thing at all.
You can only calculate the PEP of your AM transmitter's modulation envelope with a 'scope or peak-reading meter. An average-reading meter alone won't tell you this, no matter how sincerely you want it to.
The 'scope method is easy. You'll need a radio that can deliver a carrier at least four times the carrier power of the radio you want to measure.
Modulate the radio. Make a mark on the 'scope screen at the highest point the modulation peaks reach on the screen.
Now disconnect that radio. Connect the bigger radio, and turn up the carrier until IT reaches the mark on the screen. Don't modulate it, you only want the carrier for this measurement.
Now that the second radio's carrier shows the exact same spot on the scope as the first radio's peaks, read your average wattmeter. This is what the first radio's PEP will be.
73
Not the same thing as your AM modulation envelope.
If what you want is a peak modulated power reading, that is NOT the same thing at all.
You can only calculate the PEP of your AM transmitter's modulation envelope with a 'scope or peak-reading meter. An average-reading meter alone won't tell you this, no matter how sincerely you want it to.
The 'scope method is easy. You'll need a radio that can deliver a carrier at least four times the carrier power of the radio you want to measure.
Modulate the radio. Make a mark on the 'scope screen at the highest point the modulation peaks reach on the screen.
Now disconnect that radio. Connect the bigger radio, and turn up the carrier until IT reaches the mark on the screen. Don't modulate it, you only want the carrier for this measurement.
Now that the second radio's carrier shows the exact same spot on the scope as the first radio's peaks, read your average wattmeter. This is what the first radio's PEP will be.
73
We have used that one and it does what it claims.
Just one small gripe. It is easy to "bleed" with RF in the room.
Running it from a DC wall wart may cause trouble unless the radio you're measuring is hooked to a shielded dummy load. The power wire becomes a receiving antenna, feeding RF picked up in the room straight into the peak-reading adapter. Generally makes the peak reading "twitchy". If laying your hand on top of the wattmeter changes the reading, this is a hint that the adapter is being "bled" by loose RF in the room.
Running it from a battery is a pain in the neck. If you forget to flip the switch back to "average", you'll run down a 9-Volt battery before too long. But this keeps the power leads short, with the battery inside the meter. Reduces the "bleeding" problem a lot.
Just leaving the cover off of some amplifiers allowed enough RF energy to "escape" into the room that this adapter would peg the meter when the switch was in the "peak" position. Still worked fine on average, though.
Putting the cover back on the amplifier fixed the problem. Likewise, using it on an antenna that causes "RF on the coax" feeding back into the room can do this as well.
Aside from those limitations, I like that one. It just works.
73
Just one small gripe. It is easy to "bleed" with RF in the room.
Running it from a DC wall wart may cause trouble unless the radio you're measuring is hooked to a shielded dummy load. The power wire becomes a receiving antenna, feeding RF picked up in the room straight into the peak-reading adapter. Generally makes the peak reading "twitchy". If laying your hand on top of the wattmeter changes the reading, this is a hint that the adapter is being "bled" by loose RF in the room.
Running it from a battery is a pain in the neck. If you forget to flip the switch back to "average", you'll run down a 9-Volt battery before too long. But this keeps the power leads short, with the battery inside the meter. Reduces the "bleeding" problem a lot.
Just leaving the cover off of some amplifiers allowed enough RF energy to "escape" into the room that this adapter would peg the meter when the switch was in the "peak" position. Still worked fine on average, though.
Putting the cover back on the amplifier fixed the problem. Likewise, using it on an antenna that causes "RF on the coax" feeding back into the room can do this as well.
Aside from those limitations, I like that one. It just works.
73
Last edited:
So a 25w dead key in AM with good modulation will produce 100w peak.. Sounds about correct. I like the 4w-16w answer on page 1.
The math behind this is not so tricky as it may sound.
Has to do with that "amplitude" thing. As in Amplitude Modulation.
To get 100 percent modulation, the RF peaks will be twice the amplitude of the dead carrier. Amplitude here might be RF voltage, might be RF current. If you double one of them, you get double the other one, so it doesn't matter which of these two quantities you're measuring for this.
But here's where Ohm's law comes in. Put one Volt across one ohm, and you get one Amp of current.
Power is 1 Watt, right? Now boost it to two Volts. Same 1 ohm now has 2 Amps through it. But power is voltage times current. Two Volts times two Amps is now FOUR Watts. Double times double equals four.
Make it 3 Volts, times 3 Amps and the power in the 1-ohm resistor is now NINE Watts.
It's called a square law. Plenty of those found in physics. This is just one of them.
This is why a 100-percent modulated carrier has a PEP that's exactly four times the carrier power.
Double amplitude equals four times power.
73
Has to do with that "amplitude" thing. As in Amplitude Modulation.
To get 100 percent modulation, the RF peaks will be twice the amplitude of the dead carrier. Amplitude here might be RF voltage, might be RF current. If you double one of them, you get double the other one, so it doesn't matter which of these two quantities you're measuring for this.
But here's where Ohm's law comes in. Put one Volt across one ohm, and you get one Amp of current.
Power is 1 Watt, right? Now boost it to two Volts. Same 1 ohm now has 2 Amps through it. But power is voltage times current. Two Volts times two Amps is now FOUR Watts. Double times double equals four.
Make it 3 Volts, times 3 Amps and the power in the 1-ohm resistor is now NINE Watts.
It's called a square law. Plenty of those found in physics. This is just one of them.
This is why a 100-percent modulated carrier has a PEP that's exactly four times the carrier power.
Double amplitude equals four times power.
73
According to Bill Orr I think. Guru of home brew DIY amateur amps.
A "GG" grounded grid amplifier carrier cannot be fully modulated to 100%.
Unfortunately. No mention. What approximate percentage they can be modulated
to ? The Phantom 12 tube in my car. Dead keys 650 watts RMS into a 3/4 Wave
8 foot Fire-Stick. Lets say 620.watts It is not going to be 4 x 620 ? AM PEP
On SSB 16w PEP in. I get approx. 800-900 PEP on the RMS reading Coaxial Dynamics
watt meter.
I think it was Bill Orr. Been awhile. Still have that book 1973 edition.
A "GG" grounded grid amplifier carrier cannot be fully modulated to 100%.
Unfortunately. No mention. What approximate percentage they can be modulated
to ? The Phantom 12 tube in my car. Dead keys 650 watts RMS into a 3/4 Wave
8 foot Fire-Stick. Lets say 620.watts It is not going to be 4 x 620 ? AM PEP
On SSB 16w PEP in. I get approx. 800-900 PEP on the RMS reading Coaxial Dynamics
watt meter.
I think it was Bill Orr. Been awhile. Still have that book 1973 edition.
What I remember Bill saying about this had to do with using a GG stage to amplify a carrier, and then applying high-level modulated B+ to the plate circuit. This is the classic "high-level modulation" layout.
Pretty sure he wasn't discussing the use of G-G as a linear amplifier for a signal that's already been modulated. 100% modulation is no problem for that setup.
If you look at the schematic for any old-school tube-type AM transmitter, you find two things:
It's Class C
The cathode is grounded.
Like the final stage in a Tram or Browning radio.
73
Pretty sure he wasn't discussing the use of G-G as a linear amplifier for a signal that's already been modulated. 100% modulation is no problem for that setup.
If you look at the schematic for any old-school tube-type AM transmitter, you find two things:
It's Class C
The cathode is grounded.
Like the final stage in a Tram or Browning radio.
73
With all this brilliance present...
Can one of you tell me why if I drive my cobra 350 amp with anything more than
.5 deadkey watt I get back swing on avg yet forward on peak on this dosey test center which is brand new. The RCI 2950 is brand new as well other than myself adjusting high and low power to be LESS not more (set so I key .5 - 4 watts with the front panel variable) and turning up the mod it is untouched.
Surely the amp can deal with more than .5 dk?
And if so, how am I interpreting things incorrectly or correctly with regard to avg vs peak.
Can one of you tell me why if I drive my cobra 350 amp with anything more than
.5 deadkey watt I get back swing on avg yet forward on peak on this dosey test center which is brand new. The RCI 2950 is brand new as well other than myself adjusting high and low power to be LESS not more (set so I key .5 - 4 watts with the front panel variable) and turning up the mod it is untouched.
Surely the amp can deal with more than .5 dk?
And if so, how am I interpreting things incorrectly or correctly with regard to avg vs peak.
Flip the High/Low switch to Low. That amplifier should tolerate closer to 1.5 Watts of carrier. That radio is too big to run this amplifier on "High". That setting is for smaller radios that have only a single final transistor. Your radio is almost twice as large as this amplifier needs to drive it full-bore.
For that matter, a coax jumper with a poor ground connection on one end can do something like this, too. Watching the radio's SWR meter while flexing the coax jumper could reveal that.
73
For that matter, a coax jumper with a poor ground connection on one end can do something like this, too. Watching the radio's SWR meter while flexing the coax jumper could reveal that.
73
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