Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
AM Carrfier Shift




 
The AM Forum
October 19, 2019, 04:54:20 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1] 2   Go Down
  Print  
Author Topic: AM Carrfier Shift  (Read 3932 times)
0 Members and 1 Guest are viewing this topic.
W4DNR
Member

Offline Offline

Posts: 62


« on: May 19, 2019, 10:06:45 PM »

A friend has an Icom IC7300.  He says he likes it, but it has excessive carrier shift.
Why would a modern radio have carrier shift ?

Don W4DNR
Logged
KK4YY
Member

Offline Offline

Posts: 395


Your best isn't as good as you can be.


« Reply #1 on: May 20, 2019, 04:48:33 AM »

What exactly does he mean by "carrier shift" — the frequency changes under modulation? If so, I'd say there's something wrong with his particular radio or power supply.


Don
Logged

Fate does not protect its worshipers any more than its deniers.
kb3ouk
Member

Offline Offline

Posts: 1583

The Voice of Fulton County


« Reply #2 on: May 20, 2019, 06:20:43 AM »

Usually carrier shift refers to the modulation going more in one direction than the other, like 100% negative but much less in the positive direction.
Logged

Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible
Bob W8LXJ
Member

Offline Offline

Posts: 10


« Reply #3 on: May 20, 2019, 07:48:15 AM »

 
    I have listened and talked to several 7300s on AM driving amps, like I do with my TS990.
 There is no frequency shift, six kc wide, wonderful audio . Maybe that person has an  AC volt
drop problem with the icom  12 vdc power supply when in AM mode.

 Bob  W8LXJ
Logged
W4DNR
Member

Offline Offline

Posts: 62


« Reply #4 on: May 20, 2019, 10:08:40 AM »

Usually carrier shift refers to the modulation going more in one direction than the other, like 100% negative but much less in the positive direction.

My friend and I , both being in Broadcast AM for years, I took it to mean just that.   

Negative 100% and Positive 80% modulation wouldn't be that bad  ( in my opinion ) for a radio designed more for SSB.

Negative 100% and Positive 125%  ( if done without splatter ) would be better I would think.

Maybe he's just a 100/100 purist ?       

DOn W4DNR
Logged
DMOD
AC0OB - A Place where Thermionic Emitters Rule!
Contributing
Member
*
Offline Offline

Posts: 1343


« Reply #5 on: May 20, 2019, 12:47:25 PM »

According to 47 § 73.14 AM broadcast definitions:

Quote
Carrier-amplitude regulation (Carrier shift). The change in amplitude of the carrier wave in an amplitude-modulated transmitter when modulation is applied under conditions of symmetrical modulation.

Another term for carrier Amplitude regulation is carrier shift.

This seems to indicate as to how much carrier stability is maintained under modulation.

In many of the modern transceivers (and I have an Icom-7200) uses Digital Low power modulation with the modulator section feeding the linear amplifier section.

The internal ALC system largely regulates the output power under various conditions and when modulating in the AM mode, the output under modulation is similar to the older screen grid modulation in say the DX-60 where carrier power seems to drop under modulation.

Some control of power output can be done by biasing the ALC externally in many of these transceivers.


Phil - AC0OB

Logged

"What kind of Koolaid do they make you drink in the Physics Department?" Charlie Epps to Dr. Larry Fleinhardt, NUMB3RS   Smiley
W4DNR
Member

Offline Offline

Posts: 62


« Reply #6 on: May 20, 2019, 01:10:45 PM »


 the output under modulation is similar to the older screen grid modulation in say the DX-60 where carrier power seems to drop under modulation.

Phil - AC0OB



Phil,

This may be splitting hairs, but doesn't carrier always drop when modulation is at 100% ?

Modulate a carrier at 2000 cycles ( hertz )  and at 100% modulation ,
there is no carrier and all of the power is in the sidebands out at + and -  carrier .

Or is this saying that between voice peaks, the carrier is not only reduced by the modulation, but also that the whole waveform is being reduced by the slow ALC . . . ?     Reducing the possibility of 100% Positive modulation, or just reducing the whole AM envelope by a power percentage ?

Thanks

Don W4DNR

Logged
DMOD
AC0OB - A Place where Thermionic Emitters Rule!
Contributing
Member
*
Offline Offline

Posts: 1343


« Reply #7 on: May 20, 2019, 01:55:49 PM »


 the output under modulation is similar to the older screen grid modulation in say the DX-60 where carrier power seems to drop under modulation.

Phil - AC0OB



Phil,

This may be splitting hairs, but doesn't carrier always drop when modulation is at 100% ?

Modulate a carrier at 2000 cycles ( hertz )  and at 100% modulation ,
there is no carrier and all of the power is in the sidebands out at + and -  carrier .

Or is this saying that between voice peaks, the carrier is not only reduced by the modulation, but also that the whole waveform is being reduced by the slow ALC . . . ?     Reducing the possibility of 100% Positive modulation, or just reducing the whole AM envelope by a power percentage ?

Thanks

Don W4DNR


Perhaps the PDF below will explain the power relationships for Amplitude Modulation.

I am not clear about the last two sentences; were they directed toward high-level modulation systems or DSP controlled transmitters?  

A good explanation of the shortcomings of SS transceiver ALC, especially in the Icom 756 is given here:

Quote
Defeating the Internal ALC

The aggressive clamping action of the ALC is the major obstacle to overcome when trying to attain a healthy AM signal. The ALC effect is very evident when seen on an oscilloscope that is set up to monitor the RF envelope. The dirty truth is that the Pro III is simply unable to reach anywhere close to 100% modulation with the internal ALC present. When you reach somewhere around 50 - 60 percent modulation, you will begin to see the ALC restrain the positive peaks, preventing much more than 70% modulation at best. As the rig attempts to develop peak power, the internal ALC will actually cause it to heavily downward modulate. This produces a very gritty signal with strange sounding artifacts. If you don't have a scope, you can easily view what is happening by watching the AM power output of the Pro III with an average reading wattmeter. In the video below, the Pro III is running 15 watts of AM carrier. Watch the downward deflection on the meter as the rig is modulated...

http://www.w1aex.com/756AM/756AM.html


Phil

* AM Power and Modulation Summarized.pdf (64.85 KB - downloaded 38 times.)
Logged

"What kind of Koolaid do they make you drink in the Physics Department?" Charlie Epps to Dr. Larry Fleinhardt, NUMB3RS   Smiley
KK4YY
Member

Offline Offline

Posts: 395


Your best isn't as good as you can be.


« Reply #8 on: May 20, 2019, 02:49:01 PM »

I wonder how the carrier shift is being measured. As an input, is a tone generator being used or your friends voice? How is the output being measured?

There's no accurate answer here without accurate measurements in a controlled test environment.


Don
Logged

Fate does not protect its worshipers any more than its deniers.
k4ya
Contributing
Member
*
Offline Offline

Posts: 3


« Reply #9 on: May 20, 2019, 03:27:21 PM »

A friend of mine has a IC-7300 and also complained about the "AM Carrier Shift".  When asked what he was referring to, he replied that when you transmit in CW mode the max power out is 100 watts, but when in AM mode, the unmodulated carrier dropped to less than 25 watts keeping the modulated peaks from achieving 100 watts on peaks.  To me that is not "AM Carrier Shift", but I believe some folks use that terminology to describe the above.  He called Icom about it and was told that in AM mode, the IC-7300 will not allow for 25 watts AM carrier in the software to help protect the finals.  I guess the designers believed that AM mode with 100% modulation was too much if peaks reached 100 watts.  Thus it will not modulate to 100 watts peak, but will go up to about 90 watts max.

73....Myron....K4YA

Logged
Bob W8LXJ
Member

Offline Offline

Posts: 10


« Reply #10 on: May 20, 2019, 04:24:58 PM »

  On the Kenwood , when using it as an AM exciter, AM mode, power output wide open, carrier level on zero and then insert carrier for desired output of RF amplifier. Often run a passive grid driven 4-1000a in ab2, 4000vdc plate , 500vdc on the screen, 300 watts out carrier, 1,200 watts out on audio peaks.. If I want more power out, turn up the mic gain or increase the screen voltage to 600vdc and will go the 1500 out with no problems. THE KENWOOD shows about 10 watts output for carrier and 15 watts for audio peaks
Logged
DMOD
AC0OB - A Place where Thermionic Emitters Rule!
Contributing
Member
*
Offline Offline

Posts: 1343


« Reply #11 on: May 20, 2019, 09:49:56 PM »

A friend of mine has a IC-7300 and also complained about the "AM Carrier Shift".  When asked what he was referring to, he replied that when you transmit in CW mode the max power out is 100 watts, but when in AM mode, the unmodulated carrier dropped to less than 25 watts keeping the modulated peaks from achieving 100 watts on peaks.  To me that is not "AM Carrier Shift", but I believe some folks use that terminology to describe the above.  He called Icom about it and was told that in AM mode, the IC-7300 will not allow for 25 watts AM carrier in the software to help protect the finals.  I guess the designers believed that AM mode with 100% modulation was too much if peaks reached 100 watts.  Thus it will not modulate to 100 watts peak, but will go up to about 90 watts max.

73....Myron....K4YA

Ok, that is not carrier shift but is a result of transceiver design and math.

25 Watts AM carrier results in 100 Watts Peak-Envelope-Power at 100% Modulation. The maximum PEP for SSB is 100 Watts as well, the limit of the internal Linear Amp stage.

See the listing in the PDF file for a transmitter capable of 25 Watts AM carrier and compare the real AM output power with the so-called PEP values.

The ICOM-7300 Specifications show this:

Output Power:
100W (25W AM)
RX Frequencies:
    0.030-74.800
Receiver Type:
    Direct sampling

Transmitter
Output power (HF/50MHz)   SSB/CW/FM/RTTY: 2–100W, AM: 1–25W
Modulation system SSB AM FM   
Digital P.S.N. modulation
Digital Low power modulation
Digital Reactance modulation
Spurious emission   Less than –50dB (HF bands), Less than –63dB (50MHz band)
Carrier suppression   More than 50dB
Unwanted sideband   More than 50dB
Microphone impedance   600Ω

https://www.icomamerica.com/en/products/amateur/hf/7300/specifications.aspx

Phil

* AM Power and PEP.pdf (170.71 KB - downloaded 43 times.)
Logged

"What kind of Koolaid do they make you drink in the Physics Department?" Charlie Epps to Dr. Larry Fleinhardt, NUMB3RS   Smiley
W4DNR
Member

Offline Offline

Posts: 62


« Reply #12 on: May 21, 2019, 12:13:57 AM »

Ah Ha !! Grin      ALC..... I hadn't factored that into the equation ! 
A perfectly created 25 watt carrier and 100 watts at peak modulation
is squished in the next stage by the ALC.

I'll have to do another scope measurement on my TS-2000.
Last time I measured, 25 watts carrier was pretty close to 100 peak
with no ALC.   Close enough that it isn't worth an effort to improve.

With a 200 watt radio like the TS480 ,  25 watts carrier should be well below
any ALC action.     

I have an old FT-757GT ( no DSP )  that always sounded good on AM, but I don't
remember looking at it on a scope.

Then there is the Valiant, the DX-60, and the DX-40 that need  some "tweaks".
At least when I retire, I won't run out of projects.

Thanks Everyone ! !   Great Information.


Don W4DNR
Logged
R. Fry SWL
Member

Offline Offline

Posts: 91

Broadcast Systems Engineer (retired)


WWW
« Reply #13 on: May 24, 2019, 06:19:17 AM »

This may be splitting hairs, but doesn't carrier always drop when modulation is at 100% ?

Modulate a carrier at 2000 cycles ( hertz )  and at 100% modulation ,
there is no carrier and all of the power is in the sidebands out at + and -  carrier.

If that was true, it would produce maximum "carrier shift" when using A3a emission because the total power in the two AM sidebands at ħ100% sinewave modulation is only 50% that of the unmodulated carrier.

Actually, the average amplitude of an AM carrier is constant during all sinewave modulation levels to ħ100%, at which time the total r-f output power is 1.5X the unmodulated value, and the r-f current at the output of the transmitter rises to 122.5% of its unmodulated value.
Logged
KK4YY
Member

Offline Offline

Posts: 395


Your best isn't as good as you can be.


« Reply #14 on: May 24, 2019, 10:24:15 AM »

Ladies and gentlemen, it is now post-time.

The electrons are lining up at the gate...

And they're off!

Average Power takes an early lead with Peak Envelope Power close behind and Power Factor lagging as they head into the first cycle.

Around the Smith chart they come. Now Peak Envelope Power is closing in on Average Power, with Root Mean Square challenging on the outside.

And down the transmission line they come. Average Power and Peak Envelope Power are now neck-and-neck with Root Mean Square trailing as Power Factor, Spark Gap, and Modulation Index go into a deep fade.

It's Average Power. It's Peak Power.

Peak... Average.

Average... Peak.

And at the wire... it's a photon finish!!!
Logged

Fate does not protect its worshipers any more than its deniers.
w4bfs
W4 Beans For Supper
Contributing
Member
*
Offline Offline

Posts: 1292


more inpoot often yields more outpoot


« Reply #15 on: May 24, 2019, 11:02:38 AM »

term dropping at its finest !    seems the muse has visited  73
Logged

Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
steve_qix
Contributing
Member
*
Offline Offline

Posts: 2450


Bap!


WWW
« Reply #16 on: May 25, 2019, 04:58:15 PM »

Ok, let's get this cleared up.

Carrier shift is caused by AN AVERAGE SHIFT in the carrier power (also known as a DC shift).  This is NOT related to asymmetrical modulation.  Not, not not.

Carrier shift will only occur if the integral (average) power of the modulating waveform is greater in one direction as compared to the other.

I regularly modulate 150% in the positive direction, and 90% in the negative direction (at the same time) and there is no carrier shift.  That is because the areas under the curves of the positive going waveform and the negative going waveform are the same.  The area == the average power.  It's the average power changing that causes carrier shift.


Logged

High Power, Broadcast Audio and Low Cost?  Check out the class E web site at: http://www.classeradio.org
DMOD
AC0OB - A Place where Thermionic Emitters Rule!
Contributing
Member
*
Offline Offline

Posts: 1343


« Reply #17 on: May 28, 2019, 11:12:45 AM »

In high power AM broadcasting (>  25kW) there is a system that purposely creates carrier shift to save AC input power and that is:

AM Modulation-Dependent Carrier Level (MDCL)

and if you have further interest this can be found in

https://www.nrscstandards.org/standards-and-guidelines/documents/archive/nrsc-g101.pdf


Phil - AC0OB


Logged

"What kind of Koolaid do they make you drink in the Physics Department?" Charlie Epps to Dr. Larry Fleinhardt, NUMB3RS   Smiley
W4DNR
Member

Offline Offline

Posts: 62


« Reply #18 on: June 03, 2019, 12:52:20 AM »

Richard  Fry said :

Actually, the average amplitude of an AM carrier is constant during all sinewave modulation levels to ħ100%, at which time the total r-f output power is 1.5X the unmodulated value, and the r-f current at the output of the transmitter rises to 122.5% of its unmodulated value.


Richard,

I was referring to "instantaneous" carrier loss at 100% modulation....
As the negative modulating voltage approaches the same but opposite polarity on the final tube plate, the carrier goes to zero.   Too much of this creates clicks or hash that is wide as a barn door.  I can see how ALC could squash the positive going peaks on a modern transceiver, but how can a "classic" transmitter with an ample HV supply be made to get into the region of carrier shift ?

As Steve noted …. "I regularly modulate 150% in the positive direction, and 90% in the negative direction (at the same time) and there is no carrier shift.  That is because the areas under the curves of the positive going waveform and the negative going waveform are the same.  The area == the average power.  It's the average power changing that causes carrier shift.

Maybe the question should be :  If someone wanted to illustrate carrier shift , how would that be accomplished  ?     
   

Don W4DNR

Logged
R. Fry SWL
Member

Offline Offline

Posts: 91

Broadcast Systems Engineer (retired)


WWW
« Reply #19 on: June 03, 2019, 05:53:14 AM »

... If someone wanted to illustrate carrier shift , how would that be accomplished  ?

The default meaning of "carrier shift" to most readers/writers is rooted in the definition given in U.S. 47 CFR § 2.1 - Terms and definitions, which states:

      Carrier Power (of a radio transmitter). The average power supplied to the antenna
      transmission line by a transmitter during one radio frequency cycle taken under
      the condition of no modulation. (RR)

So if one asks about the instantaneous value of carrier power during amplitude modulation, that would need to be made clear in the question.

Below is a clip from a trade magazine that might be of interest here.

Note that the 930 kHz carrier in this SDR display of the r-f spectrum of this AM broadcast station essentially has constant amplitude during modulation.



Logged
KK4YY
Member

Offline Offline

Posts: 395


Your best isn't as good as you can be.


« Reply #20 on: June 03, 2019, 11:44:00 AM »

Average. I though I knew what average was, until I heard about average power.

What is average? Mathematically, the definition of average is clear - the sum of all measurement points divided by the number of points measured. Hence, the average amplitude of a sine wave is 2/pi, or 0.637 x peak. This works for voltage or current, but somehow, not for power! Nope, average power is different. Average power isn't average voltage times average current. That would be too easy. This is where √2 comes in and we start talking about r.m.s., the DC equivalent power.  So, it seems that the word "average" has different meanings in different contexts. When it comes to complex wave forms, like a modulated AM carrier, which average is average? Holy crap. This is why I get nervous anytime someone starts talking about average power as an absolute. Absolutely what?

Maybe I've got this all wrong. Or maybe I should just give up electronics and study something more clearly understood and unambiguous - like human psychology. Roll Eyes


Don
Logged

Fate does not protect its worshipers any more than its deniers.
W4DNR
Member

Offline Offline

Posts: 62


« Reply #21 on: June 03, 2019, 12:29:57 PM »

I just know that I can see "peak" modulation on a scope, or on a properly calibrated AM Modulation Monitor. 

Average power could be useful as an indicator of audio processing effectiveness.

Into a fixed resistance load, if the antenna amps go up, then antenna voltage should also go up.

This still doesn't explain how to achieve what is called  "Carrier Shift".

My point is …. if you know how to achieve "Carrier Shift" , then conversely, you should be able to prevent " Carrier Shift".

Don W4DNR
Logged
K1JJ
Contributing
Member
*
Offline Offline

Posts: 7866


"Let's go sailing, Tommy!" - Yaz


« Reply #22 on: June 03, 2019, 02:35:37 PM »

In the practical world I have always looked at carrier shift like this:

Put a steady AM carrier into a dummy load with an average reading (not peak) BIRD wattmeter inline. Then sock some audio voice yallos as you vary the audio gain up and down and observe the Bird reading. If the meter bounces upwards with heavy modulation, this is positive carrier shift.  If it bounces downwards (like with excessive alc limiting, or improper / light linear or light screen modulation loading) then it is negative carrier shift.

This effect really shows up with super heavily modulated AM balanced modulators, whereas with conventional plate modulation (with proper negative peak limiting and the rig running clean/ correctly) the shift can be slight or not there at all.

I've tailored my 4X1 plate modulated rig to run with little to no upward bounce and this is its best overall optimization for fully modulated cleanliness.

T
Logged

Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
KK4YY
Member

Offline Offline

Posts: 395


Your best isn't as good as you can be.


« Reply #23 on: June 03, 2019, 06:21:09 PM »

But, but, but...

The Bird model 43 measures voltage (it uses a detector diode), in a given direction, with a meter calibrated in watts. Its stated accuracy is +/- 5% FS when operated into a 50 ohm resistive load. I've never seen a Bird 43 in any RF lab I've worked in. An HP432A (+/- 1% FS) power meter, yes. Never a Bird wattmeter.

The HP 432A uses a thermistor, which measures heat. Heat, like r.m.s. heat. Power heat. The HP 432A is a power meter. A Bird 43 is a voltmeter calibrated in watts. So, when a Bird 43 meter needle is flicking around with modulation it's still measuring voltage (damped by the meter movement). I'm skeptical that a Bird 43 can measure a complex waveform power with any kind of accuracy. I doubt that even the HP 432A can keep up with a complex waveform, like voice.

Now, to top it all off, the word "average" does not appear in the manual for either the Bird 43 or the HP 432A. But I have a feeling the the Bird measures 0.637 "average volt-watts", and the HP measures 0.707 "average r.m.s.-watts". But I still don't know what watt is what, and which average is average. Cry

As for carrier shift, I don't have a clue where to even begin. The theory is one thing. Making meaningful measurements, can be quite another.

Alright, I got that off my chest. Whew! (But I still don't feel any better.) Sad


Don
Logged

Fate does not protect its worshipers any more than its deniers.
K1JJ
Contributing
Member
*
Offline Offline

Posts: 7866


"Let's go sailing, Tommy!" - Yaz


« Reply #24 on: June 03, 2019, 08:34:58 PM »

Hi Don,

I understand what you're saying. Making meaningful readings that we can actually use in the real world is what I am talking about.

I don't know of another simple method to get a handle on when we are getting carrier shift other than one of these meters, be it voltage or power derived.  I think looking at a voice waveform on a scope is not very effective to see carrier shift.

The Bird without the PEP kit, (a common ham meter) or any other voltage derived non-peak-reading meter may not show accurate power readings under modulation, but they can give us a relative idea of when we are putting power in one direction or the other. In my case I like to adjust things for zero carrier bounce at maximum modulation. Sure, I can get the meter to bounce upwards with my old class E rig or FT-102 running 200% modulation, but I prefer zero bounce at 130% if I can.  There are still a lot of guys using diode detectors rather than sync detectors.

Out of curiousity, I remember the popular Gates mod monitor used at most BC stations in the past having a "carrier" meter on the left side.  I never owned one. Did that indicate carrier shift or was it just a calibration for the modulation %?

Here's the manual if anyone wants to dig into it:

https://www.americanradiohistory.com/Archive-Catalogs/Gates-Harris/Gates-M-5693-Modulation-Monitor-1959.pdf

Interesting discussion.

T
Logged

Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
Pages: [1] 2   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone İ 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.079 seconds with 19 queries.