Here are some interesting numbers for a typical linear amplifier.
At 1500 watts output with a single carrier at 60% efficiency the input power
will be 2500 watts. That leaves 1000 watts of plate dissipation.
With AM at 375 watts carrier out and no modulation, the efficiency of that
amp will be around 30%. That requires the input power to be 1250 watts. That
leaves 875 watts of plate dissipation with no modulation present.
With the 375 watt carrier at 100 % (AM) modulation with a sin wave tone the
average output power will be 562.5 watts. The efficiency will be around 45%.
That will require an input power of 1250 watts. That leaves 687.5 watts of
plate dissipation.
At 100% modulation the amplifier output will be 1500 watts PEP.
Notice that the input power remains about the same but the efficiency
increases as modulation is applied and output power increases. Plate
dissipation goes down with modulation.
The amplifier must be tuned at the 1500 watt output level and must remain
tuned that way when the AM signal is applied in order to remain linear.
This is also known as one form of "efficiency modulation."
If the AM signal consisted of only one side band rather than the normal two,
we should be able to apply 375 watts of modulation power to the 375 watt
carrier. This would still leave the modulation voltage equal to the carrier
voltage as it is with double side band AM with half the modulation power.
This would increase the average output power to 750 watts while maintaining
1500 watts PEP output.
With modulation of a sin wave single tone the signal would be the same as an
SSB signal modulated with two equal amplitude tones.
However the signal with voice modulation would sound quite distorted when
listened to on a standard diode type of AM receiver detector due to the
distortion introduced in the detector. The diode detector requires the
carrier level to be several times the level of the modulation.
73
Gary K4FMX
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Fuqua, Bill
> L
> Sent: Sunday, November 29, 2015 12:59 AM
> To: Roger (K8RI); amps@contesting.com
> Subject: Re: [Amps] Amplifier Vs Plate Modulated
>
> I did not deal with plate dissipation. 562.5 Watts power is the
> average power out for 1500 Watts PEP and
> 100% sinewave modulation. Now at 60% efficiency that amounts to 375
> Watts Plate Dissipation. So there are two limits.
> One is the PEP output the amplifier can produce at low distortion, the
> second is the plate dissipation. You would have
> to chose the lowest of the two. However, most amplifiers will be PEP
> Power Output limited not plate dissipation limited.
> Please check my math.
> 73
> bill wa4lav
>
> ________________________________________
> From: Fuqua, Bill L
> Sent: Saturday, November 28, 2015 7:29 PM
> To: Roger (K8RI); amps@contesting.com
> Subject: RE: [Amps] Amplifier Vs Plate Modulated
>
> By putting all the sideband power into one sideband you have a 3dB
> advantage over traditional AM because you could go to
> a 3kHz IF filter rather than 6kHz.
> 73
> Bill wa4lav
>
>
> ________________________________________
> From: Fuqua, Bill L
> Sent: Saturday, November 28, 2015 7:26 PM
> To: Roger (K8RI); amps@contesting.com
> Subject: RE: [Amps] Amplifier Vs Plate Modulated
>
> Lets see, for legal limit you will be limited to 1500W PEP/4 or 375
> Watts of carrier.
> Sideband power for will be half of that if you are running constant
> sinewave tone into your exciter so add another 187.5 Watts.
> The total power output for 1500W PEP 100% plate modulated by sinewave is
> 562.5 Watts average power.
> Taking that into account I'd think most any modern full gallon
> amplifier could handle it.
> You could half the bandwidth but still have the same effective
> modulation by running 375W carrier and 187.5 Watts into
> one sideband only rather than split between two.
> 73
> Bill wa4lav
> ________________________________________
> From: Amps [amps-bounces@contesting.com] on behalf of Roger (K8RI)
> [k8ri@rogerhalstead.com]
> Sent: Thursday, November 26, 2015 1:27 AM
> To: amps@contesting.com
> Subject: [Amps] Amplifier Vs Plate Modulated
>
> I've posted the following on two group. They are not cross posted.
> Please do not cross post answers. If you must post to both groups,
> please cut and past rather than cross posting. Thanks!
>
> OK, I understand, there's less iron in an amp Vs plate modulation, but
> how about a low level carrier driving a legal limit, plate modulated
> stage Vs a low level AM signal into a linear amp?. Which is
> preferable? Not many commercial ham amps can stand up, to long winded,
> AM transmissions and from my experience most AMers tend to be long
> winded, me included. I talk like I write<:-) However Plate modulated,
> or linear amp, the power out limit is the same. With the new power
> limitations, AM appears to be the only loser,
>
> So, what is the advantages and disadvantages for each. Yes, I
> understand that many of today's rigs will run a nice clean AM signal of
> relatively low amplitude (25 to 75 watts, bearing in mind that the
> dissipation in class A is driving the amp right to its limit.
>
> I haven't run AM since the old plate modulated days. OTOH, I do run the
> 5000MP in class A to drive a Tetrode to the legal limit. The 5000MP amp
> only gets warm when run this way. It gets hot if I reduce the drive.
> Class A runs the maximum dissipation with no signal input to the final.
>
> Thoughts?
>
> 73
>
> Roger (K8RI)
>
> ---
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