Linear amplifiers, Advertising blurb vs reality.

[ian]

I was told to double your signal you have to × it by 10

[ch25]

I was told to double your signal you have to × it by 10

1s unit is 6dB, 6dB is power x4
As simple as that.
Chris

[WhiteNoisePoetry]

This is an easy one to solve.
The power rating of 300w is actually referring to DC POWER INPUT, not RF output.
This is as old as the hills.

To be linear, the devices (trannies / fets / valve) will need to be configured for
Class A or Class AB operation.

Maximum theoretical output of a Class A amp is 50% of it's DC input or about 70%
for Class AB1.

In the "olden days" everything used to be quoted as DC input power.

If you looks at old radio mag adverts, or handbooks you'll often see that a typical
100w rig was quoted as being a 180w rig

The old amateur radio licence specified power as DC input power too.

But anyone with common sense will know that DC input power can create issues,
because that depends upon class of amp, type of device, operation frequency vs efficiency etc
and the whole thing becomes meaningless.

Anyone / dealer worth his salt should have known that with no excuse, and should certainly not
be selling a 300w DC input device as being a 300w RF output device. As Scotty from Star Trek would
rightfully say "y'cannae break the laws of physics Captain".

Many purchasers would probably be aware of this bullshit, and despite it being wrong, will already
take it into consideration and adjust their expectations accordingly, but that doesn't help anyone
who is not learned yet. Even the experts were newbies once and had to acquire this knowledge.

- WNP -

[bigpimp347]

A lot of the sales bullshit is meant to baffle clueless idiots with more money than sense that see a model number as power..

usually the model number is reference to the PEP output and not the actual RF output.

two ways to look at the RF out put..
what ever the linear model is, halve it for real RF out,
B300P 150w
KL503 250w
or thereabouts.

AM/FM is pretty much real RF.
SSB is exactly the same as on AM/FM, it does not and never ever will double up..
PEP is usually the current drawn converted to watts or PEP input.

like an old HF radio will be 100w AM 200w PEP input (input current drawn)

i used to look at it this way..
if it does 100w on FM,
it did 100w on USB and it did 100w on LSB peak to peak is 200w
but a radio won't TX peak to peak ever on DSB and be 200w but it was a good way to explain it to those without a clue instead of trying explain input current draw.

[Trondyne]

Ok, so my first ever linear amplifier was purchased online from a well known supplier last week.
Heres my experiences with it so far.
Its an RM KL503, output as advertised is 300 watts max output for a drive power of up to 6watts.
Ive been using 4 watts to keep within the maximum specified.
Page six of the manual states: " The amplifier should give full output ( I assume 300 watts?) with approximately 4-5watts input."

Its a fairly heavy piece of kit and requires a substantial power supply to run it, 35 to 40 amps, so ive used a nice sized car battery to ensure it gets all the amps it needs.

Its proven useful on several occasions where noise or distance gets in the way of a contact, but with my swr meter being what it was reading up to a maximum of 100 watts and the needle not exactly hitting the stop with much conviction, I was not particularly convinced that the advertised output was as described so shelled out yet more money for a swr meter that could handle up to 1KW.
On hooking up that meter I was able to read the following power outputs.

AM.
1)23
2)50
3)60
4)75-80
5)90
6)130-140.

FM.
1)23/25
2)45-50
3)50-60
4)70-80
5)70-80
6)130 ish.

SSB.
1)30
2)65/70
3)70/75
4)105
5)105
6) 130/140.

As you can see its absolutely nowhere near the claimed output power!
I paid for up to 300 watts yet im seeing less than half that advertised.
Antenna swr was set at 1.1:1, battery power was 12.81 volts so within the specified range to drive it, and input set to 4 watts.
Ive contacted the supplier regarding this and received a reply stating this is what would be expected and that the 300 watt figure is obtained at theoretical maximums.
That not what Ive paid for however, I bought it due to price, and advertised output power not for "theoretical maximums".
Those words dont appear anywhere in the advertising or in the manual.
Theres clearly an issue with the power output on the selection between 4+5 as very little changes also.

I have since sent another mail and we will see whether that yields any further info, Ive also mailed the manufacturer.

Seems ive been hoodwinked at this point into believing the manufacturer hype, Time will tell.

No idea what's up here... Always found RM Italy Amps to do exactly what they said, other well known Radio folks who sell and have channels have said the same... The numbers they state assume sufficient power, correct input and the numbers given are PEAK...

[Allan666]

I wonder what the Amp output would be/show if you used a Dummy Load instead of the Aerial ?