Class B RF amplifier

[amal banerjee]

Can the class B configuration be used for RF amplifiers,
given its inherent problem of cross over distortion All
hints, suggestions are welcome. Thanks in advance.

 

On Fri, 27 Sep 2019 22:08:21 -0700 (PDT), amal banerjee
<dakupoto@gmail.com> wrote:

Can the class B configuration be used for RF amplifiers,
given its inherent problem of cross over distortion All
hints, suggestions are welcome. Thanks in advance.

RF amps usually have a tuned output network, basically a bandpass
filter that cleans up harmonics. They can be class A, B, C, D, E, or a
lot of others.

We just did a 14 MHz sine generator that starts with a square wave
from some totem-pole switchmode GaN fets. Not sure what class that
would be.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

On Fri, 27 Sep 2019 22:08:21 -0700 (PDT), amal banerjee
<dakupoto@gmail.com> wrote:

Can the class B configuration be used for RF amplifiers,
given its inherent problem of cross over distortion All
hints, suggestions are welcome. Thanks in advance.

In a single-ended class B amplifier, the conduction angle is 180
decrees, in class C the conduction angle is often much less than 180
degrees. Both can be used to generate RF power when followed by an LC
tank circuit, which ensures waveform continuation up to full 360
degrees.

Class C is mainly usable for constant amplitude modes, such as FM,
while class B is required for AM and SSB.so that the amplitude can be
accurately controlled.

Due to the tank circuit these are essentially narrow band amplifiers.

Class B or Class AB can also be used in wideband applications without
a tank, if a push-pull arrangement is used, extending the conduction
angle to 360 degrees.

 

[Phil Allison]

amal banerjee wrote:

--------------------

Can the class B configuration be used for RF amplifiers,
given its inherent problem of cross over distortion

** Class B push-pull amplifiers are used in RF transmitters.

X-over discontinuity can be reduced to any desired level - both with audio band amplifiers and also at much higher frequencies.

Class B has the advantage of zero power drain when not driven plus *linear* operation - as alluded to by another poster - and require little post filtering of the output signal due to havening inherent low distortion.

Ham radio guys like to use "linears" to boost the power of small transmitters (eg CB or hand held radios), which can them be of any kind.



..... Phil

 

[Winfield Hill]

amal banerjee wrote...

Can the class B configuration be used for RF amplifiers,
given its inherent problem of cross over distortion All
hints, suggestions are welcome. Thanks in advance.

Yes. My AMP-70A 100-watt DC-10MHz amplifier operates in
low-distortion class AB. Some people consider anything
above 0.5MHz to be RF, that's where AM radio band starts.

https://www.dropbox.com/s/elhs1whl2dfn0i7/AMP-70A-2_sch.pdf?dl=1

Discussed at length here on s.e.d, and if anyone needs
more complete info, I can provide a different link.


--
Thanks,
- Win

 

[Gerhard Hoffmann]

Am 28.09.19 um 15:53 schrieb Cursitor Doom:

On Sat, 28 Sep 2019 02:07:48 -0700, Winfield Hill wrote:

Yes. My AMP-70A 100-watt DC-10MHz amplifier operates in low-distortion
class AB. Some people consider anything above 0.5MHz to be RF, that's
where AM radio band starts.

RF starts below 500kHz, though.

That's just nervous DC.

G.

 

[Bill Sloman]

On Saturday, September 28, 2019 at 11:53:51 PM UTC+10, Cursitor Doom wrote:

On Sat, 28 Sep 2019 02:07:48 -0700, Winfield Hill wrote:

Yes. My AMP-70A 100-watt DC-10MHz amplifier operates in low-distortion
class AB. Some people consider anything above 0.5MHz to be RF, that's
where AM radio band starts.

RF starts below 500kHz, though.

Cursitor Doom probably has the BBC's radio 4 in mind, which transmitted on Long Wave at 198kHz, as well as at higher frequencies.

Win may be thinking of US AM radio.

In the circles I moved, RF was just relatively narrow band stuff that included tuned circuits.

The circuits we used to create half-nanosecond wide pulses weren't seen as RF, though the bandwidth obviously had to stretch up to above a GHz.

--
Bill Sloman, Sydney

 

[Cursitor Doom]

On Sat, 28 Sep 2019 02:07:48 -0700, Winfield Hill wrote:

Yes. My AMP-70A 100-watt DC-10MHz amplifier operates in low-distortion
class AB. Some people consider anything above 0.5MHz to be RF, that's
where AM radio band starts.

RF starts below 500kHz, though.



--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

 

[Winfield Hill]

Gerhard Hoffmann wrote...

Am 28.09.19 um 15:53 schrieb Cursitor Doom:
On Sat, 28 Sep 2019 02:07:48 -0700, Winfield Hill wrote:

Yes. My AMP-70A 100-watt DC-10MHz amplifier operates in low-distortion
class AB. Some people consider anything above 0.5MHz to be RF, that's
where AM radio band starts.

RF starts below 500kHz, though.

That's just nervous DC.

Yes. I don't think of my 10MHz power amplifier as an RF
amplifier. To me, RF amplifiers need to use RF techniques,
and therefore look like RF amplifiers. My amplifier, even
tho it stems from the 50MHz Tektronix PG508, looks like
some audio amplifiers, but made with low-capacitance video
transistors, running at much higher-than-normal currents.


--
Thanks,
- Win

 

On 28 Sep 2019 02:07:48 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

Yes. My AMP-70A 100-watt DC-10MHz amplifier operates in
low-distortion class AB. Some people consider anything
above 0.5MHz to be RF, that's where AM radio band starts.

ITU-R which is responsible for frequency allocations for freely
propagating electromagnetic radiation all over the world has made
frequency allocations from 8.3 kHz to 275 (or 400) GHz. Thus all EM
radiation in that region could be considered RF.

 

[Tauno Voipio]

On 28.9.19 08:08, amal banerjee wrote:

Can the class B configuration be used for RF amplifiers,
given its inherent problem of cross over distortion All
hints, suggestions are welcome. Thanks in advance.

There are plenty of Class B RF amplifiers around,
The cross-over distortion does not matter much if
the amplifier is not needed to be linear.

Most of the Class B linear RF amplifiers are actually
deep in Class AB, to avoid the worst cross-over distortion.

The amplifiers used for radio communications do not usually
care about distortion of the carrier frequency wave, but
distortion of the modulation envelope can spoil the results.
The carrier frequency wave is usually restored by post-filtering
the output, either with tuned circuits or with suitable
low-pass filter.

--

-TV

 

[Clive Arthur]

On 28/09/2019 15:39, Bill Sloman wrote:

<snip>

> Cursitor Doom probably has the BBC's radio 4 in mind, which transmitted on Long Wave at 198kHz, as well as at higher frequencies.

Just in case that wasn't a typo, it still does transmit on long wave.

Alien civilisations looking for life will use signal stacking on the
very weak signals available to lift signal from the random noise, locked
to the rotational period of the monitored planet, in this case Earth.
They will look for patterns repeated daily.

The Droitwich long wave transmitter used for Radio 4 has been going a
long time so would be a prime target for monitoring. The aliens will
find repeated time-signal pips, but that's not really enough to signify
intelligent life. They will, however soon identify a more complex twice
daily repeating pattern and thus identify us as their rivals in the galaxy.

There first audible greeting/warning will not be the 5-note 'Close
Encounters' sequence. It will be Barwick Green.

Cheers
--
Clive

 

On Sat, 28 Sep 2019 19:37:25 +0100, Clive Arthur
<cliveta@nowaytoday.co.uk> wrote:

On 28/09/2019 15:39, Bill Sloman wrote:

snip

Cursitor Doom probably has the BBC's radio 4 in mind, which transmitted on Long Wave at 198kHz, as well as at higher frequencies.

Just in case that wasn't a typo, it still does transmit on long wave.

Alien civilisations looking for life will use signal stacking on the
very weak signals available to lift signal from the random noise, locked
to the rotational period of the monitored planet, in this case Earth.
They will look for patterns repeated daily.

The Droitwich long wave transmitter used for Radio 4 has been going a
long time so would be a prime target for monitoring. The aliens will
find repeated time-signal pips, but that's not really enough to signify
intelligent life. They will, however soon identify a more complex twice
daily repeating pattern and thus identify us as their rivals in the galaxy.

I very much doubt that the aliens would hear anything at long or
medium wave frequencies due to the ionosphere. At HF frequencies above
about 10 MHz something will be heard once a day, when some radiation
escapes vertically up from a station.

The strong VHF and especially UHF TV transmissions as well as radar
signals beamed towards the horizon, so the aliens will hear the same
transmission from the morning rim and 12 hours later from the evening
rim with different doppler shift.

There first audible greeting/warning will not be the 5-note 'Close
Encounters' sequence. It will be Barwick Green.

Cheers