Forums

Class B RF amplifier

Started by amal banerjee September 28, 2019
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.
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