Modulators And Drivers

[Murphyv310]

Hi.
This has some history of WMR there are references to the old transmitters. http://www.wmrscotland.com/wmr_latest_news.html
Like I say I do not condone Piracy and if it's inappropriate then Mods please remove.

[Nowhere-Man]

Does anyone know what's on Shortwave these days? I have shortwave on my HMV but not sure if SW is still active.
This AM will take me a little while to digest. It is more in depth. The real goal was to learn a bit more about the mechanics of modulation but there are a few transmitter circuits to look at. The main thing I learned of real value was to do with bias. Even if you never build a transmitter, there is useful information about coupling of amplifier stages.
Single sideband I haven't yet tackled.

[pwdrive]

You can check out Ham shortwave live on any of the web SDR sites, the UK's Hack Green is a good one to start with, try the 40 meter band on that site, plenty of activity this time of night, you will need to select lower side band mode, tune by dragging the cursor then fine tune with the +- buttons, the waterfall display will show where abouts in the band the current transmission are, it might take a while to master it at first but it's easy after a while:

http://hackgreensdr.org:8901/

Hams below 10MHz are on lower sideband (LSB) and above 10MHz on upper sideband (USB)

Shanwick, Volmet etc will be on upper side band even though they may be below 10MHz

Lawrence.

[Nowhere-Man]

I don't have a PC on my boat, Lawrence. For internet all I have is a Blackberry phone. That gets me the news but runs slow. I don't watch any TV - just DVD reruns of old programs - 6000000 Dollar Man being a favourite. I even listen to radio on a 1940's Ultra (I rescued and repaired after it started to smoke). Soon I'll be on a small fibreglass coastal boat and very much isolated from things.
For company my German Shep is around. I will see if your link works on my phone anyway. Cheers.

[Nowhere-Man]

Struggled enormously with a phase inverter push pull circuit. Maybe the book over complicated the explanation but the task I had was to consider signal voltage between grid and cathode of V1 and then the drop across anode cathode, anode load series R1 and series R2. The basic idea was to use that drop to bias the grid of V2 so the phases of the voltages differ. I once had to make a simple voltage divider circuit to apply it to theory. Just a battery and bulbs and so on. I sometimes get confused but remember confusion is always a friendly process towards learning. I tried to imagine putting meter probes at various points of the phase circuit. You often find grid bias is taken from between 2 series dividers. In truth it may be simpler to just learn this by the use of a meter than using a schematic. Anyway, it stops me vegetating as I age.

[Nowhere-Man]

"Just as a side note, a very popular transmitter used by small, 250 watt, AM broadcast stations and made by Collins Radio company was a pair of 810s for the RF power amplifier and another pair for the modulator. Stations running this rig were easy to spot, they had a terrific sound."

The class A, A2, B and AB amps I figured worth learning where modulators and drivers are concerned. Most domestic vintage radios I have all use resistance capacity coupling. Once you look into AM modulation, though, differences in single end and power stages crop up. I came across push pull months ago but didn't really understand about watts and grid current.