Avoiding Splatter, RFI and other

[Ratfink]

Let us not forget that that 150% or 200% modulation pertains to ONLY the positive peaks and NOT the negative peaks.It is negative modulation in excess of 100% that causes carrier cut-off and distortion/splatter. Commercial AM broadcast stations routinely run asymmetrical modulation of 120% positive while maintaining 100% negative mod. I had a problem with the modulator in a Nautel Amphet-1 transmitter one time and tested it to 100% neg/200% pos modulation when I was done repairing it. The 'scope sure looked weird and that SOB was LOUD as hell on the air..........errrrr......make that the dummy load ......... but clean.

Lol, am broadcast stations are class c correct?

 

[Captain Kilowatt]

Lol, am broadcast stations are class c correct?

No. The old tube transmitters were class C plate modulated which means the carrier was generated using class C but it was modulated using a class B (usually) modulator amplifier. Nothing was ever amplified in class C after being modulated.Check out how plate modulation works. Things are quite different today.The solidstate transmiters use a very high class of modulation, the Nautel I had 25 years ago used class D for the carrier and pulse-width modulation.Today class H has been used as well as various forms of digital carrier control. Class C for an amplitude modulated signal is crap despite what most CBers say or think. The technical properties speak for themselves but you first have to understand those properties and be willing to accept them.

 

[Ratfink]

ok,ive allways wondered. a buddy of mine has a transmiter and spoke breifly about it

 

[Captain Kilowatt]

A lot of people think AM broadcast transmitters are class C but that is because all they hear is "class C plate modulated" and the rest either falls on deaf ears or shoots right over their head. The typical device that most CBers call a "modulator" is no in any way shape or form a modulator in the true meaning of it.They are simply a class C amplifier meant to have a really low dead key and a high "swing". A real modulator consists of simply a big audio power amplifier. The high level audio is fed through a special transformer called a ........wait for it ............modulation transformer. The audio is then fed to the plates of the class C carrier amplifier wich causes the amplitude of that carrier to change between zero and four times the unmodulated level. This is what happens in plate modulation in it's most basic terms. A typical 1000 watt AM transmitter needs about 750 watts of audio to modulate it 100%. CB type "modulators" use no audio and thus are not really modulators.

 

[Grogan]

can't help asking, but did that cb'er key up outside your property and mess up your tv pic, or was he keying up outside the hollywood studio where the moon landings were faked from?

man on the moon in 1969, lol, this is most likely what their onboard computer looked like;

I think the computer was black and white then!!!

 

[psycho]

If someone lives a few doors down and screws up my TV picture.....fine, there isn't anything good on TV anyway.

 

[The Mad Scientist]

Excellent explanation there Kapt.K., But I think it falls on deaf ears mostly as no one seems to really care anymore. I miss the good old days when there were more people that were concerned with operating their stations propperly. Nowadays most are only concerned with their class "c" mega garbage splatterers. It dosen't take a rocket scientist to know how to add a bias circuit and run it within it's limits. In the end it's all about the money to be made off these units. That goes the same for the way radios are tuned as well.

Dame shame really.