Reverse Carrier Control Comments or Schematics ?

[DMOD]

Build the 7500.  I've got a 4cx5k, socket,  filament xformer and 3 amp ccs Dahl plate xformer.   Within the next couple months,  vac variables for tune and load.


I'm scream modulating it,  a la continental 50k xmitter basis,  although I stead of a series mod,  I'm going pwm (already have a pwm capable of 1.5 kv,  hence the reason).

Build yours,  and let me know what problems lie ahead lol...

--Shane
KD6VXI

You're screen modulating the 4cx5k with a PWM signal? That ought to be interesting.

Phil- AC0OB

[KD6VXI]

It's going to be my first choice.   I had a series mod built,  from a schematic posted here,  but have since dismantled it.

If the pwm drive is no Bueno,  I'll build up the series mod again.

I asked QIX about this idea a while back and I believe it got lost in the shuffle.   As such,  only way to find out  if it's going to work is build it....   :-)

--Shane
KD6VXI

[DMOD]

You only need about a 30W modulator that varies the voltage between 250V and 500V at 50 mA max.

A PWM modulator seems like overkill and overly complex for SM.

Phil - AC0OB

[KD6VXI]

It is.   But here's the rub.

I have the pw built,  using air wound coils and then 600 volt rated #14 (iirc).   The mosfets are 1.5 kv .   I've since purchased Teflon  16 gauge.   I had built a series mod and cannabalized it fto make a hv pwm.

I modulated a triode with it,  fine business.   Learning experience.

That's what this xmitter is...   Learning experience.

If this doesn't work,  I have a 3000 new in box I'm sure I could use as the switch.

It's a case of run whatcha brung.   The modulator and processor is built.


--Shane
KD6VXI

[w1vtp]

My opinion - hope that is OK.  This whole concept seems like an awful waste of power and certainly will stress most amateur grade components

Merry Christmas, Al

[WB4AIO]

My opinion - hope that is OK.  This whole concept seems like an awful waste of power and certainly will stress most amateur grade components

Merry Christmas, Al

I agree.

I think the reason it has obtained a toehold at a few AM broadcast stations is that they are in bad shape economically and are desperate to reduce their power bills. Thus the 50-kW station using such a system is 50-kW only during pauses in speech or other programming. During full modulation, the carrier drops down to 12.5 kilowatts or so. That really saves on the power bill.

Of course, they'd save even more on the power bill if they just used standard AM and dropped down to 12.5-kW steady carrier. And it would sound better too, and be much easier to implement.

But... the FCC says that you must stay within 15 per cent. (if I recall correctly) of your assigned carrier power. If you don't there are fines and penalties. And they might recalculate your protection from other stations if you apply for a power cutback.

So the "reverse controlled carrier" operation lets them save power and still pretend they are running 50 kilowatts.

73,

Kevin.

[R. Fry SWL]

... Of course, they'd save even more on the power bill if they just used standard AM and dropped down to 12.5-kW steady carrier.  And it would sound better too, and be much easier to implement. ...

Note that a "standard AM" station with a 12.5 kW carrier modulated +/-100% has a smaller useful coverage area than one using a 50 kW carrier modulated +/-100% (other things equal).