[AMRadio] AMPX article on mod reactor

Geoff w5omr at satx.rr.com
Tue Aug 16 07:24:51 EDT 2005

Donald Chester wrote:

> <>
>> This would be the article concerning the value and design of the 
>> reactor and blocking cap value.
>> I will be building up a modulator using either a CVM4 or 5
> Depends on how low in frequency you want to pass through the 
> modulation transformer, Mark,
> and how much current you'll be running in the final section of the rig.
> Typically, 8HY per 1000 ohms of impedance load in the final is a 
> pretty good rule of thumb.

> <>That's about the standard value used in AM broadcast transmitters.

Typically then, if a transmitter had 1500VDC on it's final plates, and 
drawing around 350mA the resulting Impedeance (Z) would be in the 
neighborhood of  4300 Ohms, which would mean around 40Hy of Inductance.  
(just to be sure)

> <>
>> 8~10uF of coupling should do nicely.  Depending on where you put the 
>> coupling, will determine
>> how much of a voltage rating the capacitor needs to be.
> Actually, broadcast transmitters use much less than than, and still 
> boast of flat response down to 30~ or lower.  RCA transmitters 
> typically use 1 mfd.  Gates uses 2 mfd.  I use 4 mfd in my homebrew 
> rig @ 4000 ohms modulating impedance.

What would be the formula for calculating the capacitance needed, Don if 
one wanted to pass frequencies down as low as say... 40Hz?

73 = Best Regards,

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