Captain Kilowat, very cool that you got to meet with Mr. Kahn. I've read much about him from the earlier days of the Symetrapeak and the Powerside. It appears he got the idea for the SymetraPeak from using land lines to link the studio to the transmitter. He noticed all audio passing over the long phone lines came out being much more symmetrical.
This was the result of the long wires having series inductance and parallel capacitance. Since he couldn't sell a station a 5000 foot roll of twisted pair, Mr. Kahn used standard inductors and capacitors to simulate the long wire effect.
Rumor has it he would drive to a new city every week listening to the AM stations to find his next perspective customer. He would show up at the station, claim he could improve the audio quality noticeably and would install his equipment free of charge....for a few days.
The station engineer got the "try it before you buy it" treatment. Something you don't see today. Mr. Kahn did more than just install a box too. He was somewhat meticulous in routing out any other problems he could find in the audio chain.
He'd come back in a few days and asked if you liked it. I forgot if he charged $1500 or $5000 for this service but most stations paid up because his work did make a noticeable difference. If you didn't pay, he would reverse every single thing he did so you were right back to where you were before he arrived.
Dave457, this particular APF unit is a solid state version of Mr. Kahn's SymetraPeak. To understand if this device would be useful to you, you must understand how your voice works and what this board does.
Your voice vibrates the air both forward and backwards through vibrations. Just about everyone's voice is stronger in one direction than the other. When your voice hits the diaphragm of a microphone this translates into positive and negative vibrations in electrical current that are in step with the frequency of your voice.
Now you apply this voice modulation to an AM carrier. The negative portions of your voice can only reduce the carrier to a certain point until the carrier is cutoff. The positive portions of your voice can go as high as the transmitter has the headroom to reproduce. The higher positive peaks are on AM, the louder the modulated audio is. There are limits before distortion is noticeable.
The APF board averages your positive and negative peaks together so that they are fairly equal regardless of how asymmetrical the audio feed may be. This is handy for broadcasters since everyone's voice has a 50% chance of favoring the same peak as the next persons.
With a station that only has one operator it makes much more sense to simply identify which phase produces the most PEP output. You can do this by installing a small DPDT switch inline with your mic element or 1:1 isolation transformer that can flip the polarity.