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Phase Rotator

Discussion in 'General Ham Radio Discussion' started by dave457, Jul 24, 2013.

  1. dave457

    dave457 Sr. Member

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  2. Shockwave

    Shockwave Sr. Member

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    I have to say for two way use where one operators voice is on the mic 99% of the time, this device is a waste of time and energy. Just connect the two wires on the back of your mic element so that your voice produces the maximum PEP output.

    If you have a scope, you'll see the average voice is not symmetrical and will favor one peak being stronger than the other. Why spend money to remove the stronger peak when you can use it to your advantage gaining more PEP?

    This device is useful for broadcasters where dozens of different voices may be on the air including music over the course of the day. For cases where one person operates the mic, you're money is better spent on a negative peak limiter if AM is your game.
     
  3. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Not in amateur radio applications. I have used SymetraPeak units in broadcasting however. I even met Leonard Kahn once at a convention. He was an interesting man. Very gifted and a bit eccentric. My personal feeling is that it is not necessary for ham/CB applications if you know HOW to run your gear and understand modulation fundamentals.
     
  4. blue runner

    blue runner Member

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    The power supply is a center tap kinda DC supply. Take two 6VDC wall warts and connect the outputs in series (+ of one supply to the - of the other). Where the two supplies are connected to each other is GROUND/COMMON/NEUTRAL. The voltage between the other two wires is +12VDC and -12VDC.

    Didja plan on using it to improve your receiver or for speech processing from the microphone?

    Either way you might have to work out some impedance matching on the input & output to and from the radios circuits.
     
  5. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    If you had two 6 VDC wallwarts and connected them as you said. you would have the common connection as ground and you would then have a +6 VDC connection and a - 6 VDC connection. The total voltage across the two hot leads would be 12 volts. This is not what is required. The opamps in the circuit require a differential power supply that supplies both a positive 15 volts and a negative 15 volts as referenced to ground. I have used TA072's in audio circuits, especially balanced to unbalanced circuits before and always supplied a pos and neg supply voltage in addition to a common ground. Not too sure I would use a wallwart in an application like this unless there is a common mode rejection filter to get rid of the HUMMMMMMMMMMM that most of them create due to poor filtering. I see this circuit does not have such a filter. You may get lucky and get a wallwart that is clean however.
     
  6. dave457

    dave457 Sr. Member

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  7. Shockwave

    Shockwave Sr. Member

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    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.
     
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