[TenTec] ten tecs have 100 watts out on carrier??

[Dr. Gerald N. Johnson]

On Sun, 2007-09-30 at 22:06 -0500, Bob McGraw - K4TAX wrote:
> >From a person that runs AM, a carrier is a carrier.  AM is the modulation 
> mode.  CW is the modulation mode.  Hence the FCC emission definition of A-3 
> for AM and A-1 for CW.
> 
> A radio rated at 100 watts CW or 100 watts SSB PEP both are the same power. 
> A 100% modulated carrier, hence AM, has sideband power that is equal to 4 
> times the carrier power.  Thus for a 100 watt PEP rated radio to correctly 
> run AM the carrier must be reduced to 25 watts.  Then the PEP value is 100 
> watts.
> 
> As to the fold back issue, the Japanese radios typically use the SWR 
> monitoring circuit to adjust the drive to the PA.  Thus as SWR increases the 
> drive decreases and output power goes down.  Now with Tentec radios since 
> the Paragon and Omni series, they monitor PA current.  As PA current 
> increased above a pre determined value the drive to the PA decreases.  This 
> is specifically effective when load Z is below the design value of 50 ohms. 
> The smart part of this design is the fact the with supply voltage constant 
> at 13.8 volts as load Z decreases, drive decreases but only where PA current 
> exceeds a certain value.  Therefore the input power, volts x amps, is a 
> given and the output power remains almost constant regardless of load.
> 
> Now what must be realized is the fact the SWR is not a simple indicator of 
> load.  If the load is 50 ohms the SWR is typically 1:1.  If the load is 150 
> ohms the SWR is typically 3:1.  Now here's the kicker, if the load is 16.6 
> ohms the SWR is also 3:1.  By monitoring PA current the DC power into the PA 
> is controlled and maintained a safe value, specially with low impedance 
> loads.  The system can still deliver rated power into SWR values of loads 
> both higher than 50 ohms and lower than 50 ohms.  Simply monitoring SWR 
> won't allow this to happen thus the reason the Japanese radios fold back 
> power with SWR values above a specified amount.  Each radio company 
> determines where the foldback point begins.  Some choose 1.5:1 while others 
> choose values like 3:1.
> 
> 73
> Bob, K4TAX
> 
The software in the FT-857 has settings in the alignment menu to set the
alarm and shut down thresholds. A complete reset sets those points to
1:1.

73, Jerry, K0CQ