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
----- Original Message -----
From: "john ferro" <foxbat426@hotmail.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Sunday, September 30, 2007 3:59 PM
Subject: Re: [TenTec] ten tecs have 100 watts out on carrier??
actually you have not helped me out - you still have not answered the
question - whats the difference between an am carrier and cw carrier? if
it's the same as some people say why on a japanese radio the am carrier is
only 25 to 50 watts (depending on the radio) when the mic is keyed vs. 100
watts on the same jap radio cw mode keyed down - all assuming swr is 1? i
understand the swr fold back issue.> From: OTAKEBI@aol.com> Date: Sun, 30
Sep 2007 16:39:52 -0400> To: tentec@contesting.com> Subject: Re: [TenTec]
ten tecs have 100 watts out on carrier??> > Yes, Mike.> Now we know what
was going on once he explained it a little better.> I had a TS 180s that
at had to see a perfect, flat, SWR to put out full > output.> Like Ten
Tecs better.> Glad we were able to help him.> Dan/N4VET> > > >
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