[CQ-Contest] History of Low Power Category

[Tod Olson]

I guess I Œgo back¹ even further than Frank. I was licensed in 1952.

In 1952 power was measured, not by output, but rather as the product of the
HV on the final power tube and the current drawn by that tube.There were
transistors but most of them had an upper frequency limit of 1 Mhz ‹ not of
much interest to Hams.

For CW the tube efficiency was probably 70% so 100 watts input would have
been 70 watts in today¹s measurement system. In about 1955 Central
Electronics introduced the 10A, 10B and 20A phasing system SSB transmitter
kits and a number of us started using SSB since building a linear amp was a
lot cheaper than building an AM modulated transmitter which would require a
50 watt OUTPUT audio source for transmitter modulation. The tube of the day
was the 807 [you may have wondered about why the old guys talk about 807¹s
and beer the way they do ]. If you were a poor teenager you could buy a WW
II surplus 1625 which was a 12 volt filament 807. The commercial rigs used
807¹s or a ³new² power pentode tube called the 6146.  All of these tubes
could be operated at 100 watts input on CW or SSB. Linear amplifiers for
those rigs would usually be 400 or more watts input. Building a power amp
was a challenging thing and required acquisition of a lot of high priced
components.

As a result there was a large group of folks who only had transmitters with
an input power of 100 watts or less. That led to the decision to define low
power as being 100 watts input and anything more than 100 watts being
defined as high power. Some years later the FCC changed the rules with
respect to amateur power limits and made the rules limit power output rather
than power input. At that time most transmitters were operating AB1 or AB2
and not Class C as had been the case n the 1950¹s. As a result of the FCC
change,  to operate at a power level of 100 watts you would need as much as
200 watts input since the output circuit efficiency was about 50%. In short,
the contest limits for low power were driven by Œtransmitter demographics¹.

The selection of QRP power went through something similar but there were
many fewer QRP guys at that time. Actually, those of us who had started with
crystal oscillators and 6V6 final tubes [ maybe 300 volts times 30 ma or 9
watts input) never gave much thought to the fact that we were running ³QRP².
We just worked as many guys as we could hear and could hear us!

Randy, I am sure that in 1990, when you assert that CQ established 100 watts
as Œlow power¹, they were referring to 100 watts output. Many years earlier,
when ARRL defined 150 watts as Œlow power¹ they did it at a time when power
was measured as input power.

Because the tube efficiency was at best about 65%, in essence, these were
the same values. Today, because the FCC rules stipulate output power, the
ARRL 150 watt value <which now refers to output power> is slightly higher
than the  CQ value. A number of people bought 200 watt solid state rigs so
that they could get an extra few watts of output.

But the difference between 100 watts output and 150 watts output is about
1.7 dB. Running the extra¹ power of 150 watts output Œfeels good¹ to the
person transmitting, but usually is absolutely not able to be detected by
the person receiving the signal.
  
While the history may be interesting, the practical effect of having a
common low power definition is probably nil. I suppose that reducing
confusion might be worth something.

73, Tod, K0TO


 

On 9/16/14, 8:09 AM, "donovanf at starpower.net" <donovanf at starpower.net>
wrote:

> Hi Randy, 
> 
> Sweepstakes' 150 watt (input power) low power category goes back
> many years, long before I was licensed in 1959. Field Day was the
> same. The ARRL DX contest probably adopted the same traditional
> 150 watt low power limit.
> 
> 
> There weren't many 150 watt rigs in 1990, I suspect that swayed
> to power level for CQWW
> 
> 73 
> Frank 
> W3LPL 
> 
> 
> 
> ----- Original Message -----
> 
> From: "Randy Thompson K5ZD" <k5zd at charter.net>
> To: "Contest Reflector" <CQ-Contest at Contesting.COM>
> Sent: Tuesday, September 16, 2014 12:38:36 PM
> Subject: [CQ-Contest] History of Low Power Category
> 
> I was recently asked why the CQ Contests use 100W as the limit for low power
> and the ARRL Contests use 150W. I had not really thought about this much
> and wonder if anyone can explain how the limits were chosen.
> 
> 
> 
> The CQWW introduced a low power category in the writeup for the 1990 CQ WW
> SSB Contest (and the rules for 1991). It is assumed that 100W was chosen
> because it was easily accomplished by most barefoot transceivers or radios
> of the time. 
> 
> 
> 
> Can anyone explain the history of the ARRL selection of 150W? The slightly
> higher power level can be reached by some radios, but it also encourages
> "low power" stations to run an amplifier to gain that extra db between 100W
> and 150W. 
> 
> 
> 
> It would be nice if all contests used the same low power limit. Not because
> one limit is more right than another, but so there would be less confusion.
> Last year there was one entrant that entered CQWW as low power and then
> realized they had exceeded 100W (I think they ran 110W or 120W). They asked
> to have their entry reclassified to high power. Admirable integrity, but
> unfortunately caused by the confusion between ARRL and CQ category limits.
> 
> 
> 
> Randy, K5ZD 
> 
> 
> 
> 
> 
> 
> 
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