On 5/11/2012 7:02 AM, John G. wrote:
> I am using one of the Drake TV-1000LP right now.
Remember that the original Drake filters were designed and built when
FCC Rules restricted us to 1,000 watts PLATE INPUT power, which, for all
practical purposes, limited us to 600-700W output power, depending on
the efficiency of the output stage. I don't remember when that Rule was
changed to allow 1.5kW OUTPUT, and I don't know if the Drake filters
were later redesigned to handle 1.5kW.
Following up on Dale's suggestion that tube amps are more likely to need
an HPF than a solid state amp -- I would disagree to the extent that it
depends on the topology of the output network. My 30 year old Ten Tec
Titans use a manually tuned Pi-L output network, and their harmonic
suppression seems to be a bit better than my new Elecraft KPA500. IM
seems to also be quite low when I tune them carefully.
It is also well known that using ALC between a power amp and the driving
rig to set TX power level is a recipe for massive IMD. I suspect that it
would also increase harmonics. It's OK to use ALC to prevent damage to
the amp when something breaks in the antenna system, but NEVER to set
the power level. Power output should ALWAYS be set by controlling the
drive level.
HOWEVER -- W8JI, in an excellent applications note on his website, has
observed that MANY rigs, especially low cost rigs, put out an initial
spike of full power at the beginning of each transmission when adjusted
for less than full output. This spike WILL cause distortion -- both
harmonics and splatter. Tom recommends using a simple passive attenuator
(resistive voltage divider) between the rig and the power amp.
73, Jim Brown K9YC
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