[Antennas] RF Exposure.. Hoooey....or otherwise

2002年3月23日 20:14:02 -0600

At 01:49 PM 03/23/2002 -0600, Kevin Kidd wrote:
>Me thinks Hooey about sums it up.
>>Or maybe its that new math stuff... E times I times number of joints 
>smoked...
>>I don't claim to know everything there is to know about transmitters, 
>but... I
>have been a radio engineer for almost 20 years and a ham longer than that. If
>they can STUFF 70+KW worth of power supply and amps into a conventional 
>vehicle,
>the Harris' or Broadcast Electronics or Collin's or Contentiental's of the 
>world
>will want to talk to them. I work on a 25kw AM TX that the power supply alone
>weighs almost 2000 lbs. I work on several 30-35kW FM TX's that the power
>supplys weigh in EXCESS of 2000 lbs and are about half the size of a vehicle.
>And that is with a 240 volt Delta AC service.
>>Not to mention that in one of the clips a guy (Dave?) was describing the tubes
>in a couple of amps and he was talking about 3-500Z's and 2 of some type of
>"3000's". Granted, the "3000's" tube is probably a 3000 watt plate disipation
>tube that with proper cooling (about 80 CFM) COULD (not likely but could) make
>about 6000 watts in Class AB service. OK a pair _could_ make 12kW with proper
>power and cooling but I didn't see any evidence of any serious cooling or of
>much power supply other than a bunch of alternators.
>>A local CBer called me one day wanting help building an amp to participate in
>the CB shootouts. He wanted it to put out 20kW and be vehicle 
>powered. When I
>had HIM do the math on power supply voltages and currents he was a bit
>chagrined. I think it was about 2500 amps at 12 volts. In addition to the
>railroad alternators you would need rail road tracks for power busses.
>>Crawling back under my rock now.
Kevin,
Come out from under that rock! :) Perhaps, with the antenna arrays they 
have on those vehicles, with gain, the EIRP is 70Kw, not 70Kw into the 
antennas. That would seem to make more sense. They do have several 
verticals phased together for the antenna system.
Of course, they conveniently leave out what exactly they mean by 70Kw, 
leaving the listener (or reader) to assume it's 70Kw to the 
antennas. Maybe that's exactly what they WANT you to think.
I haven't figured it up, but it seems like they had 6 or 8 verticals, 
possibly more, phased together. Would that likely account for enough gain 
to go from 10-12Kw to 70Kw EIRP? All they would need would be somewhere 
around 8 db gain, to reach the magical 70, right? Or is my brain still 
mush from work?
NOW we're back onto an antenna subject. ;)
73's,
Wayne
KD5ICK