[AMRadio] How much is too much?

Geoff/W5OMR ars.w5omr at gmail.com
Fri Jan 19 14:44:47 EST 2007

Brett gazdzinski wrote:
> I have been watching Johnson matchboxes on ebay,
> and the KW ones go over $300.00 and I 
> don't want to spend that much as I plan on
> building something once I get the parts and design
> figured out.
> Once the antenna stuff arrives, I plan on putting up
> about 100 feet of dipole fed with homemade open
> wire line, in place of the 40 meter dipole, so
> I need to get it to work if I want to be on the air.
> The Johnson 275 watt (250?) matchboxes are less, good to
> experiment with, can they handle 275 watts of AM?
> Anyone know?

I don't see why the 275 matchbox wont work for you.  Goodness knows, 
it's built as well as these 'so-called' kilowatt matching devices of 
current day.

I'd be careful to apply full carrier to the device if it's not in tune 
though.  I did that by accident, moving the rig back to 3.880Mc from 
3.650 using a Heaktkil SA-2060 2kW impedance matching device.  Moved 
back up band, and hit that thing with about 300w into a non-matched 
load, and there were lightning flashes coming from behind the meters.  
The metering is all but gone.  It will still measure SWR (kinda / sorta) 
but a maximum of 5w of output, and I -know- I'm running 150w DC input to 
the final.

As long as you're close to being matched, I feel reasonably sure that 
the 275 will probably carry 300w of carrier.


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