[TowerTalk] tuners and power rating

[jimlux]

Roger (K8RI) wrote:
> 
> On 11/28/2010 3:26 PM, Danny Pease wrote:
>> I have noticed several
> Several? I don't know of any that are rated for "the legal limit" that 
> can handle much more than medium power.
>> so called legal limit tuners that cannot handle even
>> medium power on 160 unless the load is very close to 50 ohms already.
> Even the Palstar AT5K which is rated for 3500 watts under most 
> conditions is derated to 1000 watts for a low impedance antenna on 160. 
> However, if you raise the antenna to the point where the impedance is 20 
> or 30 ohms it will handle the full 3500 watts.  The AT5K is a physically 
> large tuner.
>>   Also,
>> note almost all tuners ratings are amplifier input, not power output.

I think that meant "input to the tuner" as opposed to "DC power to the 
final" or "RF input power to the amp"..
> I've never heard of any yet, except for the ones designed in the old 
> days where the legal limit was 1 KW input.
> The MFJ 989C will handle the full 1500 watts *into* the tuner as long as 
> the load impedance is not so low as to be out of range.

Maybe that's a way to describe it.. "will handle this power into any 
load where the tuner can be adjusted to present 50 ohms to the 
transmitter".  That kind of limits the tuner usability.. One might have 
a tuner which can operate over one range at full power, and a derated 
power over a wider range (e.g. your AT5K example)


> Many adds are "input to the tuner" but I've not seen any modern ones 
> that were rated input to the final.
>>   They
>> also do not specify at what mis-match the power rating is at.
> MFJ and Palstar do give a power limit for an impedance range, but not 
> specifics for each frequency, nor do we need such.

Do they actually give a real impedance range (as in a shaded area on a 
Smith or R/X graph?) or do they give something like VSWR<3:1.