[Elecraft] FTDX5000 Design Flaw

[Joe Subich, W4TV]

>> Personally, I'd put the priority on APD fairly down until we start
>> having common situations where the very low IM from the K3 is
>> troublesome.

Transmit IMD can be improved significantly by operating the current
100 W amplifier at reduced power output and by updating the design
with a 48V supply/50V transistors for use with a real "fixed station"
supply.

Even using 24V transistors at 150W output with an 18V supply and 75W
output with a 12.0 V supply would go a long way to reducing transmit
IMD without all of the added complexity of APD.

73,

    ... Joe, W4TV


On 11/21/2010 2:54 PM, Guy Olinger K2AV wrote:
> In my K3, the two tone IM products are better at the output of the
> 100w stage than they are at the 10W point. There IS some serendipitous
> cancellation going on.  But our excellent experience of side-by-side
> K3's at IOTA on Core Banks, and the Field Day same band 40 m CW and
> SSB stations separated by 300 feet, could not have happened in either
> venue without the K3 TX already being very clean.
>
> The adaptive predistortion would work for IM, but could not help out
> with phase noise.  Personally, I'd put the priority on APD fairly down
> until we start having common situations where the very low IM from the
> K3 is troublesome.
>
> 73, Guy.
>
> On Sun, Nov 21, 2010 at 1:02 PM, Julian, G4ILO<julian.g4ilo at gmail.com>  wrote:
>>
>>
>> P.B. Christensen wrote:
>>>
>>> Yaesu's success in their implementation
>>> of Class A amp design is clearly evident -- but it's an inefficient way to
>>> get to those Tx IMD numbers.
>>>
>>>
>>
>> Yes it would be nice to see more transceivers that are DSP based employ
>> adaptive predistortion like expensive and feature-lacking but interesting
>> ADAT ADT-200A. Could the K3 do that?
>>
>> -----
>> Julian, G4ILO. K2 #392  K3 #222.
>> * G4ILO's Shack - http://www.g4ilo.com
>> * KComm - http://www.g4ilo.com/kcomm.html
>> * KTune - http://www.g4ilo.com/ktune.html
>>