[Elecraft] K3--Too much ALC creates energy on opposite sideband?

[Bob McGraw K4TAX]

Has anyone collected IMD data on the different version of KPA3A amps?   
I seem to recall measuring IMD when I first got my K3S, s/n 10163.   
Since that time I' have experienced 2 failures of the KPA3A in my 
radio.   Elecraft replaced the last one with a newer "more stable" 
version.   I do run my radio with 14.2 volts at the radio in transmit at 
100 watts output CW key closed.   In RX the voltage is 14.5.    The 0.3 
volt difference is the IR drop in the DC power cable and connector.

Guess I need to measure that one.  But hey, it too pretty and very 
comfortable outside.   I'll save that for another lousy weather day.

73

Bob, K4TAX


On 8/29/2019 12:09 PM, Wes wrote:
> Conrad and I have corresponded about this in the past.
>
> He is absolutely correct in worrying about the IMD performance of the 
> K4.  I bought my K3S after being disappointed with the K3 TX IMD and 
> thinking that the FETs would be better.  How wrong I was. IMD was no 
> improvement and reliability was awful.  At 50 VDC, they no doubt would 
> be better but as long as Elecraft clings to "12-volt" radios, I'm 
> afraid this will persist.
>
> Wes  N7WS
>
>
> On 8/29/2019 5:04 AM, Conrad PA5Y wrote:
>> I have measured the TX IMD performance of my and 2 other K3S 
>> transceivers. In my opinion it is not possible to have anything other 
>> than mediocre TX IMD performance from a K3S or a K3 at ANY power 
>> level. I am so disappointed with this aspect of the K3S. The  mass 
>> market and cheap IC-7300 is better, especially on 6m. In all other 
>> respects I am very impressed with the K3S.
>>
>>
>> The transverter output on 10m when set to 0.5mW has incredibly good 
>> IMD performance so the problem is with the 2 PA modules. I have 
>> contacted Elecraft and so far they have not offered me a satisfactory 
>> solution. I think that I am going to go to the inconvenience of using 
>> an external PA on 6m.
>>
>>
>> The K3S has excellent TX composite noise all ruined by poor TX IMD. I 
>> can easily see 19th and 21st order IMD components on 6m in the 90dB 
>> dynamic range of my E4406A spectrum analyser - this rather negates 
>> the advantage to my neighbours when I'm on SSB. For CW and Digimodes 
>> then the K3S is superb. If I was contemplating the purchase of a K4 I 
>> would be asking Elecraft about TX IMD from the hopefully new and 
>> improved TX amplifier chain.
>>
>>
>> Not a happy message but it's the truth. Yes I have the latest FW, yes 
>> I have tried to reduce the gain from the driver using the settings in 
>> the FW yes I maintain the correct voltage on the PA, yes I have late 
>> (not the latest) revisions of the driver and final PA. I am using the 
>> 2 tone facility so there is no question of external or maladjusted 
>> audio non linearity. The fact is that it is poor. I also know what 
>> I'm doing.
>>
>>
>> Poor show Elecraft!
>>
>>
>> 73
>>
>>
>> Conrad PA5Y
>>
>
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