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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