Date: Tue, 26 Feb 2019 16:09:50 +0000
From: Chris Wilson <dead.fets@gmail.com>
Message-ID: <21240445.20190226160950@gmail.com>
To: Eric NO3M <rsgb_lf_group@blacksheep.org>
In-Reply-To: <0a79de5c-3274-caae-c000-d5f49bb44540@no3m.net>
References: <942860C848184BA2A0A9103E0EE56DF7@DELL4> <1UTEEgOcyQ.DAejAuRZtn9@optiplex980-pc> <92784b07-a799-fb4e-9080-e1e8bb167b75@n1bug.com> <1UTEEhG1Ft.EdI1dlVbFOZ@optiplex980-pc> <3062ef19-bb69-3187-e8db-6a6bf5050739@n1bug.com> <234098919.20190226111836@gmail.com> <c7ee7c98-78c6-3d45-92a0-5a2c4e700d60@no3m.net> <0a79de5c-3274-caae-c000-d5f49bb44540@no3m.net>
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Subject: Re: LF: Class D current spikes
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Hello Eric,

Yes, the output is a square wave when I use the U3S I take the output
direct from CLK0 at 2X frequency (set in the U3S menu) via a co-ax to
the input of the W1VD amp to Pin 3 of 74F74 with no 50 Ohm load
resistor. It works perfectly. It makes me think other exciters are
doing something different at the end of the TX cycle. I know not what
though...

The amp is powered all the time, the output solely depends on the
presence or not of an input signal.

Same with the TS-590S, output from the DRV socket at under 0dBm sine
wave at 2X frequency from the 590 into a squarer. Squarer drives the
W1VD amp the same, (no 50 ohm resistor) direct to Pin 3 of the 74F74.
no issues. Run the 590 at 136kHz into a W1VD doubler and a pre amp and
the FETS's life is always short. Death always seemingly occurs at the
end of a WSPR or OPERA cycle. Again the amp stays powered all the time
from either a huge linear supply or an HP SMPS 50V supply from a
server.

I have noted that running the over current limiter on the linear on
the cusp of triggering helps. The SMPS is ruthless in the doubler
scenario and FET life is *always* on the edge. The gate waveforms seem
OK, it's the drain waveform that shows the spikes as the oscillations
decay away. I would love to get to the bottom of this as I have too
many different set ups to remember :) I assumed it was some sort of
feedback from the antenna perhaps, but I am a novice and once I found
what saved me from spending loads at Farnell I gave up chasing the
cause.

Tuesday, February 26, 2019, 12:12:08 PM, you wrote:

> Or in the case of a U3S with a square wave output at CLK0 (I assume it's
> square)... a complete positive half cycle without any further "noise", etc.

> On 2/26/19 7:04 AM, Eric NO3M wrote:
>> Just a thought, perhaps the RF is ending exactly at a zero crossing, 
>> whereas a typical PC/soundcard + exciter may not be and that is 
>> causing this issue.


-- 
Best regards,
 Chris                            mailto:dead.fets@gmail.com