Is the ARRL still using a 6dB fudge with the way they measure IMD?
Carl
KM1H
----- Original Message -----
From: "Paul Christensen" <w9ac@arrl.net>
To: <amps@contesting.com>
Sent: Thursday, March 07, 2013 8:06 AM
Subject: Re: [Amps] Expert 1k amp
Steve,
I did an unscientific check with my SPE 1K. Ripple on the RF envelope at
the 1KW level is no worse than with my Alpha 77Dx and 87A at 1500W. It's
just noticeable on the scope at the maximum power level. Yes, total
drain current is about 40-42 amps.
If the QST Product Review is any indication of the amp's IMD performance,
3rd-order 2-tone is about -40 dBc. Not sure how well that figure holds up
across a sample of units. The IMD spectra of the 2K model appears very
close. Apart from fault detection and T/R, I've not spent much time with
the rest of the schematic so it would be interesting to see how they
achieve reasonably good IMD at full power that's competitive with many VT
amps.
These are not "brick-on-the-key" amps. In the case of the 1K, the
software automatically cuts back power to 50% after about 15 seconds. I
don't run high duty-cycle modes like RTTY, but I think it would be a
painful experience in a contest between automatic power reduction and fan
noise. For me, it's a good instant-on alternative for my operating modes,
but it would not be my only amp.
Paul, W9AC
----- Original Message -----
From: "Steve Thompson" <g8gsq72@gmail.com>
To: <amps@contesting.com>
Sent: Thursday, March 07, 2013 3:50 AM
Subject: [Amps] Expert 1k amp
Yesterday I did some minor repairs to a friend's amp - resoldering joints
on the current sensing resistor. Looking at the circuits later I noticed
that the main supply voltage is regulated by having SCRs in place of
diodes rectifying the transformer secondary and the main smoothing
capacitor is 47000uF.
My friend tells me the amp runs over 40A at full tilt, which means
something like 8.5V ripple on the supply (7V at 60Hz). That strikes me as
quite high and I'd expect to see some difference in amplifier gain/output
if I was running such an amp off a regulated supply and altered the
voltage that much. Has anyone measured one? Is any 100/120Hz audible on a
carrier?
Steve
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