Yes they are.
On 3/7/2013 9:58 AM, Carl wrote:
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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