>"Speaking of switching speed---- Instead of using a sequencer, my ICOM
provides a setting to delay keying the Amp. What is a considered a
reasonable delay 10ms, 20ms, 30ms ??"
Jerry, are you sure it's a delay of the amp key line? My Icom 7300 allows
for the delay of transmitted RF to assist some sluggish amplifiers on
contact-make. The amp key line should never be delayed on make.
The same Icom 7300 has a problem on break that results in hot-switching of
my fastest amps when using CW QSK mode. The 7300 is releasing the amp key
line before the RF envelope decays to zero. Despite several efforts to
alert Icom of the problem, they have yet to release a firmware fix. It's
not just me; it's been documented by several others including Rob Sherwood.
Icom's RF Delay menu should be set just long enough for the amp's relays to
engage. That's best measured and set using an oscilloscope. Typically, the
longer the delay setting, timing artifacts become increasingly apparent.
So-called "dit shortening" is a common problem with excessive RF delay
settings.
Paul, W9AC
-----Original Message-----
From: Paul Christensen [mailto:w9ac@arrl.net]
Sent: Wednesday, December 28, 2016 10:57 AM
To: 'amps@contesting.com' <amps@contesting.com>
Subject: More about amplifier keying
Brian,
Also keep an eye on published SSR on/off switching times. On my QRZ.com
page, you can see two keying interfaces about half-way down the page. One
uses a balanced pair of IRF820 MOSFETs to switch AC and DC loads. The
other uses a power MOSFET SSR block that switches substantially faster than
that shown on the Ixys datasheet. Both types quickly switch high-voltage,
high-current loads in approx. 1-2 mS.
http://ixapps.ixys.com/DataSheet/CPC1978.pdf
The IRF820 version is an adaptation of Chuck Olson's "KeyAll," with some
added logic options.
http://wb9kzy.com/keyallhv.htm
I highly recommend Chuck's kit and it will fit nicely into your 30L-1.
Although you can add it externally, it should be possible to add it
internally in a way that's 100% reversible in the event you later want to
sell the amp. Most Collins collectors are looking for unmodified gear. The
Keyall comes with a PC board and all parts for about USD $15.
I think the simplest and cheapest option has already been discussed by Jim,
W8ZR. It's tough to beat the Ixys PLA140 or the Avago series of balanced
MOSFET SSRs. Add one resistor to limit photodiode current and you're done
-- although you'll need to build it on something like Vector/perf board.
Just ensure the 30L-1's internal relay doesn't get near the 1/4 amp
switching limit of the device.
Paul, W9AC
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