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RE: [BULK] - [Amps] IC-718 and AL-811: Icom manual misleading,interface

To: Steve Katz <stevek@jmr.com>,"'Japerlick@aol.com'" <Japerlick@aol.com>, W7MJM@arrl.net,amps@contesting.com
Subject: RE: [BULK] - [Amps] IC-718 and AL-811: Icom manual misleading,interface nec...
From: "Martin J. Morgenbesser" <w7mjm@arrl.net>
Date: Fri, 04 Feb 2005 13:49:29 -0800
List-post: <mailto:amps@contesting.com>
Thanks for your responses, guys.

The SOA explanation makes sense to me, if it were a solid state device doing the switching. But as Steve points out, the IC-718's "send relay" is in fact a physical relay, as depicted in the schematic. And if it is rated for 16V @ 2A, as the manual suggests, it should be able to directly handle the 12V @ 100ma present on the AL-811's relay line.

However, given the Icom representative's stated reluctance to consider it Icom's fault if the IC-718 send relay were to fail under those operating conditions, I decided to spring for the ARB-704. Ironically, the ARB-704 is a solid state device, but one capable of handling the Al-811's relay line!

The bottom line: Icom needs to do a better job of stating the technical specs in their manual, or give the customer the benefit of the doubt. Of course, now I won't have to test their willingness to do the latter.

In any case, I'm very happy with the IC-718/ARB-704/AL-811 combination. The amp keys beautifully and puts out a solid signal. Plus, thanks to the ARB-704, I have an additional red LED letting me know I'm keying the amp. :-)

One other thing, if Tom Rauch is reading this: Thank you for designing such a nice amplifier that can be had at a very reasonable price!

See you all on the air!

At 11:36 AM 2/4/05 -0800, Steve Katz wrote:
SOA is surely something to consider, except the IC-718 uses a keying relay for the amplifier "SEND" function. Check the schematic. They rate it "16V, 2A," without any consideration for simultaneous or not; however, that still begs the question, "Why only a 16V rating for relay contacts?" It's an amazingly low rating, even for tiny TTL relays....-WB2WIK/6
-----Original Message-----
From: Japerlick@aol.com [mailto:Japerlick@aol.com]
Sent: Friday, February 04, 2005 11:22 AM
To: stevek@jmr.com; W7MJM@arrl.net; amps@contesting.com
Subject: Re: [BULK] - [Amps] IC-718 and AL-811: Icom manual misleading, in terface nec...


Actually, this is quite common in transistor switching applications. Transistors (whether FETs, Bipolars, IGBT's whatever) have have "Safe Operating Areas" which is a technical term for the range of simultaneous voltage and current levels it can safely sustain.

For example, the venerable 2N2222A is rated at 75 Volts VCBO, 40 Volts VCEO and 0.6A max Collector Current...but the max power dissipation is 0.5 watts. Obviously you cannot sustain 75V at 0.6A SIMULTANEOUSLY. Manufacturers specify a safe operating area--usually in chart form--showing how much current the transistor can pass for given voltage conditions--both in forward and reverse bias conditions. It's important to note that these charts do not necessarily correspond to a simple curve of the maximum power dissipation.

Combined with safe operating areas is the consideration of junction temperature. Almost all of these specs are given for device junctions at 25 degrees C (about room temperature). Of course, you can imagine, the ratings degrade at higher temperatures. Overtemperature and overvoltage are the two most common transistor-killers.

So, yeah, the Alpha guy is probably right...you can't get both max voltage and max current simultaneously....and it is not that simple.
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