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

["Martin J. Morgenbesser" <w7mjm@arrl.net>]

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.
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps