ICOM A-24 Impedance puzzler & Documentation denials
First thank you all for your posts to my start of this thread.
I read them with interest. I then downloaded the manuals for the A24 (ICOM America) and A24E.
I see the warnings in the A24E manual (“E” for European I presume<?>) not for use in flight/only for ground use!!!!
Now WHY<?>!!!! Would anyone buy a receiver for VORs that is to be used only on the ground!!! How utterly absurd. My personal opinion is a paper cover for a known but denied problem.
I also note that in the A24 manual the microphone impedance is listed at greater than 100,000 Ohms, while the manual I down loaded for the A24E has an apparent error. That is the index indicates [FONT='Helvetica-Bold','sans-serif']SPECIFICATIONS on page 31 and OPTIONS on page 32, whilst I find options on both pages without specifications.[/FONT]
I also searched other manufactures of Aviation Audio components and found the Microphone impedances ranging from 50 Ohms to 2200 ohms. This would indicate the A24 was not built to general aviation standards (I compare with YAESU’s posted Microphone impedance value of 150 Ohms for the VXA-710/300/220).
Of additional interest, the specification for the ICOM A23 is 150 Ohms, and their A210 panel mounted transceiver is specified as 600 Ohms…. These seem right on the mark.
Where are my Ham radio operators and electronics engineers? Tell me, what results might one expect if connecting a ~470 Ohm microphone to a transceiver with a >100,000 Ohm microphone circuit? Something like I (and others?) experience with the A24? Something like loading the microphone circuit down (I remember about 4 volts when we were bench checking ) until if fails or sets up oscillations?
Cheers
Walt (for [FONT='Verdana','sans-serif']Silvaire1 Walt stands or Want A Luscombe Too!)[/FONT]