Fellow aviators,
Below is the post I sent to ICOM service. Please respond to me if you have approached ICOM in regards to the A24 and Headset/Intercom issues, and tell me of your experience.
Cheers
Walt.
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Greetings Mike, Fred, Carl, {ICOM Services et al},
Ref: Trouble tickets ABHI215195 & ABHI1651A4
Telcon:15 Nov 2010 Mike
Telcon:22 Nov 2010 Carl
Telcon: 01 Dec 2010 Carl
Carl,
Per our last telephonic conversation on 1 December 2010, I have researched the microphone impedance’s published for general aviation audio circuits. With two exceptions all I found fell between the range from 50 to 2200 Ohms. [The two exceptions were both in regard to ICOM products; the manual for the A24 indicates >100K Ohms, and on the site http://www.mypilotstore.com/MyPilotStore/sep/5427[FONT='Helvetica','sans-serif']
indicates >100K Ohms for the ICOM A14, however the ICOM manual for the A14 indicates 150 Ohms. Thus you might contact MyPilotStore and have them correct what appears to be a typo.][/FONT]
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Thus, I continue to believe that the A24 has an inherent design issue regarding the microphone impedance (>100,000 Ohms) relative to the industry range of 50 to 2200 Ohms. [/FONT]
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Per our conversation I asked that you elevate this issue to you next level (Mr. Greg Hake was the name I noted). I repeat that request in this post.[/FONT]
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Below I list my references that you might check the veracity of my findings and note my due diligence.[/FONT]
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V/r[/FONT]
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Walt[/FONT]
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Aviation Microphone data summary
RTCA/DO-214, Audio Systems Characteristics and Minimum Performance Standards for Aircraft Audio Systems and Equipment, dated March 2, 1993.
FAA: TSO-C139 - Aircraft Audio Systems and Equipment
Manufacturer
Model
Impedance Ohms
ICOM
A24
>100K
ICOM
A23
150
ICOM
A210
600
ICOM
A14
150 or 100K: I found two different values depending on the source. The ICOM manual had the 150 value.
BOSE
A20
Microphone (Electret) Bias required: 8 to 16 VDC through 220 to 2200 Ohms.
NARCO
VHF760
Microphones - Electret > 100mV into 200 Ohm
David Clark
H10-13.4
Mic Impedance: 50 ohms +/- 20%
David Clark
[FONT='Verdana','sans-serif']H10-20 [/FONT]
Mic Impedance: 50 ohms +/- 20%
David Clark
[FONT='Verdana','sans-serif']H10-30 [/FONT]
Mic Impedance: 50 ohms +/- 20%
David Clark
H20-10
Mic Impedance: 50 ohms +/- 20%
David Clark
H10-60
Mic Impedance: 50 ohms +/- 20%
YAESU
VXA-710
Ext. Mic, Impedance: 150 Ohms
YAESU
VXA-300
Ext. Mic, Impedance: 150 Ohms
YAESU
VXA-220
Ext. Mic, Impedance: 150 Ohms
[FONT='Arial','sans-serif']PS Engineering [/FONT]
[FONT='Arial','sans-serif']PM 1000 FAA TSO Approved Intercom[/FONT]
Headphone Impedance: 150-1000 W typical, Aircraft Radio Impedance: 1000 W typical
[FONT='Times New Roman','serif']sennheiser-aviation[/FONT]
[FONT='Verdana','sans-serif']HME 26[/FONT]
[FONT='Verdana','sans-serif']150 - 2,200Ω (terminating)[/FONT]
valavionics
VAL_AP_100
600 ohms
www.ps-engineering.com/faq.shtml
You need to be sure that any headset or helmet equipped with such a plug uses general aviation microphone (150 ohm) and headphone (150 to 600) impedance. Military systems are often 8 ohm, and incompatible with civil aviation units.
http://www.ps-engineering.com/docs/PSE_Brochure.pdf
[FONT='Arial','sans-serif']Aircraft Radio Impedance [/FONT][FONT='Arial','sans-serif']510[/FONT]Ù
[FONT='Trebuchet MS','sans-serif']http://www.capitalavionics.com/tip_0909.asp[/FONT]
and for a microphone audio circuit, between 150-600 ohms (measuring DC voltage).
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