Hermes Mic Input

M1AQO
Posts: 26
Joined: Thu Apr 04, 2019 11:57 am

Hermes Mic Input

Postby M1AQO » Tue Dec 17, 2019 2:49 pm

Hi,

I'm just looking for some help with the Anan 10 front mic input.

I'm using a PC Electret mic wired:

Ground: Sleeve
Mic: Tip & Ring

The mic is working fine with the radio, apart from*

Ive checked the jumpers in the radio:

Jumper 4 (Mic) is connected to terminals 2 & 3 for "tip" mic input.
Jumper 5 (Bias) has no jumper installed which I believe is standard, therefore no Bias voltage ??
Jumper 6 (PTT) is connected to terminals 1 & 2 for "ring" PTT

After reading Phil's Hermes Handbook, I believe this to be standard from the factory.

1, I would like to know how the Electret element is being powered becuase there is no voltage going to the element. I've checked with a DMM on the tip and sleeve and there is no voltage on the tip or the ring.

2, What effect will the Mic being wired to the tip and ring simultaniously ?

*The reason I ask is that there is some background noise when I dead key the radio and I'm wondering if its because the Mic is wired to both Tip & Ring.

Regards

Glenn M1AQO
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w-u-2-o
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Joined: Fri Mar 10, 2017 1:47 pm

Re: Hermes Mic Input

Postby w-u-2-o » Tue Dec 17, 2019 5:15 pm

Glenn,

Just to clarify, I'm assuming you have a PC microphone with the mic + on the tip, and the mic bias on the ring, with sleeve being ground. This is a very common configuration, if not an outright standard for PC 3.5mm TRS microphone connectors.

If that assumption is correct, then you must provide bias on the ring terminal for the electret microphone element to work correctly. Without it microphone output will be low to unusable.

More importantly, this type of microphone wiring must be properly configured for PTT operation. All PTT input pins, either on the accessory connector, an RCA jack on radios other than the -10 or -10E, or the microphone connector itself, are paralleled. That means if you have JP6 installed PTT will either ground the tip or ring, depending on the position of JP6, thereby grounding the output of the microphone during transmit and rendering it useless.

Again, if my assumption about your microphone wiring is correct, place JP5 to provide bias to the ring terminal, and remove JP6 entirely. Then provision a separate PTT switch on the accessory connector (or use the MOX button, spacebar PTT or VOX).

73,

Scott
M1AQO
Posts: 26
Joined: Thu Apr 04, 2019 11:57 am

Re: Hermes Mic Input

Postby M1AQO » Wed Dec 18, 2019 9:41 am

Scott,

Correct on all points.

It will be interesting to see the result when the Bias is connected.

It would appear in my current setup that there is an impedance mismatch due to no Bias powering the FET in the element.

It also explains why there is only two shorting clips in the radio, because you swop out J6 for J5.

I will report back on the thread for other users.

Thanks for the clarification and help.

Glenn
M1AQO
Posts: 26
Joined: Thu Apr 04, 2019 11:57 am

Re: Hermes Mic Input

Postby M1AQO » Thu Dec 19, 2019 8:22 am

Scott,

I've changed the Jumper and all appears to be well. :P

I'm assuming that no Bias was causing an inpedance mismatch and causing the noise on the mic.

Thanks again.

Glenn M1AQO
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w-u-2-o
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Joined: Fri Mar 10, 2017 1:47 pm

Re: Hermes Mic Input

Postby w-u-2-o » Thu Dec 19, 2019 10:57 am

The lack of bias has nothing to do with impedance. On an electret microphone the bias powers a small amplifier that is part of the electret microphone element. Without that amp there is insufficient output from the element.

Glad you got it working.

73,

Scott

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