Icom IC-9700 users topic

Transceiver mods, fixes, issues, reviews
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VK4GHZ
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Re: Icom IC-9700 users topic

Post by VK4GHZ » Thu Jul 04, 2019 9:03 am

IC-9700 test report by Adam Farson VA7OJ/AB4OJ.

IC-9700 VA7OJ Test Report.pdf
(3.01 MiB) Downloaded 90 times
:popcorn:
Adam, Brisbane
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Re: Icom IC-9700 users topic

Post by VK4GHZ » Mon Jul 15, 2019 8:52 pm

Has anyone pulled their HM-219 hand microphone apart?
(Stock mic that comes with the IC-9700)

I haven't, but there is obviously some logic in there to eliminate PTT switch bounce.

HM-219.png
HM-219 PTT bounce. RX > TX - none!

Compared to an old HM-36:
HM-36 Bounce.png
HM-36 PTT bounce. RX > TX - almost 800uS of contact bounce


The old SM-8 is even grottier.
SM-8 Bounce.png
SM-8 PTT bounce. RX > TX - almost 10mS of contact bounce
Adam, Brisbane
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Re: Icom IC-9700 users topic

Post by VK3QI » Mon Jul 15, 2019 9:35 pm

Adam,

Here is a link to the circuit diagram.

http://www.g4izh.co.uk/microphone-input ... ement.html

Scroll down about half way.

I presume that the diode must act as some sort of spike shunt, coupled with the low Q of the shunted 10n capacitor.

Cheers

Peter VK3QI

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Re: Icom IC-9700 users topic

Post by VK4GHZ » Mon Jul 15, 2019 9:50 pm

Thanks Peter. :thumbup:

Not what I was expecting, but extremely effective!
Could not make the HM-219 PTT bounce at all.

All the newer Icom hand microphones & rigs power their electret mic insert via mic socket pin 1 (MICI) which has DC volts on it.
In the old days, the microphone derived its power from mic socket pin 2 (+8V).
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Re: Icom IC-9700 users topic

Post by VK3QI » Tue Jul 16, 2019 12:28 am

Adam,

I think there might be more "smarts" than that shown in that circuit diagram.

I don't have access to the HM-219 but other mikes in the series also have similar PTT switching - which in reality is just a switched line to earth. Maybe the smarts are associated with the input circuit board in the rig?

Page 73 of the service manual shows Q491-Q493 feeding the PTT into the Front CPU IC501

That circuit is in the bottom left hand corner of the Display Unit circuit diagram on page 90.

Grounding D491 through the PTT switches Q491 "off", which makes FSEND go high on the CPU.

Maybe the time constants involved are better than previous rigs????? Tracing R494 around the circuit diagram (almost a full 360 degrees) ends up at the 5 volt line - nothing special.

Cheers


Peter VK3QI

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Re: Icom IC-9700 users topic

Post by VK4GHZ » Tue Jul 16, 2019 12:36 am

No, those screen shots above is the actual PTT switch contact from the mic (with a pull-up resistor to 3V3).
In other words, straight out of the mic.
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Re: Icom IC-9700 users topic

Post by VK7HH » Tue Jul 16, 2019 11:15 pm

Two new videos!

Glen VK1XX speaks at Gippstech 2019 about the IC-9700 and GPS locking board he has designed.




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