Re: uBITX Mic Wireup

Tim Gorman


The ubitx doesn't have a balanced mic input, i.e. mic leads that don't
have one connected directly to system ground. In a balanced feed the
shield wire would be the system ground and would act as a shield to both
mic wires. Ideally in such a case the PTT would probably also have two
leads, a plus and minus, although many times the shield is just used as
the ground lead.

The PTT shouldn't be wired serially with the mic, both just use a
common ground. When the PTT is pushed the PTT switch closes the PTT
lead to the shield, i.e. system ground. At the same time the mic lead
from the element is connected to the mic lead in the cable. The minus
mic lead is connected solidly to the shield, i.e. system ground.

If the ubitx ran more power it might be necessary to take more care
with the mic circuitry. At 10-15 watts it just isn't necessary as long
as the wires inside the cabinet are dressed properly and kept away from
the PA section of the circuit board.

If you'll download the operating manual for the ftdx-3000 from the
Yaesu site and look at the page with the connector wiring, you'll see
on the microphone connector that there are two mic leads that are
separate from system shield. In fact there is even a totally separate 5v
lead for powering an electret element. Yaesu expects there to be a
blocking capacitor on the mic lead to isolate the 5v from the radio mic

tim ab0wr

On Fri, 9 Mar 2018 18:04:27 -0600
"Shaun" <slong682000@...> wrote:

" If you tear a lot of communication mics apart you will see that the
mic element is wired through the PTT switch on most of them."

That is exactly what I would expect and have seen in the past, but
again, the mic wire up I saw on an earlier post for an older version
did have the PTT as a separate circuit, not wired serially with the
electret. While it doesn't address the mic wire up specifically, the
wiring diagram for the uBITX from the website seems to suggest the
same, PTT and mic are two separate circuits. I think you have
confirmed my original way of thinking of how I should wire it up,
i.e. closure of the PTT switch applying ground to the MIC- side of
the electret, and is the way I will go. I am using an old HT
spkr\mic and going that route just means I need to move one
connection point internally and I'm where I need to be. Thank you for
the assist, Tim


On Fri, Mar 9, 2018 at 3:14 PM, Tim Gorman <tgorman2@...> wrote:


Having a live mic with a separate, unassociated PTT switch can lead
to inadvertent transmissions if the PTT gets operated accidentally.
If the mic is not live all the time then all you transmit on an
accidental PTT operation is a suppressed carrier which hopefully
won't bother anyone.

It doesn't happen a lot but it *does* happen. Someone accidentally
pushes his foot switch with a live mic and sends out a discussion
with the wife (spouse) over the air.

Admittedly you can butt transmit with a PTT CB mic or 2-meter ham
mic if you sit on it. It happens also.

For me, the switch is there in the mic and I don't see any reason
not to use it. If you tear a lot of communication mics apart you
will see that the mic element is wired through the PTT switch on
most of them. Apparently someone thinks its a good idea!

tim ab0wr

On Fri, 09 Mar 2018 07:54:26 -0800
"Jerry Gaffke via Groups.Io" <> wrote:

How is this an advantage?

On Fri, Mar 9, 2018 at 07:23 am, Tim Gorman wrote:

The mic is only actually connected when the PTT switch is
pushed. .... This is why I recommend using a communications
mike instead of a standalone mic with a separate PTT switch.

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