[ICOM] Running an IC-725 and R75 together

[Chris Mangus]

Wow, Gary!  Great information!

I love both rigs and can't wait to get started!

Thanks!

Chris / N7WBZ

On 12/27/06, Gary Fiber <gfiber at clearwire.net> wrote:
> Chris Mangus wrote:
> > Has anyone ever run an IC-725 and R75 together, using CI-V and a T/R
> > switch?
> >
> > I'd like to take advantage of the better receiver...
> >
> > Thanks,
> > Chris / N7WBZ
> >
> Should not be too hard.
> If you want the R-75 to follow the tuning of the IC-725 or vice
> versa...operate like a transceiver then:
>
> Connect the CI-V ports together, a mono jumper will do for this; no
> CT-17 required.
> Make sure the Transceive function is enabled in both radios...This is
> generally the Icom default anyway.
> As you turn the main dial and change mode on the IC-725, The R-75 should
> set itself to the exact same frequency and mode.
> As you turn the main dial and change mode on the R-75, the IC-725
> should set itself to the exact same frequency and mode.
> It will make no difference which dial or mode setting buttons you use as
> the other radio will follow. You can try this out without doing any
> fancy antenna stuff to make sure the basic tuning and mode change works.
> Just as you might do already turn down the IC-725 volume control.
>
> If you want them to operate as separates, then don't connect the CI-V
> but do the other below.
>
> The R-75 has a MUTE input. You need to ground this input when
> transmitting with the IC-725.
> If you are not running an amp you can try connecting the amplifier
> keying output on the IC-725 to the mute on the R-75. They both happen to
> be RCA connectors.
> Or you could use an external relay set up to short the mute input of the
> R-75 if you are already utilizing the amp keying out on the IC-725.
>
> Even though the mute will desense the R-75 I would still open the
> receiver antenna connection to the R-75 to protect the front end.
> In so doing that you may want to construct an external relay to open the
> antenna to the R-75 when transmitting.
>
> A 12 volt DC, DPDT relay will do. If also switch an amp you can use
> something like a 4PDT relay and use the extra contacts for switching the
> amp etc.
> Try to limit the current a bit, I would say use one that has a coil
> resistance of around 140 ohms or higher. That will limit the current to
> around 100 milliamps or less.
> Place the actual antenna center across one center contact, the receiver
> antenna to the normally closed contact so it is NOT connected when you
> are not transmitting. This contact will open when you transmit. Connect
> the IC-725 antenna to the normally open contact on that same side of the
> relay so when you transmit the antenna is connected. I think the relay
> will switch fast enough so it will not hurt anything. Putting a snubber
> diode across the coil will make the relay release faster not switch
> closed any faster so far as I know..BUT will reduce and transient
> voltages generated by the relay coil so its not a bad idea to utilize one.
>
> It will be ok to use a metal box and coaxial chassis connectors using
> the box for the ground side of the coax.
>
> Connect the receiver mute across the normally open contacts on the other
> side of the relay  so they will close and mute the receiver when
> transmitting.
>
> The coil of the relay can be connected from Pin 7 to 3 on either ACC 1
> or 2.. What will happen is every time you close the CW key, or the PTT,
> Pin 3 goes low, thus current will flow from Pin 7 through the relay coil
> closing the relay. Now the receiver antenna should disconnect and the
> receiver will be muted until you release the CW key  or PTT .
>
> Hope this helps and Have fun with the " Twins "
>
> Gary K8IZ
>
>
>
>
>
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