[Icom] IC-706

[Lefczik, Larry D]

I just checked that site (since I am the writer I thought I should check it
out. Thanks to whoever submitted it.)

I sent some corrections to the webmaster with some photos.  I hope he will
some post the photos for clarification.

Below is the text which was sent FYI.

---------------
RE:    20-08-2000        IC-706 10 watt tune modification/An Icom IC706 Tune
Trigger

In the ICOM section for IC706, please correct my email to
wa2ehz@netzero.net
Also there were some text translation problems that seem to of occurred when
posted to the sight.  In the construction section, the connection of R to C
was broken and the "extreme values" for R and C are lost.

I have enclosed the entire text below in case it is a help to you.

Attached are some photos and a word .doc file with some notes on one of the
photos if you can use them.


Thanks for your help and for maintaining such a great web site.
73 de WA2EHZ


(NOTE: I used FONT "LinePrinter 8.5" for the drawing to look OK)

An Icom IC706 Tune Trigger
(Some assembly required)

The ICOM IC-706 has a nifty feature built in to help the operator tune the
HF antenna SWR. By pushing the TUNE button on the front panel, the radio
switches to CW mode and transmits a 10 Watt carrier.  This state last for
approximately 10 seconds or the operator can terminate sooner by pushing the
button again. This was designed to work with the Icom automatic antenna
tuners.  There have been a few circuits developed to fool the 706 into
thinking there is a Icom tuner attached and produce the same tuning signal
which can be used with a manual antenna tuner or many automatic tuners, some
get quite complex.

Well, being the cheap guy I am, and being one to tinker, I felt there had to
be a simple way to do this.  I began reading the various postings on the
Internet.  I went back to an e-mail exchange I had with Ed, W1AAZ in early
April 1999 on Vartel's ICOM 706 Discussion Group.  Ed explained the
functions of the TKEY and TSTR pins on the "AH-3" connector on the 706.  

The outcome was a simple RC circuit which I have built right on a Molex
connector which plugs into the AH-3 jack on the back of the IC706. 

CONSTRUCTION:
The (+) side of C is connected to the 13.8VDC pin.  The (-) side connected
to TSTR and TKEY which are connected together.  Resistor R is in parallel
with C.  Below is a diagram of the AH4 connector on the back of the IC706
where the < indicates the pointy end of the connector (Pin 1 = TKEY).  You
can buy the Molex connector at Radio Shack (#274-0224).

	< TKEY  TSTR  13.8V  GND ]
	   |_____|       |     
	      |    R     | 
	      +--\/\/\/--+ 
	      |      +   | 
	      +----)(----+ 
	           C 

The values I use are C=1000uF 16WV R=92K Ohms 1/8 Watt which result in 15
seconds of tune time. As you can see, these are tied in parallel. If you
want to use a physically smaller capacitor such as 440 uF, you can adjust
the time by raising R.  The extreme values I found are: 
		2K<R<3.3M Ohms
		10uF<C<4700uF.

OPERATION:
Be sure to read the manual about the various Initial Settings that can
affect the operation with a tuner connected, otherwise you may go into the
TUNE mode every time you change frequency or push the PTT.  

Turn off the radio and plug in the unit.  Make sure you have some sort of
load on the HF antenna connector.  Turn on the IC706, the radio sees TSTR is
high during boot up and thinks there is a tuner connected.  Be sure the
meter is in the SWR mode.  Push the TUNE button.  The TUNE light should
flash counting the seconds and stay lit when finished, as stated in the
manual.  You may interrupt the cycle by pressing TUNE again.  

If you terminate the TUNE mode early by pressing the button again, you must
wait for the remainder of the time-out period to re-start.  If you don't
then the cycle is started over again when you press TUNE and you still must
wait, but longer.  This is why I have opted for 15 seconds instead of a
possible 30 seconds.  One way to reset the timer is by powering the IC706
off then on.

I have noticed false triggering when the supply voltage AT THE IC706 POWER
CONNECTOR drops during transmit and C has not yet totally discharged.  This
is caused by the TKEY voltage dropping through the trigger point because the
supply voltage drops while C is discharging.  This lead me to upgrade my
power supply cable so there is less voltage drop when I transmit. 

ALTERNATE DESIGN:
You can eliminate the capacitor and the TKEY to TSTR connection if you want
to manually trigger the IC706 into TUNE. You do need the pull-up resistor
between TSTR and 13VDC to make the radio think there is a tuner present
during power up. Then ground TKEY to trigger the TUNE mode as long as TKEY
remains grounded. 

Thanks to Ed, W1AAZ for the explanation of the connector.
Enjoy!
73 de Larry Lefczik, WA2EHZ@netzero.net