ICOM IC-260A CTCSS - using Pin 5 of accessory connector?
 

I need to add CTCSS to transmit of ICOM IC-260A. I have a manual (file)
but no schematic. The manual says that the accessory connector pin 5 is
"output of transmit mic amplifier" or words to that effect. Can I put
CTCSS tone signal into that pin on transmit? Other suggestion? Anyone
care to look at their schematic of this rig to tell me where this pin
of the accessory connector goes?

Very tks,

73 Dave WB0GAZ

"wb0gaz" wrote in message
oups.com...
I need to add CTCSS to transmit of ICOM IC-260A. I have a manual (file)
but no schematic. The manual says that the accessory connector pin 5 is
"output of transmit mic amplifier" or words to that effect. Can I put
CTCSS tone signal into that pin on transmit? Other suggestion? Anyone
care to look at their schematic of this rig to tell me where this pin
of the accessory connector goes?

Very tks,

73 Dave WB0GAZ

Hi
I have posted the schematic for this radio in the manuals section at.
www.mbars.co.uk

Dave,
the internal mic circuit has audio HF & LF filtering. This means that if you
were to apply a signal below 300Hz or above 3,400Hz into the mic
circuitry,then the level of this signal will be greatly reduced, or even
removed.

The CTCSS signals centre around 100Hz and therefore cannot be injected into
the mic socket.
In fact you have to travel all the way through the mic circuit until you get
to the microphone op-amp (IC1) See circuit as per Paul.

The amp IC, IC1 has a resistor/cap feedback circuit which provides the req'd
filtering. The CTCSS encoded signal output should be injected around Pin 1
(output of IC). There maybe voltages at this point ,so a capacitor must be
used to block this voltage. You will see two varicap diodes D1/D2 and it is
the varying AF voltage feeding these diodes that produces the modulation of
the carrier.

I have carried out this mod on my IC-290E, by using an external CTCSS
encoder chip (FX315) mounted in a small aluminium box with DIP switches for
selection.

I connected a small piece of screened wire from Pin1of IC1 and connected it
to a spare pin on the nine way facility socket on the rear panel. At this
point I also connected the aforementioned cap.

A transmit switched voltage for feeding the external CTCSS unit supply line
was found on this facility socket. Please check the circuit for your radio.

Remember that the CTCSS encoded signal should only be activated when you
transmit.

Dave, you must have a good look at the schematic provided by Paul and come
up with a plan of attack.

You will of course understand that you attempt these modifications at your
own risk. It worked for me on my IC290.

Do a search for FX315 encoder/decoder chip circuitry on the net. I got my
chip(not cheap) from Mode Components.(UK)

Regards and good luck and thankyou Paul for schematic.

Roger, G7JAQ


http://www.btinternet.com/~g4kqu/Mod...nts/index2.htm




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Paul and Roger - thank you very much for the very helpful information.
I've retrieved the schematic and had already obtained the user's manual
from the ICOM website. I'll study the schematic.

As for the tone generator, I'm planning on using an old laptop computer
and "nch tonegen", which is a software program that can generate an
arbitrary sinewave signal. The main task at hand is to isolate and
bring the appropriate connection point out to the back panel where I
can supply the tone on transmit.

Again, thank you both for your fine support!

73 Dave WB0GAZ

Got a close look at the schematic, and indeed the external "mic amp
output" connector pin 5 of accessory jack is basically the same as the
audio output of the microphone itself, useful for DTMF insertion but
not useful for CTCSS. It appears likely I can attach near/to the output
of the deviation control R115 which feeds through a series resistor and
capacitor to the FM modulation varactor D32. This looks like it's near
the center of the lower PC board in an area that's not too cluttered.
I'm not sure if I'll need to inhibit the tone on receive or not; the
circuit appears dedicated to transmit mode only.

Again, thank you very much for the insight - it would not have been
possible to start this project without your kind help!

73 Dave WB0GAZ

Dave,

you're more than welcome. It's all about keeping the hobby alive I suppose.

I wish you well with your laptop generated CTCSS tones. It certainly is an
interesting and novel approach!. Post again when you have some more info.

Be careful about "loading up" the varicap circuit and thereby reducing the
deviation, when you connect your soundcard? You'll need to check that the
deviation levels of voice signals mixed with CTCSS do not become excessive.

regards,

Roger, G7JAQ. Surrey, England


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"Roger Adam" wrote in message
...
Dave,

you're more than welcome. It's all about keeping the hobby alive I
suppose.

I wish you well with your laptop generated CTCSS tones. It certainly is an
interesting and novel approach!. Post again when you have some more info.

Be careful about "loading up" the varicap circuit and thereby reducing the
deviation, when you connect your soundcard? You'll need to check that the
deviation levels of voice signals mixed with CTCSS do not become
excessive.

regards,

Roger, G7JAQ. Surrey, England


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Glad i could help with the shematic.
Keep your eye on the site as over the next few months i have over a thousand
files to add to the manuals section.
good luck with the project.
Paul 2E0DXO

Hello Paul and Roger,

I wanted to tell you that tonight (about 2000 MST) my ancient ICOM
IC-260A is successfully accessing CTCSS-controlled repeaters! This is
due entirely to your help. I found easy access to the junction of R114
and C103, at the "upper" end of R114 (it is a 15K resistor on-end.) I
scraped away some of the insulation, and soldered in series a 10K and
0.1 uF capacitor, then from there a shunt 2.2K to ground, and out with
a piece of RG-174 coax. The coax is fed through one of the unoccupied
pins on the ACC connector, which I drilled out to about 3mm with a
drill bit (a tie-wrap is a strain relief to prevent pulling the coax
out from the radio.) The end of the coax is a 1/8" mono phone plug,
which goes into the audio output of my quite-ancient IBM Thinkpad 365,
running NCH Tone Generator tonegen.exe version 2.01. The output level
of tonegen is maximum (0dB) and the tone imposed on the output audio is
not very loud, but it is adequate to reach two different repeaters I
tested, and I imagine it will vary depending on the laptop and the
resistor values I used.

Anyway, this is really satisfying - with your help an old derelict
radio is now back in service in my shack, with my laptop doing duty as
the CTCSS generator. It wasn't necessary to create any T/R switching or
other controls on the tone - it just runs continuously from the laptop.

Again, very much thank you (and the manuals section you host proved
quite invaluable this time, and I'll look forward to improving my
library.)

Just as an aside, this project is actually a prototype for a ham friend
who was disabled a couple of years ago - I want him to get access to
IRLP, and I found a 2M transceiver (Kenwood TM201B) for USD 35, which
needs only CTCSS to bring it to life in a similar mode (he already has
the necessary laptop.) So your help has actually done double duty.

Thanks again,

73 Dave WB0GAZ

On 14 Mar 2005 09:05:34 -0800, "wb0gaz" wrote:

Paul and Roger - thank you very much for the very helpful information.
I've retrieved the schematic and had already obtained the user's manual
from the ICOM website. I'll study the schematic.

As for the tone generator, I'm planning on using an old laptop computer
and "nch tonegen", which is a software program that can generate an
arbitrary sinewave signal. The main task at hand is to isolate and
bring the appropriate connection point out to the back panel where I
can supply the tone on transmit.

Again, thank you both for your fine support!

73 Dave WB0GAZ

When I worked for Icom America on the tech support line I used to
advise attachment to the wiper of the deviation pot. Always seemed to
work.

Gary K8IZ

Would have worked as well - the wiper of the pot goes through the 15K
resistor and capacitor into the varicap. I'll keep that in mind should
I find a rig with no schematic in the future.

73 Dave WB0GAZ