[RTTY] MMTTY & Icom IC735 Linkage

[f6irf@free.fr]

Hi Phil

Have a 735 and still use it as a second radio for CW, but for RTTY it is
probably not the best rig around:
- No FSK generator; so you have to use AFSK
- No possibility of switching the narrow filter in SSB (unless hardware mod)
- CI-V at 1200bds without possibility of turning "CI-V transceive off" which
makes the bandmap response very slow in most contest software (except mixW)
- Unsufficient VFO demultiplication, which makes RTTY a bit hard to tune, and
operation kind of difficult especialy for a beginner...

It is why I prefer to use the 706 as second radio... the RX may not be as good,
but with my SO2R bandpass filters, and without preamp, it is usable; and the 706
has a FSK position, a narrow filter and a super-demultiplied  VFO...

However I did use the 735... the PBT and the Notch allows to narrow a bit the
audio-bandwidth (no DSP- sharp, but... something like 1kHZ is already better
than 2.4kHz)
I used the rear-panel ACC-1 connector for audio IN/OUT and for PTT... as far as
I remember there is nothing special, it should work straight ahead.

- You are right:the vox is not activated when using the rear panel audio-in
(true for all Icoms)
- It is possible to use the mic-input, but
1) use a capacitor to block the DC used to power the electret microphone
2) The minimum is to use a resistive divider (ie 1/100) so you bring your PC -
AF output to a microphone level... (you can find a diagram in MMTTY manual -
chapter soundcard hookup).
3) then turn-off  the speech-processor and make sure you keep the ALC indication
very low... recommend you put the RFpower-pot to max, and then reduce the power
to 50W, using the mic-gain (as low as possible) while maintaining the PC output
fader to abt 75% of max (to minimize the soundcard noise - also turn off
anything but wave fader and remember to turn off any windows sound, voice
synth, cluster alarm or whatever may produce sounds...).
4) make sure the power falls to 0 when the AFSK signal is off and the
transceiver still on TX... (means that you have no RF feedback, or 50hz picked
up by the cable, the PC, or by some ground loop). If possible listen to your
signal on another receiver, and make sure you are not transmitting spurious, or
noise, etc...  It is recommended to use an audio frequency as high as possible
(>2000hz) so the h2 of your audio signal falls outside the SSB TX-filter...
5) then you should be able to use the vox... but if you have a 2N2222 somewhere
in a drawer, it is worth making a proper TX/RX control  (see also MMTTY
manual... you can even remove D1 D2 and R2... it should still work !)
6) Use LSB - setup the PBT so the RX produces a "high pitch" sound > using the
MMTTY spectrum display at 1khz wide (BPF off) and mark freq at 2125 center the
audio bandwidth around the yellow lines... then turn BPF on... setup the PC
audio-in level (line or mic) so the background noise is at the bottom of the
screen, and that any 599+ signal does not trigger the "overload" indication.

That's it...
If u are using a cluster remember that stations should be spotted at real mark
RF frequency, or TRXfrq - MarkAFfreq ... the same applies if you want to find a
spotted station (you have to tune 2khz or so, higher than the spot... assuming
you are using LSB, which coresponds to the "normal polarity" with MMTTY - take
care when you change bands, you have to force LSB whatever the band you use...)

See you in the Anarts - Patrick






[RTTY] MMTTY & Icom IC735 Linkage
from [Phil & Sarah Email] [Permanent Link][Original]

To:  <rtty at contesting.com>
Subject:  [RTTY] MMTTY & Icom IC735 Linkage
From:  "Phil & Sarah Email" <philhss at tpg.com.au>
Date:  Mon, 6 Jun 2005 19:17:26 +1000
List-post:  <mailto:rtty at contesting.com>

I'm new to this list, so apologies if this subject has been covered
previously.

I'm also new to the world of RTTY, please be gentle! ;-)

I've downloaded the latest version of MMTTY, and plan to use it with my Icom
IC735. If my 'toe dipping' into RTTY gets me hooked, I plan to buy a
suitable interface, but I thought that I'd try a simplistic method first, to
whet my appetite.

The software loads nicely without a problem. I can't get the laptop to
communicate with the rig, but I'm not too bothered about that aspect, as
such. I've made a connection cable to go between ACC1 on the 735, to the
appropriate sockets on the laptop.

With quite an amount of volume from the rig, certainly more than can be
tolerated on speaker, I can get reasonable decoding on the laptop. I had
thought that the audio was a 'constant' output which was independent of the
volume control - but maybe not? No amount of output from the laptop
activates the VOX on the rig, so I'm assuming that the ACC1 Socket does not
tie-in with the VOX. With the TX button depressed to force the rig into
transmit, the rig still gives no RF output. I've checked the RF gain, MIC
gain and cable connections. The rig works perfectly with the microphone.

My next port of call is utilising the microphone socket to give the required
connectivity - has anyone had some prior experience of this please? Is it a
simple case of wiring a suitable plug or is there anything I should be aware
of??

Thanks for any assistance!

73,

Phil Smeaton
VK2BAA