Interfacing Yaesu FT 920 for digital modes!

[G4GFD]

Have been using FT 920 for RX only of digital modes on and off since last seasons Sp E's. Recently attempted to set it up for full TX / RX. It looks like there may be various cabling combinations that can be used.

I've currently got a lead made up for the dedicated data input which works however I'm concerned that the filtering that it switches to on receive is too narrow as I can't seem to decode weak JT6M transmission on both 4 / 6M that I can hear compaired to decoding a straigh SSB audio feed.

Also made a lead up to use the Mic socket input and the fixed audio out from the rear of the rig. This seems to resolve the RX problem but for some reason keeps blowing the Opto isolator on the PTT line by this method.

Has anyone got any pratical experience of the FT 920 for JT6M?


73's G4GFD

[G3PTU]

I cannot comment on the bandwidth aspect... but can on the the opto isolator problem.
I have had problems with optoisolators and the Ftx90 series. In some cases the device would not switch the unit to TX and or would die.
I found the very small DIL (TTL compatable, 14pin) relays the answer. If they do not have a overswing diodes built inside - fit one or two, maybe this is your problem with the solid devices?? you do not say what the failure mode is, the LED bit or the opto-transistor
I use the front Mic socket interface.
david G3PTU

[G4GFD]

Cheers for the comments David. Since the post I've had time to play around a little bit more. My interface works perfectly OK with my Yaesu FT 847 but not with the FT 920. In my case its the Opto transistor thats gone. This time I souced a couple from Maplin which seem to be a differant make and I've managed for almost a week without it failing.
I found if I wired the audio in to the Mic socket, I got quite bad hum despite going via the opto isolator. Currently I'm wired to the phone patch Mic input on the back using the data socket for PTT and audio out. Despite the the 2 Mic inputs being common, the hum is almost now none existant on the rear connection.
If I run ito futher trouble, I'll consider you suggestion with the relays.

73's Alan

[G3PTU]

I must confess that I always use transformers to isolate the computor 'earth' from the Rx\Tx earth (earth read -common- 0volt). A good source of these are duff 56K modem boards, although you need to be a good hand at desoldering. A gas touch (a la plumbing type) works well. After liquifing the solder tap the board on a sutable solid object and the bits fall out. Do not atempt on best Wilton carpet. The shakeier the hand the better.
Another source is the old type tranisitor output transformers, push pull output and driver. Just about anything will work. Mount cores at right angles.
The level is usually so high out of the 'audio out' on the Rx that it needs a fixed pad to normalise it to computor levels.
Download 'PPM' off the interent and install on the computor. The normal level ( zero as it is called) is '4' and it might be wise to run at say a peak of 6 (set the options up to -12db [minus 12] for domestic)
Check earthing is shack if hum common!
david G3PTU