Computer Interface

I get good signal reports with my very ordinary psk31 setup.

My name is Bill south of you in Fremont, Ca. and was listening to you this afternoon with the Digipan software while you were communicating via PSK31 at 00:37:55Z 20 meters you were solid copy here at my QTH!

You mentioned to the station I was also copying you were using an IC735 to communicate via PSK31...I have been receiving for since the first New Years day and have an IC736.

Do you mind sharing with me the type of box you are using to interface to you IC735?

Here is what I wrote Bill in response.

Bill -- Thanks for the report. I use the very simple interface described in the help file of my psk31 program. Here is what it says ...

Connect a shielded audio cable between the transceiver MIC input and the sound card LINE OUT jack through a 40 db attenuator, consisting of a 100K series resistor feeding a 1K parallel resistor. This attenuator will reduce the soundcard LINE OUT level from about 1 Volt down to the normal MIC input level of about 10 millivolts, so the higher soundcard output level does not overdrive and distort the transceiver MIC input.

... and for receiving I run my rig's headphone output straight into my laptop. My old laptop had both mic and line inputs. This one has only mic. This caused terrible distortion of the rx signal until I noticed that the window-98 sound dialogs had an option for attenuating the mic input. (I wonder how they do that?).

I have keyed the tx with the rig's vox. This works ok except when my computer makes its usual assorted noises. I didn't like it that everyone in the world could hear me reboot windows. I wired up the help file recommended transistor circuit using parts purchased from radio shack. I built their perf board and put it in a really neat key-fob sized box. By the time I finished I probably had $20 dollars in parts and two trips to radio shack.

I've noticed that one can buy an interface for $35 bucks or so. I don't know if that is kit or assembled. Considering what bare parts cost I don't think $35 is a bad price, especially since the "universal" design may have more isolation than mine. I have had occasional problems with rf feedback. rf feedback into the tx causes terrible distortion and erratic tx output adjustment. I've fixed that by running a ground strap between my rig and laptop. I haven't done so lately though and haven't had the problem. I have had the laptop touch pad pick up some rf from the rig. It makes moving the computer's cursor erratic. When that happens I just put my other hand the laptop and that is enough to stop it. I should put that ground strap back but it is just one more thing to hook up. Maybe I'll buy one of those commercial interface boxes.

The 735 has been a great rig for psk. It has rock solid frequency stability and just loafs along at 50 watts continuous. I program the registers to the psk31 segments all bands. It is great flipping through the registers looking for signals the waterfall. I now like to watch the bands close in the evening because it is so easy to watch the sequence: first 10, then 15, and so . I'm at one with the ionosphere.

I'll take some pictures of my setup and put them my web site. Check it out in a week or two. Thanks for writing and best regards. -- Ward

Here is what my interface looks like.

I once thought that I would like to receive through the 500 Hz crystal filter which the 735 can't do and still transmit ssb (perhaps it can when set up for split operation?). I've since learned that I like to watch the full audio passband in the the waterfall. Should very strong signals interfere with my reception I just tweak the passband tuning or take 'em out with the notch filter. I never used these controls much until I started working psk31.

See the station tour for more photographs.