Monday, March 17, 2014

FSK - The real deal (and other developments)

I'm still having a lot of fun with my new TS-590 and this week's addition to the enjoyment was the addition of an interface for producing real, in-rig frequency shift keying for RTTY rather than using a program like FLDigi to produce the tones in a sideband signal.  The benefit is that you don't have to worry about audio levels or producing excess IMD and when chasing RTTY spots, you don't have to figure out where to set the receiver passband.

I ordered an FTDI USB-Serial adapter  which provides 5V TTL levels which can be fed directly into the TS-590's ACC2 port for PTT and FSK.  I did not know it would be that easy though.  No, instead I started by building a transistor based switch that would drive outputs to ground when the RTS or TXD lines from the adapter were active.  The problem is, at least on OS X, when the adapter is not being actively used by a program, the RTS line is active, meaning whenever I was not operating a digital mode, the rig was being keyed.  You may think, "well on the 590 you can just change the polarity of that signal so it doesn't do that," and you'd be right, but for whatever reason, I just could not get it to work that way.  Never the less, I fooled with this transistor interface for about 2 hours until I finally gave up and hooked things up directly to the adapter.  Sure enough, it worked exactly as I wanted it to without any problems.  We live and learn I guess!

In addition to the 13 pin DIN connector for the ACC2 jack, I also ordered a 7 pin DIN for the "remote connector".  This jack is usually used to supply a keyline and ALC for amps and things like that.  I don't have an amp (yet!) but I have seen a few cases of guys applying some voltage to the ALC line to cause the output to go below 5 watts.  I don't do a lot of QRPp but especially during the QRP Foxhunts, I do like to go for broke and really turn things down, so I thought I'd give it a shot.

The idea is that you can apply a negative voltage to the ALC pin to "trick" the radio into thinking it needs to reduce the output to an amplifier.  I wired up a 9v battery and a 10k pot for some variability of that voltage and gave it a shot.  Unfortunately, I could not get the ALC to change at all, regardless of the voltage.  I didn't want to spend a few hours and get nowhere with it so I gave up relatively quickly and I'll have to come back to it another day.

So after all that playing around, I got on the air.  There was a RTTY contest on which is sponsored by the British Amateur Radio Teledata Group, or BARTG (http://www.bartg.org.uk/hfrttycontest.asp).  This is an "everybody works everybody" contest so I figured I could do OK with my 100w rig.  I decided to do a single band entry on 15m since I wasn't going to be operating much and I knew if 15 was open, it'd offer good rates.  I spent a fair bit of time CQing and found that my equipment arrangement was probably not quite the best - it seems the air flow behind the 590 is quite lacking and I had the fans kick on at high speed after about 20 min of CQing at 100w.  This isn't really unexpected but I'll have to get one of those little fans the next time I'm up at Walmart.  I did have a little 2 inch DC fan I hooked up to blow air on the back of the rig and that helped a lot.  I thin I ended up with 60 some odd contacts and about 15,500 points.  Having never done a RTTY contest before, it was interesting to see who was on.  It was nice to be able to surf the web and watch Youtube videos while I operated too, though that did cause me to miss a few QSOs when people responded and I wasn't paying attention!  I am beginning to recognize when to turn the beam from NE to NW as propagation shifts, which is something all the experienced ops have figured out to a T.

That pretty much sums up the last few days of ham radio at the W0EA shack.  I think for the next blog post I'll try to think of something with some visual elements!  This blog needs more pictures!

73 for now ..