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Re: [TenTec] FSK, PSK, let's call the whole thing off...

To: tentec@contesting.com
Subject: Re: [TenTec] FSK, PSK, let's call the whole thing off...
From: Adam Wade <espresso_doppio@yahoo.com>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sun, 19 Apr 2009 19:10:38 -0700 (PDT)
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
----- Original Message ----
> From: Bob, K4TAX

> Yes, true, but what about the other 20 or so current digital modes that are 
> available these days?  These are efficient with highly reliable data 
> throughput modes as opposed to the slow antiquated RTTY mode.  Remember 
> RTTY is the ONLY one that uses the FSK method of transmission.

This is not completely accurate, at least technically.  While many rigs only 
allow binary FSK, all the AFSK modes can be modulated by non-baseband FSK 
means,  This means Olivia, Throb, MFSK, etc.  It would not be wonderfully easy 
to build a rig that would modulate all of these modes with data in and data out 
and no baseband, as most folks find it a lot easier and more convenient to 
simply switch to a sideband with a voice bandwidth and "modulate the baseband" 
(i.e., turn the binary data into audio tones, then let the rig modulate the 
audio as RF).  The added advantage, as noted, is that you can let software 
adjust the zero point as long as the whole signal you're trying to receive is 
within the audio passband of your receiver (and all of that audio is going to 
your computer for decoding -- not really an issue for anyone who has a computer 
that was made in the past 20-25 years or so).

The reality is that, as noted, it would require slightly different hardware for 
each FSK mode to allow direct modulation/demodulation in your rig from digital 
data (binary, ASCII, what have you).  The QRP portable standalone PSK box I've 
seen for sale does this with phase shift rather than frequency shift, but the 
idea is the same.  And unlike a computer with a sound card and an SSB rig, you 
would need to have the hardware set up specifically for the mode(s) you wanted 
to work, rather than just cutting yourself a wide slice of passband and letting 
software handle it all.

I can't really see a great advantage to using FSK for hams these days, unless 
you have a really lousy sound card or a very, very slow old computer.  While a 
hardware-based FSK should have some advantage in terms of SNR for weak signal 
stuff, most ham receivers can't do any better than a good sound card/chip and 
the computing power in your computer.  Remember, a typical 10 year old computer 
has about 10-20x the computing power available for DSP or what have you than 
the latest, greatest $10k contest radio.  IT's what is DONE with that power 
that makes all the difference, IME.

Interestingly, current SDRs take advantage of the significant improvement in 
IMx (most of us only think about IM3, but all harmonics can be important in 
locking out strong neabry signals -- as anyone who has tried to work low-power 
PSK on 20m while an RTTY contest is going on could testify, if they did the 
math!) that can be had with direct conversion to baseband using quadrature 
outputs -- the technology was developed to the current state of the art (and 
thus made available for incorporation into modern SDRs) for digital cellphone 
use, where multipath and especially very strong signals not far up and down the 
band can essentially ruin two-way comms.  Cellphones can fend off nearby 
signals into the kilowatt range while getting solid, reliable comms with only 
milliwatts, and most of the noise sources are within several miles of the base 
and mobile cellphone units.  I am very interested to see if ham radio SDRs will 
eventually take more advantage of this
 with direct hardware encoding and decoding for digital modes (old-school FSK 
would be one example of this) instead of simply converting to an audio baseband 
and handing it off to other software for decoding and encoding, like the 
software we currently use for digi-modes that transmits/receives via audio 
into/out of an SSB rig.  There should be significant improvements in ability to 
copy weak signals, get reliable sigs out at QRP power levels, and a vastly 
improved ability to fend off strong nearby sigs (nearby in frequency, that is) 
well beyond concerns about IM3 (how about being able to fend off IM11 or better 
from more than a kilowatt near your receiver?)...  The DSP power to handle that 
on a hardware level is available, and would not really cost a lot more to 
implement in these radios; further, you would no longer need a computer to 
connect to your SDR.  Whatever computing functions were necessary would be 
built into the radio, making the unit very
 portable.  Using electronics made specifically for low power consumption would 
mean portable digi-modes could become quite self-contained in a single unit 
with relatively small, lightweight batteries -- the military already has this 
technology and is using it for, among other things, controlling their UAVs and 
relaying data from UAVs and sats to the field, and it should be possible to get 
it affordably into radios soon.

As another aside, I have sourced a 192 khz sound card with balanced inputs (an 
E-Mu 0404 PCI) for under $50 shipped off of eBay, and combined with the $25 
Clifton Labs Z10000 buffer amplifier and the $12 SoftRock II Lite IF "Special" 
quadrature decoder/receiver, I have made a complete SDR receiver that interacts 
with my Orion 565 directly and provides me with over 96 khz of real-time 
spectrum analysis and/or waterfall with decoding of digital modes as well as 
direct click-tuning of the Orion from what I see on the screen from the 
SoftRock.  Total cost for all the parts (which, granted, must be assembled by 
hand, and they are SMDs which are a bit of a pain to work with, and of course 
there was some minor surgery required on the first IF board of the Orion) 
including isolation xfmrs that can handle 100 khz bandwidth and a shielded case 
to keep the noise floor low and ground loops out, was under $100.  Yes, that's 
right...  I have a SDR receiver that is as
 good as pretty much anything you can get from Flex Radio (but is receive-only, 
at least for now) for $100, using the VFOs and first IF of the Orion as a front 
end.  If anyone here contests using digital modes, this is a truly amazing 
set-up to have, and it can be used just like the Flex Radios for CW contesting 
as well, using CW Skimmer and so on.  With a fast computer or two controlling 
the Orion via Ham Radio Deluxe along with running CW Skimmer and the logging 
software of your choice, you can do almost everything a $5k Flex Radio can with 
your existing Orion or Orion II.  Other radios that have serial or CAT control 
can have most or all of this capability as well, although I haven't built 
anything like this for any radios other than the 565 Orion so far.

Neat stuff, and most of it really doesn't use any concepts that experienced, 
knowledgable hams probably don't already know, they are just arranged in new 
ways that at first are non-intuitive.  And just like with the advent of 
solid-state, we get to play around and see what advantages the old stuff has 
(traditional superhet receivers with roofing filters vs. direct to baseband 
quadrature receivers) when compared against the "latest and greatest" (which 
with solid state was tubes vs. transistors -- and tubes have some very handy 
advantages if you care to use them!).  It's not really that complicated or 
difficult to learn, it's just a little different...  And aren't hams above all 
else adaptable and knowledgable about basic principles, or at least isn't that 
what ham radio was supposed to have been about, once upon a time?

> All of the 
> digital modes are available via current free software and no interface is 
> needed.

It can be hazardous to your equipment, and can introduce a heck of a lot of 
nasty noise and potential problems, to NOT isolate your computer from your rig, 
especially at audio frequencies.  I STRONGLY recommend that at the very least 
we isolate the audio path from rig to computer with quality 600 ohm 1:1 xfmrs.  
When dealing with SDRs like the SoftRock, where the sound card is being asked 
to work with sigs well beyond the hearable range of audio frequencies, finding 
appropriate xfmrs that are flat across the required bandwidth becomes a much 
larger challenge.

Also, many radios do not have a serial port or USB port interface, and those 
ones will require an interface box of some kind to allow rig control.  While 
not specifically required for working digi-modes (I have successfully worked a 
lot of digi-mode contacts using a Kenwood TS-520S, tube finals and all), if 
your rig CAN be controlled via computer interface it can work greatly to your 
advantage to have the rig connected to the PC.  For instance, the Orion can 
have nearly all of its adjustable features controlled through software off a 
computer, in mny cases to a far higher level of precision than the faceplate 
controls allow (how about not having logarithmic jumps in the microvolt 
threshold for programmable AGC?  With Ham Radio Deluxe, I can control the 
threshold in 1 uv increments, which can be very handy!), and rather than having 
to manually key the rig for xmit/rcv with digi-modes, or rely on VOX, the rig 
can be keyed by software via the serial

> My motto:  more boxes + more cables + more connectors = more 
> problems.

That's true to an extent, but if everyone adhered to that principle to the 
extreme, we'd each have a single transmitter, single receiver, single antenna, 
single feedline, and a pad of paper for a log.  In reality, the more reliable 
you make an automated or even just fairly complex piece of hardware, in any 
field, the longer you can go without a problem, but the more difficult or 
costly it will likely be to diagnose and repair the problem.  This is why we 
end up with "appliance operators" today -- it's easier to throw away your 
broken VHF handheld and get a new one if it goes wrong, and it's cheaper, too.

> Of course what do I know, I still run Class C high level modulated AM using 
> a 1956 transmitter and not a 2000 technology transmitter.  I got rid of my 
> Model 25 RTTY floor shaker at least 40 years ago.  Haven't been back on FSK 
> RTTY since.  And oh by the way, my AM transmitter doesn't use any more 
> sideband bandwidth than current technology SSB rigs and in many cases it 
> uses less.

Well, most "modern" rigs default to 2.7 khz b/w for xmit, and some to 2.4 khz.  
Are you saying you are really running an audio passband of only 1.35 khz?  I 
doubt I would be able to copy you if your xmtr was not producing more than -6 
db of your peak above 1.35 khz audio...

Horses for courses and all that, and I would assume that you probably know a 
lot more about a lot of things radio-related than I do...  And certainly I (and 
perhaps most of the list) have a lot to learn from you that can be of great use 
to us.  I find most of what I learn that is most useful was known in radio 
circles over 50 years ago, and a chunk of it over 75 years ago.  Of course, a 
lot of those things can be applied to the new and latest, but HOW is not always 
readily apparent.  Me, I like to learn PRINCIPLES so I can apply them as 
needed, and I love anything that can teach me where principles apply in 
whatever I am facing.  I continue to experiment, with the new AND the old (I'm 
as interested in tube PA design and engineering as I am in quadrature-type 
direct-to-baseband receivers), with antennas and circuits and software all, 
because I want to understand.  I appreciate all contributions to that, and I 
also appreciate that not everyone wants to
 learn on that level -- I even appreciate that there are times when I want to 
turn on my rig and have a good rag-chew without having to think, know or 
understand how it all works.  But it's awfully nice to know that I have the 
knowledge and the tools to at least diagnose and often correct problems as they 
crop up, and to design and build some of my own stuff, for fun as well as to 
save money and just plain be able to say "I made this, and not from a kit".  
And building kits has been a huge help in not only assembly technique and 
general good practices for RF circuit design, but also to help learn some basic 
concepts through physical motions rather than just reading and thinking.

YMMV, and for many it does, I think.  But that's my $0.02 worth, and you can 
keep the change.  :D
! Adam Wade -==- AF6ME -==- Ten-Tec Orion & SteppIR BiggIR Mk III !
! "I write down everything I want to remember. That way, instead  !
! of spending a lot of time trying to remember what it is I wrote !
! down, I spend z time looking for the paper I wrote it down on." !
!       - Beryl Pfizer    -=-    http://www.allthings550.com      !

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