[NLRS] VHF Field Day modes

[Dr. Gerald N. Johnson]

45 baud 170 shift ias best for conventional RTTY. 50 is odd, at least 
from the hardware machine days. 45 baud is 50 wpm, or 50 speed. 850 is 
old, 170 works better and takes up a smaller spectrum.

Some history. 850 shift with audio tones was standard on AT&T long lines 
while DC loops were common for short lines, like weather wires. In ham 
radio applications the first authorized was on VHF AM or FM AFSK and 
surplus telephone filters were used, 2125 and 2975 Hz bandpass filters 
made the discriminator. FCC rules said shift shall be 850 Hz and code 
shall be Baudot. The rules gave no tolerance for the shift, but I never 
heard of any ham being cited for shift different from 850. As time went 
on 170 shift was authorized and found to be more effective on HF partly 
because of reduced differences in path fading for the tones closer 
together. In those days I used a model 14 Teletype narrow tape (probably 
Western Union surplus) printer. Better TU designs came along that could 
copy from one tone make break or both tones FSK so that QRM on one tone 
didn't cause loss of copy. Eventually computers came along and speeds 
and codes were expanded, to 50 speed, 75 speed, and 100 speed, Baudot 
and ASCII. Weather and AP news wires ran 75 speed which made model 15s 
need considerable care and 28s only needed care once a year. Today FCC 
rules allow most any digital mode so long as the bandwidth is not wider 
than SSB and the encoding scheme is made public. No encryption allowed, 
but FEC and other innovative codes are allowed and are the basis of JT 
modes.

A weather client had a couple 28s I maintained for a few years. One year 
I picked up a Z80 based "portable" computer with serial and parallel 
ports and programmed it (CP/M operating system) to buffer the serial 
weather wire, do some simple selection and run a dot matrix printer. The 
combination ran for years with nothing but paper and ribbons, no 
maintenance at all.

PSK is a very robust digital mode, no error correction but strong error 
detection. Most 100 watt SSB rigs need to be run under 30 watts to keep 
intermod to acceptable levels. In general communications theory text 
books say phase shift keyed modes are the best for speed vs signal to 
noise. Differential PSK isn't a good as absolute PSK, but absolute PSK 
requires prior knowledge of the received phase.

Those in the Story County ARC that use digital modes more than I do 
these days especially for FD tell me that RTTY is the predominant 
digital mode on HF, but CW is far more effective at making a score just 
because of activity saturation emphasizing CW and SSB. For FD I've long 
used a straight key for CW and its my ears that fail before my arm wears 
out. I haven't decided on FD activity if any, I may spend the weekend 
working on touring and gathering antenna tower materials. I sometimes 
wonder, "I've proven on numerous occasions that I can make contacts 
under FD emergency conditions, do I need to prove it again?"

I created a club program for the Story County ARC back in January 
linking youtube videos to some html. Its now on line at 
www.geraldj.networkiowa.com/soldering.html.
In it I used 118 minutes of you tubes from fundamentals to several 
techniques for fine pitch ICs and three techniques for installing 
PL-256. I skipped some of the videos and cut several short to get the 
presentation time down to 90 minutes.

The "j-pole" is romanced these days, but I do prefer the coax connector 
and wires ground plane as being a better performer simply because the 
ground plane significantly reduces RF on the outside of the feedline and 
so puts more signal at the horizon instead of nearly straight up. 
There's benefit to sealing the connector on the antenna side with none 
corrosive RTV or hot glue.

73, Jerry, K0CQ

On 6/17/2013 11:10 AM, Doug Reed wrote:
>
>
> Thanks Matt. I'll be trying to setup FLDIGI for the W0MR Mining-SPRC
> FD VHF station.
>
> Is there anyone on the list who would like to comment about the choice
> of digital modes? I suggested PSK31 mostly because it is well known
> and widely used, with good capability for working into the noise.
>
> Jerry suggested plain old RTTY as a good option and I certainly like
> it as being instantly recognizable when I hear it. And it is known for
> good operation on HF weak paths and works well on FM too. So RTTY
> is another option. Stay with the classic 50 baud 170Hz or 850Hz Baudot
> format....
>
> I also mentioned MFSK-16 as another mode option. It isn't as well
> known as PSK31 and I don't think it can dig as far into the noise, but
> it does have the advantage of Forward Error Correction (FEC) so you see
> small blocks of text appear as each FEC block is decoded and
> corrected. So if you used MFSK-16 you would know the displayed text was
> accurate.
>
> The local ARES groups like MT63-2000 for sending digital data over FM
> radios or repeaters. It has FEC and is very fast, but isn't the best
> choice for use over SSB and a weak path.
>
> I also mentioned using meteor scatter modes, but that would probably
> be for stations who are already familiar with it and maybe have a
> second VHF station. The WSJT software is the main way to go for those
> modes.
> <http://physics.princeton.edu/pulsar/K1JT/wsjt.html>
>
> There are probably 30 other digital modes that could be used, but that
> just makes the job improbable rather than a good way to increase Q's.
> So it would be handy if just one or two digital modes were used (in
> addition to CW) for Field Day. I don't think transmission speed is a
> primary factor in the selection. I have more interest in pulling out
> weak signals and with FEC for accurate exchanges.
>
> <http://ww2.amsat.org/?p=678>
> If you really want to add to your challenges, try to grab the
> satellite bonus for making a FD Q via one of the ham satellites. The
> Oscar-50 FM satellite has become very popular for this but its so
> popular it is difficult to make any Q. The linear transponder
> satellites are also very active during FD. If someone in your FD group
> is familiar with working via satellite, it is probably on your
> things-to-do list already. :-)
>
> And if your FD group doesn't already have an Educational Activity
> lined up to get the bonus points, you could always consider doing
> something about VHF weak signal, roving, 10GHz, SDR, or whatever you
> want. I was going to suggest loading APRSIS-32 on a laptop and
> connecting a radio would let you demo APRS. Or if you have a DVB-T TV
> dongle you can demo SDRSharp and ultra-cheap SDR to the crowd.... Or
> maybe you'd like to do a short demo of SMT soldering? Or just a demo
> of how to install a UHF connector on coax? Everybody knows about
> stuffing the coax into the shell and heating it until it melts. Maybe
> you can demo a better way? Or show them how to make a quarter-wave
> ground plane from a coax connector and a piece of Romax.....
>
> That's all for now. I tend to get to hyped sometimes. Just get out to
> Field Day and get involved. If you don't know where to go, check the
> ARRL web page FD locator. Just enter your city and state and the map
> will show you what is around the area... I'm surprised to see there is
> nothing showing in central Wisconsin around Eau Claire! If you know
> any local Field Day groups, light a fire under them to put their FD
> site on the map!....
> <http://www.arrl.org/field-day-locator>
>
> 73, Doug Reed, N0NAS.
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