Discussion in 'Working Different Modes' started by NC4JB, Jun 14, 2010.
Anyone else ever use RTTY or any other digital modes on 2m FM?
Yep, been there, done that years ago using a simple Terminal Unit (TU) with an internal AFSK tone generator, simple interface, and a TRS-80 Model 1 computer running home brew Z80 Assembly Language software. Worked very well at 25 watts using a Kenwood TR-7400A into a simple 2 meter ground plane antenna up 35 feet on the top of my house.
Most users back then operated their stations using the same 170Hz shift with a Mark tone of 2125Hz and Space tone of 2295Hz. Today RTTY still uses the same 2125Hz Mark tone and 2295Hz Space tone except computer sound cards and software are used instead of terminal units. The end result in the same.
The tones are applied to the transmitter in much the same way as HF. There is one difference between HF and FM. If you apply too high a level of audio you could easily over deviate the FM transmitter which will lead to distorted audio or simply no audio heard at all in the receive signal.
Any of the digital modes that use tones, or what one hears as tones (including phase shifting), will work just fine on 2 meter FM.
My ARES group has played with PSK, RTTY WinDRM, packet, SSTV, and packlink. These work particularly well with a soundcard interface. We even played with CW, using the mic held up to a CW tone generator. The ARES group uses some 2 meter FM digital modes for certain, local emcomm.
A small Ham group in Missouri is building a packet backbone across the state, and the local access to the longer range nodes is via 2 meter FM packet.
I have been told that the singal to noise ratios of these modes on 2 meter FM is extremely good, compared to HF.
One problem is that there may be little if any such activity in your area. I would check with your local Ham clubs to see what might be going on.
Check your states ban planning organization. They determine what 2 meter FM frequencies are to be used for which modes. 70 cm also works well.
Years ago, I ran a Packet BBS, using 1200 baud, ASCII character set plus the packet transport layer, of course .
I don't understand why anyone would want to limit themselves to the baud rates and protocols that are allowed on HF ( 300 max ) when they can do so much faster and more efficient modes on the VHF/UHF bands. Maybe it is just not being familiar with the possibilities, such as being able to run 9600 baud ASCII or some other "backbone" protocol on the upper bands.
Of course, if one is typing at the keyboard, all that extra bandwidth is going to waste, but that doesn't seem to bother the users of internet chat rooms, so it shouldn't be a barrier to VHF/UHF keyboarders, either !
Interesting question. 73, Jim
Many years ago, FM RTTY on VHF was quite common. The 146.10/.70 was commonly used for RTTY repeaters, and most were home to RTTY bulletin boards.
Today, there are groups that do other digital modes on VHF FM, but there may not be any around you. As I recall, though, one of the groups experimenting with NBEMS and/or flarq were in the Carolinas someplace.
PSK31 works on FM, and I've made contacts over a distance of 150 miles that way. On SSB, however, the range increases quite a bit. From here in Minnesota, I used to check into a net every week where the net control was in Peoria - around 300 miles away. Over time, I think most of the people involved moved on to other things. PSK is not the best mode for VHF due to multipath distortion. MFSK and Olivia are much better. WSJT allows modest stations to easily work meteor scatter using random meteors.
The PSK_VHF_UHF_HAMRADIO group on Yahoogroups may be of some value. There are lots of good files there, and you may find others interested in working with you.
It seems wasteful to use the bandwidth of an FM signal to carry a narrow signal like 170 Hz shift RTTY or PSK31. If you have that much bandwidth available, why not use a mode that can make use of it?
Well there aren't any simple chat modes that are designed for FM/VHF. However you could run APRS. Contrary to popular belief it isn't just for sending position reports. You can also communicate with other hams using messages, a bit like SMS. And because you can use digipeaters and even an internet backbone called APRS-IS you can message people way beyond your normal VHF range. Plus it's spectum efficient - everyone uses one frequency (I believe it is 144.390MHz in the US) and only transmits when they have something ready to send.
You can use the AGW Packet Engine (free download) to generate the packet tones with a sound card, and interface to the radio the same way you do digimodes on HF.
For an APRS client use APRSIS32 which you can get from here http://groups.yahoo.com/group/aprsisce/ which is also the support group for it.
WinDRM uses the 2 meter/70 cm bandwidth quite efficiently. It actually sends (I believe) eight streams of data at the same time, within the normal Ham 2 meter FM rig bandwidth. One can send PDF files, Word files, photos, etc. very fast with WinDRM on vhf/uhf. It is quantums faster than the old AX25 used for packet.
When you download the WinDRM software, and run it through a soundcard interface, you don't need a packet engine (AGW?). It does it all by itself.
One thing to remember on this is simplicity. Yes it may not be efficient use of bandwidth for FM, but it is with the explosion of SSB capable qrp rigs that offer 2m and 70cm all modes. The best thing about RTTY to me is simplicity. For direct keyboard to keyboard its hard to beat without adding error correction. It is a good low power mode and compared to voice adds a modicum of security. Now it is not as simple as CW, but it is fun and easy to use as well. I am not a NO code advocate, but many a new technician can be interested in digital modes by using simple and effective starts, such as RTTY. I would be interested to see how RTTY on VHF/UHF would compare to Hellschreiber (Feld Hell). I am willing to try if anyone else is.
I recommend anyone joins FISTS, NAQCC, The FeldHell Club, GQRP, SKCC, and ARRL. All are excellent sources of information on low power, cw, and digital modes. There are also many sites devoted to RTTY and AM. Alas RTTY, like AM on VHF/UHF is more of a rarity than the norm. 73, Todd
Yep I tried RTTY and several other modes on 2 & 6 mtr FM, rumor must have been that I had the plague as I never got a taker on my CQs.