Charles,
What happened with Q15X25 ?? It looks promising, especially on VHF.
Can you fill us in on how it worked or didn't work?
Howard K5HB
----- Original Message ----
From: Charles Brabham <[EMAIL PROTECTED]>
To: digitalradio@yahoogroups.com
Sent: Monday, August 4, 2008 4:16:46 PM
Subject: Re: [digitalradio] Re: Has anyone looked into FPGA-based digitalmodes?
PACTOR, being an ARQ mode is incapable of sharing a
frequency with more than one other station. That, along with the extreme
bandwidth and lack of effective signal detection makes PACTOR unsuitable for
digital HF networks on anything but a very limited scale. - A few afficianados
can play around with it, but in that case as the network grows, more and more
participants cop out and use the internet band-aid to cover up for the mode's
basic lack of suitability for HF networking.
Or they do like WinLink and run roughshod over
their fellow hams, operating what amounts to a QRM mill that takes up more and
more spectrum as the "network" grows.
HF Packet, warts and all, is currently the only
digital mode that a serious HF network can be built upon. The secret to this
performance edge is AX25, which allows multiple stations to share a single
frequency. The more reasonable bandwith there is also a positive factor that
appeals to responsible amateurs who know how to play well with
others.
They call this "spectral efficiency" and if your
mode of choice does not have it, best to keep it for keyboard use and leave the
networking to the networkers.
It is fashionable to diss Packet radio and AX25 -
but none of the detractors have been able to demonstrate anything that does HF
Packet's job any better... In fact, nobody has come up with anything yet that
even works as well. Performance talks, and "fashionable PC attitudes" walk when
actual networkers look at the available digital modes.
That's the way it is... Maybe someday there will be
an actual improvement over AX25 and Packet for HF networking. When this
happens,
I'll be one of the first to put the new system on the air and into actual use.
BUT I have witnessed and been part of several efforts to improve upon AX25 and
Packet over the last couple of decades, and what has been found in every case
so
far is that it is awfully easy to sit around and diss AX25 Packet for HF
networking, but not so easy to come up with something that actually works as
well, much less any better.
If there was anything actually better out there,
the HF digital network would already be using it and AX25 Packet would only be
found on the VHF/UHF bands.
But there isn't, so...
73 DE Charles Brabham, N5PVL
[EMAIL PROTECTED] #STX.TX.USA. NA
----- Original Message -----
From: Jose A. Amador
To: digitalradio@ yahoogroups. com
Sent: Sunday, August 03, 2008 9:16 PM
Subject: Re: [digitalradio] Re: Has anyone looked into FPGA-based digitalmodes?
I believe that both the AX.25 and the BBS model are OK, but that the
packet channel coding is a disaster in the sense that a single erroneous
bit trashes a frame. That fires up the retries chain that are so
detrimental to the link capacity, and may sever it as well.
Pactor does a _LOT_ better, as it is able to use frames with errors that
would be useless on packet using different FEC mechanisms. Source
compression may help as well, as FBB and WL2K do. If the signalling
speed can be made to match the channel and the protocol yield
capabilities under a certain level of errors, a huge relative
improvement can be achieved.
That is the big adventage of WL2K, the use of Pactor II and its better
channel coding. The rest is much alike the old BBS system, reworked.
I believe that something that achieves similar results to those stated
above will certainly be a step ahead.
73,
Jose, CO2JA
---
Bill McLaughlin wrote:
> To echo what Rick stated,
>
> FAE400 is an extremely useful ARQ mode that has a lot of potential;
> robust yet reasonably narrow. Works very well, just a shame so few use it.
>
> NBEMS is also a good ARQ suite, but a lot slower when using HF
> friendly modes. No sure the lock-up time using MFSK16 has been
> resolved but the new FLDIGI had the mode THOR, an incremental shift
> keying mode similar to DominoEX. Not sure if that will be implemented
> into NBEMS, although it certainly has that potential, especially as it
> retains DominoEx's tolerance to frequency accuracy.
>
> The ax25 packet structure was fine; problem was/is that ax25 at 300
> Baud on HF, unless near MUF, is a less then optimum speed choice. It
> actually works fairly well at 110 Baud but it is slow.
>
> I think there are many good protocols out there, but not many want to
> experiment.
>
> 73,
>
> Bill N9DSJ
