An AMRAD "Newbie"
Sat, 06 Mar 1999 23:11:36 -0500
Thanks for your note. I am sending a copy to "email@example.com" so
that other members can read it. Maitland, AA4HS, should be able to
add your mailing address to "tacos" so you can see what's being
discussed. Today we received a license from the FCC for experiments
on 136.75 kHz and there will be some tests on LF next weekend.
If you can write an article for the AMRAD newsletter which expands on
what you mention in your note, I know the other members would enjoy
In addition to ham applications on HF, there are still a lot of ships
sailing around the world using HF, but with older SITOR or CLOVER
technology. A market exists for a low cost, high throughput HF modem.
My callbook address is in Nashville, Tennessee, but I live in
Warrenton, Virginia so I'm a "local" member of AMRAD.
Don Mills wrote:
> Hi Randy,
> I've recently joined AMRAD and read your "New Ideas" article in
> the Sept-Oct issue with great interest.
> For the past 25 years I've been in R&D Engineering in the Land
> Mobile (VHF/UHF) and Cellular businesses, mostly with Motorola in
> Chicago. Over the years, I've been migrating further from the
> antenna and closer to the phone network -- and liking it less.
> Along the way, I did gather quite a bit of system knowledge on
> IS136, IS95, and GSM -- but my personal interest really lies in
> I hadn't given digital HF much thought (except for a little RTTY
> operation) until last summer when I had a chance to visit HCJB's
> monster shortwave transmitter site in Ecuador, and one of the
> engineers mentioned that they expected to be transmitting in
> digital within a few years. That really caught my attention -- I
> guess I'd never thought that digital would be necessary or
> practical for HF, especially broadcasting. It certainly does
> present some unique challenges.
> I've spent a lot of time researching who's doing what in the
> world of digital radio, and there's a lot going on. At least
> five versions of digital for AM and shortwave broadcast are being
> developed, three in the US; the "beauty contest" part of the
> standards process should be taking place here in the next year
> for both AM and FM. Some of it seems applicable to ham radio;
> much of it does not (we don't need CD -- or even FM -- quality,
> and certainly can't afford 30 kHz bandwidth). I've also found a
> ham in the UK who's working on a digital voice implementation
> using available vocoders and building his own modem using a
> Motorola DSP EVM. [I've picked up an EVM and have been playing
> with PSK31 on it -- quite a powerful little gizmo.] The
> development model for PSK31 is perhaps the most encouraging part
> -- published source code for a readily available, super flexible
> platform. What we used to call the "soft radio" at Motorola. We
> have the "advantage" of fairly narrow channels, compared with
> cellular systems.
> It's pretty apparent that we'd need some kind of variable-rate
> coder for HF. It's hard to imagine it being acceptable to occupy
> all the bandwidth with no input. We also have to distinguish
> requirements between different modes. For example, it's OK to
> miss some voice packets, but not generally data packets. We hams
> have some unique challenges, but obviously need to "liberate" as
> much technology as possible from the commercial world.
> Paul, W4RI, has asked me to put together something on options for
> VHF/UHF, but my own personal interest lies with HF. Please let
> me know if there's anything I can do to help out. By the way, if
> your callbook address is correct I'm just down the road in
> Germantown, just east of Memphis.