2 Sep
2017
2 Sep
'17
11:32 a.m.
A couple of decades ago, the "GRAPES" WA4DSY
56kbit modem kit was
available for a moderate price. They weren't too difficult to put
together. Alignment did take a scope, but took only a few minutes. About
five people in San Diego had them. As far as I know, only three ever
made it onto the air here.
I remember that modem, but also I remember that there were quite some issues at that
time.
It was not easy to reliably make 56k HDLC using affordable hardware at that time.
For interrupt-per-character serial devices the performance of a PC-XT was not quite
enough.
There were DMA-based controllers but they were difficult to obtain, hard to find reliable
drivers for, and expensive.
Some people built 68000-based boards for that kind of datarate, and later for 1-2Mbps,
also
using DMA. I also considered using PC-LANA adapters that had all the data generating hw
as a co-processor but were not AX.25 compatible. (they use the NETBIOS interface, I
added
IP over NETBIOS to my version of NET to be able to use them)
However, no real radio link has ever been made here.
Of course wide acceptation would have been even more difficult.
Today, the computer performance problem no longer exists, but the problem of wide
deployment
of a locally designed solution still exists.
Rob