[FADCA] Status of Dual Speak Mitrek for Melbourne LAN

[bud thompson]

See bottom posting...

----- Original Message ----- 
From: "John H. Green" <wb4moz at adelphia.net>
<snip>
Sent: Tuesday, January 11, 2005 15:19
Subject: Re: [FADCA] Status of Dual Speak Mitrek for Melbourne LAN


> Hi Bud
>    Once again I urge caution in putting 9k6 and 1200b on the same
> frequency. As your tests indicate the hidden transmitter problems are
> even more evident.\

<snip>

>
>    Having said all that look at the attached as a possible way to make
> use of rfdcd from the radio.

<snip>

> 73  John
>

* * * *

John- the attachment did not come through the fadca at mailman.qth.net 
reflector.

I appreciate your cautionary comments and then those of some encouragement 
for on-going testing.

We do have the two PK-96s (1200 and 9.6kb) working with full cross-PTT and 
cross RXA DCD working.  All we have to do is provide the unsquelched Mitrek 
level back to the diode matrices to inhibit 9.6kb TX when a 1200b (carrier) 
is on channel.  I'm sure we can do that with the help from your attachment. 
We have tried all the other suggestions you made and feel we can make this 
work - to the degree it should by AX.25 protocol constraints.  We have not 
yet been able to marry a PK-96 and a Tiny-2 for TXA due to impediance mis 
matches.  We can, however atain more than 2 KHZ deviation with both, so may 
live with that..

This has been a learning process, though I now clearly see we have been 
re-inventing a wheel that won't roll very true.

That said, I'm coming to the following conclusion- which is fraught with a 
lot of variables -

Soon FADCA needs to prepare and publish a piece on "How To Get Your Area 
on/into the Florida Layered Packet Network." This would include several 
related topics, only one of which would be establishing a LAN from scratch. 
This could cover the idea that, while used 1200b TNCs and old 2M radios are 
easier/cheaper to come by, ultimately a LAN should have 9.6kb user access as 
faster is the wave of the future as more users are added.  However, 9.6kb 
not only requires a more expensive TNC but also a '9.6kb-ready" radio. 
These considerations apply not only for individual users, but for fixed 
locations such as EOCs, Hospitals, TelPac nodes, Digis, and, of course the 
LAN port at the switch.  Chuck and Russ have been discussing use of local 
VHF repeaters for piggy-backing 9.6kb packet user access, digis, etc.  This 
will also need to be addressed.

Countering the apparent additional cost for 9.6kb somewhat are (1) if a user 
presently has no equipment at all, some money has to be spent, (2) less 
expensive 9.6kb TNCs are looming on the horizon, (3) sound card applications 
are looming on the horizon, though require an interface box adding to the 
cost.

An operational consideration which we ran into during the 2004 hurricanes is 
the close frequency proximity of vhf voice and vhf packet operations at an 
EOC or other fixed site.  In fact, for the Seminole County EOC, it was 
necessary to shut down the packet operations entirely part of the time in 
favor of voice operations.  This leads to either splitting packet and voice 
operations on different bands (one 2M one UHF), or additional hardware 
(cavities, etc.), or sufficient vertical antenna separation, which is not 
available universally. For a tactical user of both voice and digital, say at 
a shelter or mobile command center, using two bands and a dual band antenna 
would be the least complicated approach.   I doubt that many groups will 
give up 2M voice operations and move to UHF.  Therefore, I feel it would not 
be unreasonable for FADCA to promote UHF 9.6kb user access for new LANS, as 
well as considering UHF that when adding 9.6kb to existing LANS.  We also 
need to be cognizant of mutual aid where users from one LAN may be mobilized 
to work in a distant LAN.

That leads to whether or not 1200b access should be supported for very long 
(if at all) on a new LAN.  Considering that where there is no LAN now, there 
is likely not anyone set up on packet (other than APRS 2M perhaps), so 
setting up user access initially on UHF would not be unreasonable.  It would 
require users to have a UHF radio (generally more expensive used than 2M), 
but if the user is going to start with 9.6kb straightaway, he/she might 
purchase a dual band 9.6kb radio to have for voice/digital operations.

On the other hand, if there were very many interested who could/would not 
move right to 9.6kb, local option may be to include both 9.6kb and 1200b 
access.  The major factor then would be the added expense/problems of an 
additonal port at the local swtich site, or start with a dual speed port and 
live with the enharent problems.

The interest in testing/experiencing 9.6kb by Vick W5SMM and Rick KN6KB, 
programmers of the Paclink AGW, Telpac, SCAMP, and other WL2K-related 
programs, is what has prompted establishing 9.6kb user access on the 
Melbourne LAN.  Three PK-96s and a high power VHF Mitrek were donated to 
PCARS through the WL2K Development Team and Ivars KC4PX.  N3PPC and I are 
doing the grunt work, gaining the experience.  The only cost to PCARS is $50 
for the Mitrek crystals.  This will, in conjunction with existing PCARS 
gear, enable the Melbourne switch to have full intra network connectivity at 
9.6kb (to Vero and to Orlando), and also have 9.6kb local user access. 
Since there have been few users on the Melbourn LAN, rather than go for yet 
another radio port at this time, I elected to try for dual 1200b/9.6kb user 
access on the 145.09 VHF port.

I did not give this plan a name, but now call this Plan A.

(Where there is a Plan A . . . )

When we get this all working (hopefully not later than shortly after 
Hamcation), there will be three users on the 145.09 LAN, each of who can use 
either 9.6kb or 1200b for on-going testing and evaluation of the WL2K 
packet-related software development as well as how the two speeds work 
together.  Anyone in the Melbourne area can choose either 1200b or 9.6kb to 
try out the system on 145.09.  There is no doubt now that once there are 
very many 1200b users it will be prudent to move to Plan B.

Plan B would require an additional low power UHF Mitrek at the Melbourne 
site and a set of crystals for a coordinated UHF LAN frequency.  Providing 
PCARS replaces the missing LAN antenna now with a dual band 2m/70cm antenna, 
there would be no additional hardware or expenditures required by PCARS to 
have dual speed access with 1200b on VHF and 9.6kb on UHF.

Karen indicated there may soon be a repeater co-located with the Melbourne 
Switch... We'll have to keep tabs on mutual interference/frequency 
coordination with that.

bud N0IA