| |
ZL3AI > APRDIG 13.05.07 05:44l 261 Lines 9666 Bytes #999 (0) @ WW
BID : 10163-ZL3AI
Read: GUEST
Subj: [APRSSIG] Vol 35 #4, 1/2
Path: DB0FHN<DB0FOR<DB0MRW<DK0WUE<F4BWT<IW2OAZ<ZL2BAU
Sent: 070513/0340Z @:ZL2BAU.#79.NZL.OC #:47565 [Waimate] $:10163-ZL3AI
From: ZL3AI@ZL2BAU.#79.NZL.OC
To : APRDIG@WW
Today's Topics:
1. RE: TO-CALL question. (Robert Bruninga)
2. Understanding packet (Andrew Rich)
3. RE: [OZAPRS] Understanding packet (Darryl Smith)
4. Re: Understanding packet (John Hansen)
5. Re: Understanding packet (scott_at_opentrac.org)
6. RE: TH-D7AG in the U.K. (Dave Baxter)
7. Balloon Launch, Friday, May4th,9:00am (AA3JY_at_Winlink.org)
----------------------------------------------------------------------
Message: 1
Date: Thu, 3 May 2007 13:50:24 -0400
From: "Robert Bruninga" <bruninga_at_usna.edu>
Subject: RE: [aprssig] TO-CALL question.
Done
Thanks
Bob
>-----Original Message-----
>From: aprssig-bounces_at_lists.tapr.org
>[mailto:aprssig-bounces_at_lists.tapr.org] On Behalf Of John Ronan
>Sent: Wednesday, May 02, 2007 2:34 PM
>To: TAPR APRS Mailing List
>Subject: Re: [aprssig] TO-CALL question.
>
>Hi,
>
>How about we use APZWIT? I'm still unsure whether the usage will
>continue into 2008.
>
>Regards
>de John
>EI7IG
>
>
>On 2 May 2007, at 17:50, Robert Bruninga wrote:
>
>>>I'm working on a small application to take a position report from a
>>>MAP27 radio (Mountain Rescue) and send it back out over APRS. Are
>>>there any conventions to using the APZ??? TO-CALL?
>>
>>Look on the APRS1.1 Addendum link to the TOCALL list. If you
>>see no conflicts, pick what matches your desires and let me
>>know. Ill add it to the list...
>>
>>Bob
------------------------------
Message: 2
Date: Fri, 4 May 2007 06:32:03 +1000
From: "Andrew Rich" <vk4tec_at_people.net.au>
Subject: [aprssig] Understanding packet
Gudday
I have a few questions concerning packet radio.
+ I think from memory that packet does not simply use 1200 = high or 2200
low.
+ Does it keep flicking between tones to "keep the energy up" in the
detector ?
+ And a non flick is a state change ?
+ From what I have been reading 0x7e or 011111110 is the start or txdelay ?
+ What is the bit stuffing i hear about ? why is that so ?
+ I have noticed an MX614 does tone changes at the zero point, what are the
distanvantages then of using xr2206 xr2211 that do not do this ?
+ Does packet use a CRC method ? is that what the passall command is in a
tnc ? show now crc chucksum valid packets ?
+ From what I can see on my bench testing, one cycle of 1200 Hz and two
cycles of 2200 Hz fits nicley into 1200 baud ? coincidence ?
Regards
Andrew
VK4TEC
------------------------------
Message: 3
Date: Fri, 4 May 2007 06:43:27 +1000
From: "Darryl Smith" <Darryl_at_radio-active.net.au>
Subject: [aprssig] RE: [OZAPRS] Understanding packet
HI Andrew
Some of these things are mentioned in the AX25 spec on the TAPR www site.
* Packet commonly uses BELL modem tones on air.
* Changing tones is used to mostly ensure bit-synchronization. Since the
data is synchronous there are no stop bits like RS232
* 0x7e/011111110 can be the start of the TX delay, but this is not
essential. According to the spec, only one 0x7e is needed at the beginning
of a packet. Some transmitters send 0x7e during TxDelay. Some do not. It is
probably a good idea to. The start and end 0's can be shared on the 0x7e,
giving the two tones swapped at about 171 Hz.
* Bit stuffing is needed to keep up bit synchronization - without it sending
huge number of 0x00's would mean that the Tx and Rx would get out of sync.
When there are too many bits without a transition, one is added.
* Zero-Crossing reduces transients on the signal. This improves the
bit-error rate, as opposed to the 2206/2211
* The Packet CRC is in the AX25 spec.
* You cannot fit two x 2200 Hz cycles into a 1200 bps bit. It overlaps a
bit. This is intentional, so that harmonics of 1200 do not get into the 2200
Hz decoder. I would recommend the TAPR book on Wireless Digital
Communications (http://www.tapr.org/products.php?type=PUBLICATION)
Darryl
------------------------------
Message: 4
Date: Thu, 03 May 2007 16:59:43 -0400
From: John Hansen <john_at_coastalchip.com>
Subject: Re: [aprssig] Understanding packet
You might find the following useful:
http://www.tnc-x.com/dcc.doc
http://www.tnc-x.com/dcc2.doc
John Hansen W2FS
------------------------------
Message: 5
Date: Thu, 03 May 2007 15:44:45 -0700
From: scott_at_opentrac.org
Subject: Re: [aprssig] Understanding packet
I wrote up some of this at http://n1vg.net/packet.
As someone pointed out to me recently, it doesn't actually seem to be NRZI
as commonly documented, but maybe more properly NRZ-S. That is, a change
in tones encodes a zero, and no change encodes a one.
The bit stuffing is there to ensure enough transitions to keep from losing
sync. Your transmitter and receiver usually don't have exactly the same
idea of how long one bit period is, and if you go too long with no
transitions then they can drift apart. The way it works is that the sender
inserts a zero (transition) every time there's a run of 5 ones, except in
the case of the 0x7e flag.
0x7e marks the start and end of the frame. You're better off sending zeros
(alternating tones) in the txdelay time to get faster receiver lock.
The frame check sequence is a CRC-CCITT16.
Scott
N1VG
------------------------------
Message: 6
Date: Fri, 4 May 2007 10:13:04 +0100
From: "Dave Baxter" <dave_at_emv.co.uk>
Subject: RE: [aprssig] TH-D7AG in the U.K.
As to APRS "Paths" etc...
The "Recommended" path for the UK (at the moment) seems to be
"RELAY,TRACE7-7" (without the quotes!)
But... You will find that does not work everywhere. Widen-N will work in
many places (WIDE1-1,WIDE5-5) but either way, coverage can be patchy to say
the least, with huge holes in what network there is, especially when you
are away from a major town or motorway. Even in towns and cities, and on
major motorways, coverage is often poor to non existent, even if you run
50W out! Although the 2m band FM usage is supposed to be 12.5kHz channel
spacing, including Data, in practice, use the normal 5kHz deviation
setting, the default for the D7AG I suspect.
Callsigns: Most travelling visitors just use their normal call, with (or
more often without) anything in the posit comment string. After all, if
there is a problem, we know where you are! (Or were...) If you have to,
use the new prefix M/yourcall or MW/yourcall etc in the comment field.
Digi's: Some about, but don't rely on one if you hear it, it may be gone
in a few hours time (unattended operation is not "switch it on and leave
it" here like it is in the US) Likewise many "home" I-Gates, very fleeting
appearances to say the least.
The major I-Gates call's will start with MB7, they are permanent fixtures
(such as we can do) but again don't rely on all of them being set up to
gate from Internet to RF for "Local" stations, so APRS messaging can be a
tad unreliable.
Sadly, a barefoot D7 on it's own whip, will not get very far at all on APRS
in the UK, unless you are very close to a gate or digi. You'll have more
luck with voice repeaters and maybe simplex call's (145.500 and 433.500 FM
simplex calling)
Check out the RSGB's website (http://www.rsgb.org/) for links to the
repeater management pages, where you can perhaps get a list of known
repeaters, locations, and frequencies etc.
http://www.ukrepeater.net/repeaterlist.htm too...
Take care with repeater shifts and band edges, 2m = 144 to 146, and 70cms =
430 to 440, but within 100kM of the centre of London (Charring Cross) you
cannot use 431 to 432! (Most 70cms FM activity is between 432.5 and 435,
including repeater inputs) Above and below our 2m band, there are several
services that can get "rather miffed" if you repeatedly (even if
accidentally) stomp on one of their RX channels.
The paging (POCSAG) transmitters that are not far from 2m, run high power
(150W the last time I checked) and yes, can and often do cause problems
with front end clobering of much amateur equipment. If your hotel has one
near (or on top of!) it, you will have problems.
Bring a copy of your licence doc's, and any CEPT papers. Then if you get
pulled by Customs, you have some evidence that you are a licensed Amateur,
or they might want to confiscate your radio. (Highly unlikely, but if they
want to, they can, and there is nothing you can do to change it!) So long
as you have a departure date to leave the UK (not an "Open" ticket) you
should be fine even if you do get pulled.
99.9% of the time, people carry Ham gear in and out of the UK with no
problems at all, but it's the 0.1% that get queried by a spiky customs
officer who got out of bed the wrong side, and then it's not fun at all.
Oh yes, our mains voltage (for battery charging) is 230V 50Hz Check your
portable charger input spec's (and anything else you may bring) You can buy
plug/socket adapters at the airport, and in some major hotels too. 12V
sockets in cars are the "normal" dodgy cigarette lighter types.
Warning! You may see some things advertised as "converters" for 115V
appliances to work on 230V. Unless they specify they are a step-down or
"Auto" transformer (and are obviously heavy) they are more often than not,
just a diode in series with the supply! "Heating" appliances (hair driers)
etc will probably work somehow, but other more delicate electronic devices
will still see one half of the 230V waveform, with predictable results.
Lastly. Mobile Phones: GSM900, GSM1800 and 3G are supported in the UK (and
EU) Check your provider and enable international roaming, if not already
done. Dialling code for the 'states, 001 then area code etc..
Enjoy your stay in the UK, remember to drive on the left, and do not use a
hand held phone when driving!
73
Dave G0WBX.
------------------------------
Read previous mail | Read next mail
| |
