| |
ZL3AI > APRDIG 13.11.06 23:36l 145 Lines 4622 Bytes #999 (0) @ WW
BID : 9039-ZL3AI
Read: GUEST
Subj: [APRSSIG] Vol 29 #11, 1/1
Path: DB0FHN<DB0RGB<DB0MRW<DK0WUE<7M3TJZ<ZL2BAU
Sent: 061113/2227Z @:ZL2BAU.#87.NZL.OC #:14787 [Waimate] $:9039-ZL3AI
From: ZL3AI@ZL2BAU.#87.NZL.OC
To : APRDIG@WW
Today's Topics:
1. RF modulations techniques (Andrew Rich)
2. Re: RF modulations techniques (Stephen H. Smith)
3. Re: RF modulations techniques (Wes Johnston, AI4PX)
4. RE: RE: VH-SJS Aeronautical mobile (Ken Brown)
----------------------------------------------------------------------
Message: 1
Date: Mon, 13 Nov 2006 06:32:57 +1000
From: "Andrew Rich" <vk4tec_at_tech-software.net>
Subject: [aprssig] RF modulations techniques
Gudday
I was driving along as you do and pondered this thought.
The existing packet radio systems turn data into tones and then modulate up
to vhf and then do the reverse.
A digi comes back down to audio and the does the reverse.
I asked myself why don't we just modulate at RF levels and use transponders
as digis ?
How does D-STARS fit into the APRS equation ?
Anybody ever played with PulsePositionModulation on APRS ? Planes use it at
1Mb/s
They can send GPS co-ords in 112us
Cheers
Andy
Andrew Rich
Amateur radio callsign VK4TEC
email: vk4tec_at_tech-software.net
web: http://www.tech-software.net
Brisbane AUSTRALIA
------------------------------
Message: 2
Date: Sun, 12 Nov 2006 16:54:34 -0800
From: "Stephen H. Smith" <wa8lmf2_at_aol.com>
Subject: Re: [aprssig] RF modulations techniques
vk4tec_at_tech-software.net wrote:
>Gudday
>
>I was driving along as you do and pondered this thought.
>
>The existing packet radio systems turn data into tones and then
>modulate up to vhf and then do the reverse.
>
>A digi comes back down to audio and the does the reverse.
>
>I asked myself why don't we just modulate at RF levels and use
>transponders as digis ?
1) Probably the main reason is that when packet first appeared on the
ham radio scene some 25 year ago, the common terminal devices were 110 baud
ASCII Teletype machines, so there was no benefit in going much faster.
1200 baud wireline modems had well-established the Bell 202 1200/2200 audio
tone pair. Modem chips for this standard were widely available and cheap
when the first TNCs were designed. Further, it was far easier to just jam
audio tones into the mic jack of existing FM transceivers. Direct FSK, as
used on 9600 baud modes, requires cutting into the radio for direct
DC-coupled access to the TX modulator and RX discriminator.
Note that we DO use direct FSK on 9600 baud VHF-FM packet. And that
300-baud audio tones used through an SSB transceiver on HF packet do result
in the net effect of direct FSK on the air.
2) The process of demodulating and then re-modulating the data at each
digipeater allows the data stream to be completely regenerated free of
noise. Passing through a linear transponder will just add the uplink noise
(if the signal is weak) and the downlink noise (as heard by the next digi
or user) to the desired signal. Not to mention that without demodulating
down to baseband data, you can't inspect the data, process paths, decrement
n-N, etc.
>How does D-STARS fit into the APRS equation ?
It's not APRS but it is purely digital no matter what you are sending
(voice, data, etc).
>
>Anybody ever played with PulsePositionModulation on APRS ? Planes use
>it at 1Mb/s
A single one-megabit/sec signal on two meters would occupy nearly the
entire band!
>They can send GPS co-ords in 112us
It's easy if you are not limited by the bandwidth of FM voice radios,
and existing channel plans that expect to place more than one channel in
the band.....
------------------------------
Message: 3
Date: Sun, 12 Nov 2006 20:07:26 -0500
From: "Wes Johnston, AI4PX" <wes_at_kd4rdb.com>
Subject: Re: [aprssig] RF modulations techniques
You can run packet thru a voice repeater (check your TNC manual for AXhang
paramater), but noise is a problem. There are also such things as bit
regenerating repeaters.
Wes
------------------------------
Message: 4
Date: Sun, 12 Nov 2006 22:01:19 -0500
From: "Ken Brown" <W2KB_at_comcast.net>
Subject: RE: [aprssig] RE: VH-SJS Aeronautical mobile
My Cardinal came with a spare belly mount aviation antenna intended for an
aviation handheld transceiver to be used in the event of main radios
failure. I use it with a Kenwood D700A in the lowest transmit power setting
and it works fine. The mismatch between 144.390 and the aviation band
doesn't appear to have any significant impact. And the antenna still
matches the aviation handheld just in case.
73, ---Ken W2KB N16019
------------------------------
aprssig mailing list
aprssig_at_lists.tapr.org
https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig
End of aprssig Digest, Vol 29, Issue 11
Read previous mail | Read next mail
| |
