| |
PA2AGA > TCPDIG 21.09.96 13:08l 172 Lines 6044 Bytes #-10879 (0) @ EU
BID : TCP_96_194
Read: DG7DAH GUEST
Subj: TCP-Group Digest 96/194
Path: DB0AAB<DB0PV<DB0MAK<DB0HOT<DB0LPZ<DB0MER<DB0NHM<DB0SIF<DB0AIS<DB0NDK<
DB0ACH<DB0RWI<PI8JOP<PI8ZAA<PI8GCB<PI8MBQ<PI8VNW
Sent: 960921/0735Z @:PI8VNW.#ZH2.NLD.EU #:6774 [Hoek v Holland] FBB5.15c
From: PA2AGA@PI8VNW.#ZH2.NLD.EU
To : TCPDIG@EU
Received: from pa2aga by pi1hvh with SMTP
id AA17718 ; Sat, 21 Sep 96 07:14:58 UTC
Received: from pa2aga by pa2aga (NET/Mac 2.3.61/7.1) with SMTP
id AA00004891 ; Thu, 19 Sep 96 21:31:31 MET
Received: from pa2aga-10 by pa2aga with SMTP
id AA00004870 ; Thu, 19 Sep 96 21:24:46 MET
Received: from pa2aga-10 by pa2aga-10 (NET/Mac 2.3.61/7.1) with SMTP
id AA00005600 ; Thu, 19 Sep 96 21:24:42 MET
Date: Thu, 19 Sep 96 09:45:05 MET
Message-Id: <tcp_96_194>
From: pa2aga
To: tcp_broadcast@pa2aga-10
Subject: TCP-Group Digest 96/194
X-BBS-Msg-Type: B
TCP-Group Digest Wed, 18 Sep 96 Volume 96 : Issue 194
Today's Topics:
higher speeds, coding etc.. (3 msgs)
TAPR offer 56002 kit?
Send Replies or notes for publication to: <TCP-Group@UCSD.Edu>.
Subscription requests to <TCP-Group-REQUEST@UCSD.Edu>.
Problems you can't solve otherwise to brian@ucsd.edu.
Archives of past issues of the TCP-Group Digest are available
(by FTP only) from ftp.UCSD.Edu in directory "mailarchives".
We trust that readers are intelligent enough to realize that all text
herein consists of personal comments and does not represent the official
policies or positions of any party. Your mileage may vary. So there.
----------------------------------------------------------------------
Date: Tue, 17 Sep 96 06:17:30 GMT
From: dayj@ozemail.com.au (John Day)
Subject: higher speeds, coding etc..
> >To follow your above request for some link budget numbers, consider a 10
> >watt 2M nbfm transceiver working a hilltop repeater from 10 miles out:
>
> >+40 dBm +10 dB antenna gain gives +50 dBm ERP
> >Path loss at 10 miles on 2M is ~100 dB
> >10 dB receive antenna gain gives +50-100=-50 dBm at the receiver.
> >NBFM has ~20 KHz bandwidth. KTB in 20 KHz is ~-131 dBm.
> >Throw in typical noise figure and call the noise floor -128 dBm.
>
> >That's C/N = -50/-128 = 78 dB.
>
> >It's obscene, all right, but the truly amazing thing is, in amateur
> >practice sometimes there is still not full quieting in a similar
> >scenario!
>
> That's because you assumed free-space propagation loss. Real
> terrestrial links over this distance are very seldom line-of-sight.
> Path losses are more like 1/(r^4) than inverse square.
>
> Nevertheless, much of the fading (chopping) that results could be very
> effectively mitigated with the proper coding, interleaving, modulation
> and power control. Our own good experiences at far lower power levels
> on 900 MHz and 1.9 Ghz with CDMA demonstrate this quite well. If it
> works up there, it ought to be a cinch at 2m.
>
> Phil
>
>
Of course the data rate, coding and interleaving characteristics would need to
be suited to the lower frequency. Fading and multi-path behaviour is quite
different at 2 metres when compared to the more 'microwave' behaviour of .9
and
1.9GHz.
Of course all of this begs the question of wether we should be contemplating
the implementation of higher speeds on 2 metres. Surely two metres is
overcrowded in most parts of the world, especially in Europe and Asia with
often only a 2 MHz wide band. Application of a bit of basic technology at 23
and 13cm would seem far more promising. Keep away from GMSK with all its
attendant complications and go for a simple scheme which needs only simple
radio equipment.
John vk3zjf
------------------------------
Date: Tue, 17 Sep 1996 14:05:57 -0700 (PDT)
From: Phil Karn <karn@qualcomm.com>
Subject: higher speeds, coding etc..
>and 13cm would seem far more promising. Keep away from GMSK with all its
>attendant complications and go for a simple scheme which needs only simple
>radio equipment.
There's a limit to how simple the scheme can be and still work. In
particular, spread spectrum is fairly complex, but it also works a lot
better. So some complexity is beneficial, especially if it can be
relegated to software or to VLSI hardware as opposed to RF hardware.
Phil
------------------------------
Date: Wed, 18 Sep 96 01:27:06 GMT
From: johnday@tbsa.com.au (John Day)
Subject: higher speeds, coding etc..
>
> There's a limit to how simple the scheme can be and still work. In
> particular, spread spectrum is fairly complex, but it also works a lot
> better. So some complexity is beneficial, especially if it can be
> relegated to software or to VLSI hardware as opposed to RF hardware.
>
> Phil
>
>
Phil,
Agreed. But then we run into the perpetual problem - human resources. If the
VLSI devices are available then maybe some of the problems are addressable.
But
when it comes to high speed designs we need to have something which is easily
replicatable at moderate cost. Then we need to ensure that it actually gets
into the field and gets used!
I have proven designs for PSK radios for 23 and 13cm - all I need is something
by way of a modem. Is their somebody with the expertise to do an EPLD or DSP
chip set which can give us the throughput we desire? If that were available it
would give me the incentive to turn my prototype radios into a kit reality for
amateur use (We used the amateur bands for prototyping products for 1500 and
2500MHz commercial products).
Anybody willing to take up the challenge?
73's John
------------------------------
Date: Tue, 17 Sep 1996 23:34:00 +0700
From: "Onno W. Purbo" <onno@kalpataru.netura.net.id>
Subject: TAPR offer 56002 kit?
I heard that TAPR is offering 56002 evaluation board
for US$90-100?
Would appreciate any pointer, we would like
to get some.
Thank you.
Onno W. Purbo, YC1DAV
yc1dav@cnrg.itb.ac.id onno@kalpataru.netura.net.id
http://kalpataru.netura.net.id/~onno/
------------------------------
End of TCP-Group Digest V96 #194
******************************
You can send your message for this bulletin
to: tcp-group@pa2aga on .AMPR.ORG-net
or: tcpaga@pi8vnw.#zh2.nld.eu on BBS-net
------
NOT TO: pa2aga@pa2aga or pa2aga@pi8vnw.#zh2.nld.eu PLEASE!!
It will get posted automatically within a few days
Read previous mail | Read next mail
| |
