[aprssig] E Coast 9600 baud backbone 15W radios.

Ev Tupis w2ev at yahoo.com
Sun May 29 10:28:31 CDT 2016


>From someone who has direct experience in this arena...the only reason is the cost of VHF SSB equipment.

There is no issue with frequency stability as an SSB transceivers' passband is at least (grin) 2.5 kHz wide and decoder software can skim the entire waterfall looking for signals to decode.  It is the premise of ACDS^31 software used by http://www.PropNET.org.

By the way...the PropNET folks are running a POP (Play On PropNET) event on 10 meters this weekend.  Here's a link to the map for the last 24 hours 
http://propnet.org/catch3.php?band=HY&center=WW&last=24&call=&maptype=G3&geo=&zoom=1

"10" pushpins are PropNET stations using the ACDS^31 software

"N" pushpins are skimmed human stations that are "N"ot using ACDS^31 software (prolly just band QSO's)
"L" pushpins are ACDS^31 stations that are "L"urking (RX only)...kind of defeats the purpose since the idea of running ACDS software it to cause your station to auto ID 24/7.


Cheers,
Ev

PS: The PropNET over-the-air protocol is based on ARRS' ;-)




----- Original Message -----
From: Stephen H. Smith via aprssig <aprssig at tapr.org>
To: Andrew Rich <vk4tec at tech-software.net>; TAPR APRS Mailing List <aprssig at tapr.org>
Sent: Saturday, May 28, 2016 9:10 PM
Subject: Re: [aprssig] E Coast 9600 baud backbone 15W radios.

On 5/28/2016 3:57 PM, Andrew Rich via aprssig wrote:
> I don't know why we don't use vhf upper side band and psk31
>

1)   Radio complexity - SSB circuity is far more complex than basic FM radios. 
You just don't find sub-$100 (US) SSB transceivers for VHF.

2)   Frequency stability - APRS operation is random transmitting in the blind; 
you don't have a chance to tune in the other station first.  You must maintain 
absolute frequency accuracy within +/- 15 Hz end-to-end for PSK31 to work. 
Unlike FM, on SSB, RF frequency errors translate hz for hz to AUDIO frequency 
errors at the receive end.   It's very difficult and expensive to achieve RF 
frequency stablility of +/- 10 Hz or so on VHF/UHF, especially in 
reasonably-priced ham gear.  (It works out to around .01 PPM at VHF.)

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Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

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