[aprssig] AFSK vs PSK
vk4tec at tech-software.net
Sun Nov 24 15:36:53 CST 2013
That might be why
Balloon projects use FSK
Where the carrier Freq is shifted between two distinct F1 and F2
Reception is done on SSB ? correct me if I am wrong.
Is this what they cal true RTTY ?
Like CW but jump high and low
- Andrew -
From: aprssig-bounces at tapr.org [mailto:aprssig-bounces at tapr.org] On Behalf
Of Stephen H. Smith
Sent: Monday, 25 November 2013 7:16 AM
To: TAPR APRS Mailing List
Subject: Re: [aprssig] AFSK vs PSK
On 11/24/2013 12:45 PM, Andrew Rich wrote:
> I often sit here listening to AX25 on AFSK and note the number of missed
> I think it is due to the SN ratio.
> Would something like PSK be a better option ?
> - Andrew -
The problem is audio tones over FM. The huge advantage is in using direct
of the FM carrier rather than modulating it with AFSK/APSK audio tones.
Direct FSK is universally done in the commercial mobile data/land mobile
4-frequency direct FSK is used by P25 digital voice and by Yaesu's new
digital voice FM radios. (It's sometimes called "C4FM".) In the C4FM mode,
carrier shifts between +1600 Hz, +800 Hz, -800 and -1600 from channel
allowing two bits to be sent per symbol or state change.
However for ham applications:
1) You have to cut into the radio to make direct DC logic-level connections
the transmitter modulator and receiver discriminator -- something that most
appliance-operator hams are reluctant or unable to do. I.e. you lose the
"stuff it into the mic jack on transmit / take it off the speaker on
simplicity of audio tone hookups.
2) Direct FSK is incompatible with the vast inventory of existing TNCs,
external stand-alone units, and built into radios like the Kenwood APRS
It's something IBM ran into years ago when they tried to alter the PC
standard with their PS/2 family of PCs. What they call the "tyranny of the
installed base". I.e. something may be superior but if it's incompatible
with the millions of existing devices, it has a tough time being accepted.
Stephen H. Smith wa8lmf (at) aol.com
EchoLink Node: 14400 [Think bottom of the 2M band]
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