[aprssig] On the Road with PSK63 APRS Mobile -- Day 4

[Stephen H. Smith]

Joe Della Barba wrote:
> I have a SSB on my boat set up for PSK31.
> What do I need to do PSK83 APRS?
>
> 73 de N3HGB 
>
>   

Full details here:

     

    <http://wa8lmf.net/APRS_PSK63/index.htm>   




>
> [Posted from Iowa City, IA Motel 6 via WiFi from another motel about 1/3rd
> mile away, using my "WiFi Super Blaster" DX antenna.]
>
> Stephen H. Smith wrote:
>   
>> I'm now on the fourth day of my cross-country trip, experimenting with 
>> 30-meters HF  APRS over PSK63.   
>>     
>
> Today I have noticed a number of STRONG   PSK63  signals that simply 
> don't decode at all.  These signals appear rather wide, and lack the
> characteristic vertical double-line "railroad track" in the middle of the
> waterfall spectrum display.  They appear to be PSK transmissions with
> excessive TX audio levels (or attempted RF power output), that creates
> intermodulation distortion in the transmitter.
>
> I have just added the paragraphs below to my PSK63 APRS page at:
>
>     <http://wa8lmf.net/APRS_PSK63>
>
> ------------------------------------------------------------------------
>
> IMPORTANT:    PSK63 is a simultaneous two-frequency transmission, unlike 
> conventional FSK  packet or RTTY which are single-tone-at-a-time constant
> power transmissions similar to key-down CW. 
>
> *It is essential to keep the _average_ output power of the SSB transmitter
> far below maximum in the PSK mode, to avoid severe inter-modulation
> distortion (IMD) of the transmitted signal. *
>
> High IMD will make your signal occupy excessive bandwidth on the air, and
> worse make it unreadable to others, even if the RF level is strong.  
> If the transmit level is PROPERLY SET, the PSK63 signal will be received
> without errors, even on signals too weak to move the S-meter.
>
>    1. Disable any speech processors, limiters or compressors in the
>       transmitter audio chain.
>        
>    2. If you are reading transmitter output power on an averaging-type
>       wattmeter, you must adjust the soundcard audio level (or
>       transmitter mic gain) for an indicated power of about 1/3rd of the
>       keydown maximum power on CW or FM.  You should NOT be showing any
>       ALC (automatic level control) voltage which would indicate that
>       you are at or trying to exceed maximum transmitter power output.
>        
>    3. If you are reading power output on a PEAK reading wattmeter (or
>       monitoring the TX signal on a scope), gradually increase the
>       soundcard output level (or transmitter mic gain) until the power
>       output stops increasing.  Then turn the level back down a bit
>       until the output drops about 20%.  This will ensure that you are
>       not saturating the transmitter power stages. 
>
>
> ------------------------------------------------------------------------
>
> --
>
> Stephen H. Smith    wa8lmf (at) aol.com
> EchoLink Node:      WA8LMF  or 14400    [Think bottom of the 2M band]
> Skype:        WA8LMF
> Home Page:          http://wa8lmf.net
>
> NEW!    *** HF APRS over PSK63 ***
>    http://wa8lmf.net/APRS_PSK63/index.htm
>
> Universal HF/VHF/UHF Antenna Mounting System
>   http://wa8lmf.net/mobile/UniversalAntMountSystem.htm
>
> "APRS 101"  Explanation of APRS Path Selection & Digipeating
>   http://wa8lmf.net/DigiPaths
>
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