[OZAPRS] Homebrew HF APRS transmitter

[Peter Wicklein]

Steve,
 
Since you are obviuosly a risk taker and like to stir the pot a bit ;-) and have brought the subject  of netting back up again... I thought I thought I would joint you and say I'm surprised that nobody has discussed the issue of  the effects of doppler on mobile stations and how it affects the the signal at 10MHZ. and what it will do to all the hours of alignment that people are currently perfoming. See my calcs below.
 




Source speed:

m/s --- METRIC --- cm/s km/s -- IMPERIAL -- inches/second feet/second feet/minute - RECIPROCAL - min/mile min/km min/5 km min/10 km --- OTHER --- km/h mph miles/second knots furl's/f'night Mach c (light speed)

Angle α

degrees (°) milliradians radians grad arcseconds arcminutes circles

Wave speed:

m/s --- METRIC --- cm/s km/s -- IMPERIAL -- inches/second feet/second feet/minute - RECIPROCAL - min/mile min/km min/5 km min/10 km --- OTHER --- km/h mph miles/second knots furl's/f'night Mach c (light speed)

Emitted frequency:

Hz (per s) - FREQENCY - kHz (per ms) MHz (per ?s) GHz (per ns) THz per minute per hour per day per week per month per year --- PERIOD --- ns ?s ms s mins hours days weeks years





Increase in frequency:

% [fraction]

Detected frequency:

Hz (per s) - FREQENCY - kHz (per ms) MHz (per ?s) GHz (per ns) THz per minute per hour per day per week per month per year --- PERIOD --- ns ?s ms s mins hours days weeks years

Muscial interval:

semitones cents quarter-tones tones perfect 5ths octaves



 
 
 
Realising this potentual problem, I reflected back to when I was young, my Platoon Sgt said, never come to me with a problem that you dont have a solution for. So in memory of Sgt Zima ( he really didnt like me much) I thought about this for awhile and the only way to be sure your on frequency exactly netted to the igate is to drive constantly at right angles to the each Igate: see below my calcs 
 




Source speed:

m/s --- METRIC --- cm/s km/s -- IMPERIAL -- inches/second feet/second feet/minute - RECIPROCAL - min/mile min/km min/5 km min/10 km --- OTHER --- km/h mph miles/second knots furl's/f'night Mach c (light speed)

Angle α

degrees (°) milliradians radians grad arcseconds arcminutes circles

Wave speed:

m/s --- METRIC --- cm/s km/s -- IMPERIAL -- inches/second feet/second feet/minute - RECIPROCAL - min/mile min/km min/5 km min/10 km --- OTHER --- km/h mph miles/second knots furl's/f'night Mach c (light speed)

Emitted frequency:

Hz (per s) - FREQENCY - kHz (per ms) MHz (per ?s) GHz (per ns) THz per minute per hour per day per week per month per year --- PERIOD --- ns ?s ms s mins hours days weeks years





Increase in frequency:

% [fraction]

Detected frequency:

Hz (per s) - FREQENCY - kHz (per ms) MHz (per ?s) GHz (per ns) THz per minute per hour per day per week per month per year --- PERIOD --- ns ?s ms s mins hours days weeks years

Muscial interval:

semitones cents quarter-tones tones perfect 5ths octaves




Add 


 
Problem solved.. but wait..then I realised, as they ( Igates) are scattered throughout the world, I fear that we will be forever going around in circles trying to net, as the propagation shifts from one gate to another... I did come up with another idea.... that is never leave home ( zero velocity), but that would defeat the purpose of HF mobile APRS.. 
 
Then the solution came to me, you net while you drive as then it is all relative.. I think its the only way to be sure..thoughts anyone?
 
on a more serious, but none the less more fun aspect of Doppler  and radio...have you ever tried 70cm SSB mobile....http://www.calctool.org/CALC/phys/default/doppler try it yourself... its fun you do get a little doppler sometimes, dependant on speed and Alpha ( angle of incidence), 1.2 GHZ is even more fun to net as you drive..
 
BTW the PSK31 kit usage is a stroke of genius, pity they are no more..!!
 
Regards
 
Peter
 

 

> Date: Wed, 6 Jul 2011 18:13:52 +1000
> From: stevez at tpg.com.au
> To: ozaprs at aprs.net.au
> Subject: Re: [OZAPRS] Homebrew HF APRS transmitter
> 
> I heard you at around 10:00 this morning. Only one packet so far though.
> 
> What a great idea in pushing a PSK31 kit into use for HF APRS. Not 
> enough of this sort of thing going on I reckon!
> 
> Steve (VK2ZSZ-4 RX only HF I-Gate, "netted" with WWVH only - oops, 
> shouldn't start that one up again! ;-).
> 
>  		 	   		  
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