Order Tray | Contact Us | Home | SIG Lists

[aprssig] Fw: [nwaprssig] UHF 9K6 Baud vs. VHF 1200 Baud

Robert Bruninga bruninga at usna.edu
Thu Oct 12 23:28:34 UTC 2006


Comments on this post:

> > I have heard:
> > a)    There is a 9db penalty for using 440Mhz  vs. 144MHz. 
> > The 9db path loss penalty -   It is true...
> > However, in every case for practical operations this is NOT 
> > a significant factor.

I don't know any application that is happy to throw away 9 dB of
performance just because it is "good enough"...

> > It does NOT reduce 
> > performance for distances used on Earth for APRS mobile or
fixed 
> > operations. The real limiter is LOS distance and curvature 
> > of the Earth.

No matter where you run out of signal on 440 due to
line-of-sight, you could have gone 9 dB further on 2 meters.  9
dB is 9 dB no matter where the path is...

> > A practical working range may be 20 miles.  This is true for

> > 144 and 440MHz.

Yes, as long as the digi is high enough and the terrain is good
enough, etc...

> > Using two identically equipped base and mobile stations on 
> > 144 and 440MHz ...the power at the mobile station antenna 
> > terminals is -55.8dbm for the 144MHz station 
> > and 9.7db less or -65.5dbm at the 440MHz station.  
> > BOTH of these signal strengths are sufficient...

Yes, but you only have that strong a signal in free-space.
Which you also claimed does not apply on earth...  So throw in
30 dB of mobile flutter and now the signals are -85 and -95 dBm.
Now throw in another 20 dB for attenuation due to foliage or
freznel zone atteunations and any of a hundred other losses, and
now you are down to -105 and -115 dBm.  Ill take the band that
gives me -105 dBm any day over the one that is 9 dB worse...

Anyway, just clarifying that point.  It is good to see some
people who have experimented with 9600 baud sharing their
experiences...

Bob






More information about the aprssig mailing list