[VHFcontesting] SPLAT!

[David Olean]

I also use Radiomobile. I find that it does a pretty good job of predicting 
performance on a particular path. There is a learning curve, and I am no 
expert, or accomplished user, but I do find it very worthwhile. Like Ron, I 
had a 56K modem, but I convinced a good friend to put the elevation data on 
a CD instead. The datasets are quite large if you want to cover much 
terrain.
    I like the feature where you can put a 5000 ft tower at ur place, and 
then see what the view looks like from the top. Wow! What a horizon! Now all 
I have to do is collect 500 sections of Rohn 55 to make it happen.

Dave K1WHS
120" of snow so far this winter, but I am not complaining.....Quebec City 
has 210" and more storms are coming. Snowpiles in parking lots are up to 80 
ft high now.

----- Original Message ----- 
From: "Ron Klimas WZ1V" <wz1v at sbcglobal.net>
To: "James Duffey" <JamesDuffey at comcast.net>; "Marshall Williams" 
<k5qe at sabinenet.com>
Cc: "James Duffey" <JamesDuffey at comcast.net>; <vhfcontesting at contesting.com>
Sent: Thursday, March 13, 2008 11:46 AM
Subject: Re: [VHFcontesting] SPLAT!


> For more accurate coverage/path analysis I prefer Radio Mobile, and
> it's still freeware:
> http://www.cplus.org/rmw/english1.html
>
> p.s. - here's a giggle, I downloaded the DEM's for the entire
> northeast quarter of the U.S. and converted them to DTEDs back in the
> days of 56k modems!
> Only took a few months! Worth every hour though.
> -73, Ron WZ1V
>
> At 09:46 PM 3/12/2008, James Duffey wrote:
>>Marshall - The coverage maps should show you path loss in a number
>>that is in dB. What is the path loss at the outer edge of the 50 mile
>>circle?
>>
>>I found the coverage circle to be a bit short here as well, it cut off
>>well before my stations capabilities gave out on some calculations I
>>made. I found the station to station calculations to be more
>>informative, so try one of those calculations with a distant station
>>you can work regularly.
>>
>>The path loss is a characteristic of the path terrain, climate,
>>distance, and the scattering medium. It is independent of the station
>>capability.
>>
>>Once you have the path loss, you need to calculate the path loss
>>capability of your station. Here is a short explanation on how to do
>>this. It helps to read the November 1983 QST article "Tropospheric
>>Scatter Propagation" by G3YGF. That is also reprinted in the ARRL
>>publication "Beyond Line of Sight"
>>
>>The path loss capability, plc, is given by
>>
>>plc = eirp + ers
>>
>>where eirp is the effective radiated power of the transmitting station
>>in decibels above 1 watt referred to an isotropic radiating source,
>>and ers is the effective receiver sensitivity of the receiving station.
>>
>>SPLAT! calculates the Path Loss, pl, for the link being attempted. Or
>>you can get a rough idea from the plots in the Antenna Handbook or old
>>VHF Handbook.
>>
>>The signal to noise ratio, snr, expected for the path can be calculated:
>>
>>snr = plc - pl
>>
>>The effective radiated power is given by:
>>
>>eirp = (10*log(P)) + Gtrans - transTL
>>
>>where P is the transmnitter power in Watts, Gtrans is the transmitting
>>antenna gain in dBi (decibels over
>>an isotropic radiator), and transTL is the transmitter stations
>>transmission loss in dB.
>>
>>The effective receiver sensitivity is given by:
>>
>>ers = -10*log(k*T*B) + Grecv - recvTL - threshold
>>
>>the first term is the receiver noise floor where k is Boltzmann's
>>constant,
>>
>>k= 1.38*10^-23
>>
>>T is the effective receiver noise temperature in degrees Kelvin
>>(absolute temperature), which can be calculated from the more commonly
>>available noise figure, nf, by:
>>
>>T = ((10^(nf/10))-1)*290
>>
>>If you know the receiving noise figure, plug it in, for most
>>mainstream multi-mode VHF rigs using 5 dB will get you close.
>>
>>B is the receiver bandwidth in Hz. 2500 Hz is a typical bandwidth for
>>SSB, 500 Hz is a good bandwidth to use for CW.
>>
>>Grecv is the receiving stations antenna gain in dBi
>>
>>recvTL is the receiving stations transmission line loss in dB and
>>Threshold is the detector threshold for the mode being used. For CW
>>and SSB it is 0, while for FM it is 10dB depending on the modulation
>>index.
>>
>>If you don't know what the guy on the other end is using, you need to
>>make some assumptions as to these numbers, but 4 or 5 dB noise figure,
>>13 to 15 dBi for antenna gain and 1 dB feed line loss are reasonable
>>assumptions for a moderately serious VHF station.
>>
>>I hope I haven't made any mistakes. I am sure that someone will
>>correct me if I did. :^)=
>>
>>  From the above calculations, it is easy to see why CW at narrow
>>bandwidth outperforms SSB and why SSB far out performs FM.
>>
>>I have had SPLAT! give some unrealistic terrain maps from time to
>>time. Bll knows about this and is looking into what the problem is. It
>>doesn't seem to affect the path loss plots though, or the path loss
>>calculated, or the table of terrain data.
>>
>>Holler if you have any more questions. Once you understand what is
>>going on you will find SPLAT! to be a valuable tool. - Duffey
>>--
>>KK6MC
>>James Duffey
>>Cedar Crest NM
>>
>>
>>
>>
>>
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>
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