hey Dave: On the news a few weeks ago they showed a video of
someone(s) that made a 50' high snow-woman up in Maine somewhere. To
give a perspective of size of her head, they wound up using dozens of
skis as her eyelashes. They said she should remain unmelted until at
least Mid-May, but going by your update, the top of her head will
stay probably covered up in a snow drift until June! Guess we know
now why you put up 100' towers, you want antennas to clear those 80'
sow drifts!
-73, Ron WZ1V, snow all melted here in FN31mp
At 08:23 AM 3/13/2008, David Olean wrote:
>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@sbcglobal.net>
>To: "James Duffey" <JamesDuffey@comcast.net>; "Marshall Williams"
><k5qe@sabinenet.com>
>Cc: "James Duffey" <JamesDuffey@comcast.net>; <vhfcontesting@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
> >>
> >>
> >>
> >>
> >>
> >>_______________________________________________
> >>VHFcontesting mailing list
> >>VHFcontesting@contesting.com
> >>http://lists.contesting.com/mailman/listinfo/vhfcontesting
> >
> > _______________________________________________
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> > VHFcontesting@contesting.com
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>
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