How Far Can I Talk on 2 Meters?
by Paul H. Bock, Jr. K4MSG
Recently, there has appeared on this forum some discussion
regarding the "working range" of the VHF/UHF bands.
This prompted
me to develop a set of tables for the 2-meter band which
demonstrate how different types of station setups can be expected
to perform.
The ranges given here are *estimates* based on *smooth earth*,
and in the interest of not misleading anyone I have tried to play
the game conservatively. The actual distances were taken from a
"path loss versus distance" graph which was first discussed by D.W.
Bray, K2LMG, in 1961 and re-published by Ed Tilton, W1HDQ, in all
three editions of "The Radio Amateur's V.H.F. Manual." If you
don't have a copy of the old V.H.F. Manual and want to understand
path loss at VHF/UHF a little better, I highly recommend looking
for one at a hamfest.
Even with conservative estimates of performance, however,
caution should be the watchword. Some locations just "seem to work
better" for VHF than others, so remember that *your* mileage may
vary. Variances aside, the tables should help newcomers understand
something about the characteristics of VHF path loss and develop
an appreciation of the necessity for carefully evaluating each
planned improvement *before* shelling out a lot of dough.
There are four tables below: two for FM, and two for SSB.
The tables are based on two *identical* stations, i.e., the
distances given presuppose that equipment performance at both ends
of the path is in all respects identical. The first table for each
mode lists communications ranges for identically-equipped stations
for 99% reliability, while the second lists ranges for 50%.
To understand why the numbers look the way they do you'd have
to actually see the path curves themselves, because path loss
increases steeply out to 50 miles (at 50% reliability) or 100 miles
(at 99% reliability), then flattens noticeably out to about 250
miles, then steepens again (but not as much as at the shorter
distances). This means that below 100 miles (or 50 miles at 50%
reliability) it takes quite a few dB of improvement to gain greater
distance, but once over the "hump" in either curve small
improvements can mean large increases in effective working range.
At the extremes of the flat portions where the curves steepen
again (about 210 dBw path loss, representing ranges of 285 and 315
miles, respectively, for 99% & 50% reliability) the two curves run
nearly parallel with about 30 to 40 miles difference between the
ranges for any given path loss, and a range increase of about 5
miles/dB out to beyond 500 miles.
Here's an example of the significance of the flat portions
after the "hump:" For 99% reliability, there is approximately a
21 dB path loss difference between 50 and 100 miles, but only a 10
dB difference between 100 miles and 250 miles. Assuming you were
at the 100-mile "hump" in the path loss curve (which is actually
a path loss of about 195 dBw), by increasing transmitter power,
reducing receiver noise figure, replacing the antenna with one
having higher gain, raising the antenna higher, or some combination
you could make a significant improvement in your working range.
A word about the "50%" and "99%" nature of the tables: "99%"
means that any time you turn on your rig you should expect to have
the working range shown, under the stated conditions. "50%" means
that about *half the time* you may work out this far, but half of
the time you *won't*, either; and it *doesn't* mean 50% of each
hour, or day, or week, it means 50% of the time over a long period
(months, certainly; probably over a year is more like it). Also,
the tables do *not* consider any of the more esoteric long-distance
modes such as sporadic E or F2 layer skip, aurora, meteor scatter,
or extreme tropo ducting caused by inversions or unusual air-mass
boundary conditions, any of which can give working ranges of many
hundreds or even thousands of miles. The tables only apply to the
routine tropospheric propagation we all know and love. ;-)
The following assumptions were made in calculating the data
contained in the tables:
1. Receiver noise figure was assumed to be 5 dB without a preamp,
and 2 dB with a preamp (preamp located at the rig, not at the
antenna; for example, an "integral" preamp common in commercial
amplifier "bricks").
2. Receiver bandwidth was assumed to be 2.5 kHz for SSB and 12 kHz
for FM.
3. Transmission line loss was assumed to be 1.5 dB, and was added
to the receiver noise figures listed above and subtracted from
transmitter output power.
4. Antenna height gain for 30-foot antenna height is 0 dB, and for
60-foot height is 4 dB. The tables assume antennas are at the same
height on both ends of the path.
5. Required SNR was assumed to be 3 dB. This may seem low for FM,
but in fact a signal 3 dB above the "capture" level can be easily
copied. What may happen, however, is that if the signal strength
fluctuates near the capture point the signal may drop in and out
continuously, making copy impossible. A SSB signal, on the other
hand, will fade in and out more gracefully with at least partial
copy even down close to the noise floor, making an exchange of grid
squares, signal report, and callsign possible even under poor
conditions. This is one reason why SSB is preferred over FM for
weak signal voice work (another being the better sensitivity on SSB
due to the narrower bandwidth and subsequently lower receiver noise
floor).
6. Antenna gain was assumed to be the same at both ends of the
path.
7. Ground reflection gain was assumed to be 3 dB (combined).
8. A factor of 7 dB was subtracted for fading loss in all cases.
I should note that the antenna gains shown were chosen to
represent typical antenna configurations used on these modes: a 5/8
ground plane, omni collinear, and small & medium yagis for FM;
two-element quad and small, medium & medium-large yagis for SSB.
Finally, as a "sanity check" on the numbers shown, I can vouch
for the ranges shown for SSB stations with 25 watts output and a
12 dB yagi at 30 feet, and with 80 watts plus preamp and the same
antenna. In fact, with 25 watts I've had QSOs out to 290 miles
with better-equipped stations without any super-unusual ducting,
just some good tropo path enhancement (but it's *definitely* in the
"50% or less reliability" category).
So, without further ado, here are the estimated working ranges
of identically-equipped FM and SSB stations for 99% and 50%
reliability at 144 MHz.
TABLE 1. FM Range in miles @ 99% Reliability
Antenna gain & height
3 dB 6 dB 9 dB 12 dB
Configuration 30' 60' 30' 60' 30' 60' 30' 60'
---------------------------------------------------------------
5W, no preamp 28 42 38 52 48 63 59 75
25W, no preamp 40 53 50 65 60 77 72 96
80W w/preamp 53 68 65 82 77 110 96 230*
160W w/preamp 59 75 70 93 87 175 130 260
* See what happens when you're located right at or over the
"hump" (i.e., at 96 miles)? The 4 dB improvement from
raising the antenna MORE THAN DOUBLED THE WORKING RANGE!
TABLE 2. FM Range in miles @ 50% Reliability
Antenna gain & height
3 dB 6 dB 9 dB 12 dB
Configuration 30' 60' 30' 60' 30' 60' 30' 60'
---------------------------------------------------------------
5W, no preamp 37 50 46 73 63 123 110 195
25W, no preamp 48 80 67 135 115 205 180 255
80W w/preamp 80 156 135 230 205 263 255 283
160W w/preamp 110 195 168 253 240 273 265 293
TABLE 3. SSB Range in miles @ 99% Reliability
Antenna gain & height
6 dB 9 dB 12 dB 15 dB
Configuration 30' 60' 30' 60' 30' 60' 30' 60'
---------------------------------------------------------------
25W, no preamp 63 80 75 100 93 215 175 272
80W w/preamp 80 130 100 245 215 280 272 310
160W w/preamp 90 200 160 268 252 295 285 325
TABLE 3. SSB Range in miles @ 50% Reliability
Antenna gain & height
6 dB 9 dB 12 dB 15 dB
Configuration 30' 60' 30' 60' 30' 60' 30' 60'
---------------------------------------------------------------
25W, no preamp 123 215 195 260 253 280 273 300
80W w/preamp 215 265 260 285 280 310 300 345
160W w/preamp 250 275 270 297 290 325 315 365
If you have questions about the tables above, please feel free
to drop me an e-mail. If there are inaccuracies or inconsistencies
in the information the fault is mine, and if you find any please
e-mail me and I'll post corrections and/or additional info as
necessary, with due credit to the finder(s).
Finally, if you'd like a photocopy of the 2-meter path loss
chart send me a *legal-size* SASE and I'll shoot one your way.
Mailing address: Paul H. Bock, Jr. K4MSG
RR1, Box 347
Hamilton, VA 22068
VY 73,
Paul, K4MSG
***************************************************************
Paul H. Bock, Jr. K4MSG FM19ee Hamilton, VA U.S.A.
pbock@melpar.esys.com (703) 882-4745 (home)
E-Systems/Melpar Div.
Falls Church, VA "Imagination is more important
(703) 560-5000 x 2062 than knowledge." - A. Einstein
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