On Dec 30, 8:50*am, Eric wrote:


So, how can I estimate the longest reliable ground wave distance on 75?

Thanks...

You need to use verticals if you want to use the ground wave on
the lower bands.
There basically is no ground wave when horizontal. Only a space
wave, which is not likely to go as far.
So in order to use the ground wave on the low bands, you need
to be using a vertical antenna to transmit.
How well that will do depends on the antenna, amount of noise, etc.
50 miles should be a good average, with some times better, maybe
others worse. IE: you will almost always do a lot better in the
winter,
than summer just due to lower noise.
Try it in the daytime. The noise is usually lower, and the ground
wave doesn't care what time it is.. :/ It should always be about
the same no matter what time of day. You lose a lot of ionospheric
clutter in the day, and can get a better idea what the ground
wave is doing. But there is still some skip in the day..
So if you end up working someone 200 miles away, it's
probably *not* via the ground wave. More likely the D layer
or whatever. But on the other hand, if you can work someone
50 miles away, and the signal is the same appx level every
day, day in, day out, it's probably the ground wave.
There could be minor season and moisture changes, but
overall it should stay fairly stable strength.
I know when I ran a 40m dipole at 36 ft, and also had a full size
ground plane with the base at the same height, the difference
in local coverage was drastic. Some times the band conditions
"NVIS" would stretch out, and I would lose the locals that were
across town if I were on the dipole.
But I could switch to the ground plane, and no problem.
In the daytime on 40m, I could often work people way out
west of town in mobiles, that the locals on dipoles wouldn't hear
due to the often long skip and lower signals due to being mobile
and vertical. Some of these were 70-90+ miles away.
I don't know how much of the total was ground wave vs space
wave, vs the ionosphere , but when I would switch to the dipole,
they would drop way down.
The ground plane did put out a pretty decent space wave
being it was elevated. Way better than the same antenna
ground mounted. And it was fairly efficient, which helps
no matter which path it takes.
The lower the frequency, the better the ground wave.
IE: tune AM radio in the daytime. Any station you pick
up that is out of town is coming to you via the ground wave.
With a good radio and antenna, you can receive quite a
distance. IE: from Houston, I can hear Dallas, San Antonio,
even farther, no problem at all. Almost pure ground wave,
and being such, it's easy to null out if needed vs sky wave
which usually comes from multiple paths.
But say take a 10m vertical at 50 ft in the air. The space
wave is the primary path in case of working local.
Not the ground wave like the low frequencies.