Can anyone tell me the best way to estimate the groundwave coverage
I'm likely to get on 75 meters?

I tried R. J. Edwards (G4FGQ] GRNDWAV3.EXE, answered all the questions
about type of terrain, frequency, power output, and antenna
efficiency, and got an answer of around 50 miles for an S-5 signal at
the other end.

(With the noise level around here, S-5 is about the minimum to shoot
for around here...)

And yet, in the real world, I am lucky to be able to establish
reliable contact with another station that's a bit less than 10 miles
away.

We are both using horizontal NVIS antennas, which I guess aren't as
good for groundwave as vertical antennas. In any case I have no idea
what to put in to G4FGQ's program for "antenna efficiency". I tried
25 percent and got the 50 miles for S-5, then reduced antenna
efficiency to 10 percent and got 40 miles for S-5... still well below
what I am seeing in the real world.

I switched to a terrain type of "City blocks, roads, streets,
industrial areas, rivers" and got 32 miles for S-5, then switched to
"Mountainous regions, bare rock, vegetation in valleys" (we do have a
few molehills around here that people call mountains) and got 28
miles... still beyond what I'm really seeing.

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

Thanks...

Eric wrote:
Can anyone tell me the best way to estimate the groundwave coverage
I'm likely to get on 75 meters?

I tried R. J. Edwards (G4FGQ] GRNDWAV3.EXE, answered all the questions
about type of terrain, frequency, power output, and antenna
efficiency, and got an answer of around 50 miles for an S-5 signal at
the other end.

(With the noise level around here, S-5 is about the minimum to shoot
for around here...)

And yet, in the real world, I am lucky to be able to establish
reliable contact with another station that's a bit less than 10 miles
away.

We are both using horizontal NVIS antennas, which I guess aren't as
good for groundwave as vertical antennas. In any case I have no idea
what to put in to G4FGQ's program for "antenna efficiency". I tried
25 percent and got the 50 miles for S-5, then reduced antenna
efficiency to 10 percent and got 40 miles for S-5... still well below
what I am seeing in the real world.

I switched to a terrain type of "City blocks, roads, streets,
industrial areas, rivers" and got 32 miles for S-5, then switched to
"Mountainous regions, bare rock, vegetation in valleys" (we do have a
few molehills around here that people call mountains) and got 28
miles... still beyond what I'm really seeing.

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

Thanks...

I don't think that a NVIS antenna is a "ground wave" antenna. It works
by sending the signal straight up and bouncing it off the ionosphere
back down covering the area around the antenna.

But you should do better than what your doing if you are using on both
ends a NVIS antenna. It strikes me that maybe the antennas are not at
the right hight to function correctly. Also if only one station is using
a NVIS antenna and the other is using a vertical or dipole that is high
off the ground that could be the problem. Those antennas have a reduced
response to signals coming in from high angles. It is a well known effect.

73

John Passaneau W3JXP

On Tue, 30 Dec 2008 10:35:41 -0500, John Passaneau
wrote:

I don't think that a NVIS antenna is a "ground wave" antenna. It works
by sending the signal straight up and bouncing it off the ionosphere
back down covering the area around the antenna.

But you should do better than what your doing if you are using on both
ends a NVIS antenna. It strikes me that maybe the antennas are not at
the right hight to function correctly. Also if only one station is using
a NVIS antenna and the other is using a vertical or dipole that is high
off the ground that could be the problem. Those antennas have a reduced
response to signals coming in from high angles. It is a well known effect.

We're both using horizontal antennas... his is a dipole up about 25
feet, and mine is an inverted vee that's up about 40 feet in the
center and 10 feet at the ends.

I know that a vertically polarized antenna would work groundwave
better, but we need to be able to maintain reasonably reliable
communications pretty much everywhere within about a 200-mile circle.
We can use 160, 80, and 40 meters to do it, and theoretically we can
use any amount of power up to the legal limit but in reality, as a
practical matter we are limited to 100-200 watts.

There are some in our group who really, REALLY think that the vertical
is the way to go, and I need some debating points. So, if I had a
decent ground-mounted vertical, should I expect to get the ground wave
distances that G4FGQ indicates in his calculation program?

Is there any area / radius that would be covered by a ground-mounted
vertical that wouldn't be covered by an NVIS horizontal (assuming that
we're operating below the critical frequency)? I have always assumed
that by the theory behind NVIS, the answer would be no... NVIS should
cover everything out to a radius well beyond groundwave distance.
But, I suppose we could install NVIS antennas AND verticals and switch
between them to see which one works best at any given time. Does seem
to be a wasted effort but WDIK?

While I'm at it, how do I estimate antenna efficiency? What is the
average range of efficiencies normally seen with a quarter-wave
ground-mounted vertical, with an adequate ground radial system, in
average soil?

There are some in our group who really, REALLY think that the vertical
is the way to go, and I need some debating points. So, if I had a
decent ground-mounted vertical, should I expect to get the ground wave
distances that G4FGQ indicates in his calculation program?

Is there any area / radius that would be covered by a ground-mounted
vertical that wouldn't be covered by an NVIS horizontal (assuming that
we're operating below the critical frequency)? I have always assumed
that by the theory behind NVIS, the answer would be no... NVIS should
cover everything out to a radius well beyond groundwave distance.
But, I suppose we could install NVIS antennas AND verticals and switch
between them to see which one works best at any given time. Does seem
to be a wasted effort but WDIK?

While I'm at it, how do I estimate antenna efficiency? What is the
average range of efficiencies normally seen with a quarter-wave
ground-mounted vertical, with an adequate ground radial system, in
average soil?

Note that radiation from the end of a low dipole is vertically polarized.
Antenna efficiency, and surface wave field strength, can be computed
with NEC.

Frank, VE6CB

"Frank" wrote in message
news:1Iw6l.480$PH1.385@edtnps82...
There are some in our group who really, REALLY think that the vertical
is the way to go, and I need some debating points. So, if I had a
decent ground-mounted vertical, should I expect to get the ground wave
distances that G4FGQ indicates in his calculation program?

Is there any area / radius that would be covered by a ground-mounted
vertical that wouldn't be covered by an NVIS horizontal (assuming that
we're operating below the critical frequency)? I have always assumed
that by the theory behind NVIS, the answer would be no... NVIS should
cover everything out to a radius well beyond groundwave distance.
But, I suppose we could install NVIS antennas AND verticals and switch
between them to see which one works best at any given time. Does seem
to be a wasted effort but WDIK?

While I'm at it, how do I estimate antenna efficiency? What is the
average range of efficiencies normally seen with a quarter-wave
ground-mounted vertical, with an adequate ground radial system, in
average soil?

Note that radiation from the end of a low dipole is vertically polarized.
Antenna efficiency, and surface wave field strength, can be computed
with NEC.

Frank, VE6CB

Given the type of antennas you mentioned with 100 W. If they are facing end
to end,
and, over an average ground, you should expect: 21uV (S7 - 8) at 20 mi, and
14 uV ( S6 - 7) at 30 mi. If the antennas are parallel then the signals
will be
10 db weaker. I used NEC for the analysis.

Frank

"Eric" wrote in message
...
On Tue, 30 Dec 2008 10:35:41 -0500, John Passaneau
wrote:

I don't think that a NVIS antenna is a "ground wave" antenna. It works
by sending the signal straight up and bouncing it off the ionosphere
back down covering the area around the antenna.

But you should do better than what your doing if you are using on both
ends a NVIS antenna. It strikes me that maybe the antennas are not at
the right hight to function correctly. Also if only one station is using
a NVIS antenna and the other is using a vertical or dipole that is high
off the ground that could be the problem. Those antennas have a reduced
response to signals coming in from high angles. It is a well known effect.

We're both using horizontal antennas... his is a dipole up about 25
feet, and mine is an inverted vee that's up about 40 feet in the
center and 10 feet at the ends.

I know that a vertically polarized antenna would work groundwave
better, but we need to be able to maintain reasonably reliable
communications pretty much everywhere within about a 200-mile circle.
We can use 160, 80, and 40 meters to do it, and theoretically we can
use any amount of power up to the legal limit but in reality, as a
practical matter we are limited to 100-200 watts.

There are some in our group who really, REALLY think that the vertical
is the way to go, and I need some debating points. So, if I had a
decent ground-mounted vertical, should I expect to get the ground wave
distances that G4FGQ indicates in his calculation program?

Is there any area / radius that would be covered by a ground-mounted
vertical that wouldn't be covered by an NVIS horizontal (assuming that
we're operating below the critical frequency)? I have always assumed
that by the theory behind NVIS, the answer would be no... NVIS should
cover everything out to a radius well beyond groundwave distance.
But, I suppose we could install NVIS antennas AND verticals and switch
between them to see which one works best at any given time. Does seem
to be a wasted effort but WDIK?

While I'm at it, how do I estimate antenna efficiency? What is the
average range of efficiencies normally seen with a quarter-wave
ground-mounted vertical, with an adequate ground radial system, in
average soil?


Why don't you connect together the two terminals of your 'NVIS' thing, drive
it with respect to a good earth, and use it as a monopole with a capacity
hat? There's a lot of chat going on about those here at the moment, and
some of it is correct, like no appreciable HP radiation from a symmetrical
horizontal hat. All it really does is to move the radiating part into a
higher-current portion of the quarter sine wave.

Chris

Eric wrote:

I know that a vertically polarized antenna would work groundwave
better, but we need to be able to maintain reasonably reliable
communications pretty much everywhere within about a 200-mile circle.
We can use 160, 80, and 40 meters to do it, and theoretically we can
use any amount of power up to the legal limit but in reality, as a
practical matter we are limited to 100-200 watts.

There are some in our group who really, REALLY think that the vertical
is the way to go, and I need some debating points. So, if I had a
decent ground-mounted vertical, should I expect to get the ground wave
distances that G4FGQ indicates in his calculation program?

You really need both. I'd not put in a vertical unless I had a
horizontal one also. If I had to choose one, it would be the dipole. But
if you can do both, the vertical has it's uses.

Is there any area / radius that would be covered by a ground-mounted
vertical that wouldn't be covered by an NVIS horizontal (assuming that
we're operating below the critical frequency)? I have always assumed
that by the theory behind NVIS, the answer would be no... NVIS should
cover everything out to a radius well beyond groundwave distance.
But, I suppose we could install NVIS antennas AND verticals and switch
between them to see which one works best at any given time.

That is the ticket. I'd done some experiments between the two antennas,
using an attenuator and antenna switch. Aside from generalities, which
have become "truth" under different circumstances, the antenna that
performed best at any given time changed, and not always in the way you
thought. Sometimes in mid-QSO.

Too many people think of take off angle as some sort of blob of RF that
comes out of the antenna at one place, and not much elsewhere. All
antennas radiate at all angles. Some just more at some angles than
others. The point of this is that that vertical better be pretty
efficient, because what use is a lower angle of radiation if it is
putting out less RF than another antenna that even though the other
antenna might have a higher take off angle, but have still more power
output at the lower angle.

While I'm at it, how do I estimate antenna efficiency? What is the
average range of efficiencies normally seen with a quarter-wave
ground-mounted vertical, with an adequate ground radial system, in
average soil?

Best way is to use an antenna design program. This would probably be a
very good idea if you need to convince your cohorts The big thing is,
don't just look at the SWR plots, and don't just look at the antenna
patterns. Looking at the bigger picture, it becomes more than just a
Ford versus Chevy argument.

- 73 de Mike N3LI -

Eric wrote in
:

On Tue, 30 Dec 2008 10:35:41 -0500, John Passaneau
wrote:

I don't think that a NVIS antenna is a "ground wave" antenna. It works
by sending the signal straight up and bouncing it off the ionosphere
back down covering the area around the antenna.

But you should do better than what your doing if you are using on both
ends a NVIS antenna. It strikes me that maybe the antennas are not at
the right hight to function correctly. Also if only one station is
using a NVIS antenna and the other is using a vertical or dipole that
is high off the ground that could be the problem. Those antennas have
a reduced response to signals coming in from high angles. It is a well
known effect.

We're both using horizontal antennas... his is a dipole up about 25
feet, and mine is an inverted vee that's up about 40 feet in the
center and 10 feet at the ends.

I know that a vertically polarized antenna would work groundwave
better, but we need to be able to maintain reasonably reliable
communications pretty much everywhere within about a 200-mile circle.
We can use 160, 80, and 40 meters to do it, and theoretically we can
use any amount of power up to the legal limit but in reality, as a
practical matter we are limited to 100-200 watts.

There are some in our group who really, REALLY think that the vertical
is the way to go, and I need some debating points. So, if I had a
decent ground-mounted vertical, should I expect to get the ground wave
distances that G4FGQ indicates in his calculation program?

Is there any area / radius that would be covered by a ground-mounted
vertical that wouldn't be covered by an NVIS horizontal (assuming that
we're operating below the critical frequency)? I have always assumed
that by the theory behind NVIS, the answer would be no... NVIS should
cover everything out to a radius well beyond groundwave distance.
But, I suppose we could install NVIS antennas AND verticals and switch
between them to see which one works best at any given time. Does seem
to be a wasted effort but WDIK?

While I'm at it, how do I estimate antenna efficiency? What is the
average range of efficiencies normally seen with a quarter-wave
ground-mounted vertical, with an adequate ground radial system, in
average soil?

Are your NVIS antennas oriented the same way, geographically? And are
you seeing a nice spike in the signals during the early part of the
evening, only to lose them later? If so, consider dropping to 160 after
signals fade in the evening. Consider 40m to be only a daytime band at
best under present conditions. You might try 60m during the day.

Ground wave on 75 and 160 can work with good quality vertical antennas,
but my experience has been that it works best with a salt water ground or
with at least a couple of KW over a good radial ground system (I used
2mhz commercially with 2 and 5kw transmitters for a long while and
typical daytime range over ocean was about 250 miles. We had a VERY
quiet location over a mile from our own tranmitters).


--
Dave Oldridge+
ICQ 454777283
VA7CZ

Predicting ground wave distances isn't exactly an 'exact' science by
any means. An 'aproximate' answer is about as good as it gets. Try
'FGQ's program with a very low and a very high efficiency number.
Average it. that'll give you a 'ball-park' figure to play with.
- 'Doc

"Eric" wrote in message
...

Can anyone tell me the best way to estimate the groundwave coverage
I'm likely to get on 75 meters?

I tried R. J. Edwards (G4FGQ] GRNDWAV3.EXE, answered all the questions
about type of terrain, frequency, power output, and antenna
efficiency, and got an answer of around 50 miles for an S-5 signal at
the other end.

(With the noise level around here, S-5 is about the minimum to shoot
for around here...)

And yet, in the real world, I am lucky to be able to establish
reliable contact with another station that's a bit less than 10 miles
away.

We are both using horizontal NVIS antennas, which I guess aren't as
good for groundwave as vertical antennas. In any case I have no idea
what to put in to G4FGQ's program for "antenna efficiency". I tried
25 percent and got the 50 miles for S-5, then reduced antenna
efficiency to 10 percent and got 40 miles for S-5... still well below
what I am seeing in the real world.

I switched to a terrain type of "City blocks, roads, streets,
industrial areas, rivers" and got 32 miles for S-5, then switched to
"Mountainous regions, bare rock, vegetation in valleys" (we do have a
few molehills around here that people call mountains) and got 28
miles... still beyond what I'm really seeing.

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

Thanks...


Consider using vertically polarised antennas because a ground wave is
predominantly vertically polarised. NVIS antennas are usually horizontally
polarised with respect to zero degrees elevation.

Chris