I just had a thought pop into my head. Why don’t we use ground “radials” as reflectors for horizontal dipoles etc?
Since my antenna is fairly close to the ground (30-20’) I’m envisioning laying some wires parallel to the antenna every 5-10’ in the direction you would want more signal reflected back from the ground. Would the radials do anything?

Off to do some research but thought I’d ask the experts here also.

You certainly could, and it's a method sometimes used for NVIS purposes.

The issue for general use is it really only helps add gain going straight up, like a 2 element beam pointed vertically into the sky.  That's not helpful for most HF skip propagation where you want your signal to go out at lower take-off angles.

ETA, here's a model of a 40M dipole at 65 ft, which would be about a half-wavelength above ground (ideal).  You can see the gain and take-off is totally unaffected by a same sized radial/reflector on the ground (I modeled it here with and without the reflector, results were identical).

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The reflector won't start having an appreciable effect until the dipole is much lower to the ground, and at that point you'll have most of your signal going off at high angles (and mostly out to space) anyway so reflecting more to the higher angle isn't helping too much.  But again, in some cases for trying for NVIS or shorter skip, it can give a bit of gain there, band choice and propagation dependent of course.

Balanced antennas don't need them. However, unbalanced ones such as long wires and end feds will benefit from them.

Can you model that same scenario at 10' and 20' AGL?

Sure.  You can see when you get that low on a 40M antenna, the high gain take-off is at 0 degrees (straight up), and even with the reflector wire, not much is changing.  I even tried doing a field of 8 radials and it didn't have any real effect, the ground itself is hampering the reflector element from doing much at all.

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Radials, as such, are always part of the vertical, ground mounted, antenna. Remember, a dipole has two halves, as the RF signal is being sent up the feed line it changes polarity each 1/2 of the oscillation. In doing so electrostatic and electromagnetic waves flow between the two halves of the antenna, these are what radiates. The same thing happens with the ground mounted vertical. The reason there is so much wire in the radial system is to make up for the ground losses as part of the fields around the radial elements get literally drug through the dirt. A vertically mounted dipole can have an impressive low angle of radiation and minimum ground loss if the end pointed down is well removed from ground effects due to the high voltage at the end of the antenna. The main problem here is getting the feed line away from the antenna at right angles. The GAP antenna line does a good job of working around this problem. In general, a ground mounted vertical is unbalanced largely due to the a-fore mentioned ground loss. Un-balanced simply means the currents flowing through the feed line are not equal. An OCF dipole suffers from out of balance current flow due to the current that flows on the outside of the coax feed line and can be responsible for RF in the shack. hth  
73,
Rob

I have 2 theories.
I did NOT stay at any motel last night and being a lowly General class this stuff makes me want to study and get my Extra.

1. What I was thinking is that the ground "reflector" and the dipole would act as a yagi type antenna.
Say the dipole is at 50' AGL and a ground reflector is parallel to it but 50' from it. Take off angle should be 45deg.
Same antenna with reflector 100' from it, 22.5deg.
Same antenna with reflector 200' from it, 11.25deg.
These distances and wire lengths would need to be adjusted for wave length but you get the idea. OR just lay a field of them every 5-10' and you would get a wide range with a sweet spot maybe?

2. Dipole at 30'. Is the ground absorbing some/most of the signal?
If so how about laying reflecting wires on the ground at intervals to reflect the signal back up at an angle equal to the incoming angle. It would seem a series of these wires could give a wider range of take off angle and also more usable signal in the air instead of heating the ground.

I appreciate the responses and will study them asap.

This whole idea came from thinking about how verticals use ground radials and a thread posted earlier.

@cjk
I think the effects of what you are talking about are related to the "far field", as in what happens as the field bounces off the earth after it leaves the antenna. A decent ground mounter vertical will have a take off angle of around 11 Degrees. (I think). Mounted up high would be even lower. Ideally, the radio wave should hit the atmospheric layer before it hits the earth the first time. hth
73,
Rob

I put some wire on the ground under my EFHW just to try it out.  My antenna is about 50' high and we do a bit of NIVS and heard it might help.  I had some old welding wire and ran 3 lengths underneath the antenna and connected them to the ground rod.  I get good signal reports and decided to leave them down for now.

I attached one arm of a radial system buried in my yard that’s left over from an old vertical installation to my EFHW sloper and it seemed to help in the direction of the slope.
Edit: Crude drawing of my setup. There are actually 18 radial wires of various lengths to fit my yard.

Yes, creating a reflective plane progressively larger should decrease the takeoff angle.

OP is describing a wire Yagi  or Wire Beam

http://www.antentop.org/w4rnl.001/hsyg.html

Ha, this novice was thinking the same thing.

Don't forget about the ground conductivity factor. It does make a very noticeable difference. Also, to my best knowledge (may be wrong), antenna modeling software assumes nearly perfect ground conductivity. Placing reflectors on the ground will help to improve NVIS pattern and efficiency for low hanging dipoles, in areas with poor ground conductivity.

I talked to a guy in Florida, who put a lot of salty sand under and around his antenna systems. He was running a 3 el. Yagi on 40 meters. He offered to work some DX in tandem. Same TX power. I was using my 2 el. Yagi. He got much better signal reports from most DX stations. He could hear better too. We had worked stations from Europe, Asia, Australia, Africa an many more places within several hours. The pile-up was huge.

I think that is called a "counterpoise" and it is usually a grid, with everything bonded together, if you want it to work right.

It's a well known technique to put reflector elements on the ground underneath low height horizontal antennas, to improve high-angle signal performance.

IMO, there's might be an interesting experiment in testing different lengths for such a ground-contact reflector element, if it would be similarly detuned as ground radials for vertical antennas are.

I zipp tied a wire under the bottom rail of my vynl picket fence and have a dipole directy over it 30 feet up I have a dipole. NVIS work at least twice as good most of the time and maybe 100 time better half the time.

Ground radials or any metal below a dipole at any height will decrease ground losses if the ground is poor to begin with. If the ground is excellent, it will do nothing.

The ground influences a horizontal yagi radiation pattern and take off angle. Putting a proper length wire on the ground to form a vertical yagi does not make a vertical yagi, it just makes a dipole with a better ground which if the dipole is at the proper height will yeild a lower takeoff angle than without the wire(s).

Having a low dipole where the radiation is mostly up due to low height above the ground will yield less ground losses( and more upward radiation )  because the wire(s) makes the ground more conductive.

That's the way I understand it, I may be wrong.

I may have to do some experimenting this summer.
Would the wires I install on the ground need to be connected together?
Should they be connected to the outer coax and or grounded?

No, a dipole already has a wire connected to the shield. If you ground the shield, you have just made a bastardized vertical in the horizontal direction with a radial wire up in the air. That does not sound like it will work very well.

The wires on the ground won't matter if they are connected together, they just make the ground more conductive. In essence, they are already connected together through the dirt. The more metal in the ground, the more conductive the ground will be