How much ground plane for a 102 whip?

[Needle Bender]

I am planning to build a ground plane base for a 102 whip to put on top of my camper. I was thinking maybe a 36" circle of plate with 8 36" wires every 45 degees? Should be plenty?

Yes, I would like an a99 and would love a moonraker 80 foot up, but I have enough problems with the owner here and would like to stay with the whip.

So can you have a TV antenna, and if so, how high can the top of the mast be above the roof?

Or you could mount the 102" on the top edge of the roof and drop a 108" 20 gauge wire basically straight down toward the ground from the mounting bracket/ coax shield.
That should make a decent center-fed vertical 1/2 wave dipole with ~3dB gain more than a 1/4 wave ground plane, roughly equal to an A99, and with maybe a 1.4:1 swr.

 

[338_MtRushmore]

So can you have a TV antenna, and if so, how high can the top of the mast be above the roof?

Or you could mount the 102" on the top edge of the roof and drop a 108" 20 gauge wire basically straight down toward the ground from the mounting bracket/ coax shield.
That should make a decent center-fed vertical 1/2 wave dipole with ~3dB gain more than a 1/4 wave ground plane, roughly equal to an A99, and with maybe a 1.4:1 swr.

This is a great idea to make a dipole like that. Would it make a big difference if this was mounted on a metal pole from the center? It would be great if I could have that on a push up pole and be able to turn it horizontal with both of the 102 whips I have. Why do you say 108" of wire, just to have plenty for tuning?

 

[338_MtRushmore]

I built a pole this morning that I can push up 15 feet above the roof. I will add a bearing and stop so I can rotate the dipole 90 degrees. My only issue is that I have metal framed steps with handrail, and if I turned the antenna vertical it would be pretty close to the handrail. Any idea how much slope I can set the vertical at and still have good vertical polarization? It probably won't be vertical often, but I would like the option.

 

[tba02]

You can try at any angle and see how it works. Proximity to the hand rail may interact and start to change your SWR reading.

See the link below, where at the bottom the specific answer is 0-20 degrees, but remember each particular setup is unique and you don't know until you try.

http://www.qsl.net/kk4obi/Dipole Slope.html

 

[Mudduckmobile]

Good link!

 

[The DB]

I agree, interesting link. I may have to play around with this myself at some point. He even posts the 4nec2 model, variables and all how convenient.

Some of the descriptions inside are not accurate. For example, the hgh variable is called "height of the feed point", but for the antenna being a center fed dipole, this is not the case as it is actually the high end of the slope. The feed point is actually the half way point of the hgh height and the hgh-Z height. Aside from that his formula's are correct.

I noticed something I haven't seen before as well, and learned from it. In 4nec2 every model I have ever seen has a segment number for its source location. Instead of a specific segment his model has a % number instead, and it works. None of the provided examples, and none of the models made by others I looked at were that way. It likely won't make that much of a difference, but it is something that is good to know...

Would it be beneficial to anyone if I duplicated this using a CB antenna with the high side about 30 feet high?


The DB

 

[Mudduckmobile]

I agree, interesting link. I may have to play around with this myself at some point. He even posts the 4nec2 model, variables and all how convenient.

Some of the descriptions inside are not accurate. For example, the hgh variable is called "height of the feed point", but for the antenna being a center fed dipole, this is not the case as it is actually the high end of the slope. The feed point is actually the half way point of the hgh height and the hgh-Z height. Aside from that his formula's are correct.

I noticed something I haven't seen before as well, and learned from it. In 4nec2 every model I have ever seen has a segment number for its source location. Instead of a specific segment his model has a % number instead, and it works. None of the provided examples, and none of the models made by others I looked at were that way. It likely won't make that much of a difference, but it is something that is good to know...

Would it be beneficial to anyone if I duplicated this using a CB antenna with the high side about 30 feet high?


The DB

Thats good to know DB, thank you I am trying to learn all of this.
As soon as I can get over to my stainless steel welder I am going to have a 3/8 x 24 male end welded on to a stainless steel whip 62in. up from the bottom of the whip so I can thread on my sirio "trucker" 5000.
That way I get the coil up higher, and have less stinger but will still have the advantage of a full 102 s.s. whip antenna.
Another thing I was thinking about is to put the sirio 5000 ciol on the very top of a 102 s.s. whip, and still use the sirio stinger to "make" a 1/2 wave mobile antenna for 11 meters, and see where else it will tune too with my FT450D.

 

[Riverman]

A single wire radial approximately 105” in length (trimmed for lowest SWR) works beautifully. Even at low heights. This is my current setup. One would think it would be somewhat directional, but I’ve found it is pretty much omni-directional. Receives and transmits great. Locals can’t believe I’m not on something larger and higher. Two of them had to come see for themselves.

It’s easy to knock, but if you put one up I know you’ll be amazed. Who’s got a whip lying around and a little time on their hands?
Oh, and any mobile antenna works too, just not quite as well as the 102” whip.

 

[somicide]

A single wire radial approximately 105” in length (trimmed for lowest SWR) works beautifully. Even at low heights. This is my current setup. One would think it would be somewhat directional, but I’ve found it is pretty much omni-directional. Receives and transmits great. Locals can’t believe I’m not on something larger and higher. Two of them had to come see for themselves.

It’s easy to knock, but if you put one up I know you’ll be amazed. Who’s got a whip lying around and a little time on their hands?
Oh, and any mobile antenna works too, just not quite as well as the 102” whip.

View attachment 71783

remember everyone: its only directional if its "in motion", aka it has an angle approx 3/4ths the way into the antenna. "in motion" usually refers to wind...hopefully it doesnt involve a tornado

if its somewhat straight up and down then its a regular omnidirectional antenna. its when you add that wind resistance and motion...etc. then its directional.