A Full-Blown 1/2 Wave Dipole?

Discussion in 'The Low Bands - 630/2200 Meters - VLF' started by WA2FXM, Nov 27, 2017.

1. W9XMTHam MemberQRZ Page

Below is a NEC4.2 plot of the elevation pattern fields at an h-distance of 1 mile from the base of a monopole, based on the same model parameters as in my original post above. A comparison is shown for that sector for the fields at 2 miles, also. These calculations include the surface wave, which is necessary to calculate/plot this scenario accurately.

Z = elevation in meters above a flat Earth, and E = field intensity in mV/m

Note that the two fields shown there have a ~1/r relationship, which is characteristic of a space wave. That relationship will be maintained for very low, but not zero-angle propagation paths reaching to, and reflected by the ionosphere.
_____

As a workaound, a Ø can be included in posts here by entering Alt+Ø216 using the number keypad.

2. K8JDHam MemberQRZ Page

Does this mean that the closer you get the stronger the field is ?
What is the size of the monopole ? By "T" that seems to mean it's less than a QW tall vertical with a two wire capacity hat ?
Not much info on the physical side of the antenna !
I want to build a real antenna.

3. W9XMTHam MemberQRZ Page

The T antenna dimensions are shown in the Comments section on the left side of the graphic in my original post about it.

4. W5DFNHam MemberQRZ Page

Okay, an update to the above post. About the time I posted this, we sold our home and moved to the property where we own and operate a private gun club. On October 10, Hurricane Michael paid us a visit setting back getting back on the air. This week I got my HF/VHF antennas back up and today I put up half of my 1/2 wave 630 meter horizontal dipole. Running the "live" leg was fairly easy. Take out four damaged oaks, and lay it out in a zigzag. The shield leg came straight down from the 20' feed point and is grounded to the tower base. Guess what it works!

6. AF7XTHam MemberQRZ Page

shunt feed ...

WA7PRC likes this.
7. WA7PRCHam MemberQRZ Page

The Wikipedia article leaves a lot of detail out. I toured NLK in the late 70s. Nominal output is around 1MW but, we were told they've had it cranked up to 2MW. When they do, Jim Creek is 1° warmer downstream. When we toured, the output current was 1296A. Into ZLOAD = 0.456Ω, that's "only" 766 kW. It made the broadcast xmtr (16 kW RFOUT) I worked on look like a QRP rig.

K3RW likes this.
8. K3RWHam MemberQRZ Page

Another solution--build a mag-loop. It really works, but it is obviously quite expensive depending on the HOW. There is a cheap way, and a really expensive way. But you want 5w EIRP. I wanted very-high QRO efficiency. So in some ways this is a much easier problem to solve.

For example, you can build a 1/4 wave mag-loop and engineer it with an appropriate range vacuum variable capacitor, all-copper tubing (big 2" stuff) and silver solder it. And run decent coax to it and fire away. I did that on 30m. It wasn't hard. I was planning to scale it up to 160m but I needed a different vacuum variable, about \$400 in copper tubing, and a trailer. Then I got bit by the VHF contesting bug. But I never gave up on it.

Since a 1/4 wave loop would be huge, go with a multi-turn loop. Its just like a Slinky but with tube elements (not solid ones).