Hi-Gain Vertical Half Wave Antenna

[hereclit]

Hi , has anyone schematics of this NRG antenna ?

cheers

[shuffy]

Not specifically, in terms of how to build it - but from memory(!) this is how Steve's antenna worked. I've tried to draw the arrangement in your photos and a schematic for the end-fed half wave. You can see the coils in the pic for your turns/ratio. Capacitor C is made from the 2 metal plates, one of which is attached to the pole (ground) and the capacitance was adjusted using the nylon screw. You could also use something like a Philips "beehive" capacitor. The whip used to be made from 2 pieces of aluminium tube, the top one fitting snugly inside the other and secured with a jubilee clip. You adjust the length for best match.

nrg_half2.jpg

[sinus trouble]

Great pics Mr clit!!
ive never seen this antenna closeup!
by looking at shuffys schematic? the tank circuit is spot on!! but thats what i hate about these antenna!
the mast is used as a counterpoise (ground) therefore your match would depend on the mast length? as a pirate? are you really gonna bother tuning this on site when a dipole gives just as much without the hasssle??

[sharky]

YES!!! If you spend the money to get one then you're obviously interested in the radiation pattern.
If you don't tune this onsite then what's the point?? You should be tuning your dipole onsite too.
Just because you have < 1.5 when you tune it offsite, doesn't mean that it'll be the same on your site.
I learnt this the hard way when i first built the 3/4 balun for a dipole. 1.2 at test site - 1.8 on mast at site.
Took me 45 mins to get it back down to 1.2.
Ground is ground and it varies at height, you should all know this by now.

[Dai Pole]

What is the material at the end of the capacitor plate made of? The part that allows the nylon bolt/nut to have some wiggle room. Is it non conducting?

[pjeva]

YES!!! If you spend the money to get one then you're obviously interested in the radiation pattern.
If you don't tune this onsite then what's the point?? You should be tuning your dipole onsite too.
Just because you have < 1.5 when you tune it offsite, doesn't mean that it'll be the same on your site.
I learnt this the hard way when i first built the 3/4 balun for a dipole. 1.2 at test site - 1.8 on mast at site.
Took me 45 mins to get it back down to 1.2.
Ground is ground and it varies at height, you should all know this by now.

That's exactly true. To tune ANY antenna properly, you need to simulate real (ttansmission site) conditions. One way is to mount antenna on similar mast (as long as possible) and far from walls, roofs etc. I live on top floor, so this is advantage. But, for test (simulation) purpose, about 4 -5 meters above ground would be just fine. Idea is to set it as close as possible to ideal. Ofcourse, check and eventual retune on site is always good thing.

[sinus trouble]

I completely agree! i would always check the SWR when installing any antenna!
but there too many variables invovled in the end fed type?
the dipole is far easier to setup! fiddling with tuning caps at height is not my idea of fun!

[sinus trouble]

What is the material at the end of the capacitor plate made of? The part that allows the nylon bolt/nut to have some wiggle room. Is it non conducting?

the variable cap plate must be connected to ground which i assume is the counterpoise? but the dimensions of the counterpoise is a mystery??

[shuffy]

It's conducting - that's why it's a nylon bolt! The dimensions of the counterpoise may be a mystery, but the capacitance is proportional to the area of overlap of the plates. I know the bit with the bolt through it is overlapping with the counterpoise, but there are plenty of other variables involved in the setup of this antenna and as sharky said you need to set it up on site. I haven't got my notes to hand but I guessed at the size of the plates and the distance between and came up with a value of about 10pf - which is why I suggested a beehive cap would do the job also.

[sharky]

It's conducting - that's why it's a nylon bolt! The dimensions of the counterpoise may be a mystery, but the capacitance is proportional to the area of overlap of the plates. I know the bit with the bolt through it is overlapping with the counterpoise, but there are plenty of other variables involved in the setup of this antenna and as sharky said you need to set it up on site. I haven't got my notes to hand but I guessed at the size of the plates and the distance between and came up with a value of about 10pf - which is why I suggested a beehive cap would do the job also.

If you want the full description of how to build one search DX zone for the antenna and scale it.
I've learnt more from HAM sites than I ever have anywhere else.

I was going to start building these a while back , but my original 1/2 wave was borrowed and never returned / paid for, so I never got round to it.
At the moment, i'm building sleeve dipoles and having great fun; granted there's little gain off them, but the match is fantastic and it has a built in balun.

Pics up at the weekend

[Dai Pole]

It's conducting - that's why it's a nylon bolt!

I thought it would be, thanks. The only reason I ask is that it looks black in the photo, so I wanted to double check it isn't ABS or something along those lines. Plus I wanted to know if I could just drill/mill a slot directly in the top plate.

...a beehive cap would do the job also.

That would be good. Then it can all be placed in a nice masthead enclosure.

[shuffy]

Have a look at this, he's using a beehive... there's also the beginnings of something which looks suspiciously like a Steve Moss "Funnel" antenna...

http://www.70mhz.org/halfwav.htm

On the subject of funnels, one of the engineers I've worked with before on stations used to cut the top off a plastic coke bottle. Very versatile, plastic coke bottles... some presenters I know have completely different uses for them!

[shuffy]

If you want the full description of how to build one search DX zone for the antenna and scale it.
I've learnt more from HAM sites than I ever have anywhere else.

Amen to that Sharky, certainly for antennas. This site was a great discovery for me a few years back:
http://www.g0ksc.co.uk/
Specifically the OWA Yagis (Optimised Wideband Array?) which are probably the simplest. I've built 3 of these so far. Start with the dimensions for 50MHz (he doesn't supply .nec files any more unfortunately), scale, then pass the parms back into 4nec2 and re-optimise - this is quite a lot of work though. First time I did one, I couldn't believe how close the real world result was to the simulation.

[Dai Pole]

The 70mhz.org link clears up a few questions I had. I like the fibreglass idea. Perhaps one could be built using copper braid and adhesive heatshrink, similar to how this lady builds a whip antenna:

[youtube]E4OlsUMbfj0[/youtube]

Although maybe that's not a good idea if using for high power.

[shuffy]

Beehive isn't a good idea either when using high power, I think that's why Steve used those whack off metal plates. I think the thing that limited the power rating of Steve's funnel antenna was the thickness of the wire used in the coils. I'm sure he did 2 versions, one with thicker wire.

[FM King]

Alot of people say the 5/8 is better than the 1/2 for achieving the furthest distance but I can't notice any difference??

[verticalvince]

try something completely different the results were somewhat desirable research "MOXON" soo many configurations just a single moxon claims a 6db gain

[verticalvince]

i have done a few mostly for other bands vids on you tube enjoy radio is my hobby not video making please bear this in mind lol

[Maximus]

A 50w version melted/snapped in half after putting 180w through it.

[RF-Head]

Do you have also a picture of the other site?
So we can see how it's made
Want to try to make a copy