Hi-Gain Vertical Half Wave Antenna

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Banus_radio
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Re: Hi-Gain Vertical Half Wave Antenna

Post by Banus_radio » Sun Dec 11, 2016 11:35 pm

Doe sthis need to be insulated from your pole?

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Re: Hi-Gain Vertical Half Wave Antenna

Post by Frequent Lee » Thu Dec 22, 2016 5:20 pm

No, you can mount the aerial straight onto your scaffolding pole etc. The mounting pole goes to ground/shield of the coax so it's not a bad thing. Remember to put a lightening strike strip onto your pole too!

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Re: Hi-Gain Vertical Half Wave Antenna

Post by Banus_radio » Thu Dec 22, 2016 6:47 pm

Frequent Lee wrote:No, you can mount the aerial straight onto your scaffolding pole etc. The mounting pole goes to ground/shield of the coax so it's not a bad thing. Remember to put a lightening strike strip onto your pole too!
ok so im confused then.. because the excel spreadsheet has measurments for bottom pole. so if i mount this to my mast it will extend that length yes??

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Hi-Gain Vertical Half Wave Antenna

Post by Maximus » Mon Dec 26, 2016 6:54 pm

Banus_radio wrote:
Frequent Lee wrote:No, you can mount the aerial straight onto your scaffolding pole etc. The mounting pole goes to ground/shield of the coax so it's not a bad thing. Remember to put a lightening strike strip onto your pole too!
ok so im confused then.. because the excel spreadsheet has measurments for bottom pole. so if i mount this to my mast it will extend that length yes??
No it will not affect the antenna as it isn't a dipole. It's a tuned half wave vertical antenna. The only part that matters is the top radiating element.

Speaking of radiating elements, I've just measured mine and it's 147.5cm for 97.00mhz. The bottom pole measures 61cm.

The spacing between the radiating element and the ground pole is exactly 4cm.

When I repair the aerial and put the thing back together, then I'll take some detailed photos along with some measurements and post them here.


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Re: Hi-Gain Vertical Half Wave Antenna

Post by Banus_radio » Tue Dec 27, 2016 11:40 pm

Maximus wrote: Speaking of radiating elements, I've just measured mine and it's 147.5cm for 97.00mhz. The bottom pole measures 61cm.

The spacing between the radiating element and the ground pole is exactly 4cm.
is 147.5 cm on your aerial for 97mhz total length as that would pretty much mean the spread sheet is bang on, or is that just your top element?

Also, I dont suppose you have the approx measument for the plates?

I intend to make on thursday so i will post pics

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Hi-Gain Vertical Half Wave Antenna

Post by Maximus » Wed Dec 28, 2016 10:36 am

147.5cm is only the top radiating element for 97.00mhz. See attached picture.

The capacitive place measures exactly 4x10cm.

Image


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Re: Hi-Gain Vertical Half Wave Antenna

Post by Banus_radio » Wed Dec 28, 2016 12:03 pm

Maximus wrote:147.5cm is only the top radiating element for 97.00mhz. See attached picture.

The capacitive place measures exactly 4x10cm.

Image


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Arrrrr I see now, thank you so much
I was getting confused with the excel spreadsheet measurements, I thought where it said bottom pole that was on the grounded side.
I will post pics of my attempt any day, picking up some batteries for the mfj today and see what I come up with

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Re: Hi-Gain Vertical Half Wave Antenna

Post by Banus_radio » Thu Dec 29, 2016 12:31 pm

Ive had a good idea ....... I think ?

Well ive been thinking about this antenna over and over again and seem the weakest point is the plastic seperating the upper and lower mounting. So ive been thinking of a way around it to maintain strength.. so how about a tubular type of capacitor same as found on a gamma match

Using ptfe teflon insulator between mounting pole and upper vertical pole, you can slide the upper vertical down until you have the correct capacitance. what do you think. Heres a rough diagram ive drawn excluding coils and coax and stuff.
teflon capacitor.jpg
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Re: Hi-Gain Vertical Half Wave Antenna

Post by Albert H » Thu Dec 29, 2016 6:15 pm

How are you going to feed the radiator? The capacitor should work well, and will be physically strong. You're going to have to keep it dry - water will cause flash-overs. You could sleeve the area above and below the exposed Teflon™ with heat-shrink tubing.....
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Re: Hi-Gain Vertical Half Wave Antenna

Post by radio-berlin » Thu Dec 29, 2016 6:54 pm

I will feed the radiator exactly the same way as the original nrg antenna but with an earth type clamp so it can easily be adjusted.only difference is instead of the plates on the outside it will be on the inside in the dry

I've found teflon pipe that fits snug inside 1 1/2 pipe, the teflon pipe has 4mm walls and then my bottom section of radiator fits very snug inside the teflon. I was going to coat in epoxy glue and use heat shrink as you said.

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Re: Hi-Gain Vertical Half Wave Antenna

Post by radio-berlin » Thu Dec 29, 2016 6:56 pm

Banus I will post up the links of my findings where to buy the pipes

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Re: Hi-Gain Vertical Half Wave Antenna

Post by Banus_radio » Thu Dec 29, 2016 7:06 pm

Thanks again. Did you get my pm? I couldn't find teflon pipe at a reasonable price so I have ordered abs. I'm only running 40 watts so this should be ok I hope. Any links would be appreciated. Thanks again

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Re: Hi-Gain Vertical Half Wave Antenna

Post by Banus_radio » Fri Dec 30, 2016 2:53 pm

Does anyone understand what this picture is trying to explain?
nrg coils.jpg
My understanding is that the horizontal coil is 10 3/4 Turns as it says and bottom coil is 7 Turns.
So what is the bit trying to explain with the screwdrivers, where it says 2t tape and so on? im confused again. Is it trying to explain how far you stretch the coil? or diamater? does anyone know the diamater of these coils, maximus???
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Re: Hi-Gain Vertical Half Wave Antenna

Post by Maximus » Fri Dec 30, 2016 4:50 pm

Sorry I haven't the foggiest. Mine is only the 50w version with the big coils which are wrapped around the plastic.


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Re: Hi-Gain Vertical Half Wave Antenna

Post by Banus_radio » Sat Jan 14, 2017 4:45 pm

Banus_radio wrote:Does anyone understand what this picture is trying to explain?
nrg coils.jpg
My understanding is that the horizontal coil is 10 3/4 Turns as it says and bottom coil is 7 Turns.
So what is the bit trying to explain with the screwdrivers, where it says 2t tape and so on? im confused again. Is it trying to explain how far you stretch the coil? or diamater? does anyone know the diamater of these coils, maximus???
Albert can you help with this? Im not sure what the screwdriver pic is trying to demonstrate

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Re: Hi-Gain Vertical Half Wave Antenna

Post by Banus_radio » Sat Jan 14, 2017 11:40 pm

Ok so today ive spent hours upon hours playing with and making aerials.

some months ago I was a fool, I didnt listen to advice and I spent a lot of money on an aareef 5/8 wave antenna. Its supplied tuned by them, its been up for about 6 weeks now and caused nothing but problems, swr protection keep kicking in on my transmitter. Today I took it down and am shocked by the state of it, all the bolts have rusted including the matching stub piece and the ground planes have all become loose. They supply m3 nuts and bolts and no shakeproof washers.
The antenna has a white calcifaction on it, looks like rain has run between the upper element stub and the bolts for the ground planes and carried current causing it to go white (a bit like when wires get wet carrying current), theres only about 2mm clearance between the ground plane bolts and the top element stub. So anyway, long story short, I connect to my new aerial analyser. I do a scan from 50mhz to 170mhz and not at any point does it swr at 1:1. lowest I got was swr of around 3 on my frequency. STAY CLEAR OF AAREEF SHIT! I will post some pics of the aerial tomorrow and some pics of the analyser readings

So anyway I decided to build a new aerial.

I first built a J pole, tunes very very nicely, can adjust feed point and get exactly 50ohms and swr right down at 1:2 (I only used wire strapped to tubing, its just a test, ill make a final antenna out of aluminium), I then added a half wave matching stub and an additional 1/2 wave section above it and swr and impedance remained the same, X = 0 or there abouts which is think is correct? im a bit unsure what X means, im guessing its if aerial is inductive or capacitive.

Next I made a simple dipole with pawsey stub, tuned bang on 1:1 first time and read about 53 ohms

Next i Made a gamma match dipole, again just using wire and a capacitor strapped to a rod, again tuned up very nicely with swr 1:1 and around 47 ohms.

But i failed miserably with the NRG 1/2 wave. Using the measurments in the excel spreadsheet and winding 10 &3/4t coil and 7t coil, using a capacitor 5-65pf for the life of me I could not a get a decent match anywhere between 88 and 108. With the top element cut to 100mhz, 10 3/4t coil and 7turn coil at 7mm best i got was around 30ohms and swr of approx 2.5 at 100mhz with capacitor around 10pf, however if i increase the capacitance it would be resonant at lower frquencies.
With capacitor fully turned off (which is around 5pf) it would make it resonant at 117mhz and a swr of about 2, but then x was high which i think means its inductive, it then also gave a inductamce nh reading (i didnt take ote of what the reading was)
with full capacitance of 65pf it would swr at 1:2 right down at around 60 - 70 mhz but x was in the minus figures which i think means its very capacitive, impedance around 45ohms.

Can anybody help with where im going wrong

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Re: Hi-Gain Vertical Half Wave Antenna

Post by thewisepranker » Sun Jan 15, 2017 2:41 pm

X means reactance and forms the imaginary part of the overall impedance. As you've guessed, it indicates whether the network is inductive or capacitive at that particular frequency, and you have got it right with which way round the signs go, i.e. negative for capacitive.

I've not had any experience of NRG antennas so can't comment.

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Re: Hi-Gain Vertical Half Wave Antenna

Post by Banus_radio » Mon Jan 16, 2017 12:11 am

sinus trouble wrote:greetings all! :)
ive been working on a low power version of this antenna (1watt) and if im correct?? it seems the whole concept is to basically to transform the 50ohm load to around 5kohm?? the radiator element length remains the same as a standard dipole??
using the parallel LC tuned circuit shown by the NRG ant and shuffys diagram needs quite a large inductor value and a very small capacitance to achieve matching?
as i have loads of variable caps ive focused on the L value so far!
using the 2 x PI x F x L formula? ive needed around 18 turns to be anywhere near 5kohm reactance?
Could i connect a 5k resistor across the tank (removing the 1/2 wave vertical) and tune the capacitor until i get a 1:1 swr and 50ohm at my desired frequency on my aerial analyser? that would get me in the right area surely??? if so how would i connect it, would it be paralell with the cap?

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Re: Hi-Gain Vertical Half Wave Antenna

Post by radio-berlin » Mon Jan 16, 2017 1:58 am

Banus i gave this a go for you. I also couldnt get a match using the tank circuit as described in the nrg files upoaded by frequent lee.

The best I could come up with was 10 turns on hot side, and 2.5'ish turns on the earthy side. I wound at 6.5mm. Capacitor tuning was very sensitive, a swing of around 5pf adjusted from 87 to 108, I guesstimate it was around 8 (high end) - 13pf (low end).

Heres the results I got using around 12.5 turns total, tapped 2.5'ish turns up from earth and using 5k resistor. see attached photos. Hope this helps you?
tank.jpg
swr 100mhz.jpg
87mhz.jpg
108mhz.jpg
I will add, this is very tricky to tune, im guessing using aluminium plates as a capacitor is a lot less sensitive. I think id advise making the plates bigger and further apart so to make much finer adjustments

Im no antenna expert so im not sure if the above readings are correct. Antennas is a whole new subject I NEED to study. One day i will make a version of this antenna and see what its like.
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Re: Hi-Gain Vertical Half Wave Antenna

Post by radio-berlin » Mon Jan 16, 2017 9:46 am

banus_radio was you using a counterpoise (ground element or grounded pole)
Ive since discovered after some google searching that the closer the length of the counteroise gets to a halfwave the closer the end fed 1/2 top element is to 5k.

With a shorter counterpoise an impedance can be as low as 1.5K where you end feed it. I have no clue of the maths behind this but im guessing this will alter the tuning to the tank circuit a fair amount and the coils used.

When NRG sold these antennas did they specify that the mounting pole had to be at least a miniumum length? My guess is they did specify this? Because if the counterpoise is at least a 1/2 wave in legth then the end fed impedance would be close to 5k, I cant see any other way they could supply these tuned to frequency, otherwise as shorter counterpoise would alter the tuning, i may well be wrong though, I usally am :D

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