2m Hentenna

[VK2ZRH]

Adrian said:

Some thoughts to consider:
- Balun of some sort should be used
- Impact of pipe dia?
- Should the loop measurements be inside, centre or outside circumfrence? (I used outside)

Balun. Yes. You should use one. See my posting on the previous page.

Pipe diameter. Greater diameter will mean broader bandwidth; smaller diameter will mean narrower bandwidth.

Loop measurements. Authors can be sloppy about mentioning this. If they don't mention it, go with pipe centre measurement. If you used outside circumference on the one you built, while the article's author used pipe centre, then your loop will be slightly short and this would explain why your hentenna's resonant frequency was higher than you expected (and why shifting the feedpoint tap/s only marginally changed the VSWR curve).

Another 2c.

73

[VK2VHF]

All good comments - thanks to everyone.

I have checked the dimensions in the first link and they seem to be correct and I agree with ZRH's comments that I should have measured to the centre of the pipe.

- Overall height = 1/2 WL = 300/144.200 x 0.5 = 1.04m
- Bottom section height = 1/10 WL = 300/144.200 x 0.10 = 0.21m
- Width = 1/6 WL = 300/144.200 x 0.167 = 0.35m

In fact the measurements hold true at 144.100 also if you round to two decimal places.

Cheers, Adrian

[VK4DD]

Hi Gents

VK2ZRH:Pipe diameter. Greater diameter will mean broader bandwidth; smaller diameter will mean narrower bandwidth.

That is true, but in this case I think a more important effect is that a
Smaller diameter pipe means.. resonant frequency will go up.
Thicker diameter pipe means ... resonant frequency will go down.

Off course there will be broader or narrower bandwidth with diameter variations.. but who cares if it is 10 or 11 Mhz wide.
More important is that the center frequency is on 144.2 instead of 146 or 147.
And that is exactly what a different pipe diameter can do.

It is a pity that Adrian grabbed so quickly the solder burner and did not experiment with taping up the antenna with a layer of PCV tape, in order to lower the resonant frequency.
He could have weather proved the antenna and fixed it at the same time.

Ron
VK4DD

[VK2VHF]

It is a pity that Adrian grabbed so quickly the solder burner ....

Yes I was rather quick to pick up the torch - playing with fire is fun!

But I plan to start work on version 2 shortly and have learnt from my mistakes.

Adrian

[VK3FKRK]

hi there it just that i noticed a differance between the metric and inperal mesurement on the pdf page, it is a differance of about 18mm between the two of them would that make differance?
ken

[VK2VHF]

Hi Ken the correct dimensions are sketched below -

* * diagram updated 12/08/09 * *

For the next prototype, I intend to build the outer rectangle with no Tee joints. I will then cut a tee along its axis to make two "half" tee shells. I can then slide the shells up and down for best VSWR and solder them on afterwards.

Adrian

[VK2VHF]

Success!

I have rebuilt the "Chooktenna" as described above and achieved a flat VSWR of 1:1 across 143-145 Mhz. This time I built the outside loop first and then attached the feed point after testing.

As a result the feedpoint was 22.5cm from the bottom (centre pipe to centre pipe) and not 21cm as depicted above. I ran a pigtail from the feedpoint with 3 ferrite beads over the coax at the feedpoint.

As tested on the MFJ259b I recorded the following results over 10 Mhz-

(Mhz = VSWR)
139 = 1.7
140 = 1.8
141 = 1.7
142 = 1.4
143 = 1.0
144 = 1.0 (144.150, R=50, X=1)
145 = 1.0
146 = 1.4
147 = 1.7
148 = 1.6
149 = 1.5

Once again thanks to everyone for your advice.

Adrian

[VK4APN]

Success!
I have rebuilt the "Chooktenna" as described above and achieved a flat VSWR of 1:1 across 143-145 Mhz. This time I built the outside loop first and then attached the feed point after testing.
Adrian

I am glad you have managed to obtain such a good match. Nobody has asked yet so I will ! ........how does it play? from a transmitting / receiving point of view.

[VK2VHF]

Nobody has asked yet so I will ! ........how does it play? from a transmitting / receiving point of view.

Let me give it a run in the RD contest and I will post an update afterwards.

Adrian

[VK4DD]

Adrian,

Congrats on getting the antenna resonant.
What does it cost to build one out of copper?

I suppose you could also make one up from aluminum tube...or square profile.

Sketch... your sketch with dimensions.
Could you edit this posting and note if these are internal, external or center to center dimensions.
That would be help full for all of us.

Cheers
Ron 4DD

[VK2VHF]

What does it cost to build one out of copper?

I suppose you could also make one up from aluminum tube...or square profile.

Sketch... your sketch with dimensions.

Could you edit this posting and note if these are internal, external or center to center dimensions.

G'day Ron,

I purchased the 1/2 inch copper pipe, elbows and tees from Reece Plumping supplies for a total cost of around $50. I preferred copper because the elbows and tees make it neat and strong once you sweat them on.

The sketch in my earlier post shows centre (dotted line) and outside dimensions. I shall update to show the height of the feed at 22.5cm instead of 21cm.

Cheers, Adrian

[VK6DZ]

Nobody has asked yet so I will ! ........how does it play? from a transmitting / receiving point of view.

Let me give it a run in the RD contest and I will post an update afterwards.

Adrian

I'm interested in giving this antenna a go.

How did it perform in the RD ?

[VK2VHF]

Hi Derek,

Free time has been in short supply so I have not had a chance to properly test the antenna yet.

I did not manage to get the antenna up for the RD contest. In any case I heard no contest activity on 2m SSB using my vertical

That said, I've made a couple of short range (~75km) tests and the hentenna performed quite well. I shall try to post some more results when time permits.

Cheers Adrian