VK Logger Ham Radio Forum Archive

Hello All

I am building a 2 element, lightweight, compact 10m yagi. Should I use a reflector or a director as the parasitic element? Give reasons for your answer.

I would like the antenna experts to "hold short of the runway" and give the newbies, especially foundation calls, a chance to answer first.

73

Wayne VK4WDM

don't understand the point of the thread actually

You want advice or you want to give advice

2 el yagis went out with the ZL specials in the 60's

Funny, I've just got home from buying some extra bits of aluminium I needed to do exactly the same thing, although this is for a mate who is still on 27Megs, with the aim of bringing it up to 10m and adding an element once I coax him through the Foundation license and his Mrs gets used to it.

Watching with interest...

Once again, experts hold off please. There is a lot more to this than just BF and gain and it would be good learning exercise for the less technically advanced.

73

Wayne VK4WDM

Very lacking on my yagi basics (i tend to copy!)
dont the directors need a reflecting plane? (reflecting element?) to excite them. (i'm probably totally wrong)

I'll leave my other comments (give others a chance)

I will explain more about my specific situation.

My Butternut HF9 vertical works quite well on 10m and I can usually work what I hear. It is the hearing bit that is the problem. Up here in Nth QLD Asian signals are often very strong most of the time. Many of the DX entities I need are either in Sth America or Africa so I need to have some directivity to reduce the Asian QRM. I have a tried a rotating dipole (located on the same boom as my 4 element 6m beam) and that certainly makes a difference. I have room to add another 10m element. Would that be worthwhile? If so, should it be a reflector or a director? I don't have room on the boom for both and extending the boom is not an option.

I need to point out that the antenna is mounted on a light weight 8m high tilt over mast and rotated by a light duty rotator.

73

Wayne VK4WDM

Hi Wayne,

Clearly characterise your "problem".

1/ Obviously, gain is only a minor consideration (if at all).

2/ Front-to-back ratio is a factor in reducing interference (in certain directions).

3/ Front-to-side ratio is a factor in reducing interference (in certain directions).

4/ Weight and windage of the additional element may be important.

A question to ask yourself (investigate): which yields the greater front-to-back ratio - DE-director or DE-reflector?

The answer may not be obvious.

Hi Roger

The answer may not be obvious.

Quite correct

An important factor to bear in mind is that the major direction that the QRM comes from is the Nth and most of the signals I am interested in come from short path Africa and short path central and Sth America, with some long path openings to both areas.

As you have probably guessed this post is more about the newbies, especially the foundation calls, to think a little deeper about yagis rather than just an answer to "my problem."

73

Wayne VK4WDM

and a moxon would do well as well.
I'm saying refector rather than director
but I know nothing

Moxon would do well as well.

Good thought!

Wayne, as I understand it which is by no means gospel.

If it is absolute gain you are after a director yields slightly more but poorer front to back ratio.

If it is front to back ratio you want then the reflector is a better option with ever so slightly reduced gain.

An end on dipole without any feedline radiation (read that as a properly balanced system with a working balun and feed line coming away at 90 degrees from the dipole element and no other conducting material close enough or orientated in such a way as to distort the field) would possibly give you a better null that either of the above. It would probably still be better even if all those requirements were not met but of course if it is not a point source of qrm as in your case all bets are off.

Perhaps 2 driven elements spaced 1/4 wave apart and fed 90 deg out of phase to give a cardioid pattern might be the answer you want?

My humble 2pc worth?

VK3AIF wrote:Wayne, as I understand it which is by no means gospel.

If it is absolute gain you are after a director yields slightly more but poorer front to back ratio.

If it is front to back ratio you want then the reflector is a better option with ever so slightly reduced gain.

An end on dipole without any feedline radiation (read that as a properly balanced system with a working balun and feed line coming away at 90 degrees from the dipole element and no other conducting material close enough or orientated in such a way as to distort the field) would possibly give you a better null that either of the above. It would probably still be better even if all those requirements were not met but of course if it is not a point source of qrm as in your case all bets are off.

Perhaps 2 driven elements spaced 1/4 wave apart and fed 90 deg out of phase to give a cardioid pattern might be the answer you want?

My humble 2pc worth?

This is what I'm looking at as probably the best option for what I'm looking at: http://www.qsl.net/dk7zb/HB9CV/Details-HB9CV.htm

Plenty of good info on the page or you can Google a couple of reasonable calculators for the HB9CV design.

I agree that there is a little to be gained (no pun intended) by adding another element to a 10m dipole.

IMHO Alan VK3XDE's suggestion of the HB9CV yagi variant is spot on (do you want me to send you a Mars bar? ). Beams using two driven elements and phasing lines such as the ZL Special and the HB9CV used to be very popular a few decades ago on HF, VHF and UHF but one seldom hears about them today. The larger ones can be fed with ladder line and used on several bands. A lightweight HB9CV is an ideal portable antenna for 6m or 10m.

There is heaps of information on the web, including calculators. Just a sample: http://www.gfmradio.org/hb9cv.php http://www.changpuak.ch/electronics/HB9CV.php

Just make sure that the capacitor used at the feed point will cope with the power.

I will put a 10m HB9CV together once I finish testing the Delta loop I have started building and report back.

VK3MEG suggested the Moxom. Certainly a contender, but I don't have and suitable spreaders, whereas I have all the materials for the HB9CV.

73

Wayne VK4WDM

Hi all.....

Oh Wayne.....the issue I have with the question not the antenna.....is the diagram you show has a reflector and a director....but technically no Driven Element......now I would think that design has 2 driven elements and no parasitic elements....similar to a LPDA...


John

Why don't you just build or borrow a 3 or 4 el yagi for 10 m?
They are only little, and you would do well to get one up right away. Stick it up on a pole in your backyard, braced to your eaves, or whatever is convenient and practical.
The more time you spend discussing it on an Internet forum (aka Procrastinating), the less time you will have working the DX, which is plentiful NOW.
Don't wait a couple of months, or you'll miss the boat.
73,
Luke VK3HJ

Hi Luke

I am working plenty of 10m stations in EU and NA with the vertical and the rotatable dipole, so certainly not spending all the time dreaming (or eating Stag chillie)

Problem on 10m up here is the QRM, mainly from Indonesian FM stns of dubious identity. They tend to peak at the same time as the Africans are coming in, hence the need to increase the directivity.

73

Wayne VK4WDM

2 driven elements and no parasitic elements....similar to a LPDA...

Hi John

Quite correct!

73

Wayne VK4WDM

VK4WDM wrote:QRM, mainly from Indonesian FM stns of dubious identity. They tend to peak at the same time as the Africans are coming in, hence the need to increase the directivity.

I don't think there is any escaping the intruder crud on the band. I've used a 4 el monoband beam, and still been irritated by all the intruders. This will remain a problem while we have good propagation on the band.
Increasing antenna directivity will certainly help, but don't expect it to eliminate all that which you don't want to hear!
Maximising your design for best side rejection would probably yield best results. Forward gain is more helpful in marginal conditions.
Nothing wrong with Stag Chilli - in moderation!
Good luck,
Luke VK3HJ

A hb9cv or a zl special will not give you as deep a null as what I proposed but it is on the right track.

Luke VK3HJ wrote:

Why don't you just build or borrow a 3 or 4 el yagi for 10 m?
They are only little, and you would do well to get one up right away. Stick it up on a pole in your backyard, braced to your eaves, or whatever is convenient and practical.
The more time you spend discussing it on an Internet forum (aka Procrastinating), the less time you will have working the DX, which is plentiful NOW.

I took these wise words on board and built a 2 element Yagi designed by DK7ZB. Gain: 4,0dBd. 10,5dB. Split dipole feed with an 8 turn choke balun. Tuned for 28.450 MHZ where the SWR is 1:1 and does not vary much between 28.000 and 29.1 MHZ.

So how does it go in practice? 10m has not been very good in the last few days but I have made some comparisons with a USA beacon and a SSB QSO.

Beacon: Foward S9, Side S3, Back S4.

In QSO with K2IGW I was S7-8 with the beam and unreadable on my multi-band vertical.

Sound's like it is working as it should. Hopefully propagation will pick and I will be able to give it a good workout.

73

Wayne VK4WDM


73

Wayne VK4WDM