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Antenna Size question

E

edfiero

Active Member
Jul 15, 2010
74
43
28
So we know there is 1/4 wave, 1/2 and 5/8 wave vertical/omni antennas, with the longer antenna giving better performance.

It seems that all directional antennas are built on roughly a half wave design with element lengths in the neighborhood of 18 feet.

Question:

1. Has any one ever made a directional antenna based on a 5/8 wave design? If so, how much better did it perform than the typcial 1/2 designs?

2. More importantly, why hasn't anyone ever built a 1/4 wave directional antenna for those of us with limited space? Granted, it could never out perform the 1/2 wave design, but seems like you would still have a signficant advantage over an omni directional.
 

Not sure about Q2 but re. Q1, perform a search on 'Extended Double Zepp' and read about this nice cheap wire that'll net you approx. 3 Dbd gain.

73, Bert

Sent from my ADR6400L using Tapatalk
 
As to the 5/8 wave center fed doublet, there's not much point. Any difference in pattern or gain would be offset by the impedance matching required to get the thing to 50 ohms. Wanna try it and see? Good, do so! Then you can tell us if it was worth the trouble.
- 'Doc
 
Long ahead of you, Doc. I'm using a 20m EDZ and it plays FB. It replaced a Carolina Window that had replaced a standard 40m double... & so on. So when I recommend this antenna, it's based on first hand experiences.

I like it so much that I'm going to build a dedicated 11m one with some birdcage spaces that I have on hand to see how a birdcage EDZ plays. A 1/4L matching section will take care of the match. Overall length, abt 43 ft.

73, Bert

Sent from my ADR6400L using Tapatalk
 
Or we can use a transmatch and feed it with open wire line. (My current set up.) Oh yeah, make that overall length abt 45 ft., not 43 as shown above. (Oops - hihi)

Sent from my ADR6400L using Tapatalk
 
WA2SI said:
Or we can use a transmatch and feed it with open wire line. (My current set up.) Oh yeah, make that overall length abt 45 ft., not 43 as shown above. (Oops - hihi)
Click to expand...
my reading shows .64 x 2 or 46' total but when you lay the eznec model for both on their side the 5/8 looks like it would provide a broader pattern but maybe with a little less gain
 
edfiero said:
1. Has any one ever made a directional antenna based on a 5/8 wave design? If so, how much better did it perform than the typcial 1/2 designs?

2. More importantly, why hasn't anyone ever built a 1/4 wave directional antenna for those of us with limited space? Granted, it could never out perform the 1/2 wave design, but seems like you would still have a signficant advantage over an omni directional.
Click to expand...


1
More gain means a narrower beam width.
More gain also means a large antenna (in either boom length or "element “length.
With that also aiming becomes more difficult.
There are a lot of antennas types who get there gain from “being wide rather than having a larger boom length".
In your question you are referring to 5/8waves and an answer is given above.
Antennas more often used for achieving gain in the "wide" categories are:
(Just a couple examples): Collinear, sterba curtain,bobtail curtain, half square or just a simple long wire can deliver gain. But also Lazy H and my personal favorite the boxkite from Mr. Brian Cake.
Most gain on 11 meter from a the smallest "square" surface is generated by beam configurations.


Although direct feeding impedance is preferred, I wouldn’t worry about it too much in first place.
As that is one of the few things you can match on an antenna. You can’t match an "antenna pattern" or "gain" etc.


2
That cannot be done without some form of loss.
Your vertical ground plane has radials which form the "other" part of the antenna.
If you put just 1 radial underneath the ground plane at a 180 degree angle you just made yourself a dipole. If we place that dipole at the center of a boom...and we add elements we have made a beam.
There are a couple ways to reduce element length:
The "folding" categories like Moxon/hexbeam/Jungle job, but also other methods have been done like linear loading / shorting traps etc. Actuele that is the way most mobile antenna's work.
The folding catergorie is without real losses, all others are. BUT you can shorten the elments for a large portion without sacrifiseing a lot.

Kind regards,

Henry `19SD348
All about antennas
 
Last edited:
Gamegetter - Thanks for the link to Mosley. Their MiniBeam is exactly what I was looking for, though that price is a bit steep.

Henry - Can you suggest any books for building Moxon antennas? I'm not interested in the theory behind them, just the nuts and bolts of how to construct one... best materials to use, etc.

Thanks
 
why couldn't one be built with coil loaded shortened mobile antennas like a 10k of fiberglass antennas like firestick/k40/skipshooter ? i know they can be used to make a dipole , and a beam is typically just a dipole with a reflector element and one or more reflectors . they can be just a driven element and one director or one reflector . my question is do the reflector or director elements need a coil to shorten them electrically to ? or would straight R/D elements with the correct + or - %5 overall length work ? the mosley looks to have all the elements loaded ......
 
Booty, the ref and dir elements must be resonant about 5% below/above the design freq. how you achieve that resonance is up to you. Either they have to be full size or use loading coils to electrically lengthen the elements. The Mosley mini beam does use loading coils in all the elements to achieve resonance with short elements. As with all short antennas the efficiency and gain will be lower than a full size antenna regardless if it is a beam or not.
 
thanks CK . i understand about shortened elements not being as efficient , but there doesn't seem to be a lot of difference between a 9 ft element vs. a 6 or 7 ft 10k for example .

it would be interesting to see the results of a 3 element beam made with a half dozen 5 ft mobile antennas compared to a full length 3 element beam .
the funny thing about this hobby is that something that's less than optimal for the masses could be perfect/preferred by a minority . the smaller wind-load , smaller turning radius and lighter rotor load will definitely be a worth the performance hit to some ....... but mosley already knows that .
 
Delta Loop for 10 to 12 meters

Hiya there;)

Im in a space limited situation, however, Im also 20m high and facing East but located in the City of London, UK.

Because, I now live in a high rise, it can be difficult getting out on some bands that really need a long vertical polarised antenna, 11m was my personal nightmare on FM. Therefore, this problem which you initially described is the same that I must face and have over come.

My suggestion, is trying using a full wave of insulated wire and, to bend the antenna back on it' self to create a loop! Even better, get two glass fiber fishing pole 7 meters long remove the top sections. Put the full wave though both pole until one end is found on each end of the fishing pole. Now, hold the poles vertically out in front of you so they make a V shape with the wire crowing the V. All you need to do now, it get some tube and mount these poles in this shape to make a delta-loop which will be directional! However, it is mostly, better to use slightly more than a wavelength when making these antennas.

Although now, you will need a 1-2-1 balun, which is a transformer which will transform the large impedances now found in the delta-loop down to your friendly 50 ohms. Additionally, you need a tuner, for most of the time, so that you can tune the frequency of operation down to a zilch. Try to get a cheapo mfj tuner, off ebay will do, that can accept ladder feed. They have an internal balun which will save time and money and do both jobs at once.

These antennas are simple and work great for DX depending on polarization, which in turn, depends on where you feed the Loop. This antenna is great at 22m long and will work all the way down to 14mhz really well. But, if you just want 10, 11 and 12 meters then around 13 meters is all the wire you need!

Good Luck
 
Hello Guys,

There are more moxon's on dx-antenna.com but here goes the 2elements:
http://www.dx-antennas.com/M2.html

please bare in mind:

If you are going to use bare wire..no problem...if you use isolated wire all element lengths should be reduced about 3 to 4 procent.
Element distance remains equal.

There are commercial version availible aswell..im sure if you google moxon 11 meter you will end up somewhere.
I wont post the link cause we construct and sell them at a commercial base aswell,that wouldnt be correct.


Dont worrie about gain in reference with rather "small" antennas.
With small antennas i would rather focus on front to back /front to rear.

Dont you just hate that you cant hear ta station "due to..others?"

In that case it would be the directivity of a antenna which could make you hear something or not.
6dB is "only" 1S-unit. And no im not misinterperting the value of a extra 0,5 dB..not at all.
With that said im only trying to say ..dont focus on gain allone.
Im confident you can work more DX without gain but with front to back and front to rear...compared to a "only" gain configuration.

If you wanna work DX put up a horizontal "thing" as high as you can.
horizontal antennas will provide additional ground gain they are the overall winners for DX


Regarding the Mobile antenna beam idea:
That has been done before using dv27:

Amateurfunkforum Mittelrhein - Yagi aus DV27 Strahlern

I believe Cebik(sk) has a good story about shorting elements on his site. The conclusion (if my memory isoke) was that you actually can shorten the elements with about 30 procent without sacrifising too much.

@slateblue...perhaps a hentenna is something to investigate, that should have slightly more gain and a bit more directivity (not muchthough)




Kind regards,

Henry 19SD348
All about antennas
 

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