2 meter antenna experiment

[Agent 48]

So I have a lot of spare coax lying about and thought I would make a few 2 meter wire end fed dipoles to experiment with, do comparison tests etc.

First antenna... I put together is just a simple halfwave, "two quarter wave sections" 9 turn coil at the base. Pretty simple antenna to make.

Second antenna... will be a full wave, this is suppose to offer some gain but whether there will be any noticeable differences is yet to be seen or heard should I say. So the design is the same as the first but with two half wave sections.

Will a full wave end fed perform better than a standard half wave?

[paulears]

These aren’t end fed though? They’re balanced centre fed? I find horizontal centre fed dipoles pretty good for nulling out when used ad a centre fed half wave. No gain of course but rotating can be useful. Increasing the length by three gives a good match but the radiation pattern has more, smaller nulls. Used vertically I like them. Horizontally not that useful. The perceived little extra gain as a vertical seems to vanish horizontally but I guess just the nulls working against not for. Never tried other lengths due to the requirement for impedance conversion.

[Agent 48]

These aren’t end fed though? They’re balanced centre fed? I find horizontal centre fed dipoles pretty good for nulling out when used ad a centre fed half wave. No gain of course but rotating can be useful. Increasing the length by three gives a good match but the radiation pattern has more, smaller nulls. Used vertically I like them. Horizontally not that useful. The perceived little extra gain as a vertical seems to vanish horizontally but I guess just the nulls working against not for. Never tried other lengths due to the requirement for impedance conversion.

They are not fed at the center. They are like the flower pot antenna so a quarter wave of outer braid of the coax and then either a quarter wave piece of wire soldered to the coax or strip back a quarter wave length then choke off the coax at the bottom "not the center" with 9 turns of coax.

Anyway these antennas proved to be pretty lousy when tested, SWR was 1.1 and bandwidth was very narrow and overall performance was poor.

A good old aluminum center fed traditional dipole worked so much better. I have quite a few I made from scrap antenna bits.

There doesn't really seem to be a whole lot of options out there for antennas other than half wave or Diamond types of antennas... A simple 5/8 wave wire antenna would be fine or double 5/8 wave... other options with be the J pole or Slim Jim which would be better over a half wave dipole. I think I'll go with the Slim Jim for its low angle take off, I will look for a design and make one from ladder line. They don't look hard to make as long as measurements are accurate.

A half wave dipole works reasonably well but because I'm not that high up with no line of sight, I need some gain on the antenna just to get my signal out further. Also the down side about using a half wave dipole is that it has to bolt onto a metal pole and I don't have anything long enough to be able to safely raise it up enough in the air to clear my roof line where as a wire antenna I can get that a good 6 foot above the roof maybe a bit more on my modified balcony fishing pole.

[Agent 48]

I would really like to try out a folded dipole and compare it with a standard dipole.

Its a bit more complex making a folded dipole because once you make the loop there is no going back to tune it like you can with a standard dipole, bearing in mind there are often extra metal inside the dipole connector that adds to the wave length of the legs, often I've had to trim the legs shorter to achieve the perfect SWR, I did managed to build one dipole that didn't require any cutting to tune by fluke but most I build do require it.

I do have a folded dipole section somewhere but its for 70CM, if I had four of those I'd build a 4 folded dipole stack antenna for UHF which I might actually do as I have one folded section that should be tuned to the 70cm band so I'll be able to make duplicates of that section.

[ch25]

Did you heard about sleeve dipole?

[Agent 48]

The sleeve antenna is interesting... what I like about the sleeve antenna is that the design leaves plenty of room for experimentation where more sections can be added to achieve some gain.

The quarter wave sleeve section is a better design than the standard flower pot style antenna & would prevent common mode a lot better.

[paulears]

I've used sleeve dipoles plenty of times, especially on marine band with decent results - never heard of the flower pot? A new one on me, but Google makes it look interesting.

[Agent 48]

I will build a sleeve antenna and if it performs well enough I may build a second one as a spare.