Simple but effective DIY civil/mil airband antenna the "double bazooka"

[radiostationx]

Hi all,
Making your own antennas is fun and rewarding.
Here is a guide on making your own coaxial dipole for civil (or military) airband.
An inexpensive but very effective antenna.

Home made coaxial dipole antenna for civil (and military) airband. – Mersey Radar

 

[W5lz]

The "secret" to antennas in this freq range is height! The higher the better.

 

[W5lz]

Should have included this above... only mistake I've made all year! (You believe that, right?)

The other "secret" is to make the/an antenna as resonant as is practical (not as possible, but practical). Resonance equates to efficiency (sort of), and that efficiency is desirable in most cases (not all, but in most cases). There always seems to be a "gotcha" with this stuff ain't there?

 

[radiostationx]

Page now updated with report from builder Adam VK3SWL in Australia.

Home made coaxial dipole antenna for civil (and military) airband. – Mersey Radar

 

[krokus]

The drain hole is a good idea, but would suggest smaller holes, or a small patch of fiberglass window screen applied over the hole, to prevent insects from entering the antenna housing.

Sent using Tapatalk

 

[W5lz]

The "bazooka" (single or bouble) antenna has been around for over 50 - 60 years. It works, but don't hold your breath for 'miracles'. They also have a few draw-backs depending on design frequency, as they get heavy and sort of expensive. Even at VHF/UHF frequencies you don't see very many of them. Ever wonder wmy? I got a hole out of a donut I'm willing to bet that it has to do with efficiency. Wanna bet?

 

[radiostationx]

I see plenty of commercial airband VHF and UHF folded dipoles, they are heavier, ...nothing fantastic and they have holes in the middle as well.
Oh and they are more expensive, willing to bet the hole and the weight has something to do with maintenance, the xtra expense well thats for the weight of the hole or "good ol nickel and diming" the client.

 

[prcguy]

In the US I see mostly ground planes, Discones, coaxial dipoles and fat dipoles inside radomes for base station aviation use but I can't say I seen a single folded dipole for the same. There is no reason you can't but apparently its just not popular here.

I see plenty of commercial airband VHF and UHF folded dipoles, they are heavier, ...nothing fantastic and they have holes in the middle as well.
Oh and they are more expensive, willing to bet the hole and the weight has something to do with maintenance, the xtra expense well thats for the weight of the hole or "good ol nickel and diming" the client.

 

[radiostationx]

This is a very popular one over here,
https://www.webb.co.za/storage/files/WEBB_FDC125_FDC145_FDC150_FDC150HD_FDC160_FDC250.pdf
sometimes stacked (from the same company).
https://www.webb.co.za/storage/files/WEBB_FOLDED_DIPOLE_ARRAYS_2_STACK.pdf

 

[chief21]

I made one of these some years ago. It was intended for receiving ADS-B signals (about 1000 MHz) and consisted of about 8 "elements". It worked very well.

 

[jusrey26]

nice find. I might have to do this.

 

[prcguy]

Something I would like to know about these is if they are actual folded half wave dipoles which are about 200 ohm impedance and would need a matching circuit, or if they are half wave dipoles with the elements folded back to ground in the middle on both sides, which are about 50 ohms. The folded grounded versions are the most common in the US and are fed directly with 50 ohm coax or when stacked, a phasing harness that is 50 ohms at each element.

The advertising for the Web antennas states the metal parts are DC grounded, which makes me think they are not true folded dipoles.

This is a very popular one over here,
https://www.webb.co.za/storage/files/WEBB_FDC125_FDC145_FDC150_FDC150HD_FDC160_FDC250.pdf
sometimes stacked (from the same company).
https://www.webb.co.za/storage/files/WEBB_FOLDED_DIPOLE_ARRAYS_2_STACK.pdf

 

[W5lz]

A bazooka type antenna is basically a half wave doublet fed through a matching network. The straight-through center conductor is the doublet part, the shielding on it is the matching network. Sort of an odd shaped "Y" fed dipole. The 'spread' between the two outer contact points of the shield with the center conductor amounts to a static and variable impedance matching system (How z'at for an analogy!). It's 'static' cause it's fixed in place, and 'variable' because of the amount of impedance change with the change in frequency, which almost stays constant.
[Ever noticed that engineers (mechanical and electrical) always have gallons of aspirin around? It's 'cause of concepts like this.]
Is this -THE- way of thinking about this? Jeez, I hope not, but it works for me...

 

[radiostationx]

Hi all,
I updated my original blog page with additional construction details and photos as I made a 300mhz military airband version of the double bazooka coaxial dipole today for a friend.
Tested out on pro-2006 and sdr play RSP1A , Im happy with the results.

Home made coaxial dipole antenna for civil (and military) airband. – Mersey Radar

 

[cmdrwill]

Good work on the article.

 

[krokus]

Hi all,
I updated my original blog page with additional construction details and photos as I made a 300mhz military airband version of the double bazooka coaxial dipole today for a friend.
Tested out on pro-2006 and sdr play RSP1A , Im happy with the results.

Home made coaxial dipole antenna for civil (and military) airband. – Mersey Radar

That looks nice, but was curious if the center attachment area has the same amount stripped? (15 to 20 mm.)

 

[radiostationx]

That looks nice, but was curious if the center attachment area has the same amount stripped? (15 to 20 mm.)

Hi krokus,
Good Question.
Yes around 15mm of sheath and braid was stripped back for the centre connections but you cannot see the dielectric or solder joints on this one.

I threaded on the heat shrink (2pcs) first but slid them futher away from the box centre towards the ends and kept it out of the way while making solder joints in the middle. Then I slid back the heat shrinks back over the pigtails so that the 2 yellow sleeves met in the centre, then it was a hair drier job to shrink it all down .