VHF AM Airband Antenna

[rocky28965]

I created a very temporary dipole antenna tuned to air band, similar to one in the link below.

https://dropsafe.crypticide.com/alecm/tech/radio/ar8k-dipole.html

Mounted on the sky dish pole it worked surprisingly well considering I live in an area surrounded by mountains.
Well, better than the std rubber ducky on my Uniden UBC92XLT anyway.
So now I want to get something more permenant to do the job.
I have three lines of thought & would appreciate your opinions on them.

1/ Build a better version of the above.

2/ Build or buy a 1/4 wave Ground Plane similar to the one below

https://www.amazon.com/Centerfire-Airband-Station-Scanner-Antenna/dp/B008H5RYP4

3/ Buy a airband tuned wip antenna.

https://www.ebay.com/itm/New-Nagoya...e=STRK:MEBIDX:IT&_trksid=p2055119.m1438.l2649

 

[popnokick]

Among the options you listed the ground plane is going to give you the best results, but only if mounted outdoors on the "sky dish pole" where you had your previous antenna (dipole?). If you are using a dipole mount it vertically (not horizontally parallel to the ground) as aircraft communications are vertically polarized.

 

[majoco]

What popnokick said +1.

Even the 'tuned whip' would work better with a ground plane so there's not a lot to gain over making a 1/4wave ground plane antenna. If you get a look at some control towers they have the exact same antenna up there so if they work well enough for them....

 

[rocky28965]

Thank you for that advice.
I think I'll go with the dipole & mounted vertically as you suggest.
Would prefer to get a ground plane but I don't think my wife would like the look of it displayed on the roof.
You didn't mention the vertical wip, so I assume the dipole would be better.
Of the three, the wip would have been the easiest on the eye.

 

[rocky28965]

What popnokick said +1.

Even the 'tuned whip' would work better with a ground plane so there's not a lot to gain over making a 1/4wave ground plane antenna. If you get a look at some control towers they have the exact same antenna up there so if they work well enough for them....

Thanks, so you are suggesting the dipole?

 

[cmdrwill]

There is a simple groundplane you can build with a female chassis mount coax connector and some 14 gauge solid wire.

Maybe some can link to it.

 

[rocky28965]

There is a simple groundplane you can build with a female chassis mount coax connector and some 14 gauge solid wire.

Maybe some can link to it.

Do you mean this one.

Build a 2 Meter Vertical Antenna | Mike's Tech Blog

 

[ko6jw_2]

Consider a discone. No gain, but flat frequency response. The aircraft band is 18 Mhz wide. Neither the ground plane nor the dipole have that kind of bandwidth. Also, the discone will cover military aircraft if you're interested in that.

 

[majoco]

What he calls a 2m vertical antenna is a ground plane antenna - one vertical rod in the centre and four radials drooping down - the radials are the 'ground plane'. You can neatly mount them on a piece of PVC pipe with the cable running down inside - not too long though as it has to support it's own weight unless you tape it to something more supporting like a length of fence wire.

Dipoles are tricky to mount vertically as you should take the cable away from the centre at right angles to the vertical for a half-wavelength or so. I use a folded dipole cut down from an old TV antenna that has a matching balun inside the connection box - works well.

"Tuned whips" still require something as a ground plane - they are usually mounted in the centre of a vehicle roof or similar. The pic of the tuned whip does not show or mention the need for a ground plane for best performance.

If your wife would be unhappy with the ground plane, she would be really grumpy with a discone..... :wink:

 

[rocky28965]

Yeah, I'm thinking it will have to be a very tidy dipole or a wip.
I already have a small Nagoya UT-106UV dual band mag mount attached to the metal house roof.
I assume it uses the roof as a ground plane.
I was surprised just how well it goes for a cheap antenna, even reasonable down to airband.
I also have a spare mag mount & thought I'd hunt round for a airband length of spring wire.
Fit that to the mount & see if it pulls in more than the other one.
If that's a fizzer I'll start on the dipole.
I'm thinking along the lines of the link below.

2 Meter Vertical Dipole Antenna by Jim Feldman - W6JMF

But I would use a smaller profile.

 

[paulears]

The dipole is such a simple animal, that if you make one that works, it's very unlikely to be improved on performance wise, but the others ready built ones - but they may be more waterproof and longer lasting. Dipoles, J poles, all that stuff - just the same recipe, with minor flavour tweaks.

 

[kayn1n32008]

Neither the ground plane nor the dipole have that kind of bandwidth.

This is absolutely false. A 1/4 wave antenna certainly does have the bandwidth.

I use a 1/4 or a 1/2 wave at work, and I operate on frequencies that can fall anywhere between 148.000MHz and 174MHz. Both a 1/4 and 1/2 waves give better than 2:1 VSWR. I even use the same antennas all the way down to 144.4Mhz with out issue.

As for dipoles, Sinclair has folded dipoles that cover 137MHz to 174MHz and 430MHz to 470MHZat less than 1.5:1VSWR. While it is not designed to be resonant on UHF, it is resonant on UHF, but pattern is likely not ideal.

I would imagine a Sinclair folded dipole for 108-137 would probably be resonant across most of the UHF military air band as well.



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[prcguy]

Commercial ground plane antennas marketed for VHF air band use a very fat vertical radiator upwards of 1.5" dia or more. These will have a great match across 118-136Mhz. A typical ground plane with an 1/8" or less dia radiator will not have adequate BW to cover the entire band unless you consider a 3:1 or worse match ok.
prcguy

This is absolutely false. A 1/4 wave antenna certainly does have the bandwidth.

I use a 1/4 or a 1/2 wave at work, and I operate on frequencies that can fall anywhere between 148.000MHz and 174MHz. Both a 1/4 and 1/2 waves give better than 2:1 VSWR. I even use the same antennas all the way down to 144.4Mhz with out issue.

As for dipoles, Sinclair has folded dipoles that cover 137MHz to 174MHz and 430MHz to 470MHZat less than 1.5:1VSWR. While it is not designed to be resonant on UHF, it is resonant on UHF, but pattern is likely not ideal.

I would imagine a Sinclair folded dipole for 108-137 would probably be resonant across most of the UHF military air band as well.



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[rocky28965]

Had a look at the Sinclair Antennas.
Very nice but well above my price range.
I'm just a retired enthusiast.

 

[prcguy]

I have a bunch of commercial airport antennas like Sinclair I would part with but I don't want to ship them.
prcguy

Had a look at the Sinclair Antennas.
Very nice but well above my price range.
I'm just a retired enthusiast.

 

[rocky28965]

The chances of you being in Central Otago, New Zealand would be very slim.

 

[KR7CQ]

I made a dipole out of 3/8" copper pipe years back....just for this band....worked very well, was cheap and easy to make. Discone for the more serious though...

 

[prcguy]

Not this week.
prcguy

The chances of you being in Central Otago, New Zealand would be very slim.

 

[majoco]

I afraid you're too late to raid the old Mount Cook Airline office at Twizel airport. They were starting to demolish the building when I went down there from Christchurch to remove all the radio gear - the discone now graces my rooftop!

I don't know where they dumped the scrap after the Mount Cook village airport control tower burnt down - there was some nice stuff in there.

 

[rocky28965]

Right, some technical info required.
I've made up the vertical dipole but haven't cut the elements to correct length yet.
From the Dipole Length Calculator

West Mountain Radio - Antenna Calculator

I get 22.3'' or 566.42mm per element for 126MHz which is the airband halfway point.
We are 116 MHz - 136 MHz in this part of the world.

Should I cut to that length if I have 6 turns of cable round the boom for a choke balun.
I don't have access to a antenna tuner.