VHF AM Airband Antenna

[majoco]

No need for a tuner - a tuner will make short aerials longer or long aerials shorter to represent the required impedance at your frequency of operation - you have or will cut the aerials to the right length so no problem. For reception it's an exact science +/- 25% anyway unless you're making something more sophisticated - a quarter wave length is fine for each leg. After all, the UHF TV antennas we have now cover from 550MHz to 800MHz without tuning. The coax choke balun should work fine too.

 

[rocky28965]

At present they are 575mm.

 

[rocky28965]

Right I got this thing mounted up on the sky dish mast.
Haven't given it a good test yet as its been too hot to get in the roof & run the cable to my man cave.
Just hooked up my Uniden UBC92XLT to the cable outside to make sure it worked.
Doesn't appear to much different to the Nagoya UT106UV, which is a bit disappointing.
Was hoping to pick up the ATIS from Queenstown Airport.
Can get approach & delivery frequencies no problem.
Would the number 8 wire not have been a good choice for the elements?

 

[majoco]

I think the Christchurch Control (although it may be on Mt. Mary) and approach transmitters are up on Coronet Peak, ground and ATIS are on the tower.

Copper wire would theoretically be better but the difference may be insignificant.

 

[rocky28965]

Thanks Martin.
Hopefully I can run the cable to my cave either later tonight or early tomorrow morning.
Then I can hook it up to a RTL-SDR on my computer & compare the signal strength.
We've been getting 25 - 30 degrees here for the last week, hate to think how hot it would be in the roof.

I made the antenna mainly from stuff I had on hand.
Just had to buy a couple of PVC tee sections.
If I had bought copper tube for the elements, then I would of needed to buy thicker PVC pipe to carry the extra weight.
As you say it may not have made much difference anyway.

I haven't discounted making a ground plane as plan B.
Been studying the design in mikestechblog

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

Looks simple enough but I'll have to buy all the bits.

 

[majoco]

I don't go up into the roof space in the summer! 26degs C outside today, the cold water tap was too hot to put my hand under until it ran through!

The trick to straightening the copper wire is to put one end in the vice, grab the other end with a pair of pliers or vice grips and jerk it hard a couple of times.

 

[K5MPH]

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.

I built one of these antennas years ago,worked pretty good but not that good really easy to make ......

 

[prcguy]

Oh my, ouch!

grab the other end with a pair of pliers or vice grips and jerk it hard a couple of times.

 

[ka3jjz]

I'm surprised no one has mentioned the off center fed dipole we have in our wiki. I understand that on many freqs, the takeoff angle is quite high, so it would be nearly ideal for commercial aircraft stuff, except (in theory) where the aircraft is directly overhead with respect to the antenna

Mike

 

[rocky28965]

I'm surprised no one has mentioned the off center fed dipole we have in our wiki. I understand that on many freqs, the takeoff angle is quite high, so it would be nearly ideal for commercial aircraft stuff, except (in theory) where the aircraft is directly overhead with respect to the antenna

Mike

Is this the one

https://wiki.radioreference.com/index.php/Homebrewed_Off-Center_Fed_Dipole

 

[popnokick]

That is the Off-Center Fed Dipole that is in the RR Wiki. It is naturally resonant on the civil aircraft band, and as a bonus works very well for the UHF milair band. Mine is in my attic and feeds three scanners through a 75 ohm splitter-amp coupler.... excellent performer for air bands.

 

[rocky28965]

Well I finally run the cable from the dipole through the roof to my man cave.
Also moved the Nagoya UT106UV to the highest point of the roof.
Very disappointed with the dipole, the $5 Nagoya is much better on airband.

 

[Ubbe]

Reception from airplanes are pretty much line of sight and doesn't need much of an antenna.
But how fun is it to listen to a one sided conversation? It is the towers you'll need to concentrate on and those are on the horizon so you will need an antenna with it's loob as close as possible to a horisontal position.

/Ubbe

 

[majoco]

Comparing the Nagoya on the roof peak to your dipole on the sky antenna is perhaps not a fair comparison. I'm still confident that a ground plane antenna right up on your roof peak would do better and if you could droop the radials down either side of the peak, they would be nearly invisible - make the centre element out of copper water pipe to broaden the bandwidth.

I have a commercial aircraft antenna that has an element 585mm long - it's designed for the old ELT's on 121.5MHz so your figures are close enough.

Have you ever received Queenstown ATIS? They are in a pretty deep valley too unless you live in Glenorchy!

 

[rocky28965]

I have improved the reception on the dipole a lot
Had a bad connection at a join in the cable.

My next project is a ground plane.
I intend to sit it on the back vent from the dunny.

 

[rocky28965]

Reception from airplanes are pretty much line of sight and doesn't need much of an antenna.
But how fun is it to listen to a one sided conversation? It is the towers you'll need to concentrate on and those are on the horizon so you will need an antenna with it's loob as close as possible to a horisontal position.

/Ubbe

I have a flight simulator here that I use periodically & quite often fly in to Queenstown & surrounding areas.
A bit of background chatter adds to the experience.

 

[majoco]

I intend to sit it on the back vent from the dunny.

Might need to run that through 'Google translate'!

Actually, when I did my first 'speed read' you said " I need to vent on the dunny "!

 

[rocky28965]

Might need to run that through 'Google translate'!

Actually, when I did my first 'speed read' you said " I need to vent on the dunny "!

Glad you got a chuckle out of it.

If I use the design here

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

it should fit neatly into the back vent which is pvc pipe & is about halfway up the roof.
Just have to remember to drill a few holes up the side of the mast to allow venting.
We don't want any explosions.
Should also be able to run the cable down the pipe & out through a hole into the roof space.

I guess I'll have to alter the lengths of the rods to suit airband?

 

[majoco]

The ground plane rods are the same length as the vertical. They should be bent down about 45degs for a guess - if you had a transmitter you cane 'tune' the radials up or down a bit to make the feedline look like 50ohms but just for reception it won't make any difference.

 

[majoco]

Unfortunately the approach charts only give the frequencies, not the actual location of the transmitters. The charts are too big to upload to here, you can download it yourself from here...


http://www.aip.net.nz/pdf/NZQN_43.1_43.2.pdf

I see the VOR/DME is no longer up on Coronet Peak, it's down by Lake Hayes which it rpobably why you can't get the ATIS. I think the ATIS at most places is lower powered than the Comms transmitters - I can barely hear the PMR ATIS but the tower is much better.