Many thanks to SWLing Post contributor, Ron, who writes:
If you like monitoring the VHF airband then this antenna might interest you.It is a half-wave dipole cut for the middle of the band. (Recall that half wave vertical dipoles do not need ground radials.)
It is very well built and pretty rugged but is not meant for outdoor use.
How well does it perform? That depends on several things…how far you are from your airport? What is the “lay of the land” where you live? Etc.
Does it work better than the supplied telescoping antenna that came with your scanner?
Yes indeed.
And you will also notice an improvement in comms from aircraft in flight, too.
I had hoped to hear the ATIS and VOR from my local airport but they are too far away (20 miles).
In addition, the eBay seller (and builder) is also very pleasant to deal with.
Maybe there is a choke INSIDE the PVC?
regarding positioning – If a continuous transmission such as an ATIS can be picked up, move the antenna about to try to optimize the strength/clarity of this.
Keep it away from switch-mode power supplies, IT equipment and so on (which can generate noise), and avoid the antenna being too near metallic objects, which will detune it.
Installing in an attic (if available) will likely give best results (considering its not suitable for outdoor install).
if there’s a choke it should be some ferrite one, but given the price and the size of the pipe, I strongly wonder it, that said, put it in the clear, stop; that’s the way to allow it to work properly, but BEFORE that, add a choke… or better, instead of buying that one, build one yourself 🙂
Looking at the (few) details shown on the eBay page and at the pic, it seems to be a so called “flowerpot” antenna
https://vk2zoi.com/articles/half-wave-flower-pot/
but lacking the bottom “choke”, that’s a bad thing since, not only it will detune the antenna, but w/o the choke the antenna will become unbalanced and this in turn will cause common mode currents to flow along the coax feeded and increase the noise picked up by the antenna, my suggestion is to wind the piece of coax dangling from the bottom of that antenna around a piece of PVC pipe (not around the one enclosing the antenna) and, from there, run a length of coax (RG-6 will do fine) all the way to the receiver, plus place the antenna outside and as “in the clear” as possible
Notice that the “flowerpot” at the link above is calculated for the 2m band (yes, it can be used for TX too) but willing to recalculate the antenna for a different band one may just use this online calculator
https://nomonsuhendar.blogspot.com/2020/12/flower-pot-antenna-calculator.html
and then build the antenna for whatever band of interest, being a vertical dipole (the true feedpoint is in the middle, where the single wire and the coax portion meet, the choke “stops” the remainder of the coax from being part of the antenna) it’s omnidirectional and it works best if placed outside and at about 0.6 lambda (or more) from ground (plane, be it real ground, a terrace floor, a roof…) that is, for the AirBand at an height of at least 1.5m (about 5ft)
Hope that the above will be of some help
Here is more info on the “flowerpot” vertical:
https://forums.radioreference.com/threads/half-wave-coaxial-flowerpot-vertical.261761/