Airborne antenna

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Crash one
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Airborne antenna

Post by Crash one » 31 May 2017, 22:24

As a newbie here I'm looking for some advice, so please excuse any dumb questions.
I'm using a handheld Yaesu FTA 550 in a wood and fabric aircraft. Transmission distance is about 5 miles, any longer than that I'm getting "station calling xxx say again" or no reply at all. The rubber duck thing is slightly better.
I believe the problem might be the aerial. The coax was replaced with probably a length of TV stuff. The ground plane is four lengths of bare braid about two feet long pinned under the roof.
I have found via Google drawings/description of an "inverted 120 degree V dipole". Which I would like to build. This would fit inside the aircraft rather than the whip on top.
The builder of this claims 30 mile TX/RX. Using 2.5mm coat hanger wire for the antenna, 23.5 inches long and decent RG 58 coax. With a BNC connector at the antenna end and a "Pawsey stub" balun? to compensate apparently for the BNC connector.
Question: if I solder the connections at the antenna is the Pawsey stub required?
If I use 6 mm steel tube rather than solid wire would that be better?
I don't have an SWR meter but looking on eBay I see some with 100--560 MHz, would that do for 118--136 airband?
My knowledge of this subject amounts to being able to press the transmit button and little else, apart from reading stuff that I don't understand.

oh5nxo
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Re: Airborne antenna

Post by oh5nxo » 01 Jun 2017, 15:36

This one? Did you notice the revised 2014 version. chrusion.com/public_files/InvVeeAntenna4ULs_rev3.pdf

Pawsey (or any other balun widget) was there to prevent the coax becoming part of the antenna. I think Dean is confused about the sensitivity of Pawsey stub to nearby objects, surely if something is so close to the balun that it "destabilizes" it, inches, it'll also affect the antenna badly. There should not be unexpected loose objects inside the fuselage anyway :)

You can omit the balun altogether, Pawsey stub and the revised ferrite ring thing. It will still work. Not quite as intended, but I suspect you'll be happy with the result.

Use copper or aluminium for the wires, avoid magnetic metals if you can.

Juha

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Metradio
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Re: Airborne antenna

Post by Metradio » 01 Jun 2017, 16:04

Quite honestly you would do better using the aerial that came with the radio..

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paulears
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Re: Airborne antenna

Post by paulears » 01 Jun 2017, 18:37

I was going to say the same things - one of the simplest and effective antennas is a half wave dipole - matches fine to coax cable without the faffing around with ferrite beads on the cable - I've never had issues with using these.

What worries me is your lack of range. With the rubber duck antenna, I'd expect far more than 5 miles. They cannot hear you, but what are they like? If they too are weak, just breaking the squelch, then you have possibly a faulty antenna socket on the radio, because my Icoms can hear Norwich sitting on my window sill at ground level in Lowestoft, 25 miles away, and I can hear aircraft out to sea, easily 50 miles away at their airways altitude. Line of sight means that if you can see it, you can work it, so 5 miles is peanuts. The VSWR meter would be fine if it covers 100-500MHz, but you might just discover there's little coming out of the radio. I don't know your Yaesu, but there's not a very low power setting that it's stuck on is there?

If you can hear the station telling you they cannot hear you really strongly, then sounds like a low power issue, but if they too are weak, then it could be an antenna socket issue on the radio if the rubber duck is about the same as the aircraft existing antenna. For certain that one you describe won't be much better if at all than the rubber duck or any other antenna with a ¼ wave driving element. Do you have a friend with one you can borrow to swap temporarily with your Yaesu? on it's rubber duck antenna.

Crash one
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Re: Airborne antenna

Post by Crash one » 02 Jun 2017, 00:35

I can hear Edinburgh traffic from my living room about 35 miles north of Edinburgh clearly, no problems also any amount of aircraft within that area, probably further. Line of sight prevents hearing Edinburgh approach, I can certainly hear them or Scottish info from 1500ft over Crail about 35miles. It's just the TX part that seems short.
There is no power setting that is adjustable. The Yaesu handheld has about 5/5.5 watts, batteries fully charged. I know several people using these handhelds with no problems using the roof mounted whip which convinces me that I have an aerial problem. The radio is fairly new, last year, so unless I've busted it trying with a seriously defunct aerial there shouldn't be a problem?
I'll build this dipole half wave using copper tube, soldered joints, no Pawsey stub nor ferrite beads. BNC plug to the radio. Would that be safe or will I fry something? I have a feeling the coax from the original whip is not compatible, in my ignorance I used some that I had lying around, I think from an old sky tv dish.

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Re: Airborne antenna

Post by oh5nxo » 02 Jun 2017, 06:47

If you decide to make the dipole, consider safety: Romex wire, two pieces, each double length, folded into a loong teardrop or tadpole shape. Then it won't puncture anything. If Romex is what you call the common soft single-strand copper in electrical wiring.
Or garden hose, tip to tip length & 2 strips of copper tape for the legs, whatever suits your situation.

Juha

I've often wondered, how does VHF behave in the busy parts of the world. Here, there's an aeroplane or two or none within 50 miles at any moment. Looking at those plane plotter sites, you have a virtual metallic roof of large planes. Another thread.

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Re: Airborne antenna

Post by LeakyFeeder » 02 Jun 2017, 12:23

On my either my vxa150 or A6E i can easily do 100 miles aircraft to aircraft..
Summat aint right with ur setup there

paulears
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Re: Airborne antenna

Post by paulears » 02 Jun 2017, 18:58

The fact the rubber duck performs similarly to the existing antenna is what concerns me - I can understand that the aircraft mounted antenna could be the proverbial damp bit of string, but then there should be a big difference between it and the rubber duck. (By the way, 75Ohm satellite feeder does make a small difference, but not a huge one. I think I'd try to borrow a power meter or VSWR meter to show something really does come out!

Seriously though, if your receive capability is normal, as it sounds, then there could well be a TX fault, and you need to know if you are really transmitting before you go too much further. If you fly from a busy site, do some ground tests and see if it's weak over more controllable distances.

oh5nxo
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Re: Airborne antenna

Post by oh5nxo » 03 Jun 2017, 12:35

Did the set get hot when talking?
Radio clubs nearby? Visit one and ask for assist with power meter (output and input too if you have a DC lead) & frequency counter.

Juha

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