Best antenna for Airband

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Jun 2, 2024
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I need to improve the airband reception (123.5 MHz) using an external antenna. So, which type of antenna can be used?

Can Yagi antenna or loop antenna can be used?

Do I have to put the antenna outside or can also be used indoors?
 

dave3825

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Can Yagi antenna or loop antenna can be used?
Yagi are directional and will not provide good consistent 360 degree coverage. I don't know much about loops but do know the magnetic (YouLoop) will go up to 300 mhz but,

Notes​

It is very likely your third party radio will not be sensitive enough to operate with the YouLoop properly. We have even seen self-documented failed attempts to build pre-amplifiers to compensate for the lack of sensitivity and/or the required dynamic range in third party radios. Use your brain, and eventually an Airspy HF+ Discovery.

Compatibility​



Do I have to put the antenna outside or can also be used indoors?

Generally, an antenna mounted outside high up will yield the best results.
 

kg4ehv

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I use this with an SDR and am very happy with it.

 

vocoder

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I use the dpd productions Air Omni and OmniX antennas. They are both cut (great gain) for and work great on the aero bands. They are by far the best antennas I have used for aero. They are built really well and work great on other bands too! Very easy to set up.

73
 

prcguy

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Find a surplus airport antenna, could be from DB Products, Antenna Products, RAMI, TACO or a dozen other companies that make them. I had a garage full at one time but only kept a few for personal use. Prices were in the $20-$35 range after passing through a few hands to me. Just last week I got a nice broad band 118-136MHz air band ground plane by Sirio for $25 off eBay. Commercial VHF air antennas are all over the place and can be very cheap.
 

TAC4

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Another vote for the Omni-X antenna. I have one in my attic
and there are outstanding for the air band. I have the MIL
band one. What ever you choose, use high guality coax and keep the run short as possible.
 

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I use this with an SDR and am very happy with it.

This seems like a dipole antenna but why should I buy it because it can be built at home.
 

chief21

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I need to improve the airband reception (123.5 MHz) using an external antenna. So, which type of antenna can be used?
Arrow Antennas (arrowantennas.com) used to offer their GP-126 air band ground plane antenna. These are the antennas you might see at many airports. They are fairly small, very well made (solid elements) at a reasonable cost. You may wish to see if it is still available: info@arrowantennas.com or give them a call at (307) 222-4712. They might even do a custom frequency for you.
 
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Ubbe

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For 125MHz a 1/4 wave are 60 centimeters. Connect one 60cm electrical wire to the center lead and another 60cm to the coax braid and hang it vertically with the 60cm wires going in opposite directions.

When I measure the impedance of a 1/4 wave it has 50 Ohm at its cut frequency and 10MHz lower in frequency (115MHz) in drops in impedance down to 35 Ohm. Going up in frequency it also drops and at 10MHz higher (135MHz) it is down to 20 Ohm.

Using a 300:75 balun will work as a 4:1 step down transformer. Receiving 1uV from the antenna will leave 0,25uV into the coax, a 75% loss. Having a 300 Ohm balun connected to an antenna that goes between 20 Ohm and 50 Ohm will give even more loss.

If you instead use a 1:1 or 1:2 balun you get a better match between antenna and coax. Minicircuits have baluns but require you to solder but they can send you one sample for free if you ask to have one for evaluating antenna concepts.

Using a balun will use the signal from both elements of a dipole and doubles the signal level. Connecting directly to a coax without balun will make one element working as a counterpoise and reduce the signal to half.

Off center feed dipoles are only for receiving two different frequency bands by compromising both bands, not needed when only receiving VHF air.

/Ubbe
 
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For 125MHz a 1/4 wave are 60 centimeters. Connect one 60cm electrical wire to the center lead and another 60cm to the coax braid and hang it vertically with the 60cm wires going in opposite directions.

When I measure the impedance of a 1/4 wave it has 50 Ohm at its cut frequency and 10MHz lower in frequency (115MHz) in drops in impedance down to 35 Ohm. Going up in frequency it also drops and at 10MHz higher (135MHz) it is down to 20 Ohm.

Using a 300:75 balun will work as a 4:1 step down transformer. Receiving 1uV from the antenna will leave 0,25uV into the coax, a 75% loss. Having a 300 Ohm balun connected to an antenna that goes between 20 Ohm and 50 Ohm will give even more loss.

If you instead use a 1:1 or 1:2 balun you get a better match between antenna and coax. Minicircuits have baluns but require you to solder but they can send you one sample for free if you ask to have one for evaluating antenna concepts.

Using a balun will use the signal from both elements of a dipole and doubles the signal level. Connecting directly to a coax without balun will make one element working as a counterpoise and reduce the signal to half.

Off center feed dipoles are only for receiving two different frequency bands by compromising both bands, not needed when only receiving VHF air.

/Ubbe
As per my calculations, it should be 120cm (each side) dipole antenna.
 
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A dipole are a 1/2 wave antenna, so that 120cm are the total length including both elements.

/Ubbe
Yes, I am sorry. I did the math incorrectly. It's 468/125 = 3.74 / 2 = 1.8 * 30 = 56.16 cm or 60cm.

I have one question---if a dipole antenna needs to be placed vertically (one arm pointing to the ground and the other arm to the sky), then why the indoor dipole TV antennas have the two rabbit antennas are always pointing only up?

Can you tell me how the loop antenna for the UHF is connected with this indoor antenna in the picture below?

 

prcguy

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Yes, I am sorry. I did the math incorrectly. It's 468/125 = 3.74 / 2 = 1.8 * 30 = 56.16 cm or 60cm.

I have one question---if a dipole antenna needs to be placed vertically (one arm pointing to the ground and the other arm to the sky), then why the indoor dipole TV antennas have the two rabbit antennas are always pointing only up?

Can you tell me how the loop antenna for the UHF is connected with this indoor antenna in the picture below?

Early TV transmitters used horizontal polarized antennas then eventually circular pol, so rabbit ear antennas were originally horizontal. You moved them all around to get the best reception and sometimes it was best mostly horizontal and sometimes vertical depending on signal reflections on the way to your house.
 

KD9KSO

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Within an old RadioShack publication on antennas are directions for constructing a 1/4 wave ground plane that works incredibly well. It can be made to any center frequency for VHF/UHF. This antenna can likely be found on the internet. The publication has been out of print for quite some time now.

It is made from an SO239 panel mount jack and measured lengths of 14 or 12 ga copper wire. If necessary, it can be made of coat hanger wire.

This can be hung in an attic, or mast mounted.

I'm still using one that I made 20 years ago. It is cut for the civil aviation band, but it still receives very well on both sides of it.
 
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