VHF Antenna

23 posts in this topic

Posted

What do you guys suggest for a VHF antenna and where on the plane do they work the best?

Thanks,

Ron

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Posted

Couple of recent threads on this topic. Mine is behind the turtledeck.

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Posted (edited)

If you didn't put the mounting plate in before covering, then you could have a problem getting it in now behind t'deck.  It attaches to crosstubes.  But, I guess it could be done from under the tubes by using some angles.  It doesn't have to be in the exact center of the fuselage if that makes it easier.

I had one mounted on a part-aluminum turtledeck - it has to be grounded good.   But it is a PIA when you want to remove t'deck.  I have the mounting plate for this plane.

For best transmission, you should have a ground plane under it with a radius of about 1/2 the length of the antennae - copper or aluminum foil glued under fabric and grounded to antennae is good enough.

EdMO

Edited by Ed In Missouri

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Posted

Best theoretical place to put the antenna is on the bottom of the plane centered on an adequate ground plane. I never did that myself. Always put on top.

 

The builder of my Magnum put a nearly vertical fiberglass dipole antenna in the tail. Didn't work worth a shit because the ungrounded dipole coupled to the nearby tubing in the tail and created all kinds of blind spots. The ungrounded dipole is a GREAT idea, but only works on composite or wood airplanes.

 

Anyone know someone building a composite or wood plane? I have a great dipole antenna for sale cheap! :-)

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Posted

Hard to have an antennae on the belly when you haul Kayaks there!

EdMo

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Posted

Ed

As long as they are not metallic it would work fine... :hammerhead:

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Posted

Wow...I didn't realize it was that complex. My other plane had a fiberglass whip mounted on the bottom and on an aluminum panel, but nothing fancy...it always worked good.

I don't want it hanging from the bottom. So I'm sure I can make some kind of mount on the top side of the empennage.

Ok...the ground plane? Am I reading right that it is foil like?

I read one of your post Joey where you said it was gold looking and was just glued to the fabric?

Can anyone give me their brand and type of antenna?

I see a lot on ebay. Any reason I shouldn't buy a used one?

Thanks,

Ron

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Posted (edited)

Mine looks like a Commant faired vertical slanted back - Can't say which is best.

Used is the way I go, if the seller has any kind of guarantee or return policy.  Prices are a lot cheaper than new.

Foil (gold?) or whatever, is easy to just glue on under fabric and ground to antennae - Even an X is better than nothing.

 If you use anything stiff under the antenna then you should put a fabric patch on it, but a thin rubber cushion under/over fabric might help.  You still have to ground your antennae.

Your plane is painted, so you want to make the mount as small as you can.

EDMO

Edited by Ed In Missouri

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Posted

I just bought an antenna from ACS for the mangy. I'll mount it to the plate welded in behind the turtle deck, where my yellow plane has one mounted which works fine. It's a fiberglass whip whip cost around $160.

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Posted

What a great idea to put it inside the fuselage and out of the airstream!  The fabric is transparent to radio signals.  Can't do this on a metal bird.   A metal ground plane is a great idea too.  Checked the correct 1/4-wavelength at 108 mHz at about 70 cm.  Supposedly the optimum for simple dipole antenna.  Drag is fuel flow.  Hopefully aluminized dope isn't opaque!

 

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Posted (edited)

Turbo,

Thanks for bringing this post back up because I ended up buying an antenna from Dale here on the forum and it works great!!!  Here is how I mounted it, but to do it correctly you would want it to run length wise instead of across/perpendicular. I riveted it to the back of the canvas bulkhead...out of sight and no drag...it works great even though I rotated it 90 degrees.

http://www.avidfoxflyers.com/index.php?/topic/3484-antenna-suggestions-vhf-kitfox-model-iii/#comment-26999

 

45233F47-25C9-4AFE-86BC-E7C05EC1615C.jpeg

A8162282-BD3F-4C3D-985E-A5E0115CA114.jpeg

Edited by RDavidson

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Posted

Best theoretical place to put the antenna is on the bottom of the plane centered on an adequate ground plane. I never did that myself. Always put on top.

The builder of my Magnum put a nearly vertical fiberglass dipole antenna in the tail. Didn't work worth a shit because the ungrounded dipole coupled to the nearby tubing in the tail and created all kinds of blind spots. The ungrounded dipole is a GREAT idea, but only works on composite or wood airplanes.

Hi Chris,

I'm using an un-grounded dipole antenna, placed on top just behind the turtle deck, and my biggest problem is that I feel like picking up communications from half of France when flying...  Can you explain the coupling issue you mention? The blind spots you are talking about are those for transmission mainly? 

This is the kind I have, no ground plane required - but maybe we are not talking about the same kind of antennas...antenne-sirio-vhf-aviation-bnc.thumb.jpg

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Posted

Hi Fred,

That is a quarter wave vertical with a counterpoise, not a dipole. That antenna should work (almost) as well as a vertical with a good ground plane. With that antenna the aircraft structure will only help, not hurt performance. That looks like a nice (and expensive) antenna!

Chris

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Posted (edited)

Here is the antenna the builder of my Magnum built into the tail of the plane before he covered it. It  was oriented nearly vertically sloping slightly backward and would have worked incredibly well in a wood or composite airplane. It is a straight dipole. A wonderful and very efficient antenna. But placing in the tail surrounded by all kinds of metal tubing did not work at all well. I have since removed it as part of the Magnum rebuild.

It is my opinion that the part of the ad that says works well in tube and fabric construction is complete BS unless it is installed and measurements taken prior to committing to the install location. there might be some place you could mount it in a metal tube aircraft and it might work OK, but I do not see how it could ever work real well with conductive materials running close and in parallel with the elements. It did not in mine.

It's for sale cheap if anyone knows someone building a wooden or glass airplane!

Capture.JPG

Edited by Chris Bolkan

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Posted

In all fairness it says it will mount in a fiberglass or plastic wing tip in metal planes.  The builder putting it in the rudder is kind of goofy unless they have updated the instructions due to this very thing.

 

:BC:

 

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Posted

Did I say rudder? Meant vertical stab. Same difference tho. Didn’t work worth a crap as would be expected. 

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Posted

Hi Fred,

That is a quarter wave vertical with a counterpoise, not a dipole. That antenna should work (almost) as well as a vertical with a good ground plane. With that antenna the aircraft structure will only help, not hurt performance. That looks like a nice (and expensive) antenna!

Chris

Thanks Chris!

Yes, they charge full price like for anything that goes on an airplane... I payed ~50USD but if you shop around you can even get it for 65...

But it works well and is very easy to install. Appears solid.

Fred

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Posted

I got one from Dale also. I zip tied it to the fuselage tubing length wise right behind the seat.  Live in Fallon NV. When I'm in the pattern, have listened to people in the pattern as far west as Truckee CA, and north to Winnemmuca NV. Very happy with the setup and performance.

Rick

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Posted

I can't imagine the vertical with counterpoise like Fred has or the dipole the builder installed inside the tail of my plane working at all well zip-tied to metal tubing, but if it works in your situation that's fantastic. You must have hit a sweet spot with the mounting. 

I have flow to Fallon twice from my home in Washington. Once to pick up a 172 a friend was going to learn to fly in and once to return it when he was done with it. They were fun flights and I liked the area.

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Posted

Please excuse a probably stupid question - but I just dont know... 

Is there any relation between reception and transmission? Meaning, if I my reception is good does that automatically mean that my transmission capability is good as well - through the same antenna? Obvious caveat for poor mic etc... 

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Posted

Fred, Broadly generalized, that's true.

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Posted (edited)

I've had some radios - not totally aircraft, but near the same frequencies - that received good, but unless the Standing Wave Ratio was matched between the transmitter and antennae the transmissions were not as good.  We used an SWR meter to get a reading as low as possible for better transmitting.  Sometimes had to cut coax to different lengths to do that.   This made more difference with the lower powered radios than those with more transmitting power.  I've been away from radio studies for too many years now, so you need to talk to a technician if you want to know more about that.   EDMO

Edited by EDMO

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Posted

I used the coax that was matched to the antenna by Dale.It was about 10 feet long. Had to wrap it around and up and down, so I didn't have to cut it. Didn't think about talking to the other acft. Figured, if I could hear them, they would hear me. Will try and talk to them next time.

RFPhtmFxr

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