R

redwards

Member
I am installing a single SL-30 along with the ever-so-popular Commant bent whip. I have read all of the posts and see that most install this antenna under the seat where the ground plane is tremendous but signal may be somewhat blocked by the wings when on the ground. If I install the antenna behind the baggage bulkhead then the signal might not be as blocked but the ground plane will be smaller. Also the orientation will be less vertical because of the slope of that part of the airframe (RV7A.) Anybody know which would best for performance?
 
Don't be concerned about signal blockage....

on the ground. When you are on the ground, you are trying to reach the tower or someone reasonably close.
I've had lots of airplanes with the com ant mounted under the wing and have NEVER had a problem.
 
As you said, fuse bottom should perform better for air-to-ground communication, fuse top should perform better for ground-to-ground communication. I'd optimize for air-to-ground, being more critical, and needing to communicate over much longer distances (60 miles +) and therefore weaker received signals than ground-to-ground (max about a mile from ramp to tower).

But if you do choose the fuse top anyway, then here are a few other things to consider:

1) Mount the antenna far enough aft of the canopy so that it has adequate ground plane in all directions (about the length of the antenna).

2) Mount the antenna at least a few feet away from any GPS antenna, since harmonics from the comm transmission can interfere with GPS.

3) A bent whip antenna on the fuselage top makes a lovely bird's perch. You'll be cleaning up a lot of bird shi*. On the fuse top I'd use a straight whip.
 
Thanks Mel and Roe.

I think I will mount it on the bottom but was just wondering if further back under the baggage area might be better for signal than directly under the wing.
 
I agree with all of you. Ground to ground will never be over a long distance, at least if everything is okay. I have a question; where would you mount the second of two comm antennaes?
I have a GPS and XM antennae farm under the cowl with a third on the glare shield. There's a comm antennae under the passenger seat and a Nav antennae in the wing tip. I need a home for a second Comm and two GS antennaes. The data sheets all want the antennaes farther apart than the plane is long!
 
And no matter which antenna I use (i.e. swapping cables over) the SL40 works better than the GNS530W.

So I would not stress too much.
 
Underneath.

Randall, I have two on the bottom of my -10. between the main landing gears...one for the SL-30 and the other for the 430W and have never had a transmit problem in three years.

Best,
 
roee said:
1) Mount the antenna far enough aft of the canopy so that it has adequate ground plane in all directions (about the length of the antenna).....
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I may be in trouble. I mounted both of my comm antennas in the outboard bay under the rear seats. I definitely do not have an antenna's length to the outboard edge. I was trying to get the two as far apart from each other as possible. Do you see any potential issues with this?

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On my first RV-10 I had both comm antennae on the bottom and only twice had an issue. Both times it was when trying to talk with a location not colocated on the (non-towered) airport to get a departure clearance. Most times it worked but a couple times not. Never had an issue in the air.

Since the airport this happened at is my home field, I am putting one on top and one on bottom this time around.

Bob
 
bcondrey said:
On my first RV-10 I had both comm antennae on the bottom and only twice had an issue. Both times it was when trying to talk with a location not colocated on the (non-towered) airport to get a departure clearance. Most times it worked but a couple times not. Never had an issue in the air.

Since the airport this happened at is my home field, I am putting one on top and one on bottom this time around.

Bob
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You have bluetooth capability in your plane? Can always get your clearance over the phone while sitting at the hold short.
 
Sig600 said:
You have bluetooth capability in your plane? Can always get your clearance over the phone while sitting at the hold short.
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I had this problem a year ago at Destin, FL. The north end of the runway butts against the water with the airport practically on the beach. In order to take off you must get clearance from Eglin Airforce Base traffic controllers. While sitting on the ground with my comm antenna mounted on the belly and surrounded by 50+ foot pine trees at sea level I could not hear ATC calls from Eglin, which was a mile or so away from the Destin airport. I had to get clearance via cell phone. Once I took off and got about 20-30 ft off the ground Eglin ATC came in loud and clear.
 
I bolted my bent wip Comant antenna just forward of the spar, under the pilot's left knee. It works fine on the ground and I have had air to air conversations of well over 100 miles.

By placing it just foward of the spar, you don't have to run the cable through the spar, taking up valuable space.

In my case, the antenna's aft two bolts go through the forward spar flange and the front two bolts are attached to a doubler plate.
 
I don't disagree that it can be done with a cell phone. Just making the point that there are times when radio comm won't work if the antenna is on the bottom of the plane. Up to each individual how they want to deal with it.

Bob

Sig600 said:
You have bluetooth capability in your plane? Can always get your clearance over the phone while sitting at the hold short.
Click to expand...
 
civengpe said:
I may be in trouble. I mounted both of my comm antennas in the outboard bay under the rear seats. I definitely do not have an antenna's length to the outboard edge. I was trying to get the two as far apart from each other as possible. Do you see any potential issues with this?
Click to expand...

Well, it's definitely not ideal. But how much it'll hurt your antenna performance is hard to say without actually testing it.

Since you've already mounted your antenna there, I'd stick with it for now, test it, see if you get adequate range, and go from there. It might still be good enough, or it might not.

But for anyone who hasn't done it yet, I wouldn't suggest locating the antennas so close to the edge.

And another potential issue at that particular location is that the flaps when lowered will be in close proximity to the antenna (pretty much running parallel to it, just a few inches away), also interfering with its desired radiation pattern.

civengpe said:
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Thanks Roee. I wish I had known that a few weeks ago.

I wish there was an "idiots guide to comms" book out there somewhere. :confused:
 
I helped wire up a friend's RV-10 and we put two bent whips under the belly, on each side, right under the rear seats, and put the transponder antenna under the battery behind the rear baggage bulkhead and they all work great in those locations.
 
RVbySDI said:
I had this problem a year ago at Destin, FL. The north end of the runway butts against the water with the airport practically on the beach. In order to take off you must get clearance from Eglin Airforce Base traffic controllers. While sitting on the ground with my comm antenna mounted on the belly and surrounded by 50+ foot pine trees at sea level I could not hear ATC calls from Eglin, which was a mile or so away from the Destin airport. I had to get clearance via cell phone. Once I took off and got about 20-30 ft off the ground Eglin ATC came in loud and clear.
Click to expand...

Used to fly for hire out of Destin, know it well. That's not a new problem!
 
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