whaledriver
I'm New Here
I am ready to put my antennas on my RV7A fuselage, I am thinking under the gear weldments. Any thoughts on this or should they go behind the carry thru spar. Thanks George CNO
Van's Air Force
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antenna placement
- Thread starter whaledriver
- Start date
az_gila
Well Known Member
Spacing....
For comm radios, 2 ft spacing (just over 1/4 wavelength) is a good minimum spacing from other antennae and metal parts - such as gear legs.
I presume you are taking about the VHF comm radio antennae....
For comm radios, 2 ft spacing (just over 1/4 wavelength) is a good minimum spacing from other antennae and metal parts - such as gear legs.
I presume you are taking about the VHF comm radio antennae....
w1curtis
Well Known Member
I noticed a lot of RV builders placing BOTH comm antennas on the belly. This is fine if you are operating primarily out of non-towered fields and don't need to use ground comm frequencies. Even with my current high wing top mounted comm antennas, I sometimes have poor transmission/reception to ground frequencies.
Consider following the certified manufacturers and placing 1 of the comm antenna (comm 2) on top of the fuselage. This would be used for ground, clearance and unicom while on the ground. Also consider worst case you land hard at an some out-of-the-way unprepared field and rip out both belly antennas. You now have no comms to call for help. Hope there is a cell antenna in range. I know it does not look as nice having one out in the wind on top, but.. something to consider.
http://nerv10.com/wcurtis/90Electrical/antenna.html
Consider following the certified manufacturers and placing 1 of the comm antenna (comm 2) on top of the fuselage. This would be used for ground, clearance and unicom while on the ground. Also consider worst case you land hard at an some out-of-the-way unprepared field and rip out both belly antennas. You now have no comms to call for help. Hope there is a cell antenna in range. I know it does not look as nice having one out in the wind on top, but.. something to consider.
http://nerv10.com/wcurtis/90Electrical/antenna.html
gmcjetpilot
Well Known Member
Compromise
Check the Archives, there are several threads.
Gil is right about distance but its hard to get separation if you put all your antennas on the belly fwd of the spar, unless you do as w1curtis shows, one up and one down. Having an antenna on top is nice for ground ops, the top being better. However you are not a major airport, Denver, LAX, Chicago or Atlanta, talking to ground is usually not an issue with a bottom antenna.
I can't get too excited about antenna separation for a few reasons. Txpdr and Com are way different freqs, 125 Mhz verse 1 Ghz (approx).
Two Com's? If you have two Com's you have a receiver bypass between the radios, that shuts down the receiver of the other Com when transmitting.
There is an actual affect of another whip being nearby. IT WILL affect the signal pattern and so will the prop, gear, fuselage, wings....etc affect the signal pattern (both tx or rx). How much? Not that you will likely notice. You can't have two Coms 6" apart, but you can violate the 2 foot rule (about the length of the antenna). I must say always follow the manufactures installation. So my advice is in contradiction to that, use at your own risk. I'm saying I have never read where some one said, "Gee my antennas are two close together".
Bottom line having two Com's or com & Txpdr closer than what Gil or the installation manual suggest has not caused a problem, from what I have read. It's not ideal and you should try for decent separation (aka as much as you practically can get while factoring in other installations issues). NOTHING is perfect. The mounting of any antenna is a compromise.
I would put it just infront of the spar and a little inboard on pilots side for one, and than opposite for two Com's. Not sure about the Model-A, under the weldments. You do want your Com away for the gear in general. I realize the weldments are talking about is inside the airplane. So anything on the coaxial side of the ground plane will not be an issue. I am thinking of just having ease of access to get at the antenna and mount. I don't think the weldment adds any stiffness to support the antenna.
The nice thing about being front of the spar, coaxial run is shorter and routing is easier. The belly skin is thick as well.
With the antenna in front of the spar, in the floor under your legs, you can make it so you'll have access to the BNC antenna connector from the pilot seat, in flight. Why would you need that? Well you could twist the BNC off and with a short coax, connect a handheld in a pinch. You could get coaxial access for a handheld by making a service break in the coaxial down stream somewhere, say under the panel, but that is more connectors, weight, cost. Are you going to use it much? Its just a thought.
Good Radio, good antenna, good ground plane, good coxial and connectors you will be fine, even if your antenna is closer to another antenna or structure. The key is having an external antenna. I am not a fan of internal wing tip antennas, at least for a Com.
Check the Archives, there are several threads.
Gil is right about distance but its hard to get separation if you put all your antennas on the belly fwd of the spar, unless you do as w1curtis shows, one up and one down. Having an antenna on top is nice for ground ops, the top being better. However you are not a major airport, Denver, LAX, Chicago or Atlanta, talking to ground is usually not an issue with a bottom antenna.
I can't get too excited about antenna separation for a few reasons. Txpdr and Com are way different freqs, 125 Mhz verse 1 Ghz (approx).
Two Com's? If you have two Com's you have a receiver bypass between the radios, that shuts down the receiver of the other Com when transmitting.
There is an actual affect of another whip being nearby. IT WILL affect the signal pattern and so will the prop, gear, fuselage, wings....etc affect the signal pattern (both tx or rx). How much? Not that you will likely notice. You can't have two Coms 6" apart, but you can violate the 2 foot rule (about the length of the antenna). I must say always follow the manufactures installation. So my advice is in contradiction to that, use at your own risk. I'm saying I have never read where some one said, "Gee my antennas are two close together".
Bottom line having two Com's or com & Txpdr closer than what Gil or the installation manual suggest has not caused a problem, from what I have read. It's not ideal and you should try for decent separation (aka as much as you practically can get while factoring in other installations issues). NOTHING is perfect. The mounting of any antenna is a compromise.
I would put it just infront of the spar and a little inboard on pilots side for one, and than opposite for two Com's. Not sure about the Model-A, under the weldments. You do want your Com away for the gear in general. I realize the weldments are talking about is inside the airplane. So anything on the coaxial side of the ground plane will not be an issue. I am thinking of just having ease of access to get at the antenna and mount. I don't think the weldment adds any stiffness to support the antenna.
The nice thing about being front of the spar, coaxial run is shorter and routing is easier. The belly skin is thick as well.
With the antenna in front of the spar, in the floor under your legs, you can make it so you'll have access to the BNC antenna connector from the pilot seat, in flight. Why would you need that? Well you could twist the BNC off and with a short coax, connect a handheld in a pinch. You could get coaxial access for a handheld by making a service break in the coaxial down stream somewhere, say under the panel, but that is more connectors, weight, cost. Are you going to use it much? Its just a thought.
Good Radio, good antenna, good ground plane, good coxial and connectors you will be fine, even if your antenna is closer to another antenna or structure. The key is having an external antenna. I am not a fan of internal wing tip antennas, at least for a Com.
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