wingtip com ant mod?

[davidsguerra]

has anybody else done the wingtip com antenna mod? i am getting a tas and they had to remove one of the com antennas on top. i am thinking i might as well remove the other one and put them in the wingtips to save some drag. besides the cost are there any other disadvantages to this ? i have a 1983 m20k rocket.

 

thanks for your input

[JoeSpeed]

I would think you loose some range and tax power due to lack of a ground plane.

If it were better and cheaper with less drag I would guess mooney would had gone that way

[yvesg]

TX power shall not change however, ratiation pattern (shape of where the signal is distributed) is something to check.

Yves

[bumper]

Being as the aviation band is vertically polarized, and I know of no way to fit an antenna in the wing tip so it's mostly up and down - - whatever you stick in there is gonna represent a significant compromise in com performance. Other performance, the go meter, may increase slightly 

 

BTW, radiated TX power most assuredly will change unless the SWR (standing wave ratio) of the new antenna is the same as the old one - - and it won't be! Metal (think wing here) will be too close to the radiating elements and in generally the same plane, thus SWR will take a hit and this will result in TX power being reflected back down the coax into the final amp. That lost power means less effective transmitted power on top of any design compromise.

 

Overall, you're likely to lose transmit range and this will be most evident when you are a good distance out (guessing more than 50 miles). Receive, not being so antenna quality critical, won't suffer as much. You'll be able to hear 'em, but they won't hear you.

 

bumper

[Hank]

My wingtips aren't metal, but the original square end is. I think my VOR antennas are out there rather than transmitting anything. But they are STC add-ons, too.

[Piloto]

As Bumper said is not worth it. You are not going to gain any measurable speed but loose significant communication range (half or more of previous range). The antenna cable routing to the wing tips is not trivial and because of the longer run you will have signal loss of 3dB due to added cable length, another 3 dB for lack of ground plane and another 3 dB due to horizontal polarization. Another option is mounting the antennas on the belly.

 

José

[yvesg]

If I recall right (from memory when I was teaching that stuff), cross polarization gives an attenuation of 17 db. Piloto is right about the cable loss, however I do not think that it would be as bad as 3db... I would check the chart for the coax in question. I would be really surprised if these antenna designers would allow a worse SWR ratio than competition...most claim SWR better than 2 with is about 89% power transmitted and 11% reflected.

Do they usually put two antennas? One in the right and one in the left wingtips? That would possibly help the radiation pattern but make it harder to tune.

Yves

[Piloto]

For every 6dB you loose half of the previous range. So for 18dB it would be .5 x .5 x.5 = 0.125 or 1/8 of the original range. A horizontal antenna at the wingtips would have maximum field intensity on the sides of the airplane but minimum at the front and rear. This would further decrease the range to ATC towers ahead like the one for your destination.

 

José 

[bumper]

For every 6dB you loose half of the previous range. So for 18dB it would be .5 x .5 x.5 = 0.125 or 1/8 of the original range. A horizontal antenna at the wingtips would have maximum field intensity on the sides of the airplane but minimum at the front and rear. This would further decrease the range to ATC towers ahead like the one for your destination.

 

José 

 

José 

 

It's roughly a 1/2 power reduction, or gain, for each 3 db change in power. But note that this does not directly correlate to range. In other words, suffering a 3 db loss will not halve the transmission range. There are many variables and vagaries in radio communication . . . and it would take someone smarter than me to know it all*  .

 

I do have a friend who knows it all . . . I can call him with a question about damn near anything in electronics and such, and that would be important to guys, and he'll come up with a reasonable answer. I refer to him as being a "veritable cesspool of superfluous knowledge".  

 

*I was a Navy electronic technician for 8 years in the 60's - - back when tubes was in.

 

bumper

[Piloto]

José 

 

It's roughly a 1/2 power reduction, or gain, for each 3 db change in power. But note that this does not directly correlate to range. In other words, suffering a 3 db loss will not halve the transmission range. There are many variables and vagaries in radio communication . . . and it would take someone smarter than me to know it all*  .

 

I do have a friend who knows it all . . . I can call him with a question about damn near anything in electronics and such, and that would be important to guys, and he'll come up with a reasonable answer. I refer to him as being a "veritable cesspool of superfluous knowledge".  

 

*I was a Navy electronic technician for 8 years in the 60's - - back when tubes was in.

 

bumper

Here http://www.qsl.net/pa2ohh/jsffield.htm

you can calculate path loss at different frequencies and distances. Like many phenomenas in physics path loss is an inverse function of the sphere area or an inverse square function of the radius. The loss due to frequency is the energy disipated by the medium. 

 

José

[N601RX]

-3db is half power. If using RG 400 coax the loss will be less than 1 db in the com frequencies. The biggest loss is going to be from the horizontal antenna. Line of site is often more critical than power, so unless you are trying to talk to some one very for away it will work fine.

We have some very expenisve software at work and 5 full time people who figure out our reciever spacing.

[Piloto]

The early B747 used HF wing tip horizontal polarized antennas. In some instances the plane heading needed to be changed slightly to improve reception. The same problem happened with trailing wires. But after they were retrofited with antennas embedded in the vertical fin the problem went away and heading chenges are no longer required.

 

On VHF antennas mounted on the fuselage the airframe ground plane plays a significant roll on antenna performance. Unlike horizontal dipoles that have no ground planes, the ground plane on vertical antennas provides a significant gain and prformance increase in all directions.

 

José