Com antenna locations

[Freemasm]

Boundary Conditions =
2 com radios ->
2 com antennas
Small belly area

Tried looking at Rocket pix that I’ve taken, forum pix, etc

For two antenna installs, it appears most are parallel, spaced as wide as physically possible (less than three feet). Most appear to be in the bays behind the spar. At least one appears to be in the bays forward of the spar.

Let me know where yours are and:
Any problems with re-radiation?
Other issues?
Any novel approaches?
Would you do it differently if you could?

Sorry and thx. Always get nervous when about to cut holes in fuse skin.

 

[swaneymj]

I'll attach aa PDFof placement on my F1. I tried for the greatest amount if separation on the belly. I haven't had any interference issues, but tried to stay out of unpaved fields since the aft one is closer to the ground.

 

[rockyfatcat]

One on top works better for ground op’s. One on the bottom for in the air.

 

[Carl Froehlich]

Some options:
- Mount the antennas off center and fore/aft to gain separation.
- Consider a wingtip mounted Comm 2 antenna.

As we know, the Archer wingtip comm antenna is a poor performer. I can say you can make your own antenna that works halfway decent. It will not be as good as a bent whip on the belly but will be adequate for Comm 2. I ran such an antenna for my single comm on my first build for a couple of years and was able to communicate as needed. The data point I can offer is flying side by side with another RV using the Archer wingtip comm antenna I had to relay ATC comms for him as ATC could not hear him.

The approach is to take the basic wingtip antenna design out of the AeroElectric bible, lengthen the arm that moves out from the wing rib as much as possible and get as much vertical drop (or rise) in that arm as the wingtip allows. As in mounting the base on the bottom of the outboard rib and angling the arm to the upper, outboard wingtip edge. Remember the first third of a quarter wavelength antenna is the high current area (the part that does most the work) and vertical polarization is preferred. The arm going fore and aft is shorten to compensate for this extra length. Find a ham radio guy to help you on this.

Carl

 

[storm_pilot]

Has anyone tried a bent whip mounted inside the wingtip or is that a dumb question?

 

[skirting_virga]

Has anyone tried a bent whip mounted inside the wingtip or is that a dumb question?

As someone with an 8 who appears to have no good topside mounting options, I'm also interested in the answer.

 

[Mel]

Has anyone tried a bent whip mounted inside the wingtip or is that a dumb question?

Com antennas need to have vertical polarization. A com antenna laying horizontally will not work very well; especially in transmit mode!

 

[rockyfatcat]

As someone with an 8 who appears to have no good topside mounting options, I'm also interested in the answer.

2 belly mounted comm antennas, or as Carl said in post #4 an antenna in the wingtip remembering that your comm antenna needs as much vertical component as possible.

I’m just guessing , but I don’t know how possible it might be to mount a comm antenna on the top of the vertical stab. It might need some additional structural support as part of that sort of installation.l, but that could be a good location.

 

[bjdecker]

2 belly mounted comm antennas, or as Carl said in post #4 an antenna in the wingtip remembering that your comm antenna needs as much vertical component as possible.

I’m just guessing , but I don’t know how possible it might be to mount a comm antenna on the top of the vertical stab. It might need some additional structural support as part of that sort of installation.l, but that could be a good location.

Top of VS is not a good location - not enough ground plane @ 0° to 45° (90° - 135° below) the feed point — as a result the impedance (Z) will be too high (R or jX - I forget which) so the antenna will not radiate properly.

edit: expanding a bit -- the above statement applies to your typical COBHAM/COMMANT CI-12x bent whip, RAMI, DP antennas which are "monopole" antennas and designed to be bottom/top mounted with a very large ground plane (the skin) beneath.

You *could* fashion a 1/4λ dipole antenna and mount it to the top of the VS, the length would be ~22" above the VS top rib. The problem with this approach is achieving a match to the 50Ω feed line. The bottom portion of this dipole would be much "longer" electrically than 22" (still need a matching device C or RL/C). Add a gamma match at the feed point and turn the whole VS + top element into antenna/radiator and then play around with your VNA / SWR meter cutting/moving the gamma match to get to 50Ω and VSWR < 2:1 for the entire Air band.

Viewed from the side, the tail would resemble a Manta Ray .

 

[rockyfatcat]

Top of VS is not a good location - not enough ground plane @ 0° to 45° (90° - 135° below) the feed point — as a result the impedance (Z) will be too high (R or jX - I forget which) so the antenna will not radiate properly.

You obviously know about this than I do. Does the wingtip have better mass for a ground plane? I know the vertical component is key.

 

[bjdecker]

You obviously know about this than I do. Does the wingtip have better mass for a ground plane? I know the vertical component is key.

Not mass but area.

The wing tip rib is sufficient fore / aft of the feed point & radiator for a ground plane (counterpoise) at the frequencies we're worried about (118 - 137MHz), but the radiator (antenna) would be aligned with the horizon - thus making it more sensitive to horizontally polarized signals (VOR, GS) (receive) and transmitting creates a field/wave that's aligned horizontally.

As Carl alluded to, the radiator would need to be positioned close to the bottom (or top*) of the wing tip rib/skin interface (flange) and then traverse to the opposite point within the wing tip volume.

Now imagine a torus field (donut) around the radiator with the minimums (nulls) at the tip/end of the radiator and at the feed point. The fat portion represents the area of highest gain (the most energy emitted and received), the "funnel" shape is the lowest gain (nulls).

As the donut moves relative to the horizontal or vertical plane, the efficiency changes accordingly. Ergo - a vertically aligned "donut" (tip at the top, ground plane beneath) will be more efficient at receiving signals/waves moving vertically, and vice-versa.

*Top to bottom orientation would present a field optimized for reception/transmission toward and above the horizon. Bottom to Top moves the field from horizon and below. Understanding this, you could use one for in air ops and the other on the ground...

 

[Norman CYYJ]

Top of VS is not a good location - not enough ground plane @ 0° to 45° (90° - 135° below) the feed point — as a result the impedance (Z) will be too high (R or jX - I forget which) so the antenna will not radiate properly.

edit: expanding a bit -- the above statement applies to your typical COBHAM/COMMANT CI-12x bent whip, RAMI, DP antennas which are "monopole" antennas and designed to be bottom/top mounted with a very large ground plane (the skin) beneath.

You *could* fashion a 1/4λ dipole antenna and mount it to the top of the VS, the length would be ~22" above the VS top rib. The problem with this approach is achieving a match to the 50Ω feed line. The bottom portion of this dipole would be much "longer" electrically than 22" (still need a matching device C or RL/C). Add a gamma match at the feed point and turn the whole VS + top element into antenna/radiator and then play around with your VNA / SWR meter cutting/moving the gamma match to get to 50Ω and VSWR < 2:1 for the entire Air band.

Viewed from the side, the tail would resemble a Manta Ray .

You might still end up with a crappy antenna. Just because you have a good 50 ohm match does not necessarily mean it is going to work well, regardless of what the VSWR meter indicates or the what the VNA shows.

 

[bjdecker]

You might still end up with a crappy antenna. Just because you have a good 50 ohm match does not necessarily mean it is going to work well, regardless of what the VSWR meter indicates or the what the VNA shows.

There is, of course, masking effects of the wing/fuselage between the station and receiver. What else?

 

[CF86301]

There is, of course, masking effects of the wing/fuselage between the station and receiver. What else?

You need to have majored in antenna theory at Hogwarts or at UIUC, U-M Ann Arbor, OSU, CU Boulder, or GIT to have a full grasp of this. Helps to have been a 2nd or 3rd gen student at Hogwarts so you could receive owls on important problems from your recent ancestors. Said with all due respect to Arthur C. Clarke.

 

[Norman CYYJ]

You need to have majored in antenna theory at Hogwarts or at UIUC, U-M Ann Arbor, OSU, CU Boulder, or GIT to have a full grasp of this. Helps to have been a 2nd or 3rd gen student at Hogwarts so you could receive owls on important problems from your recent ancestors. Said with all due respect to Arthur C. Clarke.

Yes there is a lot of wierd stuff that can happen with antennae. I think Hogwarts has the best courses on them.

 

[Ironflight]

My F1 has two DeltaPop comm antennas on the belly, under the pilot seat floor panel, just a few inches inboard of the edge of the fuselage - as much separation as they can get. They work fine - no intereference. We have the same setup on the narrower RV-3, and get just a touch of interference if you transmit on one while monitoring both. Both are superior to the setup on my RV-8 that has one belly-mounted Com and an Archer in the wingtip (for Comm 2). Comm 2 is good for formation or AWOS/ATIS within maybe ten miles.

 

[dmn056]

You could use a two-ring DDRR antenna in the wing tip, which is vertically polarised and doesn't require a ground plane.

An example is shown at DDR Antenna for 144MHz (written in Italian, but that's what translation apps are for ).

It would need to be positioned out from the wing rib as far as possible on non-conductive supports. For aviation VHF band usage, it could be 175mm diameter and 50mm high or more. To get the 118-136MHz bandwidth, need the antenna tube diameter to be at least 15mm, preferably more. Some of the larger 3003 Versatube sizes would work OK. It would need experiment with a network analyser to optimise performance.

 

[bjdecker]

You could use a two-ring DDRR antenna in the wing tip, which is vertically polarised and doesn't require a ground plane.

An example is shown at DDR Antenna for 144MHz (written in Italian, but that's what translation apps are for ).

It would need to be positioned out from the wing rib as far as possible on non-conductive supports. For aviation VHF band usage, it could be 175mm diameter and 50mm high or more. To get the 118-136MHz bandwidth, need the antenna tube diameter to be at least 15mm, preferably more. Some of the larger 3003 Versatube sizes would work OK. It would need experiment with a network analyser to optimise performance.

This is interesting!

 

[bjdecker]

You need to have majored in antenna theory at Hogwarts or at UIUC, U-M Ann Arbor, OSU, CU Boulder, or GIT to have a full grasp of this. Helps to have been a 2nd or 3rd gen student at Hogwarts so you could receive owls on important problems from your recent ancestors. Said with all due respect to Arthur C. Clarke.

So what's wrong with USC (University of Southern Cupertino)?

Yes there is a lot of wierd stuff that can happen with antennae. I think Hogwarts has the best courses on them.

Weird stuff also.

 

[Xkuzme1]

I started out with:
1) bent whip on bottom and archer in left wing.
-archer wasn't good in wing tip
2) Bent whip on bottom and tried to hide 18 inch handheld antenna in the gear leg fairing
-18 inch antenna in gear leg didn't work
3) two bent whip antennas in the center of the plane about 3 feet apart.
-works perfect

What I did learn later was that likely the archer antenna would have worked better if it was contoured with the leading edge of the wingtip... but I have landing lights there and there was no space.

My goal for com 2 antenna was just to be able to talk to a formation of planes. Options 1 and 2 were no bueno.

x

 

[GyroF-16]

I started out with:
1) bent whip on bottom and archer in left wing.
-archer wasn't good in wing tip
2) Bent whip on bottom and tried to hide 18 inch handheld antenna in the gear leg fairing
-18 inch antenna in gear leg didn't work
3) two bent whip antennas in the center of the plane about 3 feet apart.
-works perfect

What I did learn later was that likely the archer antenna would have worked better if it was contoured with the leading edge of the wingtip... but I have landing lights there and there was no space.

My goal for com 2 antenna was just to be able to talk to a formation of planes. Options 1 and 2 were no bueno.

x

Can anyone here with antenna expertise comment on the relative merits of two antennas widely spaced (laterally) on the underside of the fuselage vs placed in-line like the above post?
I’m adding a second radio and antenna to my F-1 Rocket next month, and was planning to put the two antennas side by side. If putting them both on the fuselage centerline is just as good, that could save me from having to move the existing antenna (located where the forward antenna is in the above post).

 

[Jonnyb]

As someone with an 8 who appears to have no good topside mounting options, I'm also interested in the answer.

2 belly mounted antennas, one in each passenger footwell seem to work ok.

 

[Carl Froehlich]

Can anyone here with antenna expertise comment on the relative merits of two antennas widely spaced (laterally) on the underside of the fuselage vs placed in-line like the above post?
I’m adding a second radio and antenna to my F-1 Rocket next month, and was planning to put the two antennas side by side. If putting them both on the fuselage centerline is just as good, that could save me from having to move the existing antenna (located where the forward antenna is in the above post).

Both on the center line with reasonable spacing is fine. The main drawback is if on a tail dragger the aft antenna gets close to the ground. This has little to no impact with operation on the ground other than it hitting something.

Note - regardless of where you mount belly antennas put an “eye ball” protector on each. I use a piece of tygon tubing with a stopper on one end and a red ribbing tied to it as a reminder to remove before flight. These antennas are right at eyeball level for dogs and for owners when they get engrossed on belly cleaning.

Same goes if using those ugly VOR antennas mounted under the tail or on the VS. Put it in the wingtip.

Carl

 

[Mikeyb]

Experience on VAF has shown that almost any spacing will work at some level but the closer they are to 1/4 wavelength spacing which is around 24 inches the more likely the two antennas will couple and distort the radiation pattern making it work better in one direction and worse in another.

 

[skirting_virga]

Experience on VAF has shown that almost any spacing will work at some level but the closer they are to 1/4 wavelength spacing which is around 24 inches the more likely the two antennas will couple and distort the radiation pattern making it work better in one direction and worse in another.

Does this apply for side by side as well as lengthwise? Is there a more optimal distance >24"

 

[Mikeyb]

Does this apply for side by side as well as lengthwise? Is there a more optimal distance >24"

The placing of the two will change the direction the pattern is shifted. The rule of thumb is to space them a 1/2 a wave or longer but on an RV it becomes impossible. Just avoid 24” or closer is as good as you can do.

 

[Norman CYYJ]

Does this apply for side by side as well as lengthwise? Is there a more optimal distance >24"

Yes