Comm antenna placement

[alcladrv]

Others report that the Archer comm antenna mounted in an RV wingtip doesn't give the range that one gets from a belly mounted one.

I've got a belly mounted antenna in my -7A for my Comm 1 and plan to add a second Comm radio. Question: Has anyone used a "norrmal" comm antenna, like the Comant CI-121, mounted to the last wing rib and projecting out into an RV wingtip? It looks like it might fit. Is it feasible and how would performance be affected because of the horizontal orientation?

Thanks,

Mike

 

[Ironflight]

I would expect very poor performance from a Comm antenna placed horizontally. Comm signals require a vertical component to the antenna - that's why the Archers don't do well in the wingtip, while the Nav antennas (VHF Nav signals are horizontally polarized) work fairly well.

Paul (not an RF expert, but have learned a lot from those who are...)

 

[SkywayCaptain]

I agree with Paul and I have tried mounting a com antenna on the wingtip with very poor results. Mounting the com antenna horizontally gives a signal loss of around 20db on Tx and Rx. For each 3db of loss, your signal's power decreases by 50%. A couple of other factors are the fact that your coax feedline must be longer to reach the wingtip. VHF signals experience quite a bit of loss per length of even the best coax. Another factor that makes mounting the com antenna on the belly better is that the com whip is only half of the antenna. The other half is your aircraft. Belly mounting gives a nice groundplane (other half of the antenna) which directs the signal towards the horizon, if the aircraft is level

I have my NAV antenna mounted inside the wingtip and it works fine. I have tested that it receives VOR/ILS/GS signals within the published operation service volume of navaids.

 

[elippse]

VHF signals experience quite a bit of loss per length of even the best coax..

Nope! The best coax is Andrew FSJ1-50A whose loss is 1.88 dB/100' at 100 MHz and 2.23 dB/100' at 150 MHz. At $1.49/ft it is cheaper than RG-400's $2.75/ft (ACS) and weighs the same!

 

[SkywayCaptain]

No doubt FSJ1-50A is low loss cable. The numbers you quote assume a 1:1 vswr and losses will be greater in the real world. My point was that shorter feedline lengths will have less loss no matter how good or bad your coax is. This loss small when compared to having the antenna horizontally polarized or having a poor ground plane, but losses are losses.

 

[elippse]

No doubt FSJ1-50A is low loss cable. The numbers you quote assume a 1:1 vswr and losses will be greater in the real world. My point was that shorter feedline lengths will have less loss no matter how good or bad your coax is..

Again, I can't agree with your analysis. The stated loss at 100 MHz of RG-400 is 3.9dB/100', slightly over twice as much as FSJ1-50A's 1.88 dB/100'. Regardless of load VSWR, it is still the better one to use up to and including 10GHz.
Believe me, I've used it on the Atlas Ground Guidance radar at all of this frequency range. We had been using a specially-made, phase-stable RG-8 for performing VSWR tests on our missile-borne antennas, and the least movement of the cable changed the results. When I had our lab change-over to the FSJ1-50A, we had less loss and no phase variation while moving the cable all around.
As I've written before, not taking advantage of the lower loss and immeasurable leakage of this solid outer jacket cable, at about the same installed price as RG-400, is to throw away performance on all of your installed radios, regardless of frequency or length of run.
However, I do agree with you that only a proper antenna polarization will give low loss transmissions. A truly horizontal antenna, except for a slot antenna, will have zero response to a vertically polarized signal. What transmissions do get through is only a result of having some slight off-angle or re-radiation from nearby objects.

 

[SmilingJack]

Just to comment on the in the wingtip antenna, I installed a Advanced Aircraft Electronics antenna in each wingtip. One for comm 2 and 1 for nav 1.

I am still in phase one, so my experience is only testing them to 35 miles from homebase.

Comm 2 works great in the wingtip mounted horizontally for about 10 to 15 miles, then when I am out to 20 - 25 miles I have to kind of point the left wingtip toward the airport to receive.

I mount the comm 2 antenna on the left side to allow for the standard traffic pattern best reception.

The nav seems to work well within my 35 mile limit.

 

[SkywayCaptain]

I agree that you should use the lowest loss feedline that you can justify the cost of and meets installation requirements. The shorter the feedline (using the SAME type feedline), the less the loss. I guess I didn't type it very clearly

In some installations, a 20db loss has been measured from horizontal to vertical polarization. This is simply a rule of thumb. Theoretically, there should be total signal loss, but, as you point out, signal polarization is skewed by reflections.

I still maintain that for COM radios a properly tuned vertical whip mounted on the aircraft belly, with descent coax will work acceptably well and MUCH better than one mounted horizontally on the wingtip. I think this was the thread subject.

 

[woodmanrog]

Try mounting inside the gearleg fairing.

I have found through much experience that A: an outside mounted antenna does give much better real world reception than one mounted inside, but B: that being said, If you mount a com antenna inside the gearleg fairing (Preferable against one of our wood stiffeners) your real world reception will be more than adequate. I generally see at 4500 ft around 50 to 100 nm from front to rear and much more than that side to side. make sure the antenna has a GOOD ground.
Woodman

 

[elippse]

A different tip antenna

As shown in JD Kraus "ANTENNAS", P.355, Fig. 8-15, a 30? to 60? triangular antenna 0.15 wavelength long will have an impedance of 25 ohms. Two of these placed opposite each other to form a type of half-wave antenna will have a 50 ohm impedance and very wide-band performance. An antenna I made like this had an SWR of less that 1.2 from 116 MHz to 140 MHz. Since the frequency of the geometric mean of the Comm band is 127.3 MHz, giving a wavelength of 92.5" in the atmosphere (as opposed to a vacuum). A half-wave antenna of this construction would have a length of 27.75". Imagine incorporating an antenna like this in a wingtip plate. It would enhance the aerodynamics of the plane, as well as providing superior gain in the horizontal direction relative to a 1/4 wave dipole above a counterpoise. 'Just excogitating!

 

[rvmills]

Very interesting discussion, and Paul, I'd like to explore that tip antenna you are excogitaing on (can ya say that in public?! )

I've been playing with some tip antennas for COMM 1, in an effort to remove the last of my belly whips in the search for speed (or efficiency...or both!) Pete Howell has been the R&D department, along with the local avionics shop, and I have been the beta tester. What I've done so far:

Start point:
Two belly whips
-COMM 1 = Standard CI-122 Comant
-COMM 2 = Comant CI-122SP Loran trimmed for APRS (144.39) and/or Sheriff's SAR (150.025)

One Howell J-pole in the right gear leg

Gear leg J-pole and loran ants were switchable between APRS and SAR Comm (MFG-1701 switch...I think that's the number)

Step 1

Removed 1 belly whip (the SP) and replaced it with a second Howell J-pole in the right wingtip. After playing with several configurations, settled on this one, which came up in a conversation with Pete (me: "hey, what if I loop it up and down to get more vertical polarization?" Pete: "its RF, who knows...could work!")

The bitter end starts under the top lip of the wingtip, about the third nutplate back, goes down around the leading edge then up and down as seen.

With an SWR meter, this tested out quite variable, but it had sweet spots of about 1.2 at 143 and 152 (how lucky can you get!) and works well for the SAR radio and has been very good with my APRS (good hits down to 500' agl and below, where the gear leg jpole stops getting hits at 1000' agl or higher).

OK, so I now can switch the APRS/SAR radios to either of the jpoles, and I'm happy there. Still one more belly whip to clean off the belly, and it has been a tougher nut.

Pete made up a j-pole trimmed longer for standard VHF freqs (actually 127, the center of the 118-136 COMM range). I tried several configurations (same wave as above, inverted V, etc, etc.) SWR tests on them were variable (SWRs ranged 1.2 to over 3+ between 118 and 136, and went up and down multiple times in that range, as you might expect). Performance was poor, with a lot of directionality and aspect issues (heading, angle of bank and direction to station made huge differences in performance).

Pete engineered a "Bazooka" antenna from coax cable, and it was supposed to be more wide-band, but in the end it showed similar performance to the COMM 1 j-pole. Here's a pic of one configuration attempt:

I tried wider spread and various designs...no good luck. They all work in the pattern, but no range, and a lot of directionality.

I was hangar flying with the avionics shop guys at the field, and the boss suggested trying a bent whip hung in the wingtip, and he showed me an L-39 in the shop with an inverted bent whip in the tail that was working. He gave me an old whip, on which I cut down the base enough to fit in my tip. I soldered the center wire of a coax lead to the center post of the whip, and crimped a separate wire to the shield of the coax. I then gorilla-taped the whip in place, and ran the ground wire to the outer rib, in hopes it would act as a ground plane. Here's what it looks like:

The small black wire is the ground, and the large black coax connects to the RG-400 (sorry Paul) that runs down the wing to the radio. The grey and black tie-wrapped wires are for the nav/strobe.

Not much luck here, probably just no ground plane, or perhaps just a lot of blockage from the airframe. Very poor range, despite relatively flat SWR tests in the COMM range (1.5 to 2).

Next thought is to somehow make a ground plane attached to the base of the antenna, and attached to the upper inside of the wingtip. Perhaps an "X" made of two 24" strips of metal tape. Just gotta figure out how to attach the ground plane to the antenna ground, and keep the ground plane clear of the base of the antenna itself.

Any thoughts?

Paul, can I borrow that book (or got a link to it online?)

Fun project, and it sure would be neat to find a solution! Sam Buchanan has been watching our work, and as he said, there's probably a reason bent whips are so popular! They work. Its fun to experiment, but for COMM 1, I want very good reliability, so there's the rub!!

Any better mousetrap ideas?

Cheers,
Bob

 

[elippse]

Very interesting discussion, and Paul, I'd like to explore that tip antenna you are excogitaing on (can ya say that in public?! )
Inventive dreaming!

The small black wire is the ground, and the large black coax connects to the RG-400 (sorry Paul) that runs down the wing to the radio. Paul, can I borrow that book (or got a link to it online?)

Cheers,
Bob

Sure, Bob, you can borrow it. Just buzz on over and we can do a chalk-talk on the bow-tie antenna/wingtip! Not only will it improve the plane's performance, but with a propagation loss of 31.5dB (-37.9+20(logR+logF)* from one wingtip to the other across 23', there will be no nulls in the pattern for simultaneous transmission or reception. A half wave dipole will always outperform a 1/4 wave whip over an incomplete counterpoise at horizontal angles.
I'm really surprised that as many times as I've written about the loss of the FSJ1-50A coax being half of RG-400, its much lower cost, and its unmeasurable leakage because of its solid outer jacket which allows it to be tightly bundled with other wiring with no cross talk, there as yet seem to be no takers!
John D. Kraus is/was the Director, Radio Observatory, Taine G. McDougal Professor Emeritus of Electrical Engineering and Astronomy, The Ohio State University. ANTENNAS is published by the McGraw-Hill Book Company. I purchased mine on 1989 August 10 for $57.95. He covers just about any kind of configuration and frequency range that you would want, including microstrip and patch antennas. I designed my bow-tie VOR and Glideslope antennas embedded in my wing roots based on this, but my transponder balun-fed asymmetric 1/2 wave dipole was based on the MIT Rad Lab series #12, Microwave Antenna Theory and Design. *R,ft; F,MHz

 

[rvmills]

You're on Paul...and I'll bring a dictionary, a thesauraus, an engineering definitions book, a HAM guidebook, and a good attitude to learn...along with lunch money!

I just wish you'd learn to use bigger words sometimes!

Hey, on that FSJ1-50A...how flexible and easy to work with is it? Same BNCs work with it (same crimpers, etc.)?

Pete...are you watching?

Cheers,
Bob

 

[elippse]

You're on Paul...and I'll bring a dictionary, a thesauraus, an engineering definitions book, a HAM guidebook, and a good attitude to learn...along with lunch money!

I just wish you'd learn to use bigger words sometimes!

Hey, on that FSJ1-50A...how flexible and easy to work with is it? Same BNCs work with it (same crimpers, etc.)?

Pete...are you watching?

Cheers,
Bob

Its weight is 0.045lb/ft-0.72oz/ft vs RG-400, 0.05lb/ft-0.8oz/ft, its minimum bend radius is 1", 0.29"od vs 0.19"od RG-400, and 150 lb tensile strength. It uses special connectors, which are pricier, and available in N m&f, N male rt angle, BNC male, UHF m&f, SMA m&f, SMA male rt ang, TNC m&f, mini UHF male, 7-16 DIN m&f.
I use this cable on my radios, and so does Klaus. He noticed that his Tx-Rx range really increased using this, because his Comm antenna is out in his left tip sail on his EZ. A friend of mine with Orbital, when I told him about it, did a signal study of the transponder minimum output radiated power spec of 125W, starting with 200W, RG-58 was 9' max, RG-400 is 15' max, and the FSJ1-50A would be 34'. It also showed much better performance for receive, in that the minimum trigger spec of -74dBm is about 13.5' for RG-58, 31' for RG-400, and almost 50' for the FSJ1-50A.

 

[Loboflyer]

Paul, I think the reason you don't see Heliax much on aircraft is that it is relatively unknown in aircraft? Out of sight, out of mind? In the ham world, Heliax is "the stuff to use if you have money", but thats in comparison to scrounged RG58.

Would the foam PE dielectric have any moisture issues?

I'm also intrigued by the antenna you describe. But, I don't have time to look at it in too much depth . Kraus is a classic. I would think that the close proximity to the aircraft would result in a slight capacitive shortening and probably some polarization distortion.

I'll caution to those new to antennas on the forum that relative comparisons of VSWR does not indicate a better antenna. Yes, lower is better, but it does not describe how efficient the antenna is at converting the energy to radiation. A 50 ohm resistor has a 1:1 VSWR, yet radiates nil. The best number is gain, which includes efficiency, but is much harder to measure.

Also, to those who like to experiment, realize that there are very few new antenna designs that are truly novel. In most cases, they are simply wires bent in new forms that act as tuning elements (for example, a J-pole antenna is simply a stub tuned monopole).

 

[rvmills]

Paul,

Just bought the Kraus book online...will go to school on the bowtie, then still bring lunch money for a build-it workshop, if you're game!

Pete, you can borrow the book too (if you don't already have it!)...and hey, perhaps you can escape the snows in the 9A for a post-graduate day of antenna and drag theory in Santa Maria, CA! Long X-C for that...might have to add some skiing into the mix!

Lobo, the more I dig, the more I agree with what you said...many have tried to skin this cat in all aspects of radio...my HAM Father-in-Law is having fun watching me dig!

Let's put Paul's brainpower on this and build that better mousetrap (no other racers allowed! )

Cheers,
Bob

 

[elippse]

Paul, I think the reason you don't see Heliax much on aircraft is that it is relatively unknown in aircraft? Out of sight, out of mind? In the ham world, Heliax is "the stuff to use if you have money", but thats in comparison to scrounged RG58.

Would the foam PE dielectric have any moisture issues?

I'm also intrigued by the antenna you describe. But, I don't have time to look at it in too much depth . Kraus is a classic. I would think that the close proximity to the aircraft would result in a slight capacitive shortening and probably some polarization distortion.

The 15? to 30? bow tie antenna is made of thin sheet, high-conductivity aluminum*. For the mid-comm-band it would have an overall length of 28" and the ends of each triangle, at 15?, would be 7.5" wide. This would be sandwiched in a streamlined foam-fiberglass fin. This would look like a triangle or arrow, mounted vertically on the end rib symmetrically above and below the wing, sweeping back from near the wing LE to the 7.5" wide tips on top and bottom. It would form an end plate attached to the last rib, enhancing the apparent span and lessening induced drag. Of course it would require one on each wingtip.
Since its radiation would be hemispherical above and below the wing surface, any distortion would probably be toward the wing root, but looking at free-space the rest of the way around with the superior gain and horizontal directivity of the 1/2 wave vertical dipole over the 1/4 wave dipole above a limited-length counterpoise.
The propagation loss in the direction of the cockpit would be about 24dB, so that unless the mike and PTT wiring is unshielded, there should be little chance of TX currents finding their way into the mike or PTT circuit and causing squeel.
The connectors are fitted with seals so that if properly installed there should be no more chance of moisture entrance than with any other connector or dielectric.
*The IACS relative conductivity for aluminum alloys to OFHC copper is 1.69 for 1100-0, 1.75 for 1100-H, 1.82 for 6063-T6. The others range from 2.0-3.33.

 

[rvmills]

This would look like a triangle or arrow, mounted vertically on the end rib symmetrically above and below the wing, sweeping back from near the wing LE to the 7.5" wide tips on top and bottom. It would form an end plate attached to the last rib, enhancing the apparent span and lessening induced drag. Of course it would require one on each wingtip.

Paul,

Looking for something to fit inside the wingtip. I need to measure, but not sure the 7.5" will fit. Can it be scaled, or does that change the frequency band (guessing it does).

Got an artists concept of the tip end plate you describe? Sounds like it could be incorporated into a flat racing tip, but not sure about strength issues.

Interesting rabbit hole to run down a bit though!

Merry Christmas!

Cheers,
Bob

 

[RV8RIVETER]

After seeing the Nova episode on Fractals for the second time it again peeked my interest and got me thinking about this thread. There are fractal antenna designs that greatly decrease size and increase bandwidth, what about a fractal aircraft VHF antenna design?

I can't seem to locate much on the web on fractal designs other than a few references to Koch snow flake designs.

 

[Loboflyer]

After seeing the Nova episode on Fractals for the second time it again peeked my interest and got me thinking about this thread. There are fractal antenna designs that greatly decrease size and increase bandwidth, what about a fractal aircraft VHF antenna design?

I can't seem to locate much on the web on fractal designs other than a few references to Koch snow flake designs.

For a well grounded discussion on electrically small antennas, see R.C. Hansen's book "Electrically Small, Superdirective, and Superconducting Antennas". See if you can borrow a copy from a local library. The only limit that matters is the limit on Q vs. size of enclosing sphere relative to wavenumber, defined by Wheeler, Chu, and McLean. Anything that violates that fundamental limit should be treated with skepticism (but its not impossible -- the limit isn't a law).

Also keep in mind that effective aperture is king. The larger the physical aperture (size) of the antenna, the more gain will be had. The Wheeler limit basically says that if you have an antenna of largest dimension d, then all you can do is optimally use that volume to keep the bandwidth and efficiency simultaneously high. But, the smaller that aperture is, the less possible gain there will be. Feedline radiation is usually responsible for antennas that claim impossible numbers for gain or bandwidth.

If I remember right, Hansen rails on the fractal designs. I think his reasoning had to do with the relative sequential order of element excitation, but I forget now.

 

[albertaflyer]

I just installed an Mgl v10 com radio in an rv6a that I just purchased. The previous owner has the copper tape up the inside of the windscreen for antenna. My reception is approx 5 miles at best and I get a lot of noise. I can get some out with squelch but not all. Also, I'm getting noise from the strobe through the headset. I tried my handheld and as you get closer to the strobe the feedback gets really bad. Any suggestions?
Thanks
Tony

 

[elippse]

I just installed an Mgl v10 com radio in an rv6a that I just purchased. The previous owner has the copper tape up the inside of the windscreen for antenna. My reception is approx 5 miles at best and I get a lot of noise. I can get some out with squelch but not all. Also, I'm getting noise from the strobe through the headset. I tried my handheld and as you get closer to the strobe the feedback gets really bad. Any suggestions?
Thanks
Tony

Where is the shield of the coax to the antenna connected? A copper tape glued to the inside of the windshield will work if it is properly terminated and has a ferrite bead around the coax very close to the antenna terminals to prevent antenna currents on the coax. The shield should be connected to the airframe very, very, close to the bottom of the antenna. By placing several of the copper strips side-by-side to make the antenna wider it will make it more wideband giving lower SWR across the comm band. The strips should be about 17"-19" long. You can also join two additional strips to the one you have at the coax and bring them up at a slight angle so that the ends are spaced about 3"-4" out on each side from the center one in triangles. If you are picking up the high frequency capacitor charging or the sharp snap when the strobe fires it probably means that your strobe wiring is not properly shielded, along with your poor antenna raditaion characteristics.

 

[albertaflyer]

I'm pretty sure he didn't ground it but I will have to check. I also noticed that the passenger side head phone crackles slightly when you talk in the mic. I tried both headsets and made no difference. I also pulled the phono plugs out thinking it was a grounding issue but still did it. Any idea why it would crackle when hooked up to the passenger side but not the pilot side. Pilot side is crystal clear. Also noticed when the passenger ptt is pushed you can hardly hear yourself speaking. Very faint! Thanks for the info!

 

[elippse]

I'm pretty sure he didn't ground it but I will have to check. I also noticed that the passenger side head phone crackles slightly when you talk in the mic. I tried both headsets and made no difference. I also pulled the phono plugs out thinking it was a grounding issue but still did it. Any idea why it would crackle when hooked up to the passenger side but not the pilot side. Pilot side is crystal clear. Also noticed when the passenger ptt is pushed you can hardly hear yourself speaking. Very faint! Thanks for the info!

One of the really bad things about having the antenna inside the cockpit is that the transmissions may get into the mike circuit and thence into the modulation, creating squeel and all kinds of havoc. Having an antenna that close to the modulation input means that you must have very well shielded mike and ptt wiring, preferably shielded twisted pair.
I worked on rewiring a friend's Christen Eagle that had the comm antenna on the fuselage right behind the cockpit and got lots of squeel at different frequencies. After cleaning up the wiring the problem went away.

 

[AZtailwind]

Down the gear fairing?

Bob, paul-
What do you think of putting it down the main gear fairing?
Too close to a tapered rod ground plain to be of use?
Loose too much horizontal ground plain also??

At least it is vertical, wondering if anyone has tried it?
May get better performance than the wing tip design though.

Brad

 

[rvmills]

As shown in JD Kraus "ANTENNAS", P.355, Fig. 8-15, a 30° to 60° triangular antenna 0.15 wavelength long will have an impedance of 25 ohms. Two of these placed opposite each other to form a type of half-wave antenna will have a 50 ohm impedance and very wide-band performance. An antenna I made like this had an SWR of less that 1.2 from 116 MHz to 140 MHz. Since the frequency of the geometric mean of the Comm band is 127.3 MHz, giving a wavelength of 92.5" in the atmosphere (as opposed to a vacuum). A half-wave antenna of this construction would have a length of 27.75". Imagine incorporating an antenna like this in a wingtip plate. It would enhance the aerodynamics of the plane, as well as providing superior gain in the horizontal direction relative to a 1/4 wave dipole above a counterpoise. 'Just excogitating!

Paul,

DHL just delivered the Kraus book this morning. Its the third edition (Antennas For All Applications) and it appears the page and figure numbers have changed. Can you direct me to the chapter and section that the above antenna is in? Thanks!

Bob, paul-
What do you think of putting it down the main gear fairing?
Too close to a tapered rod ground plain to be of use?
Loose too much horizontal ground plain also??

At least it is vertical, wondering if anyone has tried it?
May get better performance than the wing tip design though.

Brad

Brad,

I have a j-pole that Pete made for APRS down my right gear leg, and I use it interchangeably with APRS and my COMM 2 (the SAR radio on 150.025). Its performance is less than that of the j-pole in the right wingtip, but its passable performance (many of SAR comms are short range, and its OK on APRS down to 1000' agl). I prefer to use the gear leg for SAR, and the wingtip jpole for APRS, but can switch it on the fly from the cockpit (switch under the right side of the panel).

For a COMM 1 antenna, I'd want an antenna that is reliable at longer ranges, at all aspects, and at all frequencies. When I was playing with the longer (127 MHz-ish) jpole and the bazooka in the left wingtip, all of my patterns (flat, inverted V, looped up and down) were very directional, very aspect dependent, very short range, and it varied widely by frequency...pretty much useless!

However, I've considered putting that j-pole or the bazooka down my other gear leg, to see if it works as an alternate COMM antenna, as you are suggesting. I've been thinking about doing so, and buying a cheap(er) VHF COMM to use as a COMM 2 for FFI formation lead duties down the road. The gear leg j-pole may be very usable for intra-formation communications on company freq.

If I could make a bow-tie antenna for the left wingtip that worked at long range, I'd remove the last bent whip from my belly, and my wish-list covert antenna farm would look like this:

1. COMM 1 for ATC (SL-40): Bow Tie in left wingtip
2. COMM 2 for formation lead (scrounged radio): Left gear leg jpole
3. COMM 3 for SAR (Sheriff's Kenwood radio): Right gear leg jpole
4. APRS (MT-8000FA): Right wingtip jpole in s-loop

Items 3 and 4 are in place and working, and my GMA340 will accomodate 1-3.

Paul, all I need is the left wintip magic, and it's the slickest 4-radio race RV in town! Need a special project?

Cheers,
Bob

PS: and yes, I'd love to see someone figure out bluetoothing 4 Zulu headsets together for formation work!

 

[elippse]

Here's something else you experimenters out there (there are some, right?) might try. The VOR "V" antenna that you see mounted on a V-stab is a half-wave antenna with a balun feed. By shortening the antenna by about 12.5% to match it to the higher frequency Comm band, and mounting it vertically at the wing-tip, you now have a half-wave Comm dipole. 'Just excogitating again!
BTW, one thing antennas and props have in common is that just about any old thing will work to one degree or another, but not necessarily work well!

 

[rvmills]

Here's something else you experimenters out there (there are some, right?) might try. The VOR "V" antenna that you see mounted on a V-stab is a half-wave antenna with a balun feed. By shortening the antenna by about 12.5% to match it to the higher frequency Comm band, and mounting it vertically at the wing-tip, you now have a half-wave Comm dipole. 'Just excogitating again!
BTW, one thing antennas and props have in common is that just about any old thing will work to one degree or another, but not necessarily work well!

OK, who's got a VOR cat whisker I can "borrow"?

Paul, 12.5% of what (total length, length of each whisker, is that the same...I'm numbers challenged this morning!)

Paul, got your e-mail on the bow-tie...thanks, will find it when I get off the computer!!

Cheers,
Bob

 

[elippse]

Comm Quiz

Let's say you and a friend are flying along in opposite directions while talking on you comm radios, and you both have identical radios, antennas, and coax. Let's also say that no matter how far apart you are, the transmissions will be line-of-sight. What do you think the maximum range at which you will be able to keep up the conversation; 25, 50, 100, 250, 500, 1000, or 2000nmi?
The specs on an FL760 Transciever are 4W CW, 16W PEP and a sensitivity at 6dB S/N of less than 1 microvolt. Your antenna gain is 1dBi, and your coax loss is 2dB.
One microvolt on 50 ohms is -137dBW. For output power we'll use the 4W or +6dBW. Signal path attenuation in dB is 37.8 + 20(logR+logF), where R=nmi, F=MHz. So the total signal should be 6 +2X1 +2X-2 + 137= 141dB. Subtracting 37.8, dividing by 20, subtracting log(127.9)=3.05. This is the log of R, which means that 10^3.05=1130 nmi! If the output power was 8W, then the max range would be almost 1600nmi!
That is why I feel great distress when I read that someone can only receive to 5 mi. If your antenna and coax system is in good order, when you're at altitude you should have no trouble at all in hearing someone at 100 nmi. At 10,000', the distance to the horizon is 100 nmi and you should have line-of-sight with another plane at 10,000' 200 nmi away. At 12,500' it's almost 120nmi, for a total of 240 nmi. And with diffraction and refraction at the horizon, it would be even farther than that.
So here's a good test for your installation; see how far away you can pick up an ATIS or tower.

 

[Loboflyer]

I was thinking of doing that very calculation, Paul, but you beat me to it! My career has been spent so far mostly on circuits and antennas, but I'm now branching out to systems. Still have a bit to learn before I can do back of the envelope calculations since I didn't pay much attention in my signals classes ;-)

 

[rvmills]

Paul,

On the day in question, we in fact had four airplanes, two each going in opposite directions. Steve (the OP) and I were at 10.5 headed towards Reno, the others were lower, headed towards the Pacific coast from the valley. I had good reception throughout, as did those headed west...and they could hear both of us. Only Steve had reception issues, so as you allude...its either that squelch setting (hoping so) or the connections/cables.

Last time I had an issue with comms testing was after putting some coax in the wings. Lots of issues, but I was sure my crimps were good (after all I had that brand new $$ crimper!) Lot's of troubleshooting later...it was the crimps!

Keep your fingers crossed a little button smashing does it, so we can avoid the knuckle-smashing, wire-chasing part!!

Cheers,
Bob

 

[newimaging]

Cable lenght

Do any of you guys add a connector at the wing to fuselage connection to remove the wing, and does that degrade the signal a lot ? I am planning on using the FSJ1-50A cable that "Elippse" keeps recommending.

Also, since I dont have a fuse yet, how much cable do you guys leave hanging out of the wing if not using a connector to make it to the radios ?

I am planning 1 Bob Archer Comm in left wing
1 Marker Beacon right wing
1 Bob Archer NAV in right wing

Just want to add those 3 coax, so I can close up the wings for now. Unless I am missing anything.