Antenna positions

[Janekom]

Com antennae: I see that some builders have their com antennae under the rear seat floors. I was wondering if one could not install your two com antennas under the baggage floor just behind the steps. If one then make inspection panels in the baggage floor in the same area, you will have access to the step bolts as well as the two antennae in future?

Transponder and marker beacon antennae: I thought I will fit this under the two front seats?

VOR antenna: I would like to fit it in the last "bay" of the tailcone. Have done this in a 7 and worked well.

Any ideas will be appreciated.

 

[RV10inOz]

COM 1 below and COM2 above............. using COM1 inflight usually and COM2 when taxiing etc..... think about the position of ant & direction of signal

Markers and TXponder under........ VOR / S in the tail!

DB

 

[w1curtis]

If you operate regularly from towered fields you may want to have one comm antenna on top. Even when your antennas are on top, depending on where you are on the field, I've seen some have a hard time contacting ground and clearance delivery. Other considerations are if you make a hard landing off airport and rip out the belly antenna, you still have the top antenna to call for help.

http://nerv10.com/wcurtis/90Electrical/antenna.html

My antenna locatons.

 

[jchang10]

http://www.jline.com/log/aviation/build/airframe/fuselage/photos/sec33/index.html

some pictures above for one of many ways to do it.

as far as the first question, i thought the same and went along that path more or less. my access cover is inboard of the step bolt. if i ever needed to remove the step bolt, i would drill a hole in the baggage floor big enough for a socket. the access hole would give me access for a wrench on the nut. it also gives me a way to inspect the step, wiring conduit, and is near a comm antenna (only on left side) underneat the seats.

the main issue i had not forseen, was that the step bolts are both directly underneath access covers above them. i then made my access covers removeable (lots of nutplates). in reality, it'll be a bear to get the step bolts in and out, so hopefully, i never have to do it.

also, i decided to put my comm antenna under the seats but closer to the baggage area for some mundane reason, which i am sure i wasted much too much time thinking about.

Jae

Com antennae: I see that some builders have their com antennae under the rear seat floors. I was wondering if one could not install your two com antennas under the baggage floor just behind the steps. If one then make inspection panels in the baggage floor in the same area, you will have access to the step bolts as well as the two antennae in future?

Transponder and marker beacon antennae: I thought I will fit this under the two front seats?

VOR antenna: I would like to fit it in the last "bay" of the tailcone. Have done this in a 7 and worked well.

Any ideas will be appreciated.

 

[N282S]

Transponder location

Here's my two cents. I have com1 under the passenger knees, ELt under the glass tail fairing, Com 2 in the right wing tip (Archer) and Nav in the left tip, and the transponder behind the baggage compartment. It was mentioned by Gregg, from Blue Mountain during his Oshkosh Forum, "Aircraft Wiring For Smart People" NOT to mount the transponder antennae under the pilots'passenger legs, thighs etc. Something about the frequency being too high. His article is at: http://www.bluemountainavionics.com/download.php#appnotes and titled, "Aircraft Wiring For Smart People: Greg's take on wiring for not-so-dummies. : Greg's take on wiring for not-so-dummies."

 

[[email protected]]

I started with the two comm antennas under the passengers seats, but I am in the process of moving comm 1 to the top of the plane. When I go to SLC I have trouble talking to the tower based on the orientation of the airplane. The tower frequency is 118.3. Once in the air I do not have a problem. My most recent departure, I could talk to them in the run up area....was given taxi and position and hold instructions...... I could hear them when I got into position, but when I got my take off clearance they did not hear my read back. They kindly let me do it again after I was airborne. It looks like it is frequency dependent, ground and clearance delivery work fine. My local airport TWR is 118.7 and I do not have any problems....but OGD is relatively small.

 

[johngoodman]

Thanks for the tip on the article by Greg. Well worth reading. As far as the transponder antenna, here is his statement:
A transponder puts out a couple hundred Watt microwave pulse in a frequency band that is none too healthy to be around.
On a metal airplane this is no big deal, since the whole thing is one big, shielded can. On a composite bird, you can be sitting unpleasantly close to a powerful microwave transmitter, which is Not Good.

Anyway, it's a good point. I'm thinking of putting the transponder antenna under the front seats and a blade type on top somewhere near the tail. Reason being that one of the future "traffic alert" systems will require it to see airplanes above you. I'm no expert on it so any enlightenment would be appreciated.

John

Here's my two cents. I have com1 under the passenger knees, ELt under the glass tail fairing, Com 2 in the right wing tip (Archer) and Nav in the left tip, and the transponder behind the baggage compartment. It was mentioned by Gregg, from Blue Mountain during his Oshkosh Forum, "Aircraft Wiring For Smart People" NOT to mount the transponder antennae under the pilots'passenger legs, thighs etc. Something about the frequency being too high. His article is at: http://www.bluemountainavionics.com/download.php#appnotes and titled, "Aircraft Wiring For Smart People: Greg's take on wiring for not-so-dummies. : Greg's take on wiring for not-so-dummies."

 

[Mel]

On a metal airplane this is no big deal, since the whole thing is one big, shielded can. On a composite bird, you can be sitting unpleasantly close to a powerful microwave transmitter, which is Not Good.[/I]

Anyway, it's a good point. I'm thinking of putting the transponder antenna under the front seats and a blade type on top somewhere near the tail. Reason being that one of the future "traffic alert" systems will require it to see airplanes above you. I'm no expert on it so any enlightenment would be appreciated.

John

John, I have been working with Zaon Flight Systems and Zane assures me that on aircraft the size of ours, one antenna is entirely sufficient. I have one antenna for my MRX on the bottom of the fuselage half way between the wing and stabilizer and I have seen no problems with "shadowing." The worse case with my installation would be aircraft @ 12 o'clock high and these aircraft do show up on my PCAS.

 

[L.Adamson]

John, I have been working with Zaon Flight Systems and Zane assures me that on aircraft the size of ours, one antenna is entirely sufficient. I have one antenna for my MRX on the bottom of the fuselage half way between the wing and stabilizer and I have seen no problems with "shadowing." The worse case with my installation would be aircraft @ 12 o'clock high and these aircraft do show up on my PCAS.

Mel,

I'm assuming the MRX is the smaller cigarette pak size unit. Is this antenna an option that's required for improved reception, or does the stub antenna work okay. I'm really interested in getting one of these.

L.Adamson

 

[w1curtis]

I'd take Greg's "Aircraft wiring for ___ people" with a couple grains of salt. Some things to consider; first Greg writes from the context of a non metal airplane builder. He advocates separate ground wires for all circuits--definitely not required in a metal aircraft. His thought on the transponder antenna placement, again is from the perspective of a non metal aircraft. Aluminum is a pretty good shield for these signal and strengths.

Second his statement on 28 vs 14 volt system, his direct quote was "Aircraft are 28 volts, cars are 14 volts, enough said." Well, no it is just not that simple.

After a few of these blanket statements, I quickly determined that this is not something that should be taken with any value by an RV builder.

 

[Mel]

Mel,
I'm assuming the MRX is the smaller cigarette pak size unit. Is this antenna an option that's required for improved reception, or does the stub antenna work okay. I'm really interested in getting one of these.
L.Adamson

Larry,
The "stub" antenna that came with the unit worked fine, but I wanted to get that stuff off the glare-shield. When you install the unit and use an external antenna they highly recommend the "blade" type antenna because of it's broader band-width. You also have to install an attenuator because the external antenna has much more gain than the original stub.
I've had my MRX for several years now and really like it. Flying around DFW traffic it spots traffic that I would never otherwise see.

 

[L.Adamson]

Larry,
The "stub" antenna that came with the unit worked fine, but I wanted to get that stuff off the glare-shield. When you install the unit and use an external antenna they highly recommend the "blade" type antenna because of it's broader band-width. You also have to install an attenuator because the external antenna has much more gain than the original stub.
I've had my MRX for several years now and really like it. Flying around DFW traffic it spots traffic that I would never otherwise see.

Thanks for the info. My wife is getting quite edgy about the traffic around here.

L.Adamson

 

[paul330]

VOR/LOC

Riveting is going well but I am at the stage where I need to think about wiring runs and possible antenna locations. The info here is all great but I have a couple of questions:

- is the VOR antenna also good for LOC? Specifically, will the wing tip Bob Archer do the job?
- what about GS? I've seen VOR/LOC/GS receivers but they are double units on the VS and I am not keen especially as it is already closed up!
- how about diplexers/splitters? I have seen one which gives dual NAV and single GS from one input. What would that input be?
- do the Garmin VOR units (GNS430, SL30) also give DME? presumably another antenna is needed.
- what guage is the antenna wiring?

I'm floundering a bit here so any help would be appreciated

 

[SkywayCaptain]

I have a SL30 in my 7 and the VOR/LOC/GS antenna is a single 1/4 wave whip that I mounted in the right wingtip (home brew type antenna). I have tested my setup and it receives fine throughout the operational service volume of the ILS system and VORs. You will need a diplexer to run one NAV antenna for all functions on some radios, but not the SL-30.

The SL-30 is capable of displaying DME information from a seperate unit, but it does NOT have a built in DME tranceiver.

RG58 will work fine for NAV antenna wiring. Use the braided center conductor type to help prevent vibration breakdown of the conductor.

Hope this helps some.

 

[paul330]

That's starting to make things clearer, thanks.

See if I have this right. A NAV antenna (wherever I choose to mount it) will be good for VOR/LOC/GS. If I diplex this signal, I can then feed it to a GNS430 and SL30. If I want DME, I need a seperate antenna and black box. The output from this goes to the Garmin. Presumably, I could use one feed and make it selectable to either the GNS430 or SL30.

Is that about it?

And for Comm antenna, it's preferable to have one top and bottom for ground and air reception?

Is a marker mandatory for IFR?

Sorry for all the questions but trying to make things clear before closing up wings etc

 

[azcloudflyer]

>>>is the VOR antenna also good for LOC? Specifically, will the wing tip Bob Archer do the job?

The VOR operates 108.0 to 117.95 MHz and the localizer is 108.1 to 111.95 MHz. Therefore you can use the same antenna to receive both.

>>>>what about GS? I've seen VOR/LOC/GS receivers but they are double units on the VS and I am not keen especially as it is already closed up!

GS is on the third harmonic of LOC. 329.3 to 335.0 MHz and you can not use the nav antenna for this.

>>>>how about diplexers/splitters? I have seen one which gives dual NAV and single GS from one input. What would that input be?

A splitter is used to split the same frequency band between two receivers. For example, connecting a single VOR nav antenna to two nav receivers. Each receiver gets slightly less than half the signal power. (3 dB minus insertion loss for those familiar)

A diplexer is used to split signals in different frequency bands between two receivers with minimal signal loss. For example, an ILS diplexer has a filter for LOC (108 - 111 MHz) and a filter for GS (329 to 335 MHz). The output of each filter is the diplexer output terminals. Because you did not split power in the same band, you do not have a half power loss. Only the insertion loss of the filters which is minimal. (typically less than a dB for those familiar with that concept)

- do the Garmin VOR units (GNS430, SL30) also give DME? presumably another antenna is needed.

>>>> what guage is the antenna wiring?

Do you mean the coax? I would recommend a double shielded cable with a stranded center core. Like RG-400 or equivelant.

>>> I'm floundering a bit here so any help would be appreciated :confused

Been there myself!!

Mike Andresen

 

[Auburntsts]

GS is on the third harmonic of LOC. 329.3 to 335.0 MHz and you can not use the nav antenna for this.

Hunh? I believe that the Rami AV-532L, the Commant CL-215, and the Bob Archer wing tip nav antenna all receive VOR/LOC/GS.

 

[Auburntsts]

Is a marker mandatory for IFR?

Stricly speaking for IFR flight no. However out of paragraph 91.205 Instrument flight rules. For IFR flight, the following instruments and equipment are required:

(2) Two-way radio communication and navigation equipment suitable for the route to be flown.

So if you want to fly any ILS or LOC approach that uses an OM to define the FAF then it would be required to fly the approach. If you have an audio panel then you've already got the MB receiver--you just need to add a MB antenna.

Of course, this all assumes the UK rules for IFR flight are the same as they are here in the US.

 

[Ironflight]

If you have an audio panel then you've already got the MB receiver--you just need to add a MB antenna.

Not to be a total nit-picker Todd, but this isn't necessarily so - many Audio panels come in two versions - with and without a MB. I bought mine without, since I can almost always identify the FAF without the beacons (GPS, usually). Saves on the cost of the Audio panel and antenna!

Paul

 

[[email protected]]

1. 430 requires a splitter for NAV and GS signals from the same Archer antenna, works great for me

2. SL30 has an internal splitter and thus you just hook the Archer antenna to the NAV connector

For the MB, you can just strip the end of a peice of coax. I have not tested this. My field does not have a marker and either way GPS works better.....

 

[azcloudflyer]

1. 430 requires a splitter for NAV and GS signals from the same Archer antenna, works great for me

2. SL30 has an internal splitter and thus you just hook the Archer antenna to the NAV connector

For the MB, you can just strip the end of a peice of coax. I have not tested this. My field does not have a marker and either way GPS works better.....

The 430 requires an external diplexer to properly separate nav from GS, not a splitter which produces a higher signal loss to each internal receiver.

The SL-30 has an internal diplexer on the nav input to separate nav from GS. Not an internal splitter.

 

[azcloudflyer]

Hunh? I believe that the Rami AV-532L, the Commant CL-215, and the Bob Archer wing tip nav antenna all receive VOR/LOC/GS.

The AV-532 is rated for 108 to 118 MHz. That is VOR and Comm only. Not GS. If you want GS from your cat whisker then you have to use something like the Comant CI-157 P which is designed to do that.

Couldn't find data on CL-215.

 

[Auburntsts]

The AV-532 is rated for 108 to 118 MHz. That is VOR and Comm only. Not GS.

I hear what you saying, but even though RAMI doesn't list the 532 as GS capable, since the GS is a Harmonic, shouldn't it receive it just as well as say a Comant 157? I'm not an engineer so I have really no clue as to antenna design and properties which is why I'm asking the question.

Food for thought, here's what a pre-Garmin SL30 install manual I found online says: "It is recommended that a single VOR/Localizer/Glideslope antenna be used for the installation. Most VOR/LOC-only antennas will still provide an adequate glideslope signal for the Apollo SL30 to operate normally". Now some may say since it's not guaranteed then go with the Comant. However, if I can get a usable GS signal, I'd prefer to stick to RAMI at half the price.

Out of curiosity, anyone out there using an AV-532 and getting GS off of it?

 

[paul330]

Phew!

Sorry guys, didn't mean to start an argument

Anyway, thanks for all the good gen. Seems that a single VOR/LOC antenna with suitable diplexer will feed to both a GNS430 and SL30. The only question then becomes whether I can get a GS signal or need a seperate antenna and opinion (as always) seems to be divided. I feel that I would only need GS to one reciver and the fallback position would be a LOC only approach.

All we need now is to persuade the UK powers that permit aircraft can go IFR/night!

 

[SkywayCaptain]

Theroy and manuals aside, I am running my SL30 VOR/LOC/GS all off of one antenna. The antenna is simply a piece of steel wire mounted to the end rib of the wingtip and bent back at an angle to clear the fiberglass tip. I trimmed it to a length using and SWR meter to the mid point of the VOR/LOC/GS freq range. It works fine. I have tested it myself and have plenty of signal strength throughout the service volumes of the VOR/LOC/GS's at various headings. Recieve antennas are not too picky about being tuned exactly to freq. This does not hold true if you are transmitting.

My data point

Edit: P.S. The GS freq is a odd harmonic of the LOC