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TV antenna for VOR

maniago

Well Known Member
Can anyone tell me why using an old set of rabbit ears (set to 26" or so) wont work for a VOR/LOC/GS antenna (under canopy install)? Ham guys tell me that using the 75-300Ohm balun is fine for 50ohm coax work (and it has the freq range)....
aewk0o.jpg
 
Strips of copper tape around the back of a M-II canopy work well, and 'cat whisker' VOR antennas are basically the same thing, so why not? I don't think the copper tape antenna even uses a balun, but I can't find my copy of the plans at the moment.

Of course, leaving the rabbit ears out in the breeze might present some issues...

Charlie
 
Mani - using the 75ohm balun will produce some signal loss. Not bad enough to generally be a problem, but you will lose some range on the VOR. Where it will get more problematic is if you use a splitter downstream to split off to another NAV radio, or even splitting off the Glideslope signal. Some splitters are quite impedance-sensitive. I know you're running a GNS480 which has an internal splitter - I don't know how impedance-sensitive it might be.

On the other hand, there's no reason why you couldn't build a 50 ohm balun - it's not rocket science.

Then again, copper foils with a balun at their near-junction point would be more elegant and likely would cost you only a very few dollars more than your TV antenna setup.
 
Charlie - its under the canopy, so no breeze other than typical drafty-ness.
Also, theres a copper antenna design in the plans? Mustve missed that (ignored all the electrical and panel pages).

Canadian, yeah I have a splitter, 480 and SL30 feed from it. So I might be pushing my luck, but the TV antenna was waiting for the basement clean out anyway so its no money. Any $300 Rami antenna I buy is going to get the same splitter treatment tho.....

I gotta figure that some kind of balun is better than no balun, as most DIY antennas are running raw. Was thinking of getting a cheap VSWR meter and putting it inline and tuning the antenna length - cant get much easier with telescoping legs Id think.....
 
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Please don't put this in your airplane.

Some thoughts:
- A 'V' or a dipole antenna is already close to 50 ohm impedance. No balun required. Some old school thought is a 1 to 1 balun to transform from balanced to unbalance feed but years of data shows the gain from this is so small it is in the grass.

- Any dipole or V can be made from a couple of pieces of wire, one soldered to the coax center conductor, one to the coax shield. The wire lengths will be 25" or so. You can run the wires out from the center as desired, but recommend they run perpendicular to the fuselage axis. If you want it to conform to the canopy recommend the center feed point up high and the legs run down from it. The first third of the antenna does 90% of the work (the rest is there to bring it to resonance and such).

- Any antenna mounted in the cockpit, or under the cowl will pick up a lot of RFI. In the cockpit it will get it from all the glass panel switching power supplies. Under the cowl it will get ignition noise from being close to the ignition wires, mags and plugs. For this reason I recommend you seek a better location. Is there reason not to put it in the wingtip?

Carl
 
Not in the plans, but it was a common technique in both the M-II and the T-18 back in the 80s & in the early 90s, when I had a T-18, and M-II project for a while. The center point is at the rear of the canopy, and the legs extend around/forward a few inches above the canopy skirt. I've got the paper drawings for it around the house somewhere. If you want to play with the idea, I've got several rolls of the foil lying around, or you can order some from Spruce. Here's a link to Jim Weir's antenna book, describing how to build a foil antenna.
https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.rstengineering.com/rst/products/plasticplaneantenna/plasticplaneantenna_files/2802%2520Manual-s.pdf&ved=2ahUKEwiQyfWAmYLgAhUEOq0KHXHqAEMQFjAAegQIBBAB&usg=AOvVaw2YL3UUMehtH-GUUM0hFaW_

If the paper copy of the M-II/T-18 install turns up, I'll let you know. You might try asking over on the M-II forum, if it's still active. If any of the old guard is still around over there, they might have a copy.

Charlie

oh, edit: don't get too wrapped around the ferrite baluns in the article. I doubt you could tell the difference with a receive-only antenna.
 
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While experimenting with various antenna types during the development of the MGL N16 navigation radio I can conclude that pretty much all of the solutions presented in various pieces of literature work quite OK.
We are only receiving and this makes it somewhat less of an issue.

The main differences between solutions are overall sensitivity and directional characteristics. Sensitivity does not appear to vary too greatly as long as the structure resonates at the desired frequency but the directional characteristics can be a bummer so this needs a bit of attention.

A potential problem we found relates to the 50 ohm coax cable and it seems to make not much difference what type you use. For all types of dipols or related structures, with or without baluns we found the coax cable shield becomes live and a part of the antenna - and more than just a small part. If the antenna presents a perfect match to the cable the cable shield should be dead. This seems difficult to achieve for these antennas.
In most cases this matters little - but it can become a problem if the antenna cable happens to "receive" interference from on board electrical sources. As the cable is typically routed close to potential sources of such interference in the cockpit it can become an issue.

Practically this can express itself in unsteady VOR or localizer output on a frequency subject to interference.
Glide slope, while theoretically similar - we found to be somewhat more robust - perhaps due to typically reduced power of interfering harmonics at the higher frequencies used for GS.

Interestingly one of the best antennas we tried was a simple piece of wire perhaps 2-2.5ft long danging directly from the antenna connector of the receiver in "messy" fashion (this in a "plastic" aircraft). This was just an initial attempt to check that all was working before trying real antennas - we found most alternative antenna solutions did not perform better and often worse in some or other way (most of the tests where "rough" so your mileage can vary - it was just done to get a feel for this).

The traditional VOR/LOC/GS antennas we all know so well (towel bar types, or tail mounted V types) worked well. Still some directional issues but well defined such that the maximum sensitivities are where they are the most useful. Perhaps not the most sightly and a bit of drag perhaps but personally those are my choices.

What we found helps with a live antenna cable shield - route the cable tightly against your metal fuselage without any physical space for as much distance as possible - then when it needs to get to the nav radio route it with as short as possible path through the air or if possible against metal supports as much as possible, all the while avoiding proximity to other electrical cables and potential interference sources like EFIS systems, any form of LCD display or other digital electronics or switched power supplies.

Rainier
CEO MGL Avionics
 
While experimenting with various antenna types during the development of the MGL N16 navigation radio I can conclude that pretty much all of the solutions presented in various pieces of literature work quite OK.
We are only receiving and this makes it somewhat less of an issue.

Rainier
CEO MGL Avionics

Thanks Rainier - your whole write up was very helpful, esp the notes on live shielding vs balun use.
 
What we found helps with a live antenna cable shield - route the cable tightly against your metal fuselage without any physical space for as much distance as possible - then when it needs to get to the nav radio route it with as short as possible path through the air or if possible against metal supports as much as possible, all the while avoiding proximity to other electrical cables and potential interference sources like EFIS systems, any form of LCD display or other digital electronics or switched power supplies.

Rainier
CEO MGL Avionics

Rainier,
What about double shielded RG400 coax, such as this.....https://fieldcomponents.com/RG-400-...MI0biCr-uV4AIVDoTICh3IpAKWEAQYBCABEgKa8_D_BwE

...at $2/ft, its cheaper than regular RG400 from Spruce etal....tie the outer shield to the radio case, leave the other end floating, and no live shield to act as an antenna, no?
 
Rainier,
What about double shielded RG400 coax, such as this.....https://fieldcomponents.com/RG-400-...MI0biCr-uV4AIVDoTICh3IpAKWEAQYBCABEgKa8_D_BwE

...at $2/ft, its cheaper than regular RG400 from Spruce etal....tie the outer shield to the radio case, leave the other end floating, and no live shield to act as an antenna, no?

Sadly our experiences with RG400 show that it is not a plaster to fix antenna problems. It is good cable with very low loss as long as it is used correctly. To be honest, provided you have a well matched antenna, there is not much difference to be had between a good quality RG58 and RG400 at VHF frequencies for our use.

It is often thought (and that included me) that the extra shield somehow isolates the inner cable from interference etc. But that does not happen this way (sadly).

Essentially the inner core and the shield forms a transmission line. If all if perfectly done the signal energy travels as a wave via the center conductor and the capacitively and inductively matched shield assists in the wave traveling without radiating anywhere. The result is that all the energy arrives at the destination.
If the shield is not correctly terminated at any of the two ends (the antenna side often being the problem area) the shield does not work correctly. More to the point it becomes "live" - part of the signal traveling in the inner core is now free to couple to the shield which also gets any reflections from the antenna - just to make things worse. Of course since it has some length it forms an antenna that will resonate at a couple of frequencies based on its length but also on how it is routed (you can create shorter antenna stubs in all sorts of ways here) - the result is usually a very complex antenna (not a very efficient antenna most of the time). All of this works for receive as well - the shield receives RF and couples it to the inner core.

A live shield is what often results in radio interference - other instruments going crazy when you transmit and easily receiving interference from strobes to anything digital (in particular if it has a big LCD display).

Using an SWR meter is often used to check the quality of your installation and this is a good way - don't be fooled by statements like "2.0 is good enough". That's fine for radio amateurs 30 meter rig but not for your installation. You should really try and get it below 1.4 if you have any interference.
Now, just a word of warning - I have now come across installations using dipols with typically three ferrites mounted at the base of the antenna over the shield as some sort of balun. These arrangements tend give a very good SWR but actually do not work !!! Instead the reflected energy of the mismatched antenna is simply prevented from returning by the ferrites giving the impression that all is well. Instead, from an RF point of view, the shield is disconnected at the antenna. A quick check with a field strength meter shows that effectively the entire antenna cable is your antenna (the shield is really very live) and the half of the dipol that is attached to the core does some radiation as well - the other half does nothing much.
These antennas are becoming popular in some aircraft as you can hide them but in my experience are a really bad idea.

Back to using antennas like this for NAV (dipols with proper baluns or matching transformers or shaped to present a good match by other means) - generally they work OK. RX is somewhat less critical than TX but you still need to be aware of interference which can affect your NAV radio.
You will likely have your NAV radio plugged into an intercom system.
Switch all of your systems on (except the engine) and scan through all channels starting at 108 Mhz while listening to the background noise. Make sure none of the channels gives you interference - this should be audible. If you find a channel - switch off equipment one by one. If all is off (except the radio and intercom and nothing changes - the interference likely comes from external to your aircraft (Florescent tubes in your hangar perhaps ?).
If you do not find a single channel with interference you cannot live with - you're antenna should be good to go.
You can do a final check with engine running - just to make sure your ignition system is not a potential interference source.

Rainier
CEO MGL Avionics
 
It is often thought (and that included me) that the extra shield somehow isolates the inner cable from interference etc. But that does not happen this way (sadly).
Rainier
CEO MGL Avionics

Hmmm. I hear what youre saying. But it sure seems electrically illogical that double shielded cable would have zero positive impact to the live inner shield issue. Even from a business perspective, if theres no benefit whatsoever, what would be the point of anyone bothering to manufacture double shielded in the first place....?

Either way double shielded is almost 1/2 the price of regular Rg400, so I'll give it a shot. No harm no foil (haha).
 
Hmmm. Even from a business perspective, if theres no benefit whatsoever, what would be the point of anyone bothering to manufacture double shielded in the first place....?

I've got one word for you: PLASTI...no, that's not it...

Marketing!
 
Mani - using the 75ohm balun will produce some signal loss. Not bad enough to generally be a problem, but you will lose some range on the VOR. Where it will get more problematic is if you use a splitter downstream to split off to another NAV radio, or even splitting off the Glideslope signal. Some splitters are quite impedance-sensitive. I know you're running a GNS480 which has an internal splitter - I don't know how impedance-sensitive it might be.

On the other hand, there's no reason why you couldn't build a 50 ohm balun - it's not rocket science.

Then again, copper foils with a balun at their near-junction point would be more elegant and likely would cost you only a very few dollars more than your TV antenna setup.

+1... yes TV rabbit ears (dipole) would "work" in theory, yet NOT... One they are adjustable in length, you don't want that. You want them tuned to the VOR/ILS/LOC Freq., one length will work 25".

Angle, needs to be fixed... these TV ears are adjustable from 180 degrees (flat out) to zero degrees between elements. The plastic support.... no.

As other said you can make your own.

Cheapest new VOR antenna I found was $200 https://www.aircraftspruce.com/catalog/avpages/av532.php Suggest eBay... under $100 but don't buy any old crusty garbage. Get a new one.

Store bought VOR antenna have a heavy base and typically BNC connector built in "Balan". I bolted my to the bottom of fuselage way back under the horizontal stab on my RV-4 (fuselage is narrow there). Out of the way, low drag. For "racing" I took it off (nut plates in fuselage) and secured the coax and taped over the hole. Some put it top of Vertical Stab under the tip fairing.

Some VOR whiskers require you to splice or crimp on lugs to coaxial shield and center conductor (no BNC). Typically you make a coaxial Balun (part of building is learning). As Canadian_JOY said the impedance of the whiskers is about 50 ohms (which is good), but you have balanced dipole antenna feeding a coaxial. Coaxial is "unbalanced". One is feed and one ground, where dipole both elements are in free space (no ground). So to convert the balanced antenna to a unbalanced coaxial you need a BALAN... You can make it out of coaxial as shown in this article:

http://www.aeroelectric.com/articles/BALUN/Balun_Fabrication.html
OR
http://www.piteraq.dk/flight/jodelantenne.html
OR
http://www.vansairforce.com/community/showthread.php?t=78551
 
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Hmmm. I hear what youre saying. But it sure seems electrically illogical that double shielded cable would have zero positive impact to the live inner shield issue. Even from a business perspective, if theres no benefit whatsoever, what would be the point of anyone bothering to manufacture double shielded in the first place....?

Either way double shielded is almost 1/2 the price of regular Rg400, so I'll give it a shot. No harm no foil (haha).

It's perhaps incorrect to call it a double shield. It really just has a "tighter" shield due to double the amount of individual threads in the shield.
It has very low leakage which is the only real advantage - and also tends to be made to closer tolerances so the impedance over the length of the cable is very constant.

What you really want is double shielded coax cable where the second, outer shield is electrically isolated from the inner shield. You then ground that outer shield independent from the inner coax cable at both ends.

In this case you do have a real shield that should help. Many years ago when I was working at a university electronics lab they made their own double shielded cable this way - you can buy just the braid and you then slip in the entire coax cable so you now have a real double shield where the outer shield can have a different electrical potential to the inner shield.

Rainier
CEO MGL Avionics
 
VOR and ILS antenna

Interesting discussion !!

When I was down at Vans earlier in the week had a chance to take a look at the RV-12IS-T that has a dual Garman G3 set up and is capable of providing instrument training (but not operable in actual IFR conditions due to regulations governing the airplane certification). The VOR/ILS antenna is a "whiskers" type antenna mounted towards the top of the vertical stab. I didn't get a chance to ask what testing had been done to determine the location or measure the radiation beam pattern or any other technical data.

I plan on installing VOR/ILS capability in a RV-7A so the antenna installation was of interest to me.

The big problem is that without all the test equipment one is just shooting in the dark.

I have past experience of doing antenna measurements and testing at an antenna test site. Accurate dimensional metal model airplanes one tenth or one twentieth scale were fitted with antenna operating at ten or twenty times the expected frequency, mounted on a rotating turnstand and high enough off the ground to not have ground effects. A signal was transmitted from the airplane model antenna, the turnstand rotated and the received signal recorded as a function of the angle. The results were used to home in on the locations of the antenna on the full size airplane. The original antenna design and possible locations were all defined by theoretical analysis. There were lots of surprises, pattern lobes where not expected and impedence matching problems that took work to resolve. All took lots of money and resources and experience to get resolved.
We don't have access to that kind of capability so sticking with the TSO'd antenna in similar locations to those used on similar plan form certified aircraft is likely to have the best chance of success. (Piper, Beechcraft, Mooney are all good data points for antenna locations)

The relevent parameters to consider.
1. Cables
Characteristic impedence - matches antenna and receiver (50 ohms typical)
cable loss - should be low loss
Connectors installed correctly and cable checked for VSWR across the band

2. Antenna
Checked for impedence match across the band when installed
Checked for radiation pattern in the required directions. This may require flying a specific test pattern with a variable attenuator in the antenna to RX line to determine the link margins under specific VOR and ILS capture conditions.
3. Some theoretical analysis to determine what link margins to expect so that the range of attenuator values can be determined.

Starting off with major components that are questionable or unknown just moves the project further back towards the concept phase. Using known quantities may add considerable cost but significantly reduces the number of variables and increases the chances of success with limited resources in a reasonable timeframe.

KT
 
VOR and ILS antenna

Interesting discussion !!

When I was down at Vans earlier in the week had a chance to take a look at the RV-12IS-T that has a dual Garman G3 set up and is capable of providing instrument training (but not operable in actual IFR conditions due to regulations governing the airplane certification). The VOR/ILS antenna is a "whiskers" type antenna mounted towards the top of the vertical stab. I didn't get a chance to ask what testing had been done to determine the location or measure the radiation beam pattern or any other technical data.

I plan on installing VOR/ILS capability in a RV-7A so the antenna installation was of interest to me.

The big problem is that without all the test equipment one is just shooting in the dark.

I have past experience of doing antenna measurements and testing at an antenna test site. Accurate dimensional metal model airplanes one tenth or one twentieth scale were fitted with antenna operating at ten or twenty times the expected frequency, mounted on a rotating turnstand and high enough off the ground to not have ground effects. A signal was transmitted from the airplane model antenna, the turnstand rotated and the received signal recorded as a function of the angle. The results were used to home in on the locations of the antenna on the full size airplane. The original antenna design and possible locations were all defined by theoretical analysis. There were lots of surprises, pattern lobes where not expected and impedence matching problems that took work to resolve. All took lots of money and resources and experience to get resolved.
We don't have access to that kind of capability so sticking with the TSO'd antenna in similar locations to those used on similar plan form certified aircraft is likely to have the best chance of success. (Piper, Beechcraft, Mooney are all good data points for antenna locations)

The relevent parameters to consider.
1. Cables
Characteristic impedence - matches antenna and receiver (50 ohms typical)
cable loss - should be low loss
Connectors installed correctly and cable checked for VSWR across the band

2. Antenna
Checked for impedence match across the band when installed
Checked for radiation pattern in the required directions. This may require flying a specific test pattern with a variable attenuator in the antenna to RX line to determine the link margins under specific VOR and ILS capture conditions.
3. Some theoretical analysis to determine what link margins to expect so that the range of attenuator values can be determined.

Starting off with major components that are questionable or unknown just moves the project further back towards the concept phase. Using known quantities may add considerable cost but significantly reduces the number of variables and increases the chances of success with limited resources in a reasonable timeframe.

KT
 
+1... yes TV rabbit ears (dipole) would "work" in theory, yet NOT... One they are adjustable in length, you don't want that. You want them tuned to the VOR/ILS/LOC Freq., one length will work 25".

huh? Of course its adjustable. But isnt it obvious that one can adjust it to the proper length and "lock" it there with some AL tape? Its gonna be double-sided tapped to the underside of the canopy anyway.....

Angle, needs to be fixed... these TV ears are adjustable from 180 degrees (flat out) to zero degrees between elements. The plastic support.... no.

Same as above......

As other said you can make your own.

....um, isnt that what I'm doing? I totally dont get why you guys (except for RvCharlie) dont see this as an easy DIY.....

Coaxial is "unbalanced". One is feed and one ground, where dipole both elements are in free space (no ground). So to convert the balanced antenna to a unbalanced coaxial you need a BALAN... You can make it out of coaxial as shown in this article...

Yes the coax cable balun is easy to do, but as noted in the article, its nice, but probably not necessary anyway......
 
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It's perhaps incorrect to call it a double shield. It really just has a "tighter" shield due to double the amount of individual threads in the shield.
It has very low leakage which is the only real advantage - and also tends to be made to closer tolerances so the impedance over the length of the cable is very constant.

What you really want is double shielded coax cable where the second, outer shield is electrically isolated from the inner shield. You then ground that outer shield independent from the inner coax cable at both ends.

In this case you do have a real shield that should help. Many years ago when I was working at a university electronics lab they made their own double shielded cable this way - you can buy just the braid and you then slip in the entire coax cable so you now have a real double shield where the outer shield can have a different electrical potential to the inner shield.

Rainier
CEO MGL Avionics

Ah, ok, good. WRT the cable, I was assuming that double shielded meant two shields separated by an insulator, but if its not, then yes, thats not gonna help.

I was similarly considering using AL foil tape on the entire length of coax to make the second shield (very cheap) or running the cable inside some spare versatube for its length (not quite so cheap, but easier to gnd).
 
Mani,

If you dig through a few cabling catalogs (Belden, etc), You'll find many examples of coax with foil shields that are rated at 100% coverage. There will be a tinned, bare copper 'drain' wire that contacts the foil along the entire length of the cable, and can be used if one needs to make a soldered connection to the shield.

Having said that, there are decades of experience showing that pretty 'primitive' cables work just fine for VOR (and a/c comm) use. This might be a case where 'better is the enemy of good enough'. In my very unqualified opinion, the same applies to antennas at these frequencies. Yes, mega$ test gear on an antenna range can see differences, but in an a/c moving at 150kts+, the odds of getting between two nodes in the receive pattern, and remaining there for more than a few seconds, seem vanishingly small.
 
Mani,

If you dig through a few cabling catalogs (Belden, etc), You'll find many examples of coax with foil shields that are rated at 100% coverage. There will be a tinned, bare copper 'drain' wire that contacts the foil along the entire length of the cable, and can be used if one needs to make a soldered connection to the shield.

Having said that, there are decades of experience showing that pretty 'primitive' cables work just fine for VOR (and a/c comm) use. This might be a case where 'better is the enemy of good enough'. In my very unqualified opinion, the same applies to antennas at these frequencies. Yes, mega$ test gear on an antenna range can see differences, but in an a/c moving at 150kts+, the odds of getting between two nodes in the receive pattern, and remaining there for more than a few seconds, seem vanishingly small.

Yeah I agree - the thread is probably way out on the 6th beer end of a hangar discussion. That said, I see that triaxial cable is what I would be after to quiet down the interference....at $10/ft Ebay...ouch! Maybe not so much.....
 
'Is it broke?' (As in, do you know you have an interference problem?)

If not, don't try to fix it with heroic effort$. There are 10s of thousands of certified a/c flying around with their VOR receivers functioning just fine while using 50+ year old RG58 coax. Ponder that, while you write the check for $10/ft coax that was created for radios operating at 10X our a/c nav frequencies, and in some cases, 1/100th to 1/1000th the signal strength.
:)

Charlie
 
Huh? Are you trying to be insulting, like what I said was dumb? Did I offend you? Let me ask you WHY use a TV antenna? The radials need to be about 25" long and fixed angle. Here is why a TV antenna is a poor choice:

- Telescopic antennas are really not made to be out in weather, they have multi segments that slide into one another. Water can get in there.
The wall thickness of these antennas are thin and can be kinked. You have 4-5 feet of antenna compressed into 2 feet, not particularly light..

- Outer diameter is large, 1/4" to 5/16" will be draggy compared to some small diameter SS whips. The factory VOR antennas are also tapered, low drag.
The plastic block the TV antennas uses will not hold up to 200 mph and weather... The adjust-ability makes it weak.

- DIY? Get some 3/16 solid stainless rods.... and cut a phenolic block, and make your own VOR antenna that looks like it belongs on an airplane;
it will be durable, perform better and not much more than "Rabbit Ears"... my opinion.

- As far as angle, Huh? Trying to fix the length with tape and angle with glue on a TV antenna is just, huh?

Of course its adjustable. But isnt it obvious that one can adjust it to the proper length and "lock" it there with some AL tape? Its gonna be double-sided tapped to the underside of the canopy anyway.....
Not sure why you are so worked up about this. Do as you like. Did not say you can't or don't. but what you describe sounds ugly. A VOR antenna under the canopy... two 2' long elements at 45 degrees will be hard to fit under a canopy (with out poking your eye out), AND it will perform like **** inside the fuselage.

Some have put VOR antenna in the lower fiberglass engine cowl. The wing tip antennas you can buy I read are marginal both for NAV and COM in range. Also as suggested copper tape on the canopy is a choice, but the performance will be poor is some directions and block your view.

....um, isnt that what I'm doing? I totally dont get why you guys (except for RvCharlie) dont see this as an easy DIY.....
You don't want opinions? OK, but I think it's a bad idea. There I said it... for reasons "see above". Go do it and show us all how it turns out and performs. Change our minds. At this point it's moot to me.

Yes the coax cable balun is easy to do, but as noted in the article, its nice, but probably not necessary anyway......
What is your point. If you want a more symmetrical pattern and better sensitivity a BALUN is appropriate... EVERY modern certified VOR/ILS antenna has a Balun built into them with a BNC connector. To not use a Balun is amateur. Again do what ever you want. Up to you. You seem determine to cut every corner. You will get the expected results I promise, and I don't mean good. Why bother. Planning on flying ILS to Cat 3 mins with your TV antenna set up... good luck...
 
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'Is it broke?' (As in, do you know you have an interference problem?)

If not, don't try to fix it with heroic effort$. There are 10s of thousands of certified a/c flying around with their VOR receivers functioning just fine while using 50+ year old RG58 coax. Ponder that, while you write the check for $10/ft coax that was created for radios operating at 10X our a/c nav frequencies, and in some cases, 1/100th to 1/1000th the signal strength.
:)

Charlie
Beat to death, but you are right to an extent.
http://www.vansairforce.com/community/showthread.php?t=75839

RG400 has less loss than RG58. RG400 loss is 9.5 dB /100ft.
RG58 loss is 14 db / 100 ft. Short runs it is insignificant. However
for GPS signals it may be critical.

In short runs it is not much. However many manufactures require RG400.

Price of RG400 is not ten a foot.
RG400 can be had for just under $2.00/ft....

RG58, high quality is just under $1.00/ft.
You can get RG58 for real cheap, like $0.25/ft,
but it is some real bogus poor quality crud RG58.
 
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GPS has not entered the discussion, until now. :) We're talking about frequencies that are barely above the FM radio band, and at the middle of the old TV VHF band. And I wasn't telling him to use RG58; just that he doesn't need to spend $10 a foot on receiving a 110 MHZ signal.
 
RG-58 is solid center conductor, RG-400 is multistrand center conductor so stands up better to vibration. VOR and ILS localizer frequencies are in the 100 Mhz band the ILS glideslope is in the 300 Mhz band so the ILS antenna needs to be matched to both bands from one feed point. This requires some experience in antenna design to get both a multiband match and achieve a good omnidirectional beam pattern at the 100 Mhz band and a good forward gain at the 300 Mhz band.

Just sayin.........

KT
 
You don't want opinions? OK, but I think it's a bad idea. There I said it... for reasons "see above". Go do it and show us all how it turns out and performs. Change our minds. At this point it's moot to me.

Well I get what I deserve then. Enough said.

I'll see you guys at OSH. You'll know its me - I'm the humble antenna design engineer with the Mustang2 and ugly TV antenna under the canopy.
 
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