Multiple NAV Antennas Or Splitter

[captainglen]

I currently have 2 Comm radios only one with NAV but will be adding a 2nd NAV with Glide Slope. I have a 3 way splitter and as an avionic technician but am a bit worried about reduced range in tracking VOR stations. I understand why most owners choose a splitter over a 2nd antenna or even a 3rd with separate G/S antenna but I am my own mechanic and avionic technician. Has anyone had experience with flying a with a splitter after upgrading and if there is or is not serious reduction in reception range.

[orionflt]

I used a splitter when i did my upgrades and did not see any noticeable reduction in performance. I have also found that since I have a garmin 430 GPS I am only using my VOR as a secondary source when i am on long cross countries, and that is just to make sure they still work. 

 

Brian

 

[1964-M20E]

After I had my IFD-540 installed my other nav com (a Norco) would not pick up VORs more that 10 miles out.  Previously it received them great.  The shop had installed a new splitter (multiplexer I believe is what the shop calls it)  We ended up replacing the coax cable form the tail bulkhead to the multiplexer and now it works great I can pick up VORs with either radio 70+ miles out at cruise altitude of 50 to 110

 

So end of the day you should not have any problems with the multiplexer.

[N601RX]

This is very common practice and seems to work well.  Each stage of a splitter will reduce the signal by 3db. So a 1:2 splitter will reduce both outputs by 3db while  1:4 will reduce each output by 6db. For reference 3db is 1/2 of the available signal while 6db is 1/4 of the signal. 

[DVA]

19 minutes ago, N601RX said:

This is very common practice and seems to work well.  Each stage of a splitter will reduce the signal by 3db. So a 1:2 splitter will reduce both outputs by 3db while  1:4 will reduce each output by 6db. For reference 3db is 1/2 of the available signal while 6db is 1/4 of the signal. 

I’m happy to see that N601RX jumped in and provided some factual RF advice. Splitters are great and work well in some cases and are the worse thing you can add to save some money in others.  If you are relying on a receiver to work at its maximum ability, and you can’t compromise that for safety or range, do not put in a splitter in the antenna circuit.

I’m a ol’ RF radio engineer (well, from the 70’s) and there was a saying that people in my industry lived by: “If you had $100 to spend on a receiver, invest 99 of those dollars in the antenna."

DVA

 

[N601RX]

I pointed out the splitter losses above, but in the real world those may not translate to very much distance. Distance is more likely a function of altitude with the power level contributing a small amount if in a fringe area. I have a single nav antenna and am happy with the range. Most other planes have the same setup. It's easy to run out of places to put antennas on small planes. 

[captainglen]

1964-M20E  I am glad for the practical experience in knowing a proper antenna system will give me proper range with a splitter.

N601RX Yes I understand that I will loose 6db of signal to each receiver but want to maintain at least 50 miles of range which seems to be possible in principal.

DVA My antenna is mounted on the belly just FWD of the tail cone, I do have a 2nd position to mount another antenna for a thin wire antenna in the vertical stab but running the cable is a major undertaking. I think I will try the splitter and if I can't get 50 miles at 5,000 feet I will run the extra antenna.

[captainglen]

This my current antenna location; it may not be aesthetically pleasing but it is low drag, has unobstructed visibility to ground stations from wings or fuselage and gets good ground plane effect from the belly. The previous owner removed the coax leading up the tail to the mounting plate provided under the cover with the slot in it.

[takair]

I've seen that type of installation done on V tail Bonanzas, but not on a Mooney.  How is your current reception?

 It is rare to have two Nav antennas, in fact, I don't think I've seen it on anything but a navigation flight check aircraft.  In my experience, a proper splitter/antenna combo does not reduce range significantly.  From a practical sense, you probably wouldn't notice unless you did a flight evaluation and plotted the range. 

[Piloto]

I went with this antenna splitter from Aircraft Spruce

http://www.aircraftspruce.com/catalog/avpages/ramiav585.php?clickkey=30238

It works very well with my towel bar tail antenna. Before I had a cat whiskers dipole antenna right on the windshield center post for glide slope. I took it out and connected the glide slope receivers to the splitter. Good LOC, GS and VOR reception.

José

 

 

[Jerry 5TJ]

On August 19, 2016 at 0:55 PM, DVA said:

 

I’m a ol’ RF radio engineer (well, from the 70’s) and there was a saying that people in my industry lived by: “If you had $100 to spend on a receiver, invest 99 of those dollars in the antenna.

I'm another of those old RF engineers, DVA, and I'd add that the antenna height is part of your cost equation.  

We already spent mucho AMU to get that antenna thousands of feet up in the air.  

Put another way: Antenna height and line of sight RF path far outweigh a few dB of feed line or splitter losses.

(Off-airport VOR ground stations are often sited where they have good propagation paths.  Flying south towards the Los Angeles area at 9,000' as I did hundreds of times, the LHS VOR can be used at surprisingly long range because it sits on a ridge nearly 6,000' up. )

For an aircraft VHF receiver I'd stress reliable, solid connections to the splitter and antenna rather than worry about a few dB loss.  

 

 

 

[Aerodon]

I've just replaced the OEM nav antenna in my Seneca.  Chose a Commant VOR/ILS antenna with a built in Balun.  The old co-ax was in poor shape, lots of corrosion on the terminals and shield.  Was surprised to find a coupling at the bottom of the vertical fin.  So replaced everything from the tail to the radios, including new RG400 cable.  

Now for the splitters - some radios like the Garmin series split the VOR/GS signal internally.  Others like the KX165 need separate GS/VOR input.  And some planes have a separate GS antenna, which is usually mounted high in the windshield for improved performance.  So you can get splitters and combiners for numerous permutations - find the right one, and don't connect a 'VOR' output to a 'GS'.  If you need to split a signal to an Apollo SL30, GNC255 or other radio that is expecting a combined signal use a Mini-Circuits '5-500' Mhz splitter.  And sometimes you need to split twice, for example:  Split Ant to #1 (say GNS480) and #2.  Then split #2 into VOR/GS for a KX165.

I've seen more complicated, using splitters in reverse, to combine GS and VOR antennas, then to split into #1 and #2, then split #2 to ILS and VOR.  The GTN750 manual illustrates several acceptable permutations.

 

Don

 

 

 

 

 

 

 

[Aerodon]

On August 19, 2016 at 8:05 AM, captainglen said:

I currently have 2 Comm radios only one with NAV but will be adding a 2nd NAV with Glide Slope. I have a 3 way splitter and as an avionic technician but am a bit worried about reduced range in tracking VOR stations. I understand why most owners choose a splitter over a 2nd antenna or even a 3rd with separate G/S antenna but I am my own mechanic and avionic technician. Has anyone had experience with flying a with a splitter after upgrading and if there is or is not serious reduction in reception range.

I went and checked my notes for the TR182 that I fly which recently got a GTN750.  It has separate GS and VOR antennas with original cables.  Two mini circuits splitters were installed to split each into 2 GS and 2 VOR cables.  One of each went to the old KY197 radio.  The one of each were combined using an ANT/GS/VOR splitter in reverse.  The Ant 'output' goes to the GTN750. All per GTN750 install manual

And all navigation signals are just fine, but maybe I haven't looked that closely because of all the GPS navigation instead of VOR navigation.

Don

 

[M20F]

Second antenna is a nice to have for redundancy in event of a loss.  If we are discussing accuracy though GPS is the solution for that.  Other than for fun I can't remember the last time I actually tuned in a ground station.

[Guest]

You only have one engine and that works well.  I think adding a second VOR antenna is the ultimate over kill.

Clarence