SV-GPS-2020 mounting under the cowling?

[Bud_Keil]

I am planning an avionics upgrade to my RV-7 and was wondering about the mounting location of the SV-GPS-2020. I currently have two GPS antennas mounted on the firewall under the fiberglass cowling for my Garmin GNC 250XL and GDL-82. This location within the engine compartment has worked well for years. Can the SV-GPS-2020 be mounted in a similar location?

 

[akarmy]

Yes that's where mine is and it has been working fine.

 

[datadriver]

Yes that's where mine is and it has been working fine.

I mounted it underneath the foam/fiberglass in my Velocity and confirm a good GPS signal.

 

[swatson999]

I am planning an avionics upgrade to my RV-7 and was wondering about the mounting location of the SV-GPS-2020. I currently have two GPS antennas mounted on the firewall under the fiberglass cowling for my Garmin GNC 250XL and GDL-82. This location within the engine compartment has worked well for years. Can the SV-GPS-2020 be mounted in a similar location?

Been working fine for 8+ years now, sitting right alongside the 430W antenna.

 

[dlloyd]

Many have mounted it under the cowling, including me, with no problems. Dynon says no. What they don't want to say, is if you don't mount it as as approved, don't come to them if there is a problem.

 

[Raymo]

Mine is mounted on the glare shield inside (RV-7A). I painted it with flat black to keep it from reflecting off the windshield. I'd do the same again.

 

[DBRV10]

This is a pet topic of mine.

Just because somebody says on the internet it works fine, does not mean it is the best or appropriate place.

This is not open for argument. People do find their GPS works like this, but how well it works compared to being installed properly is another matter and one that those who do it rarely compare, because why would they? They don't know what they dont know.

I have seen many installations with GPS antenna's mounted side by side and under engine cowls where the certified (think IFR flight) GPS performs badly. The less fussy Garmin portables, the SV-GPS-250 etc with less integrity stuff going on, they just truck on, and at times with less performance than they should. I have seen the SV-GPS which generates a bit of noise by the way kill off a GTN close by. There are good reasons for this.

1. GPS antennas should be mounted with the best possible view of the sky. Simple as that. On the top skin of your tail cone is probably the best place. They should be kept well apart. You can get away with less, and read the manuals for the equipment you are using but 2 feet is a good rule of thumb for all antenna's.

2. Heat and vibration are enemies for electronics, and your GPS antenna is jammed full of them. Engine bays under cowls are a great source of heat and vibration, so what makes you think this is the best place to put them? So do not do it.

For the avoidance of doubt: This is not a debatable topic. Just because yours works does not make it right/best/optimal/acceptable performing for anyone else, and probably not optimal for you.

I know I sound harsh and berating but I cannot see a way to pussy foot around the topic.

Lets see what the experts say;

The GPS antenna should:


1. Be installed as near to level as possible with respect to the normal cruise flight attitude of the aircraft.


2. Be installed in a location to minimize the effects of airframe shadowing during typical maneuvers.


3. Be installed a minimum of two feet from any VHF COM antenna or any other antenna which may emit harmonic


interference at the L1 frequency of 1575.42 MHz.


4. Be installed a minimum of two feet from any antennas emitting more than 25 watts.


5. Be installed a minimum of nine inches (center to center) from other antennas, including passive antennas such as


another GPS or XM antenna.


6. Be installed a minimum of three inches from the windscreen.


7. Have a twelve inch center to center spacing between GPS antennas.

And;

Observe the following guidelines when choosing a location for an SV-GPS-250/2020:

• • The optimal location for the SV-GPS-250/2020 is a rigid surface on the upper fuselage of the aircraft.
• • Mounting location should be relatively level (the base of the SV-GPS-250/2020 is flat).
• • Do not locate the receiver within 3 feet of transmitting antennas.
• • Avoid antenna shadows (i.e., obstructions that block the antenna’s view of the sky).
• • All four of the SV-GPS-250/2020’s wires should all be connected to each SkyView system display for redundancy.

The diagram below shows the mounting dimensions of the SV-GPS-250/2020. Note that it utilizes a common bolt pattern found in much of general aviation.

PLEASE do not mount them side by side under the cowl.

 

[ned]

4 1/2 years no problem and always good ADSB report from FAA

 

[Bud_Keil]

Mine is mounted on the glare shield inside (RV-7A). I painted it with flat black to keep it from reflecting off the windshield. I'd do the same again.

I’m trying to remember, but I don’t think GPS antennas are supposed to be painted.

 

[swatson999]

...

This is not open for argument....
This is not a debatable topic.

Of *course* this is open for debate. Who says it isn't? You?

Enough people have done this, for many years now, without any problems whatsoever. Some have not. Assuming we're talking experimentals here, there's nothing wrong with trying it and seeing if it works.

I know for a fact that it works on mine, and has for 800 hours. No interference between the antennae...no difference in GPS signal levels on either box when the other one is turned off. Excellent antenna visibility with the exception of a narrow mask immediately aft due to the firewall.

How about your build your plane the way you want, and try not to dictate to anyone else how they must build theirs?

Geez...

 

[Raymo]

I’m trying to remember, but I don’t think GPS antennas are supposed to be painted.

Not painted with metallic paint. Non-metallic is fine.

 

[jnmeade]

Dynon says the SV-GPS-250 will work at a degraded level in conditions where the SV-GPS-2020 may not provide acceptable ADSB performance. It's in the most recent install manual. Page 8-6, install manual:

"However, the high integrity functions of the SV-GPS-2020 may require a different (better) installation location than was required by the SV-GPS-250, such as installation on the upper fuselage instead of underneath the cowling or inside a composite fuselage."

I don't see anything in print from an official or credible source about painting antennas. I called up a friend who was a radio antenna design engineer for Collins Radio for 30 years and who is also a published amateur radio antenna design guru. He said no metal paint, such as zinc chromate, should be put on a GPS antenna. Thin polyurethane or similar paint is OK, he said. He noted that "dirty" water, such as rain with grime in it will detune a narrow band antenna while it's on the ground but when flying it will run off and have no effect.

It's not surprising that Dynon would say on page 8-4 of the installation guide revision AG:
"Like all GPS devices, for most reliable performance, the SV-GPS-250/SV-GPS-2020 require a clear, unobstructed “view” of the sky. The SV-GPS-250/SV-GPS-2020 are designed to be mounted on the upper fuselage of the aircraft for an unobstructed (360° view) of the sky during maneuvers. If the SV-GPS-250/SV-GPS-2020 is mounted inside the fuselage (for example, on the top of the panel or underneath a cowling), the SV-GPS-250/2020’s view of the sky is partially or fully obstructed and GPS performance may be marginal in situations such as insufficient number of satellites “in view”."

Further,
"Observe the following guidelines when choosing a location for an SV-GPS-250/2020:
• The optimal location for the SV-GPS-250/2020 is a rigid surface on the upper fuselage of the aircraft.
• Mounting location should be relatively level (the base of the SV-GPS-250/2020 is flat).
• Do not locate the receiver within 3 feet of transmitting antennas.
• Avoid antenna shadows (i.e., obstructions that block the antenna’s view of the sky).
• All four of the SV-GPS-250/2020’s wires should all be connected to each SkyView system display for redundancy."

Since I installed mine (along with the navigator GPS) expecting IFR at night in IMC, it makes sense to me to follow the Dynon guide.

 

[jakej]

I agree about the closeness to other antennas - that applies to all sorts of transmitting/receiving antennas as the performance CAN (not WILL) be affected, so there is risk there.
Mounting Gps antenna under the cowl - I deliberately mounted mine there knowing what MAY happen & am prepared to pay the price & deal with it as I have alternative navigation capability. After 600 + hrs the Dynon 2020 is still 'locking' on well before my IFR Gps, as it always has done - so on forums don't tell us what we have to do, just educate us based on actual experience & with data.
I want the data, that's why I'm 'experimenting' with my setup.

 

[kellym]

I am planning an avionics upgrade to my RV-7 and was wondering about the mounting location of the SV-GPS-2020. I currently have two GPS antennas mounted on the firewall under the fiberglass cowling for my Garmin GNC 250XL and GDL-82. This location within the engine compartment has worked well for years. Can the SV-GPS-2020 be mounted in a similar location?

Two potential issues. I had my original GPS250 mounted there. It failed after 5 years there. Was easy to replace, since many 250 units have been replaced with 2020 units, surplus of used 250s out there.
2nd issue, using the 2020 for ADS-B it really needs full 360 view of sky and under the cowling it will have restricted view to the rear of aircraft.
I use a GTN 650 for my ADSB and its antenna is on top of cowling of my RV-10, gets me perfect performance reports on the ADS-B.
Granted top of fuselage space is limited if you have a slider canopy, but you really only need GPS antenna there, com antennas can go under belly.

 

[TouchTheSky]

Before deciding for one or the other location, I would do some live measurements (if possible) with the GPS2020 in it's intended location by watching the SkyView GPS Fix Status page. If over a certain period of time and ideally on different days, many satellites are in the green then I would consider this a reasonable location.

 

[swatson999]

for ADS-B it really needs full 360 view of sky and under the cowling it will have restricted view to the rear of aircraft.

I don't think it "needs" a full 360 degree view to perform sufficiently well. Yes, the solution uncertainty decreases with a wider-spaced geometry of satellites, but beyond a certain point, when you've got 10 or more satellites in view all over the sky, adding one or two more isn't going to change the dilution of precision by very much. You only need 4 to get at least *some* solution, and I've never seen less than 8 or 9.

In addition, if you are careful and mount it high enough, just underneath the cowling, and on a shelf so it's a fair distance forward of the firewall, the mask will be very small, perhaps 5 degrees or so. You can easily see if/how many satellites are masked by looking at the GPS status page. On mine, I only every see 1, maybe 2, at a very low elevation that are masked and not being received (and one of two things will happen...they'll come into view and get locked in, or drop below the horizon and it won't matter anymore).

I've never had any problems with GPS signals or solutions in this location, on either box (SV or 430W) because of insufficient satellites.

 

[jakej]

Just a qualification here - if it’s a composite airframe with no aluminium or metal other than the firewall blocking the signal then you will nave good satellite signal. Having the antenna close to the top cowl & 2-3” away from the firewall works too on any ‘metal‘ airframes - if you want to have the antenna ‘hidden’ & accept the risk Of possible failure, I haven’t had that experience yet

 

[DBRV10]

Geez some of you get your knickers in a twist pretty easy. Read my previous post carefully again and with the intent it was written. Save yourself the possible drama and just do it properly.

Like shielded cable for audio runs, sure you can get away with it, but chances are you will get noise. Even if you do not terminate the shields properly it will likely be way better, but hey....its your plane.

Example, IFD540 and the builder mounted the antenna under fibreglass in a aluminium bracket. Reliably it would drop integrity in turns. Think RNAV approaches. This also takes out the valid ADSB output. Cranky Dynon agent in Brisbane insisted it be moved outside. Bingo....Instant performance improvement and no more drop outs.

GTN650 with SV-GPS mounted side by side (as per photo above).........but not under the cowl, in view of the sky......relocate one antenna away, all the drop out problems stopped.

I have seen a cell phone (2003 era) kill off a Garmin portable every time it tried pinging for a tower. I have seen SV-GPS create huge noise on VHF comms, despite using RG400 and all well grounded.....

When you spend far too much time troubleshooting (usually unpaid), then arguing with the builder who refuses to believe you, only to resort to the recommended changes and discover the problem goes away, you draw the line in the sand pretty quick on what is acceptable and what is not. Like I said in my opening statement.

Just because somebody says on the internet it works fine, does not mean it is the best or appropriate place.

This is not open for argument. People do find their GPS works like this, but how well it works compared to being installed properly is another matter and one that those who do it rarely compare, because why would they? They don't know what they dont know.

 

[swatson999]

Yeah, well, that's just, like, your opinion, man.

Seriously...everyone appreciates data and real-world examples (not just "book learnin'"). But as noted...this is experimental aviation, so people are free to experiment. Under the cowling works great for some, not so great for others, but being pedantic and asserting that "this is not open for argument" or "this is not debatable" just because you say so is not really a valid way to discuss it.

FWIW, nowhere in the Dynon literature does it say it *has* to be mounted anywhere, nor does it say it *can't* be mounted FWF. It uses words like "may" or "avoid" and such.

As a friend of mine used to say when we were in the lab, wondering if something would work, "Only one way to find out!". I say mount it where you want, and then test it to see if it works.

 

[jnmeade]

What kind of test?

BTW, a very similar discussion with very similar points on each side is occurring in Van's aircraft with about an equal chance of resolution to the satisfaction of all concerned.