IowaRV9Dreamer

IowaRV9Dreamer

Well Known Member
I was thinking of mounting my two external GPS antennas (1 for the 430, 1 for the portable) on the aft rear top of the fuselage - directly behind the slider aft skirt. There is clearance there when the canopy opens. They would be mounted on either side of the slider center rail.

A local builder told me that if I do that and slide the canopy open, the GNS430 will "complain" due to the momentary interference... or maybe due to having to work through the canopy itsel.f... this might be an annoyance if I want to use the avionics with the canopy open... or open it while taxiing, etc.

In fairness, he has a GNS 480 not a 430W. Has anyone had this experience with a 430W?

I can mount them both far enough back that they won't be under the canopy, but I like the more forward location better.
 
I have the antenna for my G430W, G696, and XM weather under the cowl. They all work great in that location.
 
The GPS antenna for the GNS 430 on my RV-8 is mounted close behind the rear seat. It is always under the canopy, and a canopy frame tube goes close by over the antenna when the canopy is opened or closed. The GPS has always been very happy with things like this - I have never had any messages about lost signal, etc.

One thing to think about if anyone else does mount the antenna close behind the rear seat - put some sort of protection around the bottom of the antenna, to ensure the coax isn't damaged if you stuff the baggage area full. I noted during my annual inspection that the coax connector on my antenna is quite severely damaged - it must have happened during the OSH expedition. Looking at the amount of damage, I'm amazed that the GPS still works. I'm going to replace the straight connector with a right angle one, and make a metal shield to protect it from future damage.
 
The requirement for the 430W is that the GPS antenna cable need to be minimum of 13 feet and there is a maximum which I don't remember exactly. The antenna obviously does not need to be far, only the cable needs to be that long which can be coiled.
 
Dave,

That's where I'm mounting my 430W GPS antenna. I'm still building, so I can't say how it will work in the field, but The 430W picks up enough satellites while in my garage with the garage door closed, with the canopy open or closed, to attain integrity. My portable GPS antenna (for APRS) and XM satellite antenna will be mounted on the glare shield.

IIRC, With the 430W GPS antenna mounted there, the RG-400 antenna cable length is about 14'-15'. There is plenty of vertical clearance between the GPS antenna and the slider canopy frame. Just make sure you allow enough lateral clearance for the delrin slider block with the bolt installed.
 
i have two mounted about 15 inches apart behind the slider track. 430 and 250 garmins.
 
GPS antennas need a clear view of the sky and nothing metallic in the way. I like to mount mine on top of the panel glare shield. Take care with brackets hanging off of bulkheads as the bulkhead is an obstacle for satellites lower down. The 430W requires a certain amount of signal attenuation. Garmin suggest achieving this with a wad of expensive, heavy coax, suggesting about 20 feet of 400. That's nuts. Just put an RF attenuator with BNC connectors on it in line between the Garmin and a close-by antenna, like on top of the glare shield!

John Siebold
 
RF Attenuator for 430W?

Where does one get such an attenuator and do they have values to be considered or it just "an attenuator"?

Thanks,
 
My 430W antenna

Is mounted on top of the instrument panel under the front of the canopy with about 1.5 foot max of the gold coloured spendy coax.

Has worked just fine for three years.

My buddy is a Garmin systems engineer/test pilot and my CFI for my IFR ticket..he told me it was likely to work just fine and it did..:)

Frank
 
Then you're one of the lucky ones! The old non WAAS 430's never had a problem with that type of isntallation and short antenna cables, but I can tell you that we've had dozens of people call after installing their 430/530W GPS with short cables and no love. Almost universally those with very short cables end up with issues either right away or fairly quickly and the solution of adding more cable almost always fixes the issue. Not saying it'll never work with a short cable, but my experience is that 90%+ of the time they don't....been there answered lots of phone calls troubleshooting that!

Anyway, in regards to mounting the actual antennas the location mentioned in the first post seems to be a location that works. Any place on the top of the airplane is usually pretty good.

My 2 cents as usual.

Cheers,
Stein

P.S....what's with starting the body of your post in the title box? No big deal, but it is a bit weird to read posts like that - I'm just wonderin why people do that - nothin personal!? :) When you go to reply, part of your post gets missed and it also makes the archive searches weird too.


frankh said:
Is mounted on top of the instrument panel under the front of the canopy with about 1.5 foot max of the gold coloured spendy coax.

Has worked just fine for three years.

My buddy is a Garmin systems engineer/test pilot and my CFI for my IFR ticket..he told me it was likely to work just fine and it did..:)

Frank
Click to expand...
 
The attenuation requirements for the WAAS GPS receivers was changed a while back. The cable length requirements are minimum of 6.5? and a maximum of 35?. The attenuation values are minimum of 1.5dB and maximum of 6.5dB. This cable loss applies when the GNS 430W/530W GPS software is 3.0 or higher. RG 400 coax has a loss factor of 26.1 dB per 100 feet at the GPS frequency of 1575MHz.

Placement of the WAAS antenna under a non metallic surface is OK but be mindful of shadowing from other parts of the airframe when the antenna is not on the highest point. The WAAS antenna looks for satellites as low as 5 degrees off the horizon to achieve the accuracy it requires to produce the GPS precision approaches. If the antenna is not ?seeing? enough satellites and consequently does not have enough accuracy to produce the LPV approach the 430W/530W will automatically downgrade the approach to LNAV. Because of the capability to see satellites as low as 5 degrees off the horizon we dictate to have two WAAS antennas a minimum of 6 inches apart edge to edge. Understanding antenna real estate is usually at a premium this may not be always possible. These are some things to keep in mind when deciding where to mount the WAAS GPS antenna.
 
SteinAir said:
the location mentioned in the first post seems to be a location that works. Any place on the top of the airplane is usually pretty good.
Click to expand...

So Stein - you think it will work up there even as I slide the canopy open? As an avionics guy I'm expecting to spend a lot of ground time sitting in there playing with stuff!
 
g3xpert said:
The attenuation requirements for the WAAS GPS receivers was changed a while back. The cable length requirements are minimum of 6.5? and a maximum of 35?. The attenuation values are minimum of 1.5dB and maximum of 6.5dB. This cable loss applies when the GNS 430W/530W GPS software is 3.0 or higher. RG 400 coax has a loss factor of 26.1 dB per 100 feet at the GPS frequency of 1575MHz.
Click to expand...

Where does one find this information? It is not in my 400W series installation manual, at least not in the section detailing GPS antenna location requirements.
 
You can find the info you need in

Section 3-10 of the Rev B. manual (Nov. 2006).

.. it is secured so I cannot copy it here. :mad:

Bascially it says to meet intermod specs, you should have 3-7dB of loss between the antenna and the receiver. It says each connection "costs" 0.2dB and it also says that a typical 20' cable with 2 connectors is 4dB. Finally, it describes for "very short runs" you should coil up extra cable.

Yeah right - I'll be installing a small TNC attenuator at the antenna.
 
IowaRV9Dreamer said:
So Stein - you think it will work up there even as I slide the canopy open? As an avionics guy I'm expecting to spend a lot of ground time sitting in there playing with stuff!
Click to expand...

I think that since you won't fly with the canopy open and mainly use it to futz around and play with on the ground it should probably be fine. There are lots and lots of them installed that way with no problems, yours shouldn't be any different.

Cheers,
Stein
 
SteinAir said:
it should probably be fine.
Click to expand...
Since I got Stein's aviation grade iron-clad guarantee, I went ahead and mounted the antennas (shown temporarily in place):

Plenty of clearance when the canopy is opened:

Hopefully this will work for my extensive "futzing" phase :p
 
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