Today's Message Index:
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1. 02:28 PM - 1.5DB??? (William Hunter)
2. 03:05 PM - Re: 1.5DB??? (Chuck Birdsall)
3. 04:53 PM - Re: 1.5DB??? (user9253)
Message 1
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Hi,
I am installing a GTN-650 in my Velocity and the antenna location is only
2.0 feet from the unit itself. The Garmin instruction manual states that
the cable loss needs to be between 1.5 and 6.5 DB. The manual also states
that the calculated loss of a 6.5 foot cable with two BNC ends is 1.5 DB.
I assume that this means that I need to run a 6.5 foot cable for my short
run?
If so, what is the minimum radius of the bends I would need to make in the
cable to coil it up?
Thanks for your kind help!!!
Bill Hunter
Message 2
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Bill,
Yes, you need a minimum of 6.5 feet of cable length. The GPS antenna is an active
antenna, having a pre-amplifier built into it that's powered by a bias voltage
applied on the antenna center conductor (power comes from the GTN). The 1.5
dB of loss is to keep the receiver in the GPS unit from being over-driven and
thus degrading the signal.
The minimum 1-time bend radius from the RG400 spec is 1" - and the FAA spec from
AC 43.13-1 is 10 times the diameter of the cable (which would make it just under
a 2" radius). Both of these are a bit tight in my mind, and I would suggest
a 3" radius (6" dia) or larger loop. That'll give about 19" of length per
loop, which means three loops would get you what you need (or there about).
Chuck
---- William Hunter <billhuntersemail@gmail.com> wrote:
> Hi,
>
> I am installing a GTN-650 in my Velocity and the antenna location is only
> 2.0 feet from the unit itself. The Garmin instruction manual states that
> the cable loss needs to be between 1.5 and 6.5 DB. The manual also states
> that the calculated loss of a 6.5 foot cable with two BNC ends is 1.5 DB.
>
> I assume that this means that I need to run a 6.5 foot cable for my short
> run?
>
> If so, what is the minimum radius of the bends I would need to make in the
> cable to coil it up?
>
>
> Thanks for your kind help!!!
>
> Bill Hunter
Message 3
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In order to meet the minimum cable length requirement, I purchased a 10 foot RG400
cable with TNC connections from eBay for $12 with free shipping. Item number:
131817000902
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=468711#468711
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