Hi!

I have a SL30 and a GNS 430 in my plane. They use the same antenna via a
splitter.
When I dial in the same VOR in both units the SL30 catches up the
radials always between 20 and 50 nautical miles earlier than the GNS
430! (Altitude about 3000 ft, flat area)

Is this normal?
What is your experience?
How far away do you have a reception of a VOR with your GNS 430?

Fly safe!
Maik

I can't speak for the GNS 430, but the SL30 has UNBELIEVEABLE signal
processing capability. I can track a good VOR well over 100 miles, and
I've got a mediocre cats whisker antenna mounted on my tail. I'm told
the SL30 uses digital signal processing; I don't know what the GNS 430 uses.

In short, I'm not at all surprised by your experience.

Rich


Maik wrote:
> Hi!
>
> I have a SL30 and a GNS 430 in my plane. They use the same antenna via a
> splitter.
> When I dial in the same VOR in both units the SL30 catches up the
> radials always between 20 and 50 nautical miles earlier than the GNS
> 430! (Altitude about 3000 ft, flat area)
>
> Is this normal?
> What is your experience?
> How far away do you have a reception of a VOR with your GNS 430?
>
> Fly safe!
> Maik

It would seem that UPS-AT technology is significantly better than Garmin's.

Rich wrote:
> I can't speak for the GNS 430, but the SL30 has UNBELIEVEABLE signal
> processing capability. I can track a good VOR well over 100 miles, and
> I've got a mediocre cats whisker antenna mounted on my tail. I'm told
> the SL30 uses digital signal processing; I don't know what the GNS 430 uses.
>
> In short, I'm not at all surprised by your experience.
>
> Rich
>
>
> Maik wrote:
>
>> Hi!
>>
>> I have a SL30 and a GNS 430 in my plane. They use the same antenna via
>> a splitter.
>> When I dial in the same VOR in both units the SL30 catches up the
>> radials always between 20 and 50 nautical miles earlier than the GNS
>> 430! (Altitude about 3000 ft, flat area)
>>
>> Is this normal?
>> What is your experience?
>> How far away do you have a reception of a VOR with your GNS 430?
>>
>> Fly safe!
>> Maik
>
>

On 29-Sep-2004, Rich > wrote:

> I can't speak for the GNS 430, but the SL30 has UNBELIEVEABLE signal
> processing capability. I can track a good VOR well over 100 miles, and
> I've got a mediocre cats whisker antenna mounted on my tail. I'm told
> the SL30 uses digital signal processing; I don't know what the GNS 430
> uses.
>
> In short, I'm not at all surprised by your experience.


VOR reception range is dominantly determined by line-of-sight. However, in
marginal situations (i.e. the station is just over the horizon) receiver
quality and/or antenna cable loss can make a significant difference. I do
not know if he VOR processing system in the GNS 430 is similar to the one
used in the SL30, however a simpler explanation for the difference could be
different RF losses in the cables from the splitter to the receiver. By the
way, a VOR test system could quantify the sensitivity difference very
quickly with a simple over-the-air test.

--
-Elliott Drucker

The VOR signal out of the receiver is a 9960Hz sine wave that is AM
modulated at 30Hz and FM modulated at 30Hz. The phase difference
between the AM and FM signals is the bearing to the station.

Outside of the standard service volume of a VOR, this signal starts to
get quite noisy. This makes domodulating the AM and FM components
more difficult as the signal to noise ratio degrades. The quality of
the filtering of the 30Hz and 9960Hz bandpass filters (or equivalent
digital bandpass filters in a DSP) determines how far out you can
accurately receive the station. Apparently the SL30 does a better job
of filtering out the noise than the GNS430.

Dean

Maik > wrote in message >...
> Hi!
>
> I have a SL30 and a GNS 430 in my plane. They use the same antenna via a
> splitter.
> When I dial in the same VOR in both units the SL30 catches up the
> radials always between 20 and 50 nautical miles earlier than the GNS
> 430! (Altitude about 3000 ft, flat area)
>
> Is this normal?
> What is your experience?
> How far away do you have a reception of a VOR with your GNS 430?
>
> Fly safe!
> Maik

>>
The VOR signal out of the receiver is a 9960Hz sine wave that is AM
modulated at 30Hz and FM modulated at 30Hz. The phase difference
between the AM and FM signals is the bearing to the station.
<<

How does that work. =Something= has to be directional, no?

Jose

--
(for Email, make the obvious changes in my address)

"Teacherjh" > wrote in message ...
> >>
> The VOR signal out of the receiver is a 9960Hz sine wave that is AM
> modulated at 30Hz and FM modulated at 30Hz. The phase difference
> between the AM and FM signals is the bearing to the station.
> <<
>
> How does that work. =Something= has to be directional, no?
>
Yes, one of the two signals is swept directionally either by electronic or
mechanical means (it doesn't matter which one as long as they are moving
in the right direction relative to the other).

I wouldn't be satisfied with the answer that one unit is more sensitive or
has better demod until I knew that the splitter, connectors, and coax were
all in good shape. Then I'd wonder if the Garmin was detuned somehow instead
of jumping right on poor or lesser design.

Dan

Jose,

The FM component goes out the same in all directions from the VOR
station. The AM component varies with the angle from the station.
North of the station there is no phase difference. At 45 degrees the
AM component lags the FM component by 45 degrees, and so on. The AM
component is phase shifted by a phased-array of antennas around the
VOR station.

Dean

(Teacherjh) wrote in message >...
> >>
> The VOR signal out of the receiver is a 9960Hz sine wave that is AM
> modulated at 30Hz and FM modulated at 30Hz. The phase difference
> between the AM and FM signals is the bearing to the station.
> <<
>
> How does that work. =Something= has to be directional, no?
>
> Jose

Not quite.

There is a subcarrier modulation on the main carrier that is 9960 Hz. amplitude
modulated onto the main carrier. The subcarrier is FM modulated with a 30 Hz.
reference signal. The subcarrier is transmitted equally in all directions.

The carrier is also transmitted by a series of antennas spaced around the
station. These antennas are fed by a mechanism rotating at 30 Hz. and
phaselocked to the subcarrier reference. The rotating antenna is calibrated so
that the rotating signal and the reference signal are perfectly in phase at due
north of the station. As you rotate around the station, the phase between the
rotated (variable) and constant (reference) signal changes degree of phase for
degree of rotation.

(There is another way of doing it, far more technically difficult to explain.)


Jim


(Teacherjh)
shared these priceless pearls of wisdom:

->>>
->The VOR signal out of the receiver is a 9960Hz sine wave that is AM
->modulated at 30Hz and FM modulated at 30Hz. The phase difference
->between the AM and FM signals is the bearing to the station.
-><<
->
->How does that work. =Something= has to be directional, no?
->
->Jose

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

All he has to due is swap coax cables between the units to find out...

"DP" > wrote in message news:<kuK6d.69$lf2.60@trnddc09>...
> I wouldn't be satisfied with the answer that one unit is more sensitive or
> has better demod until I knew that the splitter, connectors, and coax were
> all in good shape. Then I'd wonder if the Garmin was detuned somehow instead
> of jumping right on poor or lesser design.
>
> Dan

Maik > wrote in message >...
> Hi!
>
> I have a SL30 and a GNS 430 in my plane. They use the same antenna via a
> splitter.
> When I dial in the same VOR in both units the SL30 catches up the
> radials always between 20 and 50 nautical miles earlier than the GNS
> 430! (Altitude about 3000 ft, flat area)
>
> Is this normal?
> What is your experience?
> How far away do you have a reception of a VOR with your GNS 430?
>
> Fly safe!
> Maik

You may want to try swapping the coax leads at the splitter. That
would quickly tell you if you had any splitter / connection / coax
issues.

Jack