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Anybody know of any differences in performance between the OEM satellite antennas and the Terk models? Looking at Grubbs, the OEM Sirius antenna is 28.99 whereas the low profile Terk is 47.99 and the micro Terk is 66.99. For half the price, I'd just as soon go with the OEM one, as I'm not really all that concerned about how big it is, since I'm going to most likely do the hidden install in the top of the lift gate. But since I'm doing the hidden install, I don't want to use an antenna that's only so-so for reception when it's out in the open. Thoughts are appreciated....
 

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you might also want to check out the nissan low profile they offer as an accessory. we just received the accessory list for the 2005 mo and they have that listed as a new choice. i want to say it was $35ish and it should work with the earlier models of the sat.
 

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There's a number of electrical specifications that determine the performance of an antenna.

As an example, let's look at the Terk SIR3. This is a single connection antenna. Is a single connection better for a dual input receiver? No. There's signal loss through the splitter and the additonal connectors.

Now to the electical specs:

Electrical Specifications:
Element Frequency:
2320 to 2332.5 MHz

Like 88 to 108 MHz on your FM band, this is just a range of operation that the antenna is designed to operate over.

Terrestrial Gain:
-5 dBi min,1 º elevation

Terrestrial is the land based repeaters and this gain number determines how well your antenna performs with ground based signals, when you can't receive well from satellite, due to obstructions. Like in downtown areas.

The actual gain is -5 dBi dB is the same dB used in many places, including audio and it's a relative measurement. In this case, it's relative to i which stands for isotropic. 0 dBi is equal to an theoretical point source antenna. -5 means it's much worse. The higher this number, the better. -5 means it's an antenna with power loss, not power gain.

Quick dB lesson. Every change in 3 dB is a double (going up) or half (going down) in power. For audio nuts, going from 50 watts to 100 watts power on an amp, is only a 3 dB increase.

1 º elevation means at an angle of 1 º above horizontal, which is the direction that the antenna most likely needs to receive the terrestrial signal at. Or thereabouts.

Satellite Gain:
1.8 dBic min,20 º elevation
2.5 dBic min,25 º-45 º elevation
5 dBic min,50 º-85 º elevation
4 dBic min,90 º elevation

Works the same way. See these numbers are positives, so this antenna actually has gain for satellite reception. Elevation that's important to you, depend on how far north or south you are and to a lesser extent, east and west. Depending on the system, XM or Sirius, the satellite is going to be at some angle in the sky, relative to where you are.

Generally speaking, the further north you live, the more important the 20 degree and 20-45 degree numbers become for best performance. If you were right under the satellite, the 90 degree performance is important. This is highly unlikely to happen to most people so it's really a pointless specification.

Best gain is at 50-85 degrees angle which is where most of us will be. The antenna designers obviously recognise that.

Impedance:50 ohms

They're all this impedance. This is a standard radio frequency equipment impedance and is used almost everywhere, except in the CATV and Broadcast Video industries.

Azimuth:Omnidirectional

Just means it can receive from all directions. Unlike a satellite dish, or yagi TV antenna.

Polarization TER:Linear Vertical

Terrestrial polarisation. Vertical like an FM car antenna. This works best for ground based radio systems.

Polarization SAT:LHCP (Circular)

Circular for the Satellite system works best to deal with all the possible angles that could occur as well as being better when dealing with a lot of reflected signals. This a deep discussion I'm not going to get into here.

LNA Gain:36 dB,typical

This antenna has a Low Noise Amplifier to amplify the signal before it feeds it down those antenna wires that you were extremely careful with when installing, to make sure they weren't crushed or bent too severely. If you did damage them this way, you just wasted your time and money researching antennas.

Noise Figure:0.7 dB,maximum

Noise Figure is a measure of how much noise the antenna added to the signal. The smaller the better. This is not an issue unless the signal is weak and you need to "hear" it.

Current Drain:170 mA,maximum

How much power it consumes. mA are 1/1000 of an Amp. So this takes about 0.17 of an Amp in power.


So what does this all mean when you add it up?

Well when the signal comes from the satellite at, for example, an angle of 75 degrees, the antenna will make it 5 dB better. The amplifier will bring it up another 36 db so it's now 41 dB better. There will be signal loss, going into the antenna wires, perhaps at the most 1 dB, if it's well designed. So now we're at 40 dB. The wires might have (I haven't looked a the specs on their wires, so this is an educated guess) 5 dB loss and then the connector to the receiver will have another .5 to 1.5 dB loss. So now we're down to 34 dB gain. Oh and the noise floor just came up .7 dB because of the amplifier's noise figure, so let's call it 33 dB of gain.

So which antenna is the best? Don't know, I'd have to do a detailled analysis... Generally speaking, I'd say, if you live in the south, buy what ever you like because you have lots of signal to work with. If you're in the North, performance will make more of a difference when you're in areas with lots of trees overhead or just generally far north.

And to those who just couldn't follow it all... the bigger the Satellite gain numbers, the better.
:D
 

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I used to work in radio, can you tell?
;)
 

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Hey, not a bad idea, if you guys thought of it...

I'll talk to the admin about doing that.
 

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If I use an aftermarket single connection Sirius antenna to connect to the OEM Sirius Tuner, can someone please tell me where to order the necessary splitter (if required) to connect that antenna to the tuner?

Thanks.
 

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The best place to ask, would be the manufacturer of your antenna. They'll be able to recommend the best solution.
 
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