FlightAware Discussions

Do I Need A Filter?

#273

The bigger the percentage of Messages > -3dbFS means that I’m getting more short range than long range planes?

#274

Those are messages with very strong signal. It’s likely that you are receiving some messages with a signal even stronger that can’t be received anymore.

So you aim for about 5% of those messages and hope that there aren’t too many “even stronger” messages which can’t be received.

Or if you only care for planes far away you just ignore the percentage.
That could mean you don’t receive planes flying close by very well but depending on the case it can increase reception at least a bit for planes far away.
This is not guaranteed though, depending on electrical noise it might not help going higher with the gain.

Also see this thread:
Thoughts on optimizing gain

#275

The label of this L-band Satellite Amplifier (RCA D903) says 950 - 2050 MHz

This gives an impression that this Amplifier has a built-in band-pass filter 950 - 2050 MHz

If this is true, then it is amazing. LNA+band-pass filter for $4 (I have purchased it from local electronics store for $4).

I have used it during 2013~2016.
After purchasing ProStick+FA antenna+FA Filter in 2016, I dismantled it.

I am planning to fire it up again with generic DVB-T, and conduct two scans.

  1. Scan with the amplifier.
  2. Scan without the amplifier.

If this satellite amplifier has an effective built-in band-pass filter, it will remove (or at least reduce) the interference of GSM800 Mhz band, which is very strong at my place.

#276

I’ve got a couple of the unbranded 20dB sat amps and they certainly do not have any filtering.

One thing to be aware of with any sat amp is that they are DC pass-through. An antenna with a DC short (J-pole, CoCo with top short etc.) will not play well.

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#277

The one I have is from a very reputable manufacturer RCA, and that is why I expect that it really cuts-off outside its specified frequency range (950~2050 Mhz). A scan and heatmap will reveal the truth.

#278

While RCA is a reputable company, this is just an amp for a domestic sat receiver, not even for commercial applications. My guess is that the specs should be interpreted to mean the amp will provide 13~18dB in the range of 950~2050 Mhz, and the gain outside that range is simply not specified.

If something is too good to true - it probably isn’t.

I found an ebay listing showing the rear of this amp. The back panel is just a press fit and can be levered out (and popped back in).
If you get bored, do you want to open it up and see what makes it tick?
image

Knowing how it performs is subtly different to knowing why.
(I like the ‘why’).

#279

I would have thought that the frequency range quoted was the range it was within spec. I.e. gain is as specified within this frequency range.

There is nothing to suggest there is any filtering outside that frequency range.

I await the results of the scan.

S

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