How does such an amplifier work?


#1

ebay.com/itm/281500624570?_t … EBIDX%3AIT

There’s only one input and one output, no line for extra power, no battery. So how does the signal get amplified?


#2

You will need to power the amplifier using something like in the link below & a power supply.

ebay.co.uk/itm/DC-Line-Power … 257ef9bc9a


#3

Ah, that starts to make some sense. So does it go antenna - amp - power inserter - receiver?

Edit:
OK, I’ve found a diagram that confirms this.


#4

The amplifiers are usually designed for insertion int a satellite dish downlead - as such are designed to pass power up to the electronics box in front os the dish. so do ensure your antenna wont present a DC short circuit or insert a DC blocker above the amplifier.


#5

What’s a DC blocker? A diode?

Edit: I found my answer: http://www.wisegeek.com/what-is-a-dc-block.htm


#6

This is a pretty wide band amp. As such it is supposed to amplify a down-converted block of frequencies from a satellite to frequencies more suitable for transmissions over a coax cable (sometimes called IF frequencies).

When you connect such an amp to an antenna being use to receive the 1090 MHz sig this amp is going to not only amplify the 1090 MHz freqs you desire but any and all other frequencies from 950 MHz to 2 GHz … including possibly higher power local transmitters used to support mobile devices in the 900 MHz range. That could actually overload your USB SDR dongle device and have the opposite effect: you may decode less 1090 MHz packets.

The solution when using broadband amps and broadband receivers is filters - ideally a narrow band pass filter centered on the 1090 MHz frequency (rejecting unwanted frequencies above and below 1090 MHz).


#7

Also note: as confirmed with NooElec their USB SDR dongles are 50 ohm impedance input. This means that the coax and antenna should likewise be 50 ohm impedance.

Most of the consumer satellite equipment is 75 ohm … especially if its got US style CATV F-connectors on it.


#8

It’s a bit strange, because the tuner itself is specced as 75 ohm. I wonder if they just put a 50 ohm MCX connector on it?

That said, the loss from a 50/75 ohm mismatch isn’t huge (<1dB IIRC?)


#9

It is in fact 75ohms. This link gives details of a filter design that looks interesting IF you use a wideband amp at the antenna.

superkuh.com/gnuradio/R820T_data … locked.pdf

See fig 4.1