Hello Everyone,
So I have been starting to learn how to use Outernet recently and I have what I hope is an interesting observation about antennas. I have been using a 17 inch 1540 MHz yagi antenna and even with the polarization mismatch, I have been getting 6-8 dB SNR each night I have it running. It goes down significantly during the day, while still working, possibly from interference? I can certainly write up a general design for this as I found it much easier to build then a helical antenna as the angles are all 90°.
My question is whether there is a way to turn off the bias tee in outernet in a box? I had been seeing the signals in cubic sdr with the LNA taken out of the loop and the software gain all the way up. I am hoping that a slightly larger antenna (~30 inches/~75cm) may be able to work without the amplifier.
(edited to help clear up the second part)
Hello,
When you turning off the bias tee (and the LNA is still connected) you simply turning off the RF signal chain, as the LNA is not routing it anymore. If that was behind your question it’s not works (no bypass chain in the LNA by other words)
You can remove physically the LNA however, take care to use a DC blocking capacitor if your antenna is grounded.
However the chance that you can receive Outernet signal without an LNA is quite low (maybe with a really big L-Band optimized parabolic dish). Not just the LNA gain but the low noise parameter of the LNA important which enable us to receive the signal, having lower noise floor. The SDR tuner’s embedded LNA has much much higher (worse) noise figure which is far from perfect in space communication reception sensitivity levels.
Just a quick point here on the yagi.
If you mount the yagi instead of horizontal or vertical,so it is at 45 degrees, you may get better gain with the circular polarization. If 45degrees one way doesn’t help. the try the other way.
That advise is from experience (on lover frequencies admittedly), but it can make like a 3db difference!
And as @zoltan says, beware of antennas that present as a short at DC (like most yagis!) with the RTL-SDR if you don’t use a preamp, as it will short out the Bias-T and damage it.
yeah, that short circuit easily can avoided by a series 22pF on L-Band (or an SMA DC block from Minicircuits, etc)