Separation of antennae A and B

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AussieSusan
Posts: 26
Joined: Wed Aug 16, 2017 6:50 am

Separation of antennae A and B

Postby AussieSusan » Tue Apr 24, 2018 3:39 am

Following on from a previous post (viewtopic.php?f=5&t=3006) I was playing around with my antennae last night and connecting them in various ways.
One thing I noticed was that my discone (on aerial input A) was picking up a NOAA satellite better than my QFH (on aerial input B) which did not really make sense to me. So I swapped them around and fund that the QFH on Aerial input A was now performing better than the discone on aerial input B.
Originally I had an LNA being fed by the bias-t on aerial input B but I found that it was drawing more current than it should when it was working (I had not checked the specs properly).
Using the LNA raises the noise floor but that is all - it is as though it swamps the signal that I can (just) see with the LNA off. I have the gain reduction set to its mid-range on the SDRplay software with the RF AGC on. (If there are other settings that are of interest, please let me know)

I was wondering if I could have damaged the front-end electronics on aerial input B by abusing the bias-t supply?
Susan

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AussieSusan
Posts: 26
Joined: Wed Aug 16, 2017 6:50 am

Re: Separation of antennae A and B

Postby AussieSusan » Tue Apr 24, 2018 3:42 am

(Sorry but I can't edit this post - I have no idea what "two poll options" are that I need to select).
I mean to say that I'm using the SDRuno software (not the SDRplay software).
Susan

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RSP2user
Posts: 85
Joined: Mon Oct 09, 2017 7:11 am

Re: Separation of antennae A and B

Postby RSP2user » Thu Nov 08, 2018 9:59 am

My understanding is that powering an external LNA on port B of the RSP that uses more current than can be supplied by the RSP will simply cause the RSP to shut down power to the external LNA and not cause any damage. Regarding optimized gain settings in SDRuno for NOAA satellite passes, refer to the article here: viewtopic.php?f=5&t=2529 . Though IF AGC is working better in the latest versions of SDRuno, at this time you can still get better NOAA satellite reception not using IF AGC. Assuming that you are using a QFH antenna and an 18 dB gain LNA, the process for optimizing the gain settings is to set the overall gain to 85.5 (or other value depending on the antenna and LNA gain) using a combination of setting the gain slider to its maximum position and adjusting the IF Gain, until the overall gain is set to 85.5. This setting will work well much of the time. You can get still better operation by tweaking the IF AGC during a few passes to get it to the point where it is as high as it can be set without causing clipping of the signal as the satellite is passing directly overhead (ADC overload indicator will be on earlier than when problematic clipping actually occurs). I have also obtained even better results by adjusting the overall gain to maximum and adjusting the IF Gain even higher at the beginning and end of the pass and lowering it to the point just under clipping as the satellite passes overhead. It takes some trial and error to optimize this process. If, on the other hand, you don't want to go through all the trouble, just using the IFAGC will get you most of the pass pretty well, but it has been my experience that you will lose about 25 percent of the image that you could have otherwise received well.

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