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Airspy HF+ Gain conntrol

Posted: Fri Apr 20, 2018 3:22 pm
by P-40 Warhawk
The way I see it the HF+ is running at max gain , this hides the weak signals in the noise floor . Well last century I had gotten a RF signal attenuator from Radio shack ( remember them ) . Now I can do some righteous DXing . The HF+ with the RF signal attenuator in front of it is a good combination .
My two Penney's worth .

Re: Airspy HF+ Gain conntrol fixed

Posted: Fri May 11, 2018 2:10 pm
by P-40 Warhawk
Some kind person told what I need to know . Well now I don't need a external RF signal attenuator . Come to find out their is RF Firmware Update that fixed the problem and that was what was needed . If you go to the products page for the HF + , it's on the bottom of the page . Also it is talked about in Airspy forum page . I am from the middle of last century and I give the HF + a two thumbs up . 8-)

Re: Airspy HF+ Gain conntrol

Posted: Sun May 13, 2018 12:47 am
by JEL
P-40 Warhawk wrote:
Fri Apr 20, 2018 3:22 pm
HF+ is running at max gain , this hides the weak signals in the noise floor .
Since you found your answer, I hope it's ok I ask a side-question in this thread, since it's partly related to your topic.

I know, from own experience with SDR-reception, that raising the gain too much hides weak signals.

But I don't really understand why that is.
I thought more gain will just raise everything without doing any harm until reaching the point of overload.

Is there an explanation for why that is not really the case?

The quantisation-noisefloor of a dongle, as I understand, is the very minimum-strength a signal has to breach to be clearly detectable.

The radio-noisefloor is the dynamic noise-floor (Actual incoming radio-energy), and raising gain will raise both that, AND any other signal, by the same relative amount.

Yet, when we raise gain too much... it seems we begin to raise the unwanted radio-energy but not the wanted radio-energy.
It is as if they no longer remain the same power relatively.
I'm wondering what the explanation for this behavior is (Google hasn't provided an answer)

Re: Airspy HF+ Gain conntrol

Posted: Wed May 16, 2018 2:11 pm
by P-40 Warhawk
Hi Jel .

Well my thinking on the noise floor is that their is two noise floors . One noise floor is in the equipment ( radio receiver ) . The other is in the Ether , meaning the atmosphere , sky , space what ever the antenna see's . Now the sun is what makes the noise floor that comes in from the antenna and that is around -120dbm . That does change daily . Their is a program called Artemis that has solar weather reports , you can get it at this website ( ) . The program also has radio signal recognition . Now getting back to the point , any receiver that has a noise floor lower than what is in the Ether will receive everything that is out their . Of course I have keep this simple , antennas , that is a whole other thing .

I have no idea of what dynamic noise-floor is and if you haven't found it on the internet , it may be a new buzz word .

If anyone has anything to add , go a head I would like to hear it .

To answer your about raising the gain , I don't know it's just the way it is . Now I use HDSDR and I keep the noise floor at about -120 dbm .

Re: Airspy HF+ Gain conntrol

Posted: Sat May 19, 2018 3:01 pm
by JEL

I keep playing with gain, and there definitely is a sweet-spot somewhere in the middle (I'm not using HF+ though, but the AirspyR2 for this)

If I go too low, the wanted signals go away and the noise-floor settles on some minimum it won't go under.
If I set it too high, the wanted signals don't rise, but the unwanted noise does (This is the effect that puzzles me)

I tend to adjust for a noise-floor (When there is no wanted signals) between around -70 to -60 dB.
I'm just assuming this works best with 16-bit audio, but I don't know if it relates the same way when using an SDR as it does when using audio, so I could be making a mistake here.
With normal audio I find digital aliasing artifacts get easy to hear when signal-level gets below about -60 to -70 dB (At least on my computer's sound-setup, which is 16bit)