Topics

Gain control #HF+

Pete Smith <n4zr@...>
 

I am trying to use my Airspy to qantitatively assess the noise environment at my QTH, and I'm seeing what seem to be significant gain variations between the ham bands and other frequencies.  Is this the case, and are there provisions for setting up a flat profile as well?

73, Pete N4ZR
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On 3/13/2018 8:47 AM, prog wrote:

On Tue, Mar 13, 2018 at 05:33 am, Giovanni Carboni wrote:
I did not check carefully

Please check VERY carefully the gain settings. Different firmwares will have different settings.

prog
 

On Tue, Mar 13, 2018 at 06:36 am, Pete Smith wrote:
I'm seeing what seem to be significant gain variations between the ham bands and other frequencies. 

How significant is "significant"? What are the numbers? What is your test setup? And what are your expectations in dB?

Pete Smith <n4zr@...>
 

Can't really quantify.  This is something I encountered while doing a full HF survey for RFI.  I ran into one emitter of clear signals every 8 KHz, and noticed that it jumped up in strength on the ham bands as compared to 1-MHz slices above and below the bands.  What I was wondering is whether the Airspy HF+ has different preamp gains settable by band, or whether gain is supposed to be uniform across the HF range.

73, Pete N4ZR
Check out the Reverse Beacon Network 
at <http://reversebeacon.net>, now 
spotting RTTY activity worldwide. 
For spots, please use your favorite 
"retail" DX cluster.
On 3/13/2018 9:41 AM, prog wrote:

On Tue, Mar 13, 2018 at 06:36 am, Pete Smith wrote:
I'm seeing what seem to be significant gain variations between the ham bands and other frequencies. 

How significant is "significant"? What are the numbers? What is your test setup? And what are your expectations in dB?

jdow
 

1) Is this with a 50 ohm dummy load attached?
2) Better, is this with a low noise signal generator set to about -70 dBm IN the band of measurement attached?
3) Do you know what you are measuring?
4) Do you know how to interpret what you are measuring?
5) Do you know what measurements matter?

Item 2 is the way you are going to get the best measurements for the AirSpy HF+'s noise floor. If you have a REAL antenna for HF use, do you realize that AirSpy HF+ noise is the LEAST of your noise problems, some of which are endemic to a real world environment within this universe at approximately this distance from a furiously radiating fusion heat generator?

{o.o}

On 20180313 06:01, Pete Smith wrote:
I am trying to use my Airspy to qantitatively assess the noise environment at my QTH, and I'm seeing what seem to be significant gain variations between the ham bands and other frequencies.  Is this the case, and are there provisions for setting up a flat profile as well?
73, Pete N4ZR
Check out the Reverse Beacon Network
at<http://reversebeacon.net>, now
spotting RTTY activity worldwide.
For spots, please use your favorite
"retail" DX cluster.
On 3/13/2018 8:47 AM, prog wrote:
On Tue, Mar 13, 2018 at 05:33 am, Giovanni Carboni wrote:

I did not check carefully


Please check VERY carefully the gain settings. Different firmwares will have different settings.

jdow
 

Bingo - question 2 is very pertinent. You need to learn what "decimation" can do to apparent noise levels. And remember that with SDRSharp you are measuring dB relative to full scale and that AirSpy HF+ has nicely effective AGC options.

{^_^}

On 20180313 09:52, Pete Smith wrote:
Can't really quantify. This is something I encountered while doing a full HF survey for RFI.  I ran into one emitter of clear signals every 8 KHz, and noticed that it jumped up in strength on the ham bands as compared to 1-MHz slices above and below the bands.  What I was wondering is whether the Airspy HF+ has different preamp gains settable by band, or whether gain is supposed to be uniform across the HF range.
73, Pete N4ZR
Check out the Reverse Beacon Network
at<http://reversebeacon.net>, now
spotting RTTY activity worldwide.
For spots, please use your favorite
"retail" DX cluster.
On 3/13/2018 9:41 AM, prog wrote:
On Tue, Mar 13, 2018 at 06:36 am, Pete Smith wrote:

I'm seeing what seem to be significant gain variations between the ham
bands and other frequencies.

How significant is "significant"? What are the numbers? What is your test setup? And what are your expectations in dB?