Date   
Re: USB cable quality and QRM in a spyserver setup with an Airspy Hf+ and Raspberry PI3. 6 microUSB cable test. #airspyhfplus #bestpractice #raspberrypi

Dana Myers
 

On 3/13/2018 9:32 PM, Ian DXer wrote:
Hi Dana,

Pleasing to read your report on your success with the Volutz USB cables.
Thank you.


I was looking at the Volutz Facebook page & I note that Volutz have just released a new Apple Lighting Cable.
For noise immunity I like the metal shroud that links the foil shield of the cable & surrounds the connector & components
underneath. One also gets a better look at the dual cable shielding from the drawing on the Facebook page.
Are these SMD components part of the lightning spec or are they part of Volutz's attention to EMI/EMC or impedance
matching?
I do not know anything really about Lightning (the only Lightning cables in
my house are associated with my wife's iPhone).

I see a similar shroud on their USB C cable from their Facebook page.
What's not clear to me is if Volutz use a metal shroud on their connectors for their USB 2.0 to micro USB cables or
any filtering SMD components (if that's what they are?) similar to their new Apple Lightning Cable.
The Volutz website is scant with close up pics & tech data.
I do not know the details; I just know I found one graphic that says the power
lines in the USB cable are 22 AWG :-)
A further improvement to their USB 2.0 to micro usb cables would be to have a foil shield between the data & power pairs.
Perhaps, but what are you seeking to address with this? The data lines are a
differential pair and surely twisted (but I don't know for a fact). Given that the
data lines are very low current, I'd be surprised if they induce meaningful noise
into the power lines. On the other hand, I'd expect noise from the power lines
to be induced as common-mode into the data lines and thus disappear from
the data.

73,
Dana  K6JQ

Re: USB cable quality and QRM in a spyserver setup with an Airspy Hf+ and Raspberry PI3. 6 microUSB cable test. #airspyhfplus #bestpractice #raspberrypi

Dana Myers
 

On 3/14/2018 7:53 AM, Graham wrote:
You can even buy the end parts to make your own cables with the cable of
your choosing if you are particular.
Is this really practical, especially from a mechanical ruggedness perspective?

73,
Dana  K6JQ

Re: USB cable quality and QRM in a spyserver setup with an Airspy Hf+ and Raspberry PI3. 6 microUSB cable test. #airspyhfplus #bestpractice #raspberrypi

Dana Myers
 

On 3/14/2018 7:35 AM, David Ranch wrote:

For a 2-pack of 10' cables [Volutz], $17 on eBay was a deal.
Looks like there's a better deal on Amazon - free same-day shipping
with Prime, $12. Shop around. It's nice having a ridiculously long
cable in my shack, BTW.

Wow.. 10'?  I'd assume there is some pretty serious voltage drop over that!  Regardless, I'll have to give them a look.  Thanks.
Let's do some math, because we're scientists :-). A graphic at the
Volutz website says the power wires in their USB cables is 22 AWG.
I believe we can safely ignore the data wires here; as long as the
cable isn't dropping frames, it's OK.

Consulting Wikipedia:
https://en.wikipedia.org/wiki/American_wire_gauge#Rules_of_thumb

We see that the approximate resistance of  this wire is 16 ohms / 1000'.
So, 10' of the wire (power and return) has about ~ 10/1000 * 16, or
0.16ohms, resistance per leg, or a total of 0.32 ohms.

Assuming a 200mA load (I don't actually know the Airspy HF+ current
consumption), that means the +5V rail at the HF+ drops by 0.032V,
or 32mV, and the ground rail at the Airspy HF+ increases by 32mV. In
other words, the +5V supply to the Airspy HF+ drops by 64mV.

Given that I bet nothing inside the Airspy HF+ runs from higher than a 3.3V
rail, this is plenty of margin for an LDO (you can do worst case math with USB
host power rail of 4.5V and LDO minimum differential of 0.6V and still have
500mV of margin).
Assume I'm wrong  and the HF+ uses 500mA (the max spec for a
USB port, right?). That's 160mV drop to the HF+; still plenty of margin
for a 3.3V LDO (worst-case above would be > 400mV).

The keen observer might have noticed I suggest the DC ground
in the HF+ is ~32mV higher than the USB host ground. Note that
this doesn't matter because the USB signalling is differential data,
not analog.

OK, maybe we're not scientists, we're ham radio operators. In which
case you can disregard the above and say "it works great" (like the way
J-Pole antennas are 3/4-wave verticals :-)).

73,
Dana  K6JQ

HF+ Quickstart?

Roel
 

Is there a quickstart page just like https://airspy.com/quickstart/ but for the HF+?
I installed the WinUSB Compatibility Driver and I get a waterfall and lots of noise but e.g. no FM stations.
Are there any settings I have to do?
Thnx!

Re: Using SDR# and HF+ for FM modulator measurement #airspyhfplus #sdrsharp

prog
 

On Wed, Mar 14, 2018 at 09:30 am, Moij2x wrote:
What can cause this

Same list discussed earlier in this thread.


how to find and fix?

Fix what? What are your expectations? How do you define normal operation?

Re: USB cable quality and QRM in a spyserver setup with an Airspy Hf+ and Raspberry PI3. 6 microUSB cable test. #airspyhfplus #bestpractice #raspberrypi

PMM
 

One thing I noticed was with my printer, it not grounded through power supply so having a good usb lead was important to kill the noise even though it only in standby mode, in fact printer contributed 20db of noise to the sdr near computer.  Plugging in a decent usb cable pulled noise floor down 20db verse unplugged and against lesser quality usb cable.

So sometimes it can be said a poorly grounded device/non grounded psu can benefit from a good grounding given by usb cable, this seems to validate some of the cable choices due to better shielding/grounding wires in there construction.



On Wed, 14 Mar 2018, 15:11 Graham, <planophore@...> wrote:
Another good document that some may find interesting on this subject:

https://www.ti.com/sc/docs/apps/msp/intrface/usb/emitest.pdf

cheers,

Re: Using SDR# and HF+ for FM modulator measurement #airspyhfplus #sdrsharp

Moij2x
 

I made more test on different PC-s, even in way that SDR#+HF+ was on one PC, REW for measurement on other PC with EMU sound card on ASIO drivers, PC-s where connected from audio out to EMU input with good cable.
Measurements with digital sound transfer from SDR# to REW soft was made with Jack2 Audio and EMU ASIO driver in one Win 7 PC. When this digital transfer measurements where done, I disabled all Windows Audio services, so Windows audio was not involved only ASIO driver and Jack2 Audio.
In many measurements KT-6040 THD is lower on same modulator input levels than HF+ in higher than 500 Hz range. HF+ had lower noise on lower modulator input levels.
Probably it is caused by PC. I not find significant difference in SDR# result made with digital transfer or when made from one PC to other with physical cable.
Interesting thing I find is that THD peaks on SDR measurement are on different frequencies in different PC-s.
Below 2 images of THD measured with SDR. First where SDR was in one PC, measuring soft REW in other. Second where all was in on PC.
On first case SDR was running in Windows 10 PC 2,9 GHz CPU, where SDR# CPU usage was about 16% from total, on second faster Win 7 64bit 3,5 GHz PC, SDR# used about 7% from total CPU. In both cases all settings of SDR# where identical.

As can be seen generally lines and figures are very similar except THD peaks in higher region on lower levels are on different frequencies.
What can cause this, how to find and fix?
 






Re: USB cable quality and QRM in a spyserver setup with an Airspy Hf+ and Raspberry PI3. 6 microUSB cable test. #airspyhfplus #bestpractice #raspberrypi

Graham
 

Another good document that some may find interesting on this subject:

https://www.ti.com/sc/docs/apps/msp/intrface/usb/emitest.pdf

cheers,

Re: USB cable quality and QRM in a spyserver setup with an Airspy Hf+ and Raspberry PI3. 6 microUSB cable test. #airspyhfplus #bestpractice #raspberrypi

Graham
 

Some of the better manufacturers put some details on their web site but
at that is usually still somewhat sparse.

for USB micro and apple cables I prefer Anker which are quite well
reviewed and their web page does provide some technical details.

Also, Sabrent and Volutz.

Tyco / TE Connectivity makes some decent USB cables. In their USB A to B
cables they have versions which have 25 AWG for the data pair and 20
AWG for power.

I have destructably disassembled (i.e. cut apart) a number of cables
from cheap to moderately priced. There are differences and you do get
what you pay for.

You can even buy the end parts to make your own cables with the cable of
your choosing if you are particular.

something else to consider is the cable shields. The metal parts at both
end of the cables should not be connected to the ground pin of the
connectors but should be connected to the shield (if there is any) of
the cable. In fact, sometimes it is better to just have the shield
connected to the shell on the end that plugs into the computer and not
connected on the other end. This creates what is called a Farady shield
(or cage if you prefer) over the cable. Connecting both ends can
sometimes create ground loops in the shield. I have run out of fingers
and toes to count the number of times that I have seen where a cable
having the shield connected at one end only solves EMI/RFI issues where
another cable with the shield connected at both ends only made the
problem worse or was in fact the source of the problem to begin with.

Solving EMI/RFI issues is a mixed bag of science and sometimes a bit of
black magic.

This is a could introductory and practical text on the subject:

http://audiosystemsgroup.com/SAC0305Ferrites.pdf

cheers, Graham ve3gtc

On 3/14/2018, "David Ranch" <airspy-groupsio@...> wrote:


For a 2-pack of 10' cables [Volutz], $17 on eBay was a deal.
Wow.. 10'? I'd assume there is some pretty serious voltage drop over
that! Regardless, I'll have to give them a look. Thanks.

--David
KI6ZHD

Re: USB cable quality and QRM in a spyserver setup with an Airspy Hf+ and Raspberry PI3. 6 microUSB cable test. #airspyhfplus #bestpractice #raspberrypi

David Ranch
 


For a 2-pack of 10' cables [Volutz], $17 on eBay was a deal.


Wow.. 10'?  I'd assume there is some pretty serious voltage drop over that!  Regardless, I'll have to give them a look.  Thanks.

--David
KI6ZHD

Re: Gain settings with Firmware 1.6.2 #airspyhfplus #firmware #bestpractice

prog
 

On Wed, Mar 14, 2018 at 04:21 am, Chris Smolinski wrote:
I'd need to check my email history for the exact details, but I went through a series of tests, passing the information back to Youssef, when I first got the AirSpyHF+. From memory, the MW intermod/images/aliases were a function of the station frequency and the AirSpyHF+ center frequency, as well as a 5 kHz tuning offset (part of the library on the computer side). Again I don't recall the exact relationship, it has been several months. I can mostly work around them with careful selection of the center frequency. They're not present to any degree with other radios, SDRs or otherwise, using the same (or other) antennas. I mostly use the AirSpyHF+ on HF where it isn't as much of an issue. I believe I have occasionally noted some similar products on HF involving mixing of strong SWBC stations. It doesn't happen often, and Radio Habana Cuba (the land of inept radio engineering) is often involved, so draw your own conclusions :)

Chris Smolinski
Black Cat Systems
Westminster, MD USA
http://www.blackcatsystems.com

Chris, this is a completely different topic. We are discussing the impact of the latest firmware that affects the control of the analog front-end.

You can start a new thread for the IQ correction algorithm and how it behaves with different signal situations. This will avoid more confusion.

Re: Gain settings with Firmware 1.6.2 #airspyhfplus #firmware #bestpractice

Chris Smolinski
 

I'd need to check my email history for the exact details, but I went through a series of tests, passing the information back to Youssef, when I first got the AirSpyHF+. From memory, the MW intermod/images/aliases were a function of the station frequency and the AirSpyHF+ center frequency, as well as a 5 kHz tuning offset (part of the library on the computer side). Again I don't recall the exact relationship, it has been several months. I can mostly work around them with careful selection of the center frequency. They're not present to any degree with other radios, SDRs or otherwise, using the same (or other) antennas. I mostly use the AirSpyHF+ on HF where it isn't as much of an issue. I believe I have occasionally noted some similar products on HF involving mixing of strong SWBC stations. It doesn't happen often, and Radio Habana Cuba (the land of inept radio engineering) is often involved, so draw your own conclusions :)

Chris Smolinski
Black Cat Systems
Westminster, MD USA
http://www.blackcatsystems.com

On Mar 13, 2018, at 11:03 PM, jdow <jdow@...> wrote:

Check the FCC requirements for harmonic radiation imposed on broadcast stations. Once done you will have a suitable "Aha" moment, one hopes, when you figure out that X dB down from Y dB over S9 (er 50 uV at 50 ohms unless you are Collins in which case it is 100 uV at 50 ohms) and just how big a signal S9 really is. Of course you will see harmonics. And it's nothing to do with your receiver. Now you use the word "images". If the signals are not on frequency they are leakage through the front end filtering and that implies they would properly be called aliases. Images are a superheterodyne receiver phenomenon and occur on the opposite side of a conversion process's IF frequency from the tuned frequency. It will be a different frequency. And while the AirSpy HF+ SDR with your computer is "sort of" a superhet receiver the IF in question is possibly 0 Hz. So images are "interesting" to contemplate. (I've not tried to figure this out.) A good set of numbers taken with variable center frequency tuning can give enough numbers to determine all the variables that might be involved. That will help you define your local "Don't DO that!" conditions.

(And if the tech on the phone asks you to make sure your computer is turned on, fire back at him, "I didn't know computers had a sex life!")

{^_^}

On 20180313 06:42, Chris Smolinski wrote:
I notice the same levels of intermod on LW/LW with firmware version 1.6.2 vs previous versions, it does not seem any worse. This is using SdrConsole which AFAIK keeps the AirSpyHF+ AGC turned on.
While playing around with SDR# I was of course able to generate lots more intermod/etc by switching AGC off and turning the gains up too high and overloading things, as you'd expect.
I don't have any nearby strong MW stations, the nearest is about 10 miles away, and I think 5 kW. With AGC on I can occasionally see images from it on LW and MW, although careful tuning can eliminate them. (Setting the center frequency such that the station is outside the 768 kHz passband)
Any guesses when there will be a library update to further improve the AirSpyHF+ filtering?
Chris Smolinski
Black Cat Systems
Westminster, MD USA
http://www.blackcatsystems.com
On Mar 13, 2018, at 8:33 AM, Giovanni Carboni <@IZ5PQT> wrote:

Hello everyone,

I had to disinstall version 1.6.2 of the firmware (20180309) on my AirspyHF+ since it caused horrible
intermodulation below 1 MHz.

Less than 15 km from my QTH there is a 50 kW MW TX on 657 kHz (Rai Coltrano). The signal at the
radio antenna input is -21 dBm measured with an ELAD S2 and checked with a scope. The two measurements
agree within errors (20 mV peak on the scope). It is a quite large signal so I am clearly in an extreme
situation.

With all firmware versions until 1.6.1 the receiver did not show intermodulation problems (except of course
for a narrow band around 657 kHz). With 1.6.2 a terrible
intermodulation occurred making reception impossible on all the MW spectrum up to 1000 kHz. I did not check
carefully but it looks like reception below 500 kHz was not affected.

I had to go back to 1.6.1 and things became normal.

I do not have instrumentation to perform more accurate measurements but the test is
easily reproducible in a lab.

73 Giovanni IZ5PQT



Re: AirSpy HF+ flashing again #firmware

I L
 

Thanks Dave for answering my questions! I have now successfully updated the firmware from 1.00 to the very latest from 20180309 using the standard procedure.

Regards,
Ingemar



2018-03-13 14:21 GMT+01:00 D R via Groups.Io <robsond90@...>:

Hi Ingemar,

1.  Look under Source:Airspy HF+ in SDR Sharp.
2.  You can use any version whenever you like.
3.  You'll get many answers to this question, as peoples' experiences appear to differ.  In my case I need to use the recovery procedure for every update, but others can use the "standard" procedure.  Neither option is anything to be afraid of.
4.  It will probably die at some time, but hopefully not for several years, and after many updates

Regards,
Dave



From: I L <ingemar.lekteus@...>
To: main@airspy.groups.io
Sent: Tuesday, 13 March 2018, 12:48
Subject: [airspy] AirSpy HF+ flashing again #firmware

I am new to the group and a new HF+ owner. I have not been able to find answers to a couple of questions. In case they already have been discussed I hope you will apologize me for bringing them up again.

1. How do I find out what firmware version my HF+ uses?
2. When I want to upgrade, can I go directly to the latest version or do I need to follow a certain sequence?
3. There is a recovery procedure mentioned in README.txt. As I got the RX just recently I suppose the firmware version is not the first one so I hope I can use the standard procedure.  But to be sure I need an answer to the first question and I also need to know the version number of the first firmware.
4. Can I be sure not to end up with a dead unit?

Best wishes,
Ingemar, SM0ECF





--
------------------------------------------------------
Ingemar Lekteus
Älgstigen 2
178 52  EKERÖ

E-post: ingemar.lekteus@...
Mobil: 0704-71 33 30

Re: USB cable quality and QRM in a spyserver setup with an Airspy Hf+ and Raspberry PI3. 6 microUSB cable test. #airspyhfplus #bestpractice #raspberrypi

jdow
 

Screening is good. Breaking ground loops, AF or RF, is a good thing, too. Ferrite makes the ground loops lossy as it breaks them. This is sort of the best of both worlds. And there is something to be said for keeping RF that is outside of cables where it belongs, on the outside of the box. So making a good electrical bond from each of the box's connectors to the box itself may provide you with a quite worthwhile improvement in behavior. It should not make it any worse. (And done carefully it will not change the cosmetics of the box. Braided shield from small diameter coax is a nice tool for this. Clean the inside of the holes and the inside of the box for the 10 MHz ref (AirSpy only) and USB connector holes. Then when installing the cover mush some of the braid between the edges of the hole and the connector shield. For the RF clean off a space just to about half way to the outside of the lockwasher. Then when tightening it you will get a nice ground to the coax shields for the RF input connector(s).

Also, unless you are running a very low efficiency antenna at HF, test for the interference when the band is open. If you cannot see it then it doesn't matter even if you can see it with a 50 ohm dummy load and with a small test signal present.

{^_^}

On 20180313 21:32, Ian DXer wrote:
Hi Dana,
Pleasing to read your report on your success with the Volutz USB cables.
I was looking at the Volutz Facebook page & I note that Volutz have just released a new Apple Lighting Cable.
For noise immunity I like the metal shroud that links the foil shield of the cable & surrounds the connector & components
underneath. One also gets a better look at the dual cable shielding from the drawing on the Facebook page.
Are these SMD components part of the lightning spec or are they part of Volutz's attention to EMI/EMC or impedance
matching?
I see a similar shroud on their USB C cable from their Facebook page.
What's not clear to me is if Volutz use a metal shroud on their connectors for their USB 2.0 to micro USB cables or
any filtering SMD components (if that's what they are?) similar to their new Apple Lightning Cable.
The Volutz website is scant with close up pics & tech data.
A further improvement to their USB 2.0 to micro usb cables would be to have a foil shield between the data & power pairs.
I purchased a replacement USB cable (CableCreation/Xillie) from the Internet last week. It arrived on Monday. It is supposedly triple shielded, but I suspect these are 'just
words' from a Chinese supplier via Amazon. I compared the the noise performance between AIRSPYHF+ supplied USB cable with my own
added mix of ferrites attached, also a Samsung USB cable, the CableCreation USB & the CableCreation Lead with a mix of ferrites.
Test freqs were roughly every 1MHz between 2 & 30MHz. Conclusions: I didn't gain the results I expected from the CableCreation USB cable, results were
similar to the plain Samsung Cable. But what brought best results was having ferrites on either the existing AirSpyHF+ USB cable or the CableCreation USB cable (similar results).
That said, for my own electro smog environment results were typically only a 2dB improvement to noise floor for the USB cables with the ferrites attached.
But on the better end of the results scale 'on some' frequencies I noted a 6-10dB improvement (with ferrites).
I'm sure if I purchased a better screened USB cable (similar to the standard of my router CAT6 S/FTP patch cables) I should hopefully see better results.
Every dxer has a unique RFI environment with their own unique challenges, some requiring a huge investiture of time & effort (mine's only in the early stages).
Our new Samsung refrigerator is the latest to be added to the RFI hit list (I'll try to mute my grumble).
73
Ian

Re: Airspyhf+ flashing

Ian DXer
 

RE: >AirSpy HF+ Firmware Update Instructions

>Howard M. Harte, WZ2Q - February 22, 2018

 Hi Howard,

There's one omission from your write-up that I would strongly recommend adding or highlighting. That is to 
add a line WARNING owners that their calibration will be lost during the initial firmware update procedure after the RESET.
That said, mine didn't vary too much & was still within spec.
(But one has to then re-enter any stored notch entries within the IF processor plugin, if used)

73

Ian
 
 
 

Re: USB cable quality and QRM in a spyserver setup with an Airspy Hf+ and Raspberry PI3. 6 microUSB cable test. #airspyhfplus #bestpractice #raspberrypi

Ian DXer
 
Edited

Hi Dana,

Pleasing to read your report on your success with the Volutz USB cables.

I was looking at the Volutz Facebook page & I note that Volutz have just released a new Apple Lighting Cable.
For noise immunity I like the metal shroud that links the foil shield of the cable & surrounds the connector & components
underneath. One also gets a better look at the dual cable shielding from the drawing on the Facebook page.
Are these SMD components part of the lightning spec or are they part of Volutz's attention to EMI/EMC or impedance
matching?

I see a similar shroud on their USB C cable from their Facebook page.
What's not clear to me is if Volutz use a metal shroud on their connectors for their USB 2.0 to micro USB cables or
any filtering SMD components (if that's what they are?) similar to their new Apple Lightning Cable.
The Volutz website is scant with close up pics & tech data.

A further improvement to their USB 2.0 to micro usb cables would be to have a foil shield between the data & power pairs.

I purchased a replacement USB cable (CableCreation/Xillie) from the Internet last week. It arrived on Monday. It is supposedly triple shielded, but I suspect these are 'just
words' from a Chinese supplier via Amazon. I compared the the noise performance between AIRSPYHF+ supplied USB cable with my own
added mix of ferrites attached, also a Samsung USB cable, the CableCreation USB & the CableCreation Lead with a mix of ferrites.
Test freqs were roughly every 1MHz between 2 & 30MHz. Conclusions: I didn't gain the results I expected from the CableCreation USB cable, results were
similar to the plain Samsung Cable. But what brought best results was having ferrites on either the existing AirSpyHF+ USB cable or the CableCreation USB cable (similar results).
That said, for my own electro smog environment results were typically only a 2dB improvement to noise floor for the USB cables with the ferrites attached. 
But on the better end of the results scale 'on some' frequencies I noted a 6-10dB improvement (with ferrites).
I'm sure if I purchased a better screened USB cable (similar to the standard of my router CAT6 S/FTP patch cables) I should hopefully see better results.

Every dxer has a unique RFI environment with their own unique challenges, some requiring a huge investment of time & effort (mine's only in the early stages). 
Our new Samsung refrigerator is the latest to be added to the RFI hit list (I'll try to mute my grumble).

73

Ian

Re: Gain settings with Firmware 1.6.2 #airspyhfplus #firmware #bestpractice

jdow
 

And do remember that if you switch from a signal generator output with signal set at -70 dBm-ish (-90 dBm will also do) to a live antenna with some signals present and the noise increases by more than a little bit (1 or 2 dB) you can insert more attenuation at the receiver's input and not lose any weak signal ability. Obsessing about HF noise figure is one of the silliest obsessions I've seen in innately perverse animate homo sapiens, IPAHS. (Pronounce it.) And, I admit, before I found a good book describing noise figure and atmospheric noise I fell down that rabbit hole of frustration myself.

{o.o}

On 20180313 15:15, Roberto Zinelli wrote:
Giovanni, with 1.6.2 i put  AIRSPY-HF ACG OFF and set attenuator -12 DB,   the overral noise figure for me is better then 1.6.1
On Tue, Mar 13, 2018 at 11:03 PM, Giovanni Carboni <@IZ5PQT <mailto:@IZ5PQT>> wrote:
Here are three spectra around 738 kHz taken with a) FW 1.6.2;  b) FW
1.6.2 plus an external 20 dB attenuator;  c) FW 1.6.1.
As you see in case a) the reception is totally washed out. The only way to
get a reasonable spectrum with 1.6.2 is to turn off the AGC in SDR# and
insert a lot of attenuation.
73 Giovanni

IF Spectrum Tuning #sdrsharp

Bingo TheClowno
 

Has the IF Spectrum tuning been disabled?
I can't fine tune in the IF Spectrum display anymore in the latest SDR#.
I prefer this way than zooming in all the way.
Is there an option I need to enable?

Re: Airspy noise figure

jdow
 

(She screws up her face thinking furiously before creebing that measuring RMS signal plus noise and noise within an FFT spectrum summing the power for every FFT bin within the specified bandwidth should potentially be VERY accurate when reduced to a noise figure when using an SDR. Thanks for provoking me into analyzing your statement when it "bothered me" a little. It will likely be most accurate when your bandwidth of interest includes 1000 or more FFT bins and you diddle the calculated values to account for the FFT weighting algorithm. And I bet Leif has already done this in the past.)

{^_-} Joanne

On 20180313 10:06, doug wrote:
There's another method of getting a noise figure number, if you have a
pulsed RF source: carefully adjust the source so that the detected rf
pulse is tangential. What this means is that
the average noise at the bottom of the detected pulse is equal to the
average noise of the baseband, where there is no pulse. The value is
equal to 8dB above signal equals noise. Now if you
know the bandwidth of the receiver, you can determine the noise figure,
since you know that at 1 Hz BW, a perfect receiver would have a
sensitivity of -174 dBm. For every increase in
bandwidth, the s/n ratio decreases by the value ratio. For example, at
1KHz bandwidth, a perfect receiver would have s=n at -144 dBm. This
method is not as precise as a calibrated noise source,
but it's close.
--doug. WA2SAY, retired RF engineer.
On 03/13/2018 05:46 AM, jdow wrote:
Given a choice I'd prefer to try liquid funnygas er Helium for the
cold source.

{^_-}  Just being imaginative and silly again.

On 20180312 09:15, David Eckhardt wrote:
Yes, there is nothing to compete with the hot/cold 'noise' source.
kTB is very specific.  However, knowing the information bandwidth
introduces errors for our amateur receivers unless we rigorously
measure that as well. I've always preferred the hot/cold noise
source, but don't keep LN2 around.  However, these days, most larger
grocery stores carry dry ice.

Dave - WØLEV

On Mon, Mar 12, 2018 at 4:06 AM, Marcus D. Leech <mleech@...
<mailto:mleech@...>> wrote:

    On 03/11/2018 09:00 PM, David Rowe wrote:

        Thanks Dave - sounds like you have a great experimental set
up there for
        NF measurements.  For anyone interested in NF measurements,
I've blogged
        on my humble experiments here:

        http://www.rowetel.com/?p=5867

        I mentioned your results in the post Dave, hope thats OK.

        Cheers,

        David

    I'll point out that single-point noise-figure methods are rather
    error-prone, which is why the industry has standardized on the
Y-factor
    method, in which
       you have TWO sources of known noise power distribution.

    For noise figures above 3dB, you can usually use a high-quality
terminator
    at room temperature -- whose PSD will be -174dBM/Hz, and then a
calibrated
       noise source, usually in the 20-35dB ENR range.  You take
averaged
    measurements of both, and use that to determine the noise figure
of the DUT.

    Once you start going to noise-figures below 2-3dB, it's better to
have a
    "cold load" as one of the noise sources.  Labs that care about
noise figure
       measurements for "good" LNAs usually use an LN2-cooled load
for the
    "cold" load, and again a calibrated noise head for the "hot" load.





        On 12/03/18 10:18, David Eckhardt wrote:

            I have a calibrated noise source good to 18 GHz and several
            precision attenuators (HP, both single value and
switched).  Knowing
            the noise output of the noise source, I attenuate until
the noise
            just goes into the 'noise', tangential noise.  The
difference
            between the noise source known output and the
attenuation  is my
            noise figure.

            Dave - WØLEV

            On Sun, Mar 11, 2018 at 10:27 PM, David Rowe
<david@...
            <mailto:david@...> <mailto:david@...
            <mailto:david@...>>> wrote:

                 Thanks Dave,

                 Could you tell me a little more about how you
measured NF?

                 Thanks,

                 David

                 On 12/03/18 08:37, David Eckhardt wrote:

                     I've measured both the R1 and my present R2.
They both come in
                     around 4 dB.  I believe 7 to 8 dB is a bit much
based on my
                     experience with them.

                     Dave - WØLEV

                     On Sun, Mar 11, 2018 at 9:34 PM, <david@...
            <mailto:david@...>
                     <mailto:david@...
<mailto:david@...>>
            <mailto:david@... <mailto:david@...>
                     <mailto:david@...
<mailto:david@...>>>> wrote:

                          Hi - I've been setting up a system to
measure noise
            figures
                     of SDRs
                          in real time, an extension of some similat
tests we
                     performed a few
                          years ago:

            https://www.rowetel.com/?p=5057
<https://www.rowetel.com/?p=5057>
                     <https://www.rowetel.com/?p=5057
            <https://www.rowetel.com/?p=5057>>
                     <https://www.rowetel.com/?p=5057
            <https://www.rowetel.com/?p=5057>
<https://www.rowetel.com/?p=5057
            <https://www.rowetel.com/?p=5057>>>

                          I'm getting a NF of 7-8dB for a new Airspy
R2 and Airspy
                     mini.  The
                          spec quotes 3.6dB.  Has anyone else
measured the NF?

                          I note the 3.6dB figure is exactly the same
as the front
                     end tuner
                          R820 tuner.  However a system noise figure
will always be
                     poorer
                          than the front end device.

                          Thanks,

                          David




                     --         *Dave - WØLEV
                     *
                     */Just Let Darwin Work/*







            --             *Dave - WØLEV
            *
            */Just Let Darwin Work/*









--
*Dave - WØLEV
*
*/Just Let Darwin Work/*


Re: Gain control #HF+

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?