HB9VQQ testing Kiwi SDR


Rolf Ekstrand
 

Greetings y'all 

HB9VQQ is presently performing a test of  Kiwi with Rpi4 running WD  against  an Airspy HF Discovery running Wsjtx with Rpi4   on the same antenna through a splitter      https://groups.io/g/wsprbeacon/topics

It looks like the Airspy set up  at times outperform the  Kiwi, but as things usually goes, sometimes things can be deceiving. It is interesting though.   Comments anybody? 

73 Rolf K9DZT 



Bruce KX4AZ
 

Rolf,
I wouldn't be at all surprised if the Airspy HF+ Discovery outperforms the KiwiSDR for WSPR spot counts, give the different architecture and narrower bandwidth on the Airspy.  In my informal comparisons of the two (attached to a simple y-splitter), the Airspy had a measurably higher S/N ratio on the weakest signals.  It appears that modest signal amplification (very carefully applied) can compensate for the difference.  I'll leave it to the experts on this forum to (like KA7OEI) to detail the pluses/minuses of amplification.

I just started setting up a new Pi4 today and hope to get the wsprdaemon running with the KiwiSDR one of these days.

I also wanted thank you for your post, calling my attention to yet another groups.io that I'll need to join!  Might be a good place to discuss my current 10 microwatt WSPR experiments.
73,
Bruce KX4AZ


Jim Lill
 

From my experience on both my own and KD2OM kiwi,  above 10 MHz or so, the Kiwi may need a bit on gain in the path depending on what antenna is used.  You may note that both Steve KD2OM and Tom WA2TP both rank high in wspr reporters and use kiwi.

-Jim

WA2ZKD

On 10/13/21 4:49 PM, Bruce KX4AZ wrote:
Rolf,
I wouldn't be at all surprised if the Airspy HF+ Discovery outperforms the KiwiSDR for WSPR spot counts, give the different architecture and narrower bandwidth on the Airspy.  In my informal comparisons of the two (attached to a simple y-splitter), the Airspy had a measurably higher S/N ratio on the weakest signals.  It appears that modest signal amplification (very carefully applied) can compensate for the difference.  I'll leave it to the experts on this forum to (like KA7OEI) to detail the pluses/minuses of amplification.

I just started setting up a new Pi4 today and hope to get the wsprdaemon running with the KiwiSDR one of these days.

I also wanted thank you for your post, calling my attention to yet another groups.io that I'll need to join!  Might be a good place to discuss my current 10 microwatt WSPR experiments.
73,
Bruce KX4AZ


Rob Robinett
 

Hi Bruce,

In case you and others in this group missed my posts' to Roland's WSPR Beacon Project Telegram group on this subject,  I'll copy those remarks here,  but the subject of how to construct high performance (and what that means needs to be defined), easy to deploy and cost effective WSPR receive site is far more complex than can be covered in one post, but here is my perspective:

Roland wants to deploy a wspr rx system which mirrors his tx system and feels that to do that the cost of each site needs to be $200 or less.  At $400 for a Kiwi + Pi4, on cost alone that system doesn't qualify, so he could have stopped there and settled on the Airspy + Pi and compared it against other single channel SDRs.  However he also wants to know how well his low cost system compares in performance to the Kiwi + Pi used by many of the top spotting sites.  But in making that comparison he put the Kiwi system at a severe and undocumented disadvantage by not adding the AM and LNA requried to properly utilize the Kiwi which is used at those top sites.  

As one of many examples of the disadvantages potentially suffered by the Kiwi in such a comparison, without an AM blocking filter the Kiwi (and and wide band SDR) is likely to be frequently going into overload.  The Kiwi GUI displays those events with the flash of a red OV next to the S-meter, but if you are comparing over a 24 hour period there is no place to find out on the Kiwi the number and severity of those events.  In order to document this problem, wsprdaemon records the frequency and severity of OV events to a log file which the operator should examine to see if there is sufficient filtering to minimize overload events.

As a second example, if there is no blocking filter and no overload events, there is evidence that the Kiwi system is not receiving a strong enough RF signal and it needs a  LNA ahead of it.

While a single channel SDR probably doesn't need blocking filter(s), it too can suffer from impairments introduced by its installation environment, and those are much harder to identify than when using a wideband SDR.

People write whole books on the subject of building a good receive station and I worry that the effort to deploy low-cost plug-and-play rx systems will result in many 'deaf' stations.  Certainly by listening only to the bands and wspr cycles when/where WSPR Beacon stations are transmitting, many potentially interesting spots from non-Project stations will be missed.  So I think it is a shame to invest a lot of time and money in rx stations which could be far more useful to the wider community.

But Roland deserves credit for funding this and I hope his rx stations do make a contribution to our understanding of radio propagation.  But his tests don't prove the Airspy is a 'better' WSPR receiver than a Kiwi.  The Airspy just works better in the way he has been testing and the way he wants to deploy his systems.

73,

Rob



==========

"I understand your application requirements are different, but for many users the Kiwis are cheaper and better solutions when they are properly deployed.  My point here is to clarify to others that your comparison tests are for your specific application:  band hopping with no external filters or amplifiers.

Rob Robinett AI6VN, [Oct 10, 2021 at 1:35:29 PM]:

Given your cost and single band at a time requirements, then the Airspy seems the better choice.  But the Kiwi is not 'bad', it has different features and testing by many knowledgeable hams has shown how to optimize its performance to match that of other top quality receivers like the Airspy.  So I don't think it is appropriate to characterize the $40/rx channel Kiwi as 'worse' than' than the $170/channel Airspy when your test criteria precludes optimizing the Kiwi's RF feed.   I think you have identified the Airspy as the right SDR for your application, but that doesn't mean it is the 'best' SDR for all applications"



On Wed, Oct 13, 2021 at 1:49 PM Bruce KX4AZ <bruce@...> wrote:
Rolf,
I wouldn't be at all surprised if the Airspy HF+ Discovery outperforms the KiwiSDR for WSPR spot counts, give the different architecture and narrower bandwidth on the Airspy.  In my informal comparisons of the two (attached to a simple y-splitter), the Airspy had a measurably higher S/N ratio on the weakest signals.  It appears that modest signal amplification (very carefully applied) can compensate for the difference.  I'll leave it to the experts on this forum to (like KA7OEI) to detail the pluses/minuses of amplification.

I just started setting up a new Pi4 today and hope to get the wsprdaemon running with the KiwiSDR one of these days.

I also wanted thank you for your post, calling my attention to yet another groups.io that I'll need to join!  Might be a good place to discuss my current 10 microwatt WSPR experiments.
73,
Bruce KX4AZ



--
Rob Robinett
AI6VN
mobile: +1 650 218 8896


Rolf Ekstrand
 

Thank you Rob

No doubt there could be a difference between a narrow band Air Spy  and the Kiwi in a band hopping application.  Another possible issue that could influence the outcome will be the splitter design on a single antenna.  

73 Rolf


Rolf Ekstrand
 

Hi again y'all

I have run my Kiwi  here with AM filter for more than a year now almost 24/7 and I am very happy with it.  I am only using an old ground mounted  Cushcraft R7.  I am still planning to expand with additional kiwis  for the low bands and a vertical log periodic towards middle EU.  In the meantime I like to try a LNA ( with a 50 ohm HP on let say 10 Mhz) on the vertical.     

I guess I could cobble together a Norton amp or similar and the HP filter, but before doing so,  what are the "big gun" WD kiwi stations out there using if they need a boost??

73  Rolf


WA2TP
 

Not sure I’d consider myself a big gun, but I have had very good results with high spot counts. 

I am not using any and pre-amplification on the resonant antennas. 

The only antenna with a pre-amp here, is the wellbrook active loop. 

I have been plagued with CM paths and local noise sources, which is what I focused on.

I built my own filters for the AM BB problem stations. 

Tom
WA2TP 

On Oct 15, 2021, at 7:44 AM, Rolf Ekstrand <rekstrand@...> wrote:

Hi again y'all

I have run my Kiwi  here with AM filter for more than a year now almost 24/7 and I am very happy with it.  I am only using an old ground mounted  Cushcraft R7.  I am still planning to expand with additional kiwis  for the low bands and a vertical log periodic towards middle EU.  In the meantime I like to try a LNA ( with a 50 ohm HP on let say 10 Mhz) on the vertical.     

I guess I could cobble together a Norton amp or similar and the HP filter, but before doing so,  what are the "big gun" WD kiwi stations out there using if they need a boost??

73  Rolf


KD2OM
 

Rolf,
I am using three different amplifiers built by N4CY Everett Sharp. They all are 11 dB gain. He has changed the version several times, one has a relay to disconnect the antenna when no power is supplied. I am feeding power to them using a bias T, also built by Everett. 
I do need to increase the gain for my beverage antenna, candidates are a 20 dB gain amplifier from Advanced Receiver Research and a 23 dB amplifier designed by K8ZOA from DX Engineering.

73,
Steve KD2OM 

On Oct 15, 2021, at 13:44, Rolf Ekstrand <rekstrand@...> wrote:

Hi again y'all

I have run my Kiwi  here with AM filter for more than a year now almost 24/7 and I am very happy with it.  I am only using an old ground mounted  Cushcraft R7.  I am still planning to expand with additional kiwis  for the low bands and a vertical log periodic towards middle EU.  In the meantime I like to try a LNA ( with a 50 ohm HP on let say 10 Mhz) on the vertical.     

I guess I could cobble together a Norton amp or similar and the HP filter, but before doing so,  what are the "big gun" WD kiwi stations out there using if they need a boost??

73  Rolf


Glenn Elmore
 

Rolf
Using "Quiet receiving site", curve C and "galactic noise" curve D from ITU-R P.372.8 as a guideline, one can probably stand a system noise more than 20 dB above KTB before it impacts SNR  from a losslessly matched antenna. This presumes that not only receiver side noise and NF but also IMD, ADC non-linearity and common-mode and similar QRM ingress is no higher.  It also recognizes that ground losses and ground noise currents can be a significant part of the feedpoint impedance and noise floor even  up at 10 MHz and particularly for horizontally polarized antennas.

If the SNR present on the antenna being used is substantially due to far-field sources, propagated signal and propagated noise, then except for IMD and ADC issues the receiver used shouldn't impact things much. In real environments of course that's the rub.  Both near-field sources and strong signal overload from out-of-band signals can make this not the case.

It does say that for a well matched antenna (well matched to radiation resistance, not necessarily the presented feedpoint resistance),  NF of the preamp and rx probably don't matter much. When one starts using poorly matched antennas, particularly a problem for electrically small antennas, then the requirements on the rx system hardware and ingress mitigation get greater.

If you are seeing appreciable difference between receivers/detectors then I suspect you have a problem with ingress,ADC/IMD and that these need to be eliminated.

Just my opinion from HF active antenna, preamp and receiver investigations...

Glenn n6gn