KFS reception quality - IMD and other (internal?) noise sources...


Rob Robinett
 

I have just returned from 5 hours at KFS and have time for only a brief report:

1) I removed the Nooelec AMB BF and 6/9 dB pads which were between the Qbit LNA outputs and the Kiwi RF inputs.  
    There are 2 Mhz HPF out at the antennas and I have muted the whole of the AM band, so no user can tune there on a Kiwi.  
    So the Omni Kiwis have additional 6 dB gain and the others an additional 9 dB gain.  I will monitor WD's overload log to verify those changes don't result in significant overload events.
2) I confirmed that the NW feed from the primary multicoupler is suffering from severe AM IMD in the 2-4 Mhz region, so this IMB is generated in that multicoupler or more likely by the LNA out at the antenna
    Omni A and B also show that IMD but to much lesser extent.  Fixing these will require help from ARINC
3) Thanks to Glenn's AA and the tinySA, I tracked down the source of the every 40 Khz switcher RFI:  it is a vertically polarized signal generated at the cell phone equipment shed at the base of the cell phone tower shared with the NW antenna.  Again, ARINC is going to have to get  that fixed if they care about it.  That same RFI can be heard on the Omni which is the other antenna closest to the cell phone shed (about 100M away).  The SE and SW antennas are about 200+M away from that shed and so that RFI is barely noticable on those antennas.
4)  I see other switcher RFIs, so I'm sure there are many other bugs to squash, but the signals we see on the Kiwis are pretty much what the portable Kiwi sees when connected to the primary multicouplers.  So all indications are the problems are outside the building. 
4) Glen''s AA + the portable Kiwi showed a very clean spectrum when I got 300M away from the cell shed and main building.  There is very good wifi coverage out in the fields, so I think deploying a solar powered AA + Kiwi as far as possible (e.g 400M)  from the cell shed would result in a very clean full spectrum.

I now understand the location of all the antennas and can see why the NW and Omni will always be impaired by the cell shed.

Rob


On Thu, Jun 10, 2021 at 12:33 PM ON5KQ <ON5KQ@...> wrote:
In the meantime, I must correct my report from above. There are indeed also during the night severe man-made noise sources, which I believe are produced somewhere in the signal distribution system.,,,,more detailed reports I have sent to Rob, to help to find a solution and support kfs...



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


ON5KQ
 

In the meantime, I must correct my report from above. There are indeed also during the night severe man-made noise sources, which I believe are produced somewhere in the signal distribution system.,,,,more detailed reports I have sent to Rob, to help to find a solution and support kfs...


ON5KQ
 

Yes - now at local California midnight observing (dead) 20m band... All antennas show noise - strongest warterfall bars are every 180kHz.....
Also the empty 10m looks rather dirty... yesterday this was not the case!  Lets see, if this changes day by day... especially it will be interesting to see, what happens on the weekend.
In my neighborhood, there is a big improvement at the weekend of industrial noise (from the commercial centers here at about 3-5miles from my location)

Ulli


Rob Robinett
 

Thanks Ulli,

I don't have time this morning to respond fully, but my quick look showed no IMD but the switcher RFI still present.  I will compose a report later which fully explains my observations.

Rob

On Thu, Jun 3, 2021 at 5:30 AM ON5KQ <ON5KQ@...> wrote:
Hello,
This is to report my findings from night time usage of the kfs-antennas. I understand, that you have tried to find the various noise sources and reason for strong 'birdies' and other unwanted signals, which is believed to be produced by the KFS system somehow...
I also understand that most of the investigation has been done during daylight hours.
Now, due to the big time difference for me from Europe it is very easy to verify to degraded reception quality during middle-of-the-night - dead band conditions....

And to make things short:
- I could not find any of the problems you showed during our zoom meeting session at local morning time.

I checked at local midnight in California:
- the Weather Fax from Japan at 7985 kHz was very strong (radio jmh) The north west antenna was S9.... switched to South East - completely clear channel..... EMPTY! these antennas really work, from pattern point of view! South west antenna was weaker on the Japanese FAX, but still good copy - similar than the omni, which were both 10db down to the directional LP to NW...
- I searched the 8.5MHz aviation band for any 'unwanted noise sources'..... could not find any! Bandnoise was at -105dbm (S-meter) with some qrn, but very good reception quality... the 530 was at least as comfortable to listen to, than at the same time at northern Utah omni... (I checked...)
- Checked all amateur bands: Yes on 20m there were some regular birdies, but not as single carriers - it was a mix of several carriers concentrated within 100Hz - every 60kHz or so... I have the same here, when searching for it on completely dead band....
Could you check, if the Kiwi's are very closely placed in the rack ? I found, that even without antennas connected the one kiwi picks up noise from the kiwi next to it - it is only a few db, but you can see the lines in the spectrum. The only way to check it, is run every kiwi with all other kiwi's switched off. then switch on the other kiwi's one by one... you see the noise from the 'neighbor' kiwis in the rack... I plan to place the kiwi's with at least 30cm space to every other kiwi... may be something to check, when visiting KFS next time...

At least I can say:
- whenever a shortwave band was open - reception was great ! No big deal with noise sources! If this is what the operators hear in their commercial traffic = no wonder they do not understand the amateurs claiming noise.... so better to search more:
- could you please check at very late in your local evening at midnight or even later, if you are able to to so....  My guess now is indeed local radiated noise from the neighborhood of kfs (up to 20km is absolutely possible, with such large antennas!). This noise is only at daytime...
- I checked in the morning - 4h30 local California time.... clean bands... or at least as clean as you can get it realistically..... you are not in a remote area at half moon bay... hundreds of miles to the next powerline....hi
- It could even be, that although the noise you have seen during daytime is common-mode problem, this problem goes away, as the noise creator is switched of at late evening for some reason....

So, I hope my observations help finding the problem. Especially it my be useful information, if you plan to contact the commercial people about it with a written letter... before you send a letter I would better examine the location and also verify, that this noise is indeed 24h/7day a week, being a fundamental problem.
But my findings show, that there are times (at least) where there is NO Problem....

I will keep checking it and perhaps we find a kind of "schedule" for the noise...

regards,
Ulli, ON5KQ



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


ON5KQ
 

Hello,
This is to report my findings from night time usage of the kfs-antennas. I understand, that you have tried to find the various noise sources and reason for strong 'birdies' and other unwanted signals, which is believed to be produced by the KFS system somehow...
I also understand that most of the investigation has been done during daylight hours.
Now, due to the big time difference for me from Europe it is very easy to verify to degraded reception quality during middle-of-the-night - dead band conditions....

And to make things short:
- I could not find any of the problems you showed during our zoom meeting session at local morning time.

I checked at local midnight in California:
- the Weather Fax from Japan at 7985 kHz was very strong (radio jmh) The north west antenna was S9.... switched to South East - completely clear channel..... EMPTY! these antennas really work, from pattern point of view! South west antenna was weaker on the Japanese FAX, but still good copy - similar than the omni, which were both 10db down to the directional LP to NW...
- I searched the 8.5MHz aviation band for any 'unwanted noise sources'..... could not find any! Bandnoise was at -105dbm (S-meter) with some qrn, but very good reception quality... the 530 was at least as comfortable to listen to, than at the same time at northern Utah omni... (I checked...)
- Checked all amateur bands: Yes on 20m there were some regular birdies, but not as single carriers - it was a mix of several carriers concentrated within 100Hz - every 60kHz or so... I have the same here, when searching for it on completely dead band....
Could you check, if the Kiwi's are very closely placed in the rack ? I found, that even without antennas connected the one kiwi picks up noise from the kiwi next to it - it is only a few db, but you can see the lines in the spectrum. The only way to check it, is run every kiwi with all other kiwi's switched off. then switch on the other kiwi's one by one... you see the noise from the 'neighbor' kiwis in the rack... I plan to place the kiwi's with at least 30cm space to every other kiwi... may be something to check, when visiting KFS next time...

At least I can say:
- whenever a shortwave band was open - reception was great ! No big deal with noise sources! If this is what the operators hear in their commercial traffic = no wonder they do not understand the amateurs claiming noise.... so better to search more:
- could you please check at very late in your local evening at midnight or even later, if you are able to to so....  My guess now is indeed local radiated noise from the neighborhood of kfs (up to 20km is absolutely possible, with such large antennas!). This noise is only at daytime...
- I checked in the morning - 4h30 local California time.... clean bands... or at least as clean as you can get it realistically..... you are not in a remote area at half moon bay... hundreds of miles to the next powerline....hi
- It could even be, that although the noise you have seen during daytime is common-mode problem, this problem goes away, as the noise creator is switched of at late evening for some reason....

So, I hope my observations help finding the problem. Especially it my be useful information, if you plan to contact the commercial people about it with a written letter... before you send a letter I would better examine the location and also verify, that this noise is indeed 24h/7day a week, being a fundamental problem.
But my findings show, that there are times (at least) where there is NO Problem....

I will keep checking it and perhaps we find a kind of "schedule" for the noise...

regards,
Ulli, ON5KQ