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Technical Topics => SDR - Software Defined Radio => Topic started by: Teotwaki on March 11, 2022, 0216 UTC

Title: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: Teotwaki on March 11, 2022, 0216 UTC
Tried tuning in 11,175 KHz yesterday and I could see activity on the waterfall but no audio. Then I noticed this tag
(https://i.ibb.co/25m5c1Z/Masked.png)

So what sort of feature is this on the SDR and what is it normally used for? It was not applied to other global HF frequencies.

Thanks!
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: ChrisSmolinski on March 11, 2022, 1236 UTC
KiwiSDR owners can mask or block certain frequencies or bands, so they cannot be listened to.

Usually this is done in response to abusive users, who will sit on a particular frequency for hours on end, tying up the receiver and preventing others from using it.

I've had to do it on a few frequencies, myself.
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: Teotwaki on March 11, 2022, 1603 UTC
Thanks! That makes perfect sense. I had not thought about what the owner of a public SDR has to go through with abusers. I try to get in and out of SDRs as quickly as possible.
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: ChrisSmolinski on March 12, 2022, 1614 UTC
I certainly don't mind if someone sits on a frequency for an extended period while they are actively listening - that's what the KiwiSDRs are for.  But sometimes you have to wonder...

The worst case I've had here is someone from Taiwan who would connect to all 7 of the KiwiSDRs here at the same time, and sit on a CHU frequency for 12+ hours. 
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: Charlie_Dont_Surf on March 12, 2022, 2102 UTC
The worst case I've had here is someone from Taiwan who would connect to all 7 of the KiwiSDRs here at the same time, and sit on a CHU frequency for 12+ hours.

I'm sure it was some long term propagation studies with multiple antennas. The timestamps are built in. ;D  Or he reeeally wanted to be very, very, very sure that he had the time in English and French every minute.

I've seen this on some Russian KiwiSDRs too, where they have blocked reception of The Buzzer or the like. Example: http://msk.swl.su:8074/?f=4625usbz6 (http://msk.swl.su:8074/?f=4625usbz6)
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: Teotwaki on March 15, 2022, 0212 UTC
I've seen this on some Russian KiwiSDRs too, where they have blocked reception of The Buzzer or the like. Example: http://msk.swl.su:8074/?f=4625usbz6 (http://msk.swl.su:8074/?f=4625usbz6)

That's a neat example
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: cyphermatic on November 02, 2022, 1912 UTC
LOL, just don't block Brother Stair.  Actually, I have noticed certain Russian KiwiSDR sites with dozens and dozens of masked frequencies. The only sense I could make of those is that they're manipulating SNR calculations.

As to 11175 being blocked, well... there's still 8992 and a few others.  There are better locations to listen from for the HFGCS / Nightwatch net. Try northern California, Idaho, Montana, and southern Alberta for nice reception -- and around Cape Cod in the eastern states. With good propagation, you can receive the white noise from the phone lines / satellite links to those ground stations.
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: Josh on November 02, 2022, 2148 UTC
LOL, just don't block Brother Stair.  Actually, I have noticed certain Russian KiwiSDR sites with dozens and dozens of masked frequencies. The only sense I could make of those is that they're manipulating SNR calculations.

As to 11175 being blocked, well... there's still 8992 and a few others.  There are better locations to listen from for the HFGCS / Nightwatch net. Try northern California, Idaho, Montana, and southern Alberta for nice reception -- and around Cape Cod in the eastern states. With good propagation, you can receive the white noise from the phone lines / satellite links to those ground stations.

What's amazing to me is russia allows kiwis in the first place, considering their soviet past. Never in a million years thought I'd see the day when anyone in the world can tune in to a sdr located in russia or warsaw pact country. Back in the day we had to ring them ruskiis with listening posts and pray for good conditions, now an hf rx in moscow be tuned by any browser anywhere on earth.
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: Charlie_Dont_Surf on November 12, 2022, 0646 UTC
What's amazing to me is russia allows kiwis in the first place, considering their soviet past. Never in a million years thought I'd see the day when anyone in the world can tune in to a sdr located in russia or warsaw pact country. Back in the day we had to ring them ruskiis with listening posts and pray for good conditions, now an hf rx in moscow be tuned by any browser anywhere on earth.

I hear you. I wondered if the Russians and the Chinese block SDR feeds from receivers outside their borders but then I would see a lot of users with IP addresses in Russia and China using Kiwis.

I always thought this was surprising given that the Chinese block Facebook, for example. On the other hand, SW radio isn't a mass medium anymore.
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: ChrisSmolinski on November 12, 2022, 1337 UTC
I hear you. I wondered if the Russians and the Chinese block SDR feeds from receivers outside their borders but then I would see a lot of users with IP addresses in Russia and China using Kiwis.

I always thought this was surprising given that the Chinese block Facebook, for example. On the other hand, SW radio isn't a mass medium anymore.

I do often see Chinese IP addresses on the KiwiSDRs here, sometimes sitting on frequencies for hours. Often monitoring .mil stuff which makes me suspect they are government users and not DXers. I've tried banning them, but it's like whack-a-mole.
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: ~SIGINT~ on November 12, 2022, 1458 UTC
The blocking of IPs is best handled with a featured call "geoip blocking" based on the GeoIP database. Many commercial firewalls now include this feature, sometimes at a cost. There are free alternatives available. It has been several years now since I have worked with this but there were community editions of, for example, pfSense and Sophos UTM just to name a couple, that are widely popular. Obviously, this is best managed at the network edge but there are also independent Linux packages available which may allow the possibility of implementing the geoip blocking feature directly in the Kiwi's OS.

Here are a couple of links for reference:

Need a cheap firewall that can geo-block IP's outside of USA (https://community.spiceworks.com/topic/1853358-need-a-cheap-firewall-that-can-geo-block-ip-s-outside-of-usa)

Block IP range from countries with GeoIP and iptables (https://docs.rackspace.com/support/how-to/block-ip-range-from-countries-with-geoip-and-iptables/)
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: cyphermatic on May 22, 2023, 1000 UTC
The People's Republic of (and not Taiwan - just "the Republic of) China is a funny place. They jam the hell out of a lot of shortwave broadcasts and block streams from Western media, bit they don't block many SDRs. There is a site where you can test urls to see what they block, and the PRC doesn't care about many of those SDRs. Perhaps the party is run be a lot of boomers who don't understand the tech.

Oddly, there are people operating internet SDRs from within the PRC. I noticed that chat boxes are absent, as there is some sort of rule requiring moderation anywhere people talk to other people. But the SDRs are there and you can listen around. LOL the Firedrake Jammer isn't blocked.
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: Pigmeat on May 23, 2023, 0455 UTC
The "Boomers" there died in large numbers in the chaos of the Cultural Revolution of the 60's. The Great Helmsman, Mao, was a sterling leader, he'd lead you right to your grave, but you got spiffy outfit and cap along with a "Little Red Book" for participating.
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: ZL/KF6VO on June 23, 2023, 0055 UTC
Quote
The only sense I could make of those is that they're manipulating SNR calculations.

After a while we realized this was a bug. So the masked areas are now excluded from the SNR calculation.

Regards,
John, ZL/KF6VO
KiwiSDR
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: Charlie_Dont_Surf on July 14, 2023, 2013 UTC
Quote
The only sense I could make of those is that they're manipulating SNR calculations.

After a while we realized this was a bug. So the masked areas are now excluded from the SNR calculation.

Regards,
John, ZL/KF6VO
KiwiSDR

Pardon the stupid question but before you excluded the masked areas form the SNR calculation, were they showing as SNR = 0 dB (which is my first thought) or are they showing as SNR = "huge dB", because the signal level is still available to the SNR calculation (despite the mask) and the noise in the masked area is basically zero?
Title: Re: KFS omni kiwi sdr "Masking" USAF global HF Frequency??
Post by: ZL/KF6VO on August 17, 2023, 1952 UTC
Quote
Pardon the stupid question but before you excluded the masked areas form the SNR calculation, were they showing as SNR = 0 dB (which is my first thought) or are they showing as SNR = "huge dB", because the signal level is still available to the SNR calculation (despite the mask) and the noise in the masked area is basically zero?

Apologies for the late reply. I don't read here very often.

The answer to your question is "it depends". The SNR ranking algorithm takes a sample of all the waterfall bins (in dB), sorts them, uses the value of the 50% bin (median) as the "noise" level, and the 95% bin as the "signal" level. The difference (95% value - 50% value) is taken as the SNR. Prior to eliminating the masked bins this means that if there were enough of them to effect the 50% noise level value (after sorting) the SNR would become huge (noise level = -200 dB or something).