Posts Tagged ‘WiFi’
LHS Episode #163: Let’s Get Astrophysical
March 1st, 2016 | 
Author: 
Hello, listeners! Another universe-shattering episode of Linux in the Ham Shack is upon you. During this little slice of now, your hosts discuss the safety of wireless networking, colliding black holes, a popular Linux distro site being hacked, a tablet Linux OS, browser-based logging applications, ChromeOS on the Raspberry Pi and much more. Time is running out! Please donate to our Generosity campaign. We want you to see us at Hamvention this year. Thank you!
73 de The LHS Crew
PLT Devices – Have I welcomed the Devil in to the shack?
I need to set up the ability to remotely operate the station via the internet as well as experiment with internet linking systems but the wi-fi link to the shack isn't fast or reliable enough. Now if I do a scan looking for wi-fi networks I can see well over a dozen, some of them quite strong and more are popping up all the time and I suspect this congestion is part of my problem.
The Samsung Smart TV in the house was also wi-fi linked but we were having increasing issues with the BBC iPlayer and Netflix with buffering or poor quality images because of poor signal and data rates.
Ideally I would be like to fit proper ethernet cables but it is totally impractical without major upheaval or unsightly trunking a definite no-no. In the end the only workable and affordable solution seemed to be to get some of those evil Powerline Transmission (PLT) devices.
I have suffered strong sporadic QRM myself which I have assumed were neighbours PLT networking devices as I'd read the horror stories, seen the videos and anecdotal reports of mains borne noise caused by them. So I hadn't even considered it until I saw a post and video by Dan Trudgian (M0TGN) about his experiences of using some Netgear devices and the apparant lack of interference to his radio activities. Some members of South Kesteven ARS had also started using them, so I took the plunge and ordered some Netgear ones reduced on Amazon in the Boxing Day sales.
Setting them up was easy, but the acid test was how much noise did they generate? I set up one device in the shack at the far end of the mains cable run to maximise radiation. Streaming internet radio and a HD movie on Netflix I then used the FUNCube Dongle PRO+ SDR connected to the OCFD to see what noise they were generating.
Here are my observations going through the various HF bands. Where noise is present I first stopped the streaming and then powered off the devices to eliminate them as the cause, where they were the cause it seemed eliminating the network traffic was sufficient to greatly reduce the effect.
80 Meters
While the antenna isn't optimised for 80m, signals can be seen as well as noise. Before you get excited this noise has been present for quite a while and isn't being caused by the new Netgear devices. This noise is what I suspected was generated by PLT devices used by my neighbours.
60 Meters
Shocking noise but again this isn't caused by my new devices, the noise has the same characteristics as that seen on 80m.
40 Meters
The band was busy, there is some noise again but not from the new devices, this was looking encouraging. I have also showed the adjacent broadcast band.
30 Meters
Again, largely noise free
20 Meters
Still largely noise free, the QRM that is present still wasn't due to the new devices
17 Meters
This was the first indication of QRM from the new devices, however it appears effectively filtered to leave the amateur allocation clear. The faint noise in the middle picture is not from the new devices.
15 Meters
Again this band was clear of noise
12 Meters
Showing the two ends of the band again the clear signal/noise from the devices again seems effectively filtered
10 Meter
I didn't observe any additional noise on this band, but unfortunately deleted the screen grabs ;-)So where was the QRM?
While the amateur bands appear to be filtered, the transmission can of course can clearly be seen on some non-amateur bands and apart from 16 meters seems to avoid the broadcast bands.
Conclusion
These Netgear XAVB5221 devices seem effective, indeed doing a speedtest in the shack was more than acceptable (the dire upload speed is a 'feature' of my cable ISP)
This fairly rudimentary testing has largely given me confidence that they won't be any issues. The band conditions weren't brilliant when I did test, but even with the absence of signals on the band any noise would be evident as seen. Yes they clearly do generate QRM but thankfully not it seems in the amateur bands. I haven't heard any extra noise on any of the radios over the last few days so all is looking promising. I will keep you posted if there is any change.
PLT Devices – Have I welcomed the Devil in to the shack?
I need to set up the ability to remotely operate the station via the internet as well as experiment with internet linking systems but the wi-fi link to the shack isn't fast or reliable enough. Now if I do a scan looking for wi-fi networks I can see well over a dozen, some of them quite strong and more are popping up all the time and I suspect this congestion is part of my problem.
The Samsung Smart TV in the house was also wi-fi linked but we were having increasing issues with the BBC iPlayer and Netflix with buffering or poor quality images because of poor signal and data rates.
Ideally I would be like to fit proper ethernet cables but it is totally impractical without major upheaval or unsightly trunking a definite no-no. In the end the only workable and affordable solution seemed to be to get some of those evil Powerline Transmission (PLT) devices.
I have suffered strong sporadic QRM myself which I have assumed were neighbours PLT networking devices as I'd read the horror stories, seen the videos and anecdotal reports of mains borne noise caused by them. So I hadn't even considered it until I saw a post and video by Dan Trudgian (M0TGN) about his experiences of using some Netgear devices and the apparant lack of interference to his radio activities. Some members of South Kesteven ARS had also started using them, so I took the plunge and ordered some Netgear ones reduced on Amazon in the Boxing Day sales.
Setting them up was easy, but the acid test was how much noise did they generate? I set up one device in the shack at the far end of the mains cable run to maximise radiation. Streaming internet radio and a HD movie on Netflix I then used the FUNCube Dongle PRO+ SDR connected to the OCFD to see what noise they were generating.
Here are my observations going through the various HF bands. Where noise is present I first stopped the streaming and then powered off the devices to eliminate them as the cause, where they were the cause it seemed eliminating the network traffic was sufficient to greatly reduce the effect.
80 Meters
While the antenna isn't optimised for 80m, signals can be seen as well as noise. Before you get excited this noise has been present for quite a while and isn't being caused by the new Netgear devices. This noise is what I suspected was generated by PLT devices used by my neighbours.
60 Meters
Shocking noise but again this isn't caused by my new devices, the noise has the same characteristics as that seen on 80m.
40 Meters
The band was busy, there is some noise again but not from the new devices, this was looking encouraging. I have also showed the adjacent broadcast band.
30 Meters
Again, largely noise free
20 Meters
Still largely noise free, the QRM that is present still wasn't due to the new devices
17 Meters
This was the first indication of QRM from the new devices, however it appears effectively filtered to leave the amateur allocation clear. The faint noise in the middle picture is not from the new devices.
15 Meters
Again this band was clear of noise
12 Meters
Showing the two ends of the band again the clear signal/noise from the devices again seems effectively filtered
10 Meter
I didn't observe any additional noise on this band, but unfortunately deleted the screen grabs ;-)So where was the QRM?
While the amateur bands appear to be filtered, the transmission can of course can clearly be seen on some non-amateur bands and apart from 16 meters seems to avoid the broadcast bands.
Conclusion
These Netgear XAVB5221 devices seem effective, indeed doing a speedtest in the shack was more than acceptable (the dire upload speed is a 'feature' of my cable ISP)This fairly rudimentary testing has largely given me confidence that they won't be any issues. The band conditions weren't brilliant when I did test, but even with the absence of signals on the band any noise would be evident as seen. Yes they clearly do generate QRM but thankfully not it seems in the amateur bands. I haven't heard any extra noise on any of the radios over the last few days so all is looking promising. I will keep you posted if there is any change.
LHS Episode #156: Beer and Balloons
Hello, podcast listeners! In this episode of Linux in the Ham Shack, your intrepid hosts discuss APRS software, Bluetooth TNC hardware, FCC regulations on WiFi hardware, UK ham radio licensing issues, the crazy idea that Microsoft might buy Canonical and much more. Thank you for tuning in, donating and subscribing and just being a friend of the show. Thank you also for sticking it out while we work hard to get back to putting our show out on time despite all of life's obstacles.
73 de The LHS Guys
Repeater work on Sandia Crest
I had the opportunity of a lifetime to traverse through the nation’s most RF dense mountaintop towersite, and possibly reduce my chances of having children by a large amount…in any case, today’s work was bucket loads of fun.
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| Towers lining the crest. [Wikimedia user Skoch3, Photo] |
The work at the site was simple — some regular maintenance to the W5MPZ D-STAR repeater and gateway.
So, I got up early and headed off to Ed’s (KA8JMW) place to pick up the caravan to the peak. We packed the truck with some server rack shelves and tools, and headed to pick up Brian (N5ZGT), then Chris (NB5T).
And then, the 10,768 ft (3,255m) summit.
The road was blocked by the Forest Service since the park was closed due to fire danger. Thanks to some prior planning, we had no trouble getting past.
And not two turns in to the curvy mountain road, we meet our first deer, head on. Thanks to Ed’s quick foot on the break (maybe he was practicing for QLF?) the deer zipped across the road, perhaps only with a bruised tail.
We were warned that with the lack of humans, nature tends to take over a bit
The one thing I though of going up the road is, what if you had this road all to yourself (like we did then) with a nice, fast rally car?
I think deer would have a problem with that.
Anyway, we got to the top, and met the first obstacle:
Chris dispatched the lock on the well-signed gate and we were in. At that point, we had entered the danger zone; the steel forest. With at least 26 FM stations, almost half being over 20 kilowatts, 33 TV stations, more than half over 100 kW, and an uncountable number of microwave dishes, log periodics, yagis, verticals, radomes, funny looking phased arrays and dipoles supported on dozens of massive towers, I swear I could hear KOB in my teeth.
After driving through the entire site, we arrived at our final destination: the Sandia Nat’l Lab’s personal radio playhouse.
The guys began working on equipment, while I snapped photos and gazed in awe of the city of Albuquerque all within my field of view.
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| Chris, Ed, and Brian “working.” |
Brian took the job of tightening the D-STAR antenna, which he did adamantly, without falling, thanks to his fancy harness. It’s funny how dinky that antenna seems, but being over 3,000 ft ( 914m) above the rest of the world, it can see almost 100 radio miles (150km). With my 40w mobile radio, it comes in full signal in Socorro, NM, 75 miles (50km) away.
The team was successful of getting things done, cleaning up the shelves of an obtrusive monitor, keyboard and mouse (by going SSH only) and installing a NetIO internet-controlled AC power killswitch.
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| Before… |
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| After. Notice the new black box on the top right. That controls power for the whole thing via the web. |
The work was complete right on the dong of noon, and we had ribs for lunch. YUM! After that, Chris’s wife treated us to some homemade ice cream at his place, and we toured his shack, nestled on the edge of a HOA-restricted subdivision. That doesn’t stop him from loving ham radio!
Next on the list is to move this stuff to its permanent home on server racks. Sadly, I won’t be here, with only two weeks left in my VLA internship. I don’t wanna leave! 🙁
I would like to thank Ed James KA8JMW, Chris Aas NB5T and last but not least, Brian Mileshosky N5ZGT for taking me on this mighty heighty outing. Perfect timing for knocking another thing off my New Mexico to-do list.
The only part I forgot on that list was to bring a spectrum analyzer up there. It would have probably blown up in my hands.
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| Me, Ed, Chris and Brian on the edge of the crest. |
Don’t play Ingress at Radio Observatories
A few weeks ago, the IPG got some curious email from some ABQ-ians asking if they could play Ingress at the VLA to capture some GPS-based portals. If you’ve never heard of Ingress, think of it as geocaching with a Virtual Reality spin. Check out their website here.
Ingress is played on smart devices, which require data connections to operate. These data connections are fine and dandy unless you’re at the world’s greatest radio observatory; here they aren’t so dandy.
RF-EMS
Below is a screencap of our RF-EMS (Radio Frequency-Environmental Monitoring System) which captured two WiFi access points (the darker blotches) from an RV containing a Verizon 4G hotspot and another router for something else.
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| Your VLA on WIFI |
In the last blog I described the 10′ dish for pinpointing RFI. We also have a (usually) 24/7 monitor that uses some pretty nifty antennas and preamps on a 50′ tower, sending it to an HP 70000 Spectrum Analyzer in a RF-shielded room from which we can record and upload plots like the one above, every day for the past 5+ years.
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| RF-EMS Tower and Bunker |
The biggest downfall is adequate locating of interfering transmitters. Currently, I’m designing a method which will allow the IPG to quickly and accurately pinpoint people with any kind of transmitter, be it a cell phone, hotspot, or vehicle keyfob (if we wanted to locate such things). My idea is based on multilateriation, which uses multiple receivers around the site which compare arrival times to calculate a four dimensional location. Keeping the bill of materials as low as possible, simplicity, ease-of-use and network integration (without causing RFI itself) a prime focus.
It may be overkill, but it gives me something to do in the free time.
Other Doin’s: Testing out and Debugging the 74 MHz System
When I’m not having free time, this is what I’m doing. A new feature of the Expanded-VLA is observations on the 4 meter band. The current system in place uses these simple crossed dipoles hoisted a few meters below the sub-reflector.
The cross dipoles connect to our receiver, which hooks up to the rack that magically digitizes the signal and turns it into pulses of light which the correlator feeds upon.
One of the problems we face are things broken that don’t have to do with our antennas and receivers. For example, the first test we do to examine the receivers performance is a band pass plot. Often times, we see something like this:
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| A bad bandpass plot caused by a faulty relay in the T301. |
This is ugly! What we want to see is this:
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| A beautiful bandpass! You can see 4 band on the left, and P-band in the middle with RFI spikes all over. |
First we go digging in the LO-IF and FE racks for a place to stick a spectrum analyzer to…
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| Eric the BAMF next to the LOIF and FE rack. Our culprit is on the left, in the middle of the top rack of modules |
And from that we figure its’ this T301 which does the first IF up-conversion from 0-1GHz to 1-2GHz.
We get a new one, stick it in, turn it on and voila, it’s alive!
