Here is a topic for all kind of investigations and experiments regarding increasing SNR during Outernet reception of the DIY kits,Lanterns and other upcoming receivers.
Ferrite Isolator Test
Likewise as Cecil did, I installed a Radio Shack snap on ferrite isolator on the cable between my SDR/hub and the CHIP, and observed higher SNRs at low Rssi receive signal levels.
An SNR of 6.23 dB (with an Rssi signal level of -113.93 dBm) is about 3 dB better than I usually get at that Rssi signal level. I could only wrap the cable twice, as the pigtail from my hub to the CHIP is too short. (The ferrite isolator is right above my USB stick in the picture). @zoltan @Abhishek please take note.
Interestingly enough, before I repacked my Alpha Lantern, I had all the components laid out and had the hub connected to the CHIP with a 4 ft USB extension cable with 2 wraps thru the ferrite isolator. (My LNA/SDR was 4 feet away from the CHIP with the ferrite isolator placed midway.) In that layout, my SNR performance was up another 3 dB peaking at around 12 dB with Rssi levels of -110 dBm
I know this is a more subjective test as signal levels bounce around, but I took observation over a 1 minute period in each case within a 10 minute time period.
The CHIP noise impact on the LNA/SDR appears to be proximity related, and can be mitigated successfully in the Lantern the way I did. No doubt those of you that have longer cable runs between your PATCH antenna and LNA/SDR should see even bigger improvements.
I’m wondering if I moved the LNA/SDR to the far left next to the battery in the Lantern case, if that would make a difference. I’ll try that next time I open the Lantern by putting a shorter USB extension cable between the LNA/SDR and the hub. Ken
This is really interesting! We have seen already EMI issues around. My best guess that this is not a conducted EMI problem but the antenna (and the 2x19dB gain 2 stage LNA) picking up the noise coming from CHIP+USB HUB.
Moved this post into this HW topic as this is a really important issue for all of us, let’s talk about it and get better understanding.
My advise in this topic that when hunting for disturbing noise some can turn CHIP + SDR into a small spectrum analyzer, installing GQRX on CHIP. I can confirm it’s worked for me! Could compile it on CHIP and start working. Really on the edge performance wise but works. There from the live spectrum plot it’s easier to investigate.
GQRX running on CHIP:
just out of interest what usb hub is that ?
my kit contains this (or very similar)
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What you say @zoltan brings to mind the potential of a Faraday Shield made of screen all around the CHIP. I can try that too on my next shut down. Do you think aluminium screen material might work, or do I need to find a copper screen? In either case, the screen will let the CHIP expel heat as it now does in the case.
Ken, its the mesh size more so than the material. Having said that, copper conducts much better and is the preferred method of Faraday cages. Hopefully you have another type of connection to the CHIP than the wifi as putting on this shielding is going to block all connectivity to its wifi.
That’s the point! Due to the on-board wifi it’s quite problematic do make a full shielding. Perhaps for shake of testing a (linux native) USB wifi dongle can routed out, while the on-board wifi is muted (if possible).
Luckily the antenna is not omnidirectional but has a main lobe thus less sensitive to the backplate, where CHIP usually sits now. The problem we are so close to the antenna that the EMI source is in the near field where things works a bit different. Saying this only as some sort of bigger metal back plate (copper foil sheet?) can also augment the noise problems.
Damn you’r good ki4its
I should have thought of that - - the best shield will work perfectly, but guarantee the total system won’t work!!
I don’t have another way into the CHIP right now other than the WiFi. Maybe, I can put a wire into one of the pins on the CHIP pin-outs to extend my WiFi out of the Faraday Shieled CHIP. I would have to put a WiFi repeater right next to the CHIP to send my home WiFi into the CHIP at that closer range.
I also thought for a quick and dirty test lasting only a few minutes, I could just wrap the CHIP in aluminum foil.
What do you think of that? Over - Ken
But as somebody already said before: the best is to place the antenna and LNA close and move the CHIP and HUB a bit away via SMA cable, thus gaining benefit of the natural isolation of distance.
(looks like sold out now…)
Yes, and that will work for folks not using the Alpha Lantern as I am.
I want to put the Alpha Lantern through its paces to see how bad I can break it. Now my Lantern is all buttoned up and working with high SNRs I have never achieved before the addition of the Ferrite Isolator.
Ken, can you share with us the exact part number of the ferrite? I have one hanging around but there are lot’s of different types, filtering on different freqs
Sorry I misunderstood I was thinking he still wanted to access the chip to get other data from within.
Not all is lost. Doesn’t the CHIP have a serial output? RS232 perhaps? if so, figure out which pins they are and break them out to a DB9 or to a usb to serial converter thingy. Then just use PUTTY or whatever terminal program you have to interact with it
UART TX and RX pins exposed on the GPIO headers
Here are the pinouts for anyone needing them. They are down the page a bit.
The Radio Shack SKU is 2730105 - - search on their site. My store had a whole bin full of them this weekend.
By the way, I borrowed a bigger Ferrite Isolation core from a friend thru which I can loop 4 turns as Cecil did. Tomorrow I plan to test it with my LNA/SDR moved to the left of the PATCH antenna lead in the Alpha Lantern.
All things considered, unless you are at the poles, SNRs of 10 at 39 deg North Lat should work for everybody. There should be no need to achieve perfection, when the “good” will surfice! Ken
Look for this section. You can do this numerous easy ways.