FlightAware Discussions

Shielding FA Dongle / Pi from Antenna - Directly Connected - No cable


#1

I’ll be raising a waterproof box with directly connected FA antenna / FA blue dongle / PI 3 B+ over (no cables in between). Should I be considering some kind of shielding around the dongle and/or Pi to ensure no interference to the antenna (just 6-8" away)?

I have it burning in now hanging in the window. Seems to be working ok. Will prob fly it next weekend.

Scott
https://flightaware.com/adsb/stats/user/vannossc#stats-96353


#2

When it is directly below the antenna it shouldn’t be a problem.
(The antenna is pretty deaf in that direction, having it next to the antenna would be a much bigger problem)

You can try shielding the dongle itself but for me that didn’t make a difference or at least i couldn’t tell any difference.

Also i hope there is at least a short cable otherwise bending is not nice for circuit boards.

Depending on how much electrical noise you have in the area i would consider a FA filter in front of the pro stick plus. But it may well be that it works better without one, such things are basically trial and error in my experience.


#3

Another related question:
Is there any shielding provided between built-in antenna and rest of RF circuitry in Cell/Mobile phones?

Remember Cell/Mobile Phones are not receive only, these are trancievers:
transmit+receive simultaneouly (uplink+downlink, two channels)


#4

Got it…understood. I didn’t think it would need anything although I read some where having trouble with USB cables and needing RF chokes. No issue here with that.

In all reality the dongle with screw onto the antenna (one adapter only!) and the Pi will “hang” from the dongle. I’ll support it in some fashion - won’t hang when in production mode. :slight_smile:
If I get snowed in this week I’ll fabricate thew whole assembly and get it ready to go outside.


#5

Mobile phones should be time multiplexed.
(https://en.wikipedia.org/wiki/Time-division_multiplexing has GSM mentioned)
(3G and 4G use more compliclated multiplexing, but i don’t think they transmit and receive at the same time either)

For truly simultaneous tx+rx you would probably need two antennas and two frequency bands.
Receiving on a transmitting antenna must surely be one of the more impossible tasks.
Edit: It seems i’m wrong and they do rx+tx at the same time on the same antenna.

RF circuitry is almost always shielded with cans. But cans are rather expensive in regards to manufacturing. Large product numbers of course make them a bit cheaper.

Could almost imagine you @abcd567 having electrical devices in the receiving plane of your antennas is a factor in needing the filters you need. (But probably it is just the cell tower on top of your building especially if you are rather high up in the building)

the tale of the usb hub

One USB 3.0 hub in the house was completely annihilating 2.4 GHz WiFi for me, that was hard to debug because it would only be relevant when there was data transfer over the hub, for example a USB 3.0 hard drive being accessed via the hub.
I’m not sure what that hub would do in regards to ADS-B, but my antennas always were at least 4 m higher than the hub and with a cantenna or spider, they really don’t receive pretty much anything from below them.
(Anyway i used some aluminium foil tape to coat the interior of the USB hub housing to quiet it down.)


#6

Personally i would probably prefer a pigtail but finding a quality one can be challenging, especially at a reasonable price.

You could also use a short USB cable: https://www.amazon.com/6in-Black-Extension-Adapter-Cable/dp/B00S2N2Q4U

But then shielding the dongle from the pi might actually be more relevant than without. (the ethernet port and all usb ports kinda create a bit of an RF shield between dongle and pi)


#7

Not relevant but they do. Uplink and Downlink bands. Also this:

Orthogonal Frequency Division Multiplex, OFDM is a form of signal format that uses a large number of close spaced carriers that are each modulated with low rate data stream. The close spaced signals would normally be expected to interfere with each other, but by making the signals orthogonal to each other there is no mutual interference. The data to be transmitted is shared across all the carriers and this provides resilience against selective fading from multi-path effects.
For the LTE uplink, a different concept is used for the access technique. Although still using a form of OFDMA technology, the implementation is called Single Carrier Frequency Division Multiple Access (SC-FDMA).

One of the key parameters that affects all mobiles is that of battery life. Even though battery performance is improving all the time, it is still necessary to ensure that the mobiles use as little battery power as possible.
With the RF power amplifier that transmits the radio frequency signal via the antenna to the base station being the highest power item within the mobile, it is necessary that it operates in as efficient mode as possible. This can be significantly affected by the form of radio frequency modulation and signal format.


#8

These are not time-division multiplexed, these are frequency-division multiplexed, as there are two distinct frequency bands for transmitting & receiving.

BAND UPLINK (Transmit) DOWNLINK (Receive)
GSM-850 824 - 849 MHz 869 - 894 MHz
GSM-900 890 - 915 MHz 935 - 960 MHz

#9

GSM had indeed, inside of each of those bands, time-multiplexing. However, GSM networks are starting to be shut down, and their frequencies repurposed for LTE/4G (or next gen 5G).
For our hobby of ADS-B tracking… it’s all noise :slight_smile:


#10

They sure must have some very nice filtering going on with RX on the TX antenna.

I guess some fancy machined cavity filters or something like that :slight_smile:


#11

There is indeed some clever hardware there, but keep in mind it does fit into your average phone :slight_smile:


#12

I guess cavity filters are too big huh? Do know which type of filtering they use?


#13

There is no need for cavity filters, not for RF power under 10W.
People think that they are magical, but they are not better than a SAW. A true ceramic filter is better for low power. Sometimes even higher.
Thise guys have ITAR complaint filters:


#14

These diagrams are dated 2010, so dont represent latest technology, but are good for understanding the principle.

Source: http://cellphonerepairtutorials.blogspot.com/2010/08/understanding-how-rf-circuit-works-on.html

BlockdiagramGSMRFCircuit

.
.
rf%20circuit%20components%20layout

.
Quote:


#15

Still looking for the answer to my original question about cell phone’s built-in antenna.

  • If answer is YES, then how it is done?
  • if answer is NO, then why should we shield FA Antenna from ProStick / RPi ?

#16

The effect is negligible. The same technical solution - https://imgur.com/gallery/dpyGo



#17

Thanks. That’s the exact post I’m using as inspiration. Bigger box tho as I’ll likely put in some active cooking (*EDIT cooling) fans etc. more to come.


#18

Oh, well, people insist in cooking their Pi’s and receivers. More power to them.

I keep my Airspy Mini receiver and Pi3 indoors. 150 feet (45 meters) RG6 cable with F Type Female Jack To SMA Male Plug Coax Coaxial Connector RF Adapters at both ends.
Amp/1090MHz SAW filter in a 6"x6" PVC box.

Stats show that this is a good setup performance-wise:



#19

MaxLink AluBox IP-56 280 x 220 x 100mm
Mounted on the mast in the city of Salekhard ( It crosses the Polar circle, the main parts being about 1 kilometer (0.62 mi) south and suburbs stretching to the north of the circle).


http://forum.adsbradar.ru/f4/f-usdd2-salehard-rossiya-yanao-1959/index7.html#post39351


#20

Are those peltier elements for heating? Or what are those plates?

Also:

Location: (66.6, 66.6)