I’ve built a PiAware as described here - amazon.ca/dp/B00WZL6WPO?tag=fligh01-20 , but I’m not sure what cable I will need to run between this antenna and the dongle. Any suggestions?
Thanks,
Pete
Hi Pete,
In a perfect world, you’d just buy a low-loss 50 ohm cable of the proper length with an SMA male on one end and an N male on the other and plug it together.
Since you probably won’t be able to find exactly that, you’ll need to get creative with adapters and readily available cables.
Keep the following in mind:
Try to have the shortest run possible from the antenna to the dongle. Is it possible to move the receiver to an attic for example?
Use as few connections/adapters as possible.
Go with a larger cable for longer runs. See if you can find the proper length with the N male on one end, then adapt (from the other end of that) to the SMA male with the shortest cable/adapter you can find. Cables with PL-259 ends are very common, but you’ll need to add another adapter at the antenna.
It’s a good idea to waterproof any outdoor connections and adapters with self-fusing tape. Also be aware where you penetrate the building with your cable that you don’t introduce a water leak into your attic (or anywhere else for that matter)
Also be aware that if you live close to sources of RF interference (cell towers are notorious) you could actually have worse ADS-B reception due to overloading the radio. In almost all cases, a filter between the antenna and the radio will greatly improve reception.
There are also numerous threads discussing adding an amplifier into the mix. Depending on your location, you may see significant improvement, or only a slight increase.
I will also mention that you can build a “spider” or “can-tenna” with an SO-239 on it for a few bucks and get outstanding reception with an outdoor antenna…
Hope any or all of this helps you out,
Thad
Thad has given some good advice. Pete, can you give us a little more information about your setup like expected distances between antenna and dongle/pi? Will the antenna be in a room? in the attic? mounted outside?
There are two important factors to know before a proper answer can be given.
(1) Where the antenna will be installed? outdoors (roof , mast etc) or indoors (attic, window etc)?
(2) What is the estimated length of cable between antenna & dvb-t receiver?
The most commonly available & low cost cable is RG6, but other types can also be used.
Whatever type of cable you use, the antenna end should be fitted with a N-connector (I think Male, but I am not sure. Those who have used FA antenna can tell better). The dvb-t end should be fitted with F-male, which will connect to dvb-t receiver through a F-female to MCX-male pigtail.
Thanks for the replies.
The antenna will be mounted on a roof. Assuming I can get the wifi dongle to work, I won’t need more than about 10 feet of cable.
The FA antenna has a N female end and will need an N male connector. You could use something like this
for your cable run http://www.amazon.com/TRENDnet-Reverse-Weatherproof-Connector-TEW-L208/dp/B000FICJ8S
(EDIT: ughh, there are 3 options on that amazon URL; it is the one with the N female to N male option, ~19ft. …and instead the following might be even better, cheaper and closer to the length you mentioned…
http://www.amazon.com/Premiertek-3-Meter-Female-Coaxial-PT-NM-NF-3/dp/B006UZSJPM/ref=sr_1_3?s=industrial&ie=UTF8&qid=1452744034&sr=1-3&keywords=N+to+N )
Then use an N to MCX pigtail to connect to the dongle.
http://www.amazon.com/coaxial-cable-assembly-right-angle/dp/B00CSFCCYW/ref=sr_1_1?ie=UTF8&qid=1452742936&sr=8-1&keywords=mcx+to+n
This described setup does not have a pre-amp (or filter). If a preamp or filter is involved it likely means a conversion thru SMA (not RP-SMA) or F connectors. Typically one tries to insert the preamp as near the antenna as possible and filter near the dongle, but this isn’t always possible. We can go thru that as well. As abcd mentions, it might be worthwhile in that case to use an N to F connect right at the antenna and then run cabling with F connectors. (I prefer an N cable connector run, but honestly cannot say if it makes that much difference); it is certainly easier with F connectors.
N-male to F-female adaptor for antenna end
DVB-T dongle has MCX connector, NOT SMA connector.
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DVB-T receiver’s input impedance is 75 ohms.
FA antenna & Jetvision antenna have impedance of 50 ohms
If 50 ohm cable (RG58) and connector (N) are used, these match with antenna, but mismatch with DVB-T receiver.
If 75 ohm cable (RG6) and connector (F) are used, these match with DVB-T, but mismatch with antenna.
So both the 75 ohm & 50 ohm cable systems have one mismatch, and should perform equal.
Many thanks for the excellent advice and suggestions!
Input impedance of dvb-t’s tuner chip R820T = 75 ohms
Reason: The DVB-T USB is designed as TV Reciever, and TV’s defacto standard is 75 ohms.
For HAM Transmitter/Receivers, the defacto standard is 50 ohms.
As far as I know, the Flightfeeder, FR24 feeder, Kienetic Beast Receivers are all based on HAM standard and have 50 ohms impedance.
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Just a question, if what I see above is correct, do the dongle send +5V to the coax ? The dongle could supply the F5ANN active antenna ?
The circuit left of the R820T chip (including ANT +5V) is NOT a part of the dongle, but a circuit “RF ESD/S1 Filter” which can be added if desired. In fact this diagram is only for the R820T tuner chip, not the DVB-T dongle, which has a second chip RTL2832U also.
Please see “Figure 4-1 : Reference Application Schematic” on page 17 of R820T’s data sheet which you can download from here:
http://rtlsdrblog.rtlsdrblog.netdna-cdn.com/wp-content/uploads/2013/04/R820T_datasheet-Non_R-20111130_unlocked.pdf
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Since the DVB-T dongle is intended for TV, it has an input impedance of about 75 Ohms. However, the mismatch loss when using 50 Ohm cabling and/or antenna, will be very minimal at around 0.177 dB. So dont worry, be happy, smile and mix the 75 ohm with 50 ohm system 
Food for mathematical minded:
How I arrived at figure of 0.177 dB?
When 50 ohm mixed with 75 ohm,
Reflection Coefficient Γ = (75-50)/(75+50) = 0.2
SWR = (1+Γ)/(1-Γ) = (1+0.2)/(1-0.2) = 1.2 / 0.8 = 1.5
Mismatch Loss in dB = -10 log (1 - Γ²) = -10 log (1 - 0.2²) = -10 log 0.96 = 0.177 dB ---- Q.E.D.
***Q.E.D. is an initialism of the Latin phrase “quod erat demonstrandum”, meaning “which is what had to be proven”.
*
My mention of SMA above is that some preamps/filters use SMA connections. In those cases, it is likely easier to stay in a N, SMA, MCX connection scheme so there is only one transition between 50 and 75 ohm impedance.
Your mention of SMA is perfectly ok as it refers to the filter, and you have clearly mentioned MCX for dongle.
My remark “MCX not SMA” (in red) did not refer to you, but thadm77 has by mistake mentioned SMA at the dongle end, and to avoid ordering coax with wrong connector, I have given the remark about it.