Antenna Cable Length Signal Loss vs Higher Elevation?


#1

Your opinions needed please!

I have a 3 meter antenna cable connecting my Rpi to my antenna:

http://www.ebay.ca/itm/291469401256?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Currently, height/trees/obstacles are limiting the directionality of my ADS-B captures. I could just ‘be happy’ with what I have, or:

  1. Leave my Rpi where it is (under a house deck, away from bright sunlight, etc.), buy some sort of ‘extension’ antenna cable, and get my antenna higher (less obstacles but what about signal loss?):

http://www.ebay.ca/itm/50-3-5M-N-male-to-N-female-RG58-Coaxial-Cable-for-phone-Signal-repeater-booster-/281317203679?pt=LH_DefaultDomain_2&hash=item417fcfdedf

or

  1. Move my RPi, antenna cable, and antenna higher – except that the RPi will be more exposed to the elements (hotter?) – and might destroy my plans to add some weather sensors to the RPi since it will no longer be shaded properly

Anyways, adding a 5 meter antenna cable extension will help me to get higher, but will this be cancelled out by signal loss?

P.S. My RPi is currently sealed inside a plastic coffee container, so it won’t get ‘wet’ no matter where I move it.


#2

RG-58 signal loss isn’t great, at 1GHz it’s something like 65dB/100m. So a 5m extension will lose you something like 3dB (+ connector losses) - i.e. 50% of the signal. (It’s not as bad as it sounds, but you will probably lose your weakest signals)

For comparison WF100 (commonly used for satellite installs around here) is around 20dB/100m @ 1GHz. Something with that sort of loss would probably make the extension more feasible.


#3

DItch the RG-58 and go with a good 75 Ohm satellite cable, such as RG-6 or WF100. It’s cheaper and has far lower signal loss. F-style connectors are also easier to work with. Remember that you need to make the connector at the antenna watertight, such as by using self-vulcanizing tape covered with a good electrical tape (Scotch 88), or enclosing the whole thing to keep out the elements.

I’m rapidly coming to the conclusion that folks are much better off using RG-6 style cables for ADS-B unless they’re RF freaks and/or will be transmitting along the same or close-by cables. 50 Ohm cables for 1 GHz that are low loss are expensive, hard to handle, and use expensive connectors.

bob k6rtm


#4

I use RG-6 Quad shield cable made by South wire. I crimp my on end on. Works pretty good for me.


#5

The R820T dongle has 75 Ohm impedance as do power injectors, Satellite LNB amplifiers and so on that we often use - we might as well go to 75 Ohms up by the antenna and run the whole down feed at that impedance.

It would be good if antenna, amplifier and filter designers also realised that most of the people using this stuff for ADSB are amateurs with a limited budget that they are willing to spend on this - and designed everything with a small budget in mind (make it 75 Ohms, ditch the SMA and N connectors in favour of the easy to fit F-connectors.

The limited budget is the reason the Pi + R820T + SD card reciever has taken off so well, it’s low cost and some result is almost guaranteed.


#6

I’d be so happy if most things available were fitted with F-connectors, that’s all I use because I have coax and connectors left over from various satellite setups.


#7

I used RG-6 because of the price. My run I have from the antenna to my USB dongle is only around 12-14 feet long if that. So I don’t have to worry about a long run… But here is the Spec for what I was.


#8

Thanks for all the feedback, folks! Some of it is a bit too technical for me, though! :slight_smile:

This is my current connection setup:

  • antenna has a female ‘N’ connector (this cannot change!)
  • cable has an ‘N’ male connector, is 3 meters of RG58, and ends with a male ‘BNC’ connector
  • pigtail cable adapter is female ‘BNC’ connector, and ends in ‘MCX’ male connector (to RTL-SDR)

From another project, I had an ‘F’ to ‘MCX’ pigtail adapter, so I can consider a RG6 cable if you think it is best, so it would be:

  • antenna with female ‘N’ connector (this stays the same!)
  • new additonal ‘N’ male to ‘F’ female adapter (see below)
  • regular RG6 cable (say, 5+ meters instead of 3) with male ‘F’ connectors at both ends
  • my other ‘F’ female to ‘MCX’ male pigtail connector (to RTL-SDR)

Is this a good plan? Is the following what I would be looking for?

http://www.ebay.ca/itm/N-Type-N-Male-Plug-to-F-Female-Jack-RF-Coaxial-Adapter-Connector-Zinc-Alloy-EAL-/151748676188?hash=item2354ed0a5c


#9

You got it right ! RG6 and F connectors are widely available and inexpensive. Then, if you want power injection and amplifications, you can buy standard F connector satellite supplies off the shelf at great prices. I like the compression style connector for rugged service but the silicon gel filled crimp on style will also prevent water entry.

Also, antenna construction is dirt cheap using RG6. But, I have to say adding a N to F adaptor to the Flight Aware antenna provides an industrial strength, really high performance antenna system (looks good and compact).


#10

Go for it!

By the way I use twist on F connectors [get the ones that match the cable diameter … same supplier] and wrap with self amalgamating tape - no tools required beyond a craft knife

Them the next experiment would be a satellite amplifier ebay.ca/itm/220750618448 (would need an female-female F barrel connector) and a power injector - Someone in Canada will advise what is available and inexpensive there


#11

I’ll have the FA antenna and a run of about 3 feet to my dongle…then a 12 foot USB cable to my laptop. So antenna, N to F connector, professionally made RG-6 to F-MCX adapter to dongle. This will replace a spider 4 leg and 35 feet of RG-6. Hoping for more range but in reality I just want to see if it works better. Filter next (when FA is shipping).

Scott
Schenectady NY
gI


#12

my run to the antenna is about 35 feet from the dongle and i’m getting hits in the 180-240mi arc (or so the stats page tells me) on a homemade collinear. i’m not sure what my loss is but i’d say don’t be terribly discouraged to use a long run to your setup.


#13

So what is the max run of RG6? Bought an antenna and going from F to coax. Have some good quality RG6 (about 50 feet). Tried it out and picked up NOTHING on the antenna. Plugged the little mini that FA recommended way back when and “ding,” everything came back up.

Any comments?


#14

Rg6 has a loss of about 6 dB per hundred feet
50 feet will lose 3 dB

3 dB loss is = 50 percent reduction in signal strength.


#15

Try a short length of the RG6 - see if that’s your problem or it’s something else

(are you sure it’s RG6, I’m wondering if it’s marked on the reel or cable - other [more lossy] cables look similar)


#16

I use a Blue Rigger 10m USB cable to keep the antenna cable to a minimum but still allow a long run to the PC. My dongle is housed in the base of the antenna housing.

amazon.co.uk/BlueRigger-Acti … rigger+usb


#17

It’s marked RG-6 High Performace 75 ohm (courtesy of a satellite provider.)

If I want to put the antenna up on a mast, say 30 feet up, will an inline amp help? Power injector?

Jim


#18

Yes, but you should see something without an amplifier, even if it’s nearby traffic.

So still check with just a short length of the RG6 - there is something wrong if you’re receiving nothing, you need to find out what it is [by elimination / substitution] before climbing a mast.

check for no short circuits between coaxial core and shield on the RG6 with a multimeter and so on.

It would be better to eliminate the problems before adding complexity with amplifier, power injectors and so on.


#19

Well said. I fully agree.

My setup - everything 75 ohms - running satisfactorily:

SYSTEM 1 (65 ft Coax, With Amplifier, Maximum Range 250 nm)
Home made indoor antenna (8 element open top CoCo with F connector) >> 15 ft cheap quality RG6 Coax >> RCA Satellite amplifier 18 dB >> Home Made Power inserter >> 50 ft cheap quality RG6 Coax >> 20 inch RG316 pigtail F to MCX >> DVB-T Dongle inserted directly into RPi Model 2 >> 6 ft network cable from RPi to router.

SYSTEM 2 (10 ft Coax, No Amplifier, Maximum Range 250 nm)
Home made indoor antenna (Cantenna with F connector) >> 10 ft cheap quality RG6 Coax + 20 inch RG316 pigtail F to MCX >> DVB-T Dongle inserted directly into RPi B+ >> 15 ft network cable from RPi to network switch (network switching hub) >> 15 ft network cable from network switch to router


#20

Can you easily configure for System 1 with no amplifier - to see how much difference it makes

on mine, I think it added maybe 10% to range and 20% to positions / hit’s … picking up many more aircraft more often that were within the previous maximum range.