Range Expectations

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RickWakeman
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Joined: Sun Aug 23, 2015 9:53 pm

Range Expectations

Post by RickWakeman » Wed Sep 02, 2015 1:39 am

What are the range expectations for receiving ADB-S signals? I am getting about 80 nm using a homemade cantenna, LNA4ALL preamp and using a short run of the wrong type of coax (75 ohm impedance) to make the short run from the antenna to the preamp and the receiver.

I plan on swapping out the 75 ohm coax with 50 ohm but I am trying to figure out what my range expectations should be.

jonfear
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Location: Wick St Lawrence
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Re: Range Expectations

Post by jonfear » Wed Sep 02, 2015 7:46 am

Hi Rick

RickWakeman wrote:What are the range expectations for receiving ADB-S signals? I am getting about 80 nm using a homemade cantenna, LNA4ALL preamp and using a short run of the wrong type of coax (75 ohm impedance) to make the short run from the antenna to the preamp and the receiver.

I plan on swapping out the 75 ohm coax with 50 ohm but I am trying to figure out what my range expectations should be.


Because of geography, line of sight and simple trigonometry the maximum range at sea level should be about 250 nautical miles. As you increase elevation ASL, that will increase by a small amount.

Depending on your location, you should be seeing further than 80nm.

I tend to use an 8 or 12 element co-linear made up from Sky TV satellite cable which is 75 ohm. I buy it off eBay for about £15.00 for 100m. Do not get to hung up about the impedance of the cable. As this is receive only, the mismatch is of little significance. I connect the antenna to the dongle using F type plugs and adapters. This seems to be quite low loss. With the LNA4ALL preamp, the losses are more than compensated. Having a dedicated high quality cable will help with a few more contacts but frankly with the dongle set up, is it worth it?

You don't say what your set up is, however if it is the TV dongle and Dump1090 set up, then getting the gain set to -10 and ensuring your ppm is set correctly is more important. Do try to mount the antenna as high as possible, if possible outside and free from as many obstructions as possible.

Hope this helps

Jon
http://www.360radar.co.uk, the new name for MLAT Radar in the UK and Western Europe.

Former PP feeder Bm. No longer feeding. I do not have time to sort out imaginary problems with NTP
when it has been working fine for 2+ Years.

RickWakeman
Posts: 4
Joined: Sun Aug 23, 2015 9:53 pm

Re: Range Expectations

Post by RickWakeman » Wed Sep 02, 2015 9:43 pm

Thanks Jon. My antenna is only about 5 feet of the ground and I have not found the ppm offset yet. I have also been manually setting the gain. I will try changing it to -10.

drk
Posts: 3
Joined: Fri Sep 11, 2015 11:20 pm

Re: Range Expectations

Post by drk » Mon Sep 21, 2015 3:38 am

Newbie to ADSB, VRS and anything associated with them. I was an amateur radio operator for 30 years and work in the RF Communications field.

I got the bug to put something together after hearing guys at work discussing problems with commercial ADSB equipment, did a web search, so the dongles and picked-up a R820T2 SDR. I read up a bit about it, the antennas being used etc. I designed and built my own version of a collinear GP.
I live 4.5 miles East of KCLE. And except for looking directly at KCLE, on my rooftop, I have a clear view in all directions.

Now to range expectations.
I've been testing using ADSB# and VRS.
After testing and modifying my antenna slightly and with it sitting 1.5 mtrs off the floor on a shelf in my home, I was picking up signals from as far away 150 kilometers with A/C @ 40,000ft. I added a small LNA, moved the antenna outdoors, strapped to a gutter about 3.3 mtrs AGL (lowered the RF Gain with ADSB#) and adjusted the "confidence to 3". Then received data from A/C @ 40,000ft - 420 km away.
Based on the low AGL the values I've presented here seem too good compared to what I've read.

I suspect I won't really gain much more distance by moving the antenna to the top of the roof (to about 8mtrs AGL), but by moving it to the top, I should have better coverage to the South, right now the best is 140 miles with A/C @ 40,000ft. And I'm trying to understand if I'm missing something or did I just have beginners luck?

TIA,
Last edited by drk on Mon Sep 21, 2015 10:15 pm, edited 1 time in total.

jonfear
Posts: 365
Joined: Sat Feb 09, 2013 12:15 pm
Location: Wick St Lawrence
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Re: Range Expectations

Post by jonfear » Mon Sep 21, 2015 7:30 am

I would suspect that 420km or 260 miles is about right based on line of site. As with everything RF and line of sight, the higher the better. So if you can mount the antenna 8m AGL then all the better, it will have an effect on the data quality right out on the range limits. You do not say your local ground level ASL however this also has an effect on the range.

As a general rule approximately 250 Nautical miles is the maximum range when at Sea level.

Hope this helps and welcome to an absorbing hobby!

Jon
http://www.360radar.co.uk, the new name for MLAT Radar in the UK and Western Europe.

Former PP feeder Bm. No longer feeding. I do not have time to sort out imaginary problems with NTP
when it has been working fine for 2+ Years.

drk
Posts: 3
Joined: Fri Sep 11, 2015 11:20 pm

Re: Range Expectations

Post by drk » Mon Sep 21, 2015 1:33 pm

jonfear wrote:snip
You do not say your local ground level ASL however this also has an effect on the range.

As a general rule approximately 250 Nautical miles is the maximum range when at Sea level.

Hope this helps and welcome to an absorbing hobby!

Jon
I'm close to 700ft ASL.

Thanks

jonfear
Posts: 365
Joined: Sat Feb 09, 2013 12:15 pm
Location: Wick St Lawrence
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Re: Range Expectations

Post by jonfear » Mon Sep 21, 2015 5:38 pm

Try this site for size!

http://www.heywhatsthat.com/

It should give a theoretical maximum range for your location and any limiting factors...

Enjoy.
http://www.360radar.co.uk, the new name for MLAT Radar in the UK and Western Europe.

Former PP feeder Bm. No longer feeding. I do not have time to sort out imaginary problems with NTP
when it has been working fine for 2+ Years.

gergmchairy
Posts: 6
Joined: Wed Sep 16, 2015 2:29 pm

Re: Range Expectations

Post by gergmchairy » Tue Sep 22, 2015 9:05 am

Hi Guys, sorry to hijack but as you're talking antennas and range...
I've got a homebrew colinear (12 section WF100) which is up on my roof (about 2ft above my TV antenna if it matters).. attached via about 12ft of wf100 to a USB Tuner on a raspberry thats sat in my loft. For long distance this is working well, capturing up to 250miles in all directions. However, i'm not able to see local traffic (<15 miles) as it just dissapears when it gets close. Any thoughts ?? Thanks !! Greg

GaryG
Posts: 60
Joined: Wed Jan 30, 2013 1:26 am

Re: Range Expectations

Post by GaryG » Wed Sep 23, 2015 3:08 am

Hi

With a gain antenna (your 12-element co-linear as an example), the closer you are to having the antenna point at the signal source, the lower the gain. When the plane is overhead, very little signal will be actually received. I think this is referred to as the donut effect, if it's right overhead, you probably end up with no or very little signal due to the radio wave actually travelling along the antenna instead of hitting all the elements simultaneously.

You might do better with fewer sections, I have read that six elements is a reasonable stopping point.

I'm fairly sure this info is reasonably close to being correct.

GaryG

gergmchairy
Posts: 6
Joined: Wed Sep 16, 2015 2:29 pm

Re: Range Expectations

Post by gergmchairy » Wed Sep 23, 2015 8:10 am

Thanks Gary, I wondered if i might get a bit of a dropout nearby, but 'hoped' that the increased signal of the aircraft being closer might overcome it.. I quite like the range i'm getting though - so I might look at running both 12 & 6 element as a catch all !! :-)

Greg

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