All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 18 posts ] 
Author Message
 Post subject: Dramatic drop in aircraft sightings
PostPosted: Sat Mar 18, 2017 3:26 pm 
Offline
joecalw - FlightAware user avatar

Joined: Sun Nov 06, 2016 5:03 pm
Posts: 9
Hi all, I have a problem with a dramatic drop in aircraft sightings.
I live on the Northeast coast of the UK and my setup is Rpi 3 with dongle running Piaware 3 and a homebrew 6 element colinear antenna.
My problems started on 8th March when I thought I would try an inline amp to try and pull in more aircraft from the Pennine hills to the West, and the Cleveland hills to the South. From NNW to the East I was more than happy as I was picking up aircraft at up to 300 Mls.
So I connected up the amp and power and had a look to see absolutley nothing so I thought to myself well Bugger that for an Idea and disconnected them, So putting all back in place only to find I am getting no more than 100 Mls in range.
I thought maybe the power and the amp have done something so I tried a reboot.I also tried my backup of piaware. I ran a fresh feed of coax which was due anyway, I checked all my connections all to no avail so I put together another 6 element antenna. And still no joy I even went as far as buying another dongle the same as my original but piaware does not see it for some reason.
Any ideas folks welcome.
Thanks in advance guys. Joe :x


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Sat Mar 18, 2017 4:57 pm 
Offline
NeoDuder - FlightAware user avatar

Joined: Sat Nov 26, 2016 11:17 am
Posts: 25
Location: EGPH
Maybe overloading the dongle by using an amp. Try reducing the gain on the dongle. Which dongle are you using? Are you using a filter?

Oh and the North East coast of the UK is nowhere near the Pennine hills :wink:


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Sat Mar 18, 2017 5:34 pm 
Offline
joecalw - FlightAware user avatar

Joined: Sun Nov 06, 2016 5:03 pm
Posts: 9
NeoDuder wrote:
Maybe overloading the dongle by using an amp. Try reducing the gain on the dongle. Which dongle are you using? Are you using a filter?

Oh and the North East coast of the UK is nowhere near the Pennine hills :wink:



Hi as I say I have taken the amp off now and I would not know where to start reducing the gain my stick is USB 2.0 Digital DVB-T DAB FM RTL2832U FC0013B SDR TV Radio Receiver Stick.
PS of course I know where the pennines are :lol: :lol: :lol: I'm trying to get past them in range :P :P


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Sun Mar 19, 2017 2:32 am 
Offline
FlightAware Member
abcd567 - FlightAware user avatar

Joined: Sat Feb 15, 2014 3:08 am
Posts: 1980
Location: Toronto CYYZ
CoCo is a high impedance antenna, higher than 75 ohm input impedance of DVB-T, causing impedance mismatch.

Incidently, the impedance "seen" by the DVB-T dongle depends on length of coax between Antenna and DVB-T.
As the length of coax is increased/decreased, the impedance "seen" by DVB-T gradually varies from antenna's impedance to a lower value and then back to antenna's impedance in a cyclic manner (see second image below). This cycle repeats every 1/2 wavelength. There is one point in every 1/2 wavelength section of feed coax which gives lower value of impedance, and hence better performance. The last half wavelength section at DVB-T also has one such point, and if feed coax is chopped to that point, impedance matching improves.

Chop the end of feed coax at DVB-T end, in 10mm steps for say 5 to 6 steps. After each chop, run your system for a while and note what maximum range you get. It is very likely that you will re-gain your lost mileage.

Please note that success is not guaranteed, as it depends on exact impedances of antenna & coax. However since this is an easy method, there is no harm in trying.

At each step you will have to redo the end connector. If feed coax's end connector is twist-on F-male type it is very easy to remake with each trim, and you can use the same F connector again and again. If connector is crimp type, it is more effort and you will waste many connectors.

Image



Image


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Sun Mar 19, 2017 5:32 am 
Offline
FlightAware Staff
obj - FlightAware user avatar

Joined: Tue Sep 30, 2014 7:14 pm
Posts: 3459
joecalw wrote:
my stick is USB 2.0 Digital DVB-T DAB FM RTL2832U FC0013B SDR TV Radio Receiver Stick

Surprised you get anything at all, many FC0013s are deaf at 1090MHz


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Sun Mar 19, 2017 7:43 am 
Offline
NeoDuder - FlightAware user avatar

Joined: Sat Nov 26, 2016 11:17 am
Posts: 25
Location: EGPH
In addition to the above, if you're going to use an amp, you need a filter.


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Sun Mar 19, 2017 8:49 am 
Offline
joecalw - FlightAware user avatar

Joined: Sun Nov 06, 2016 5:03 pm
Posts: 9
I have come to the conclusion that my best bet is to buy a decent stick so I have ordered a Flightaware stick and filter from Amazon so I will wait for them to arrive and then take it from there.
In the meantime I will have a little play with what I have got at the moment.
Thanks everyone.

Ps a USA Globemaster passed over me while walking the dog this morning he was only about 3000 ft . Very Impressive.


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Sun Mar 19, 2017 9:32 am 
Offline
FlightAware Member
abcd567 - FlightAware user avatar

Joined: Sat Feb 15, 2014 3:08 am
Posts: 1980
Location: Toronto CYYZ
It is a good decision to replace generic DVB-T by Flightaware ProStick and Filter.

Last year I replaced my "DVB-T DAB FM RTL2832U R820T" USB stick by Flightaware ProStick+Filter, and my stats jumped up by about 30% using same antenna and coax as with generic DVB-T stick.

You have mentioned that your "DVB-T DAB FM RTL2832U FC0013B" stick used to give you 300mi in some directions. If it is deaf at 1090mhz (as pointed by obj), how come it is receiving any aircraft signals? Very strange!


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Sun Mar 19, 2017 12:49 pm 
Offline
FlightAware Member
abcd567 - FlightAware user avatar

Joined: Sat Feb 15, 2014 3:08 am
Posts: 1980
Location: Toronto CYYZ
What is the connector type at the end of antenna coax?

The Flightaware Filter has a SMA-female connector. If the connector at the end of your antenna coax is NOT SMA-male, you will need to order a pigtail: SMA-male to "female-of-whatever-connector-your-antenna-coax has".

Image


CAUTION: Be careful not order RP-SMA male by mistake. It looks very similar to SMA-male, but it's center pin is missing. It is mostly used in WiFi. Avoid purchasing one which says WiFi.
Image


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Sun Mar 19, 2017 1:23 pm 
Offline
joecalw - FlightAware user avatar

Joined: Sun Nov 06, 2016 5:03 pm
Posts: 9
abcd567 wrote:
It is a good decision to replace generic DVB-T by Flightaware ProStick and Filter.

Last year I replaced my "DVB-T DAB FM RTL2832U R820T" USB stick by Flightaware ProStick+Filter, and my stats jumped up by about 30% using same antenna and coax as with generic DVB-T stick.

You have mentioned that your "DVB-T DAB FM RTL2832U FC0013B" stick used to give you 300mi in some directions. If it is deaf at 1090mhz (as pointed by obj), how come it is receiving any aircraft signals? Very strange!



here are before and after shots

Image


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Sun Mar 19, 2017 1:53 pm 
Offline
FlightAware Member
abcd567 - FlightAware user avatar

Joined: Sat Feb 15, 2014 3:08 am
Posts: 1980
Location: Toronto CYYZ
joecalw wrote:
here are before and after shots

Image

Images did not show in my browser, incorrect URL.
The URL is not that of image, but of your "One Drive" page for sharing the images.
It may be showing in your browser from browser cache.

Below are images using "image URL" from your One Drive sharing page.
The drop is really dramatic for no apparent reason!
Did you try trimming end of coax in 10mm steps, as suggested in my earlier post?

ImageImage


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Sun Mar 19, 2017 9:39 pm 
Offline
FlightAware Member
joelwiley - FlightAware user avatar

Joined: Mon Mar 12, 2012 7:46 pm
Posts: 844
joecalw wrote:
Ps a USA Globemaster passed over me while walking the dog this morning he was only about 3000 ft . Very Impressive.
Who was walking the dog, you or the Globemaster? :)
If the latter, it must have been a looong leash :D


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Mon Mar 20, 2017 2:07 am 
Offline
joecalw - FlightAware user avatar

Joined: Sun Nov 06, 2016 5:03 pm
Posts: 9
abcd567 wrote:
joecalw wrote:
here are before and after shots

Image

Images did not show in my browser, incorrect URL.
The URL is not that of image, but of your "One Drive" page for sharing the images.
It may be showing in your browser from browser cache.

Below are images using "image URL" from your One Drive sharing page.
The drop is really dramatic for no apparent reason!
Did you try trimming end of coax in 10mm steps, as suggested in my earlier post?

ImageImage



Yes I have done that, it took eight trims to get me up to 120 miles


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Mon Mar 20, 2017 4:01 am 
Offline
FlightAware Member
abcd567 - FlightAware user avatar

Joined: Sat Feb 15, 2014 3:08 am
Posts: 1980
Location: Toronto CYYZ
joecalw wrote:
Yes I have done that, it took eight trims to get me up to 120 miles

Try one or two more trims. Chances are that you will improve further.


The 6-element CoCo is a high SWR antenna with both resistance and reactance components being high (see simulation results below). Trimming alone will improve somewhat, but full impedance matching requires other means of impedance matching. Using a LNA, such as integral pre-amplifier of ProStick, also helps in overcoming the deficiency introduced by high SWR/impedance mismatch.

SIMULATION RESULTS FOR 6-ELEMENT COCO MADE OF RG6 COAX (VF=0.83)
Image


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Mon Mar 20, 2017 12:07 pm 
Offline
joecalw - FlightAware user avatar

Joined: Sun Nov 06, 2016 5:03 pm
Posts: 9
Tried another couple of trims but no change, I have a feeling its my stick at fault here, I discovered how to alter the gain but adjusting it up or down makes no difference to the signal at all.


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Mon Mar 20, 2017 3:34 pm 
Offline
kraviec - FlightAware user avatar

Joined: Wed Sep 07, 2016 11:10 am
Posts: 8
Presence of water in antenna or connectors checked?


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Mon Mar 20, 2017 3:57 pm 
Offline
joecalw - FlightAware user avatar

Joined: Sun Nov 06, 2016 5:03 pm
Posts: 9
kraviec wrote:
Presence of water in antenna or connectors checked?

The antenna is in plastic tubing and coax is new


Top
 Profile  
 
 Post subject: Re: Dramatic drop in aircraft sightings
PostPosted: Fri Apr 14, 2017 11:44 am 
Offline
Anson3 - FlightAware user avatar

Joined: Fri Dec 30, 2005 9:00 pm
Posts: 4
Just checked my antenna connector. The tape had come off and there was water IN THE CONNECTOR. Removed, cleaned and re-sealed. Checking stats now.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 18 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: cancellier, claudep, Google [Bot], myalias and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: