Radarbox is "blind" for the planes above my head

[DaveReid]

SSR, Mode-S and TCAS use two antennas, top and bottom of fuselage.

And ADS-B position squitters are sent twice per second, alternately from the top and bottom antennae.

[vic_atc]

If you are not in Singapore from where the same behaivour was reported before:
Your box may not be able to detect 112 bit Mode-S signals when a certain reception power is exceeded. It seems that 56 bit signals still come through. There is a floating reference detector which may not work properly for 112 bit. I would think it is best to return the box.

Yes, that could be a good explanation. I'm from Romania and unfortunately there are only a few guys who own a RB. Personally, I know only one person. I asked him to make some tests together near the airport and to compare the devices.
Yesterday night I've made a trip right under a very busy route and I was able to see 2 planes flying over the radarbox (only 2 planes have flown on this 'busy' route while I was there :) ). The tests performed until yesterday always took place in a single location. Yesterday was the first time when I changed this position. Maybe there is an interference in the first location .. or I don't know.
But this doesn't explain why I can't see the app/dep planes when I'm located near the airport.

Regards

[puddy]

I have the same issue, I thought it was because the airspace around me is closed military airspace.

I can see the planes visually they dont show up within a 10 miles radius on my radar box.

I had thought it was my aerial apart from this issue I have no other problems

I wanted to track a plane to spain today but the network been down
I am based near Boston (UK)

Puddy

[MikeC]

I tried an experiment, swapping the external antenna for a magmount for the ANRB.

I used my SBS-1e magmount as I've misplaced the ANRB one.

As can be seen. the AirFrance showed up within the approx 10 nm radius on both Basetation and the RB.  But then the aircraft started to lag a bit on the RB screen, though it caught up again when it was well past my 10 nm radius.

The side-by-side screenshots were taken simultaneously.

Not conclusive, but I wish I had an ANRB magmount to try.

[Runway 31]

Plenty of aircraft fly over my house each day inbound Glasgow and outbound Edinburgh as well as high level fly overs and I see them all the way over the house with no gaps.

I am however using a different loft mounted antenna but never had any problems when using the Airnav supplied one.

[MikeC]

I had no problems when both boxes were sharing the external antenna.  I was just trying to test if the supplied one was an issue.

[t1mb0]

Hi

got bored reading the many fanciful explanations.
Vertically mounted antenna, ie pointing up/down produce greatest 'gain' in the horizontal plane, and practically nothing straight up/down, so maximising your range towards the horizon.
I reckon if you place the antenna on its side, you'll get uninterupted coverage over the top, but you won't get much range(well you might, but it will be perpendicular to the axis of the antenna)

[palmar]

The thread was originally talking about low flying airplanes (approaches, departures seen from the airport fence) within 10 miles or airplanes on the ground. While I agree that antennae may have a blind spot right above them this would not be an issue for this kind of traffic.

[tarbat]

Not conclusive, but I wish I had an ANRB magmount to try.

Didn't you get one supplied in the box?

[Hawkeye]

Ref Reply #21
A bit of a strange first line methinks.
The RB antenna supplied is quite capable of picking up aircraft overhead (see attach).
Unfortunately I am not knowledgeable enough to put forward a suggestion as to the cause of vic-atc's problem, but the explanation put forward as conclusive in this reply is clearly not the answer.
The always helpful members of this group have put forward various suggestions to try to solve the problem. That is how this forum works and generally someone will come up with a solution sooner or later, 'fanciful' or not.

Syd

[vic_atc]

Good evening,

Thanks a lot to all of you guys for all the investigations you did. Some of them are very useful.
Last week I ordered a MyDel BS1105 antenna and it arrived today, in the morning. I'll check to see if the problem disappears using this external antenna. I've contacted an other RB user from Romania (it is very difficult to find one here :) ) and we will do some 'parallel' tests on weekend. First test will be done near the airport, for the low flying airplanes. In the other test we will target the cruising airplanes.

Now please let me answer to some of you to amplify/eliminate some clues:

I reckon if you place the antenna on its side, you'll get uninterupted coverage over the top, but you won't get much range(well you might, but it will be perpendicular to the axis of the antenna)

As far as I recall I already tried that. While having a plane right over my head, I've placed the antenna parallel to the earth. Still no result :(

I can see the planes visually they dont show up within a 10 miles radius on my radar box.

What kind of antenna you've been using when you saw this behavior? Was the supplied antenna? Thanks.

I tried an experiment, swapping the external antenna for a magmount for the ANRB.

I used my SBS-1e magmount as I've misplaced the ANRB one.

Not conclusive, but I wish I had an ANRB magmount to try.

Thank you very much for this accurate test. That could be a clue. So I should conclude that maybe SBS1 has a better sensibility than RB?

While I agree that antennae may have a blind spot right above them this would not be an issue for this kind of traffic.

This is my opinion too. More than that: I still cannot see the airplane on the map even if it's located aside from my RB's antenna (talking about the low level flights). Probably there's something wrong with my device when it has to decode high power squiters containing 112 bits DF17 message.

Regards.

[Mike_Tassy]

I have the same problem.  I am elevated 180 mtrs asl and my null zone is 68 nm radius.  I have just received my box back from UK for repairs under warranty.  The invoice stated a new board was fitted and all was working A1.  But the problem is exactly the same. 
Mike

[Allocator]

I've never seen this problem and I'm at a loss to see how it can happen.  I can understand a loss of range, either due to an antenna problem or a RB hardware problem, but to loose contacts in the overhead out to 68nm - I have no idea.

Are you seeing aircraft disappear into this 'overhead' and if so, at what height?  Is there any pattern to what you are seeing in height/distance?

Why not set the aircraft trails to maximum in Preferences - Seconds to Remove Trails - and post a screen shot here to give us a better idea of the problem.

The maximum is 10000 seconds - I just enter 999999 and hit apply.

[Allocator]

Just did a quick test with my box - no problems with the overhead at all.  TOM38B about 2 miles east  of the overhead climbing through FL170 and RYR8274 about 10 miles west at FL300.

Are you sure that you haven't got any filters selected?

[Mike_Tassy]

No filters selected, it happens on 2 different computers with fresh installs.  I have a high gain home made antenna and supplied antenna is same. 
It works ok out to 260 nm, when the a/c reach 68 nm they dissapear from the map, but remain in the list as mode-s and continue to be updated. When going past and reaching 68 nm the opposite side they reappear on the map. 
I have my own theory about this.  I think the RB has a problem with multiple path signals (ADS-B only)  ie signals direct from the a/c and up reflected from the ground.  Once the a/c approaches a certain distance I receive these multi signals,  most of my signals are across water which is where it is worst
Mike