RTL-SDR Dongle and Antenna

[francoisvl]

I managed to pull my RTL-SDR Antenna apart when I was packing up. I can't see a replacement on the website, can anyone recommend one that is easily purchasable online to replace this? I did Google, but wasn't confident which ones would work with the PAW unit.
Many thanks in advance for your assistance - I'm not at all skilled with things electronic!

[Paul_Sengupta]

https://www.ebay.co.uk/itm/HQ-5dBi-DVB-T-HDTV-Digital-Booster-Magnetic-Based-Antenna-MCX-Male-Connector/162772143312

[francoisvl]

Many thanks Paul, appreciated.

[exfirepro]

I managed to pull my RTL-SDR Antenna apart when I was packing up.

Hi francois,

What did you do to it? If you just pulled the cable out of the antenna base you could fix it quite easily and that would give you a spare. Take a look at this thread which clearly shows what it should be like inside the base and also gives some tips about shortening the vertical wire part if you need / want to....

 http://forum.pilotaware.com/index.php/topic,438.msg5661.html#msg5661

It would also give you the opportunity to shorten the cable length at the same time if the existing one was too long. Just a thought.

Just a word of warning... if cutting the cable very short, be careful not to pull the inner wire out of the centre of the MCX plug when you are trying to cut back the plastic 'dielectric' tube, .....like I did with one of mine some time back. If it's the 'plug-end' that's damaged, it's probably not worth the bother to fix at the cost of the replacement Paul has suggested, but keep the 'whip' as these have a habit of dropping off if not properly tightened in place.

Cheers

Peter

[francoisvl]

Hi there - I did pull it out, and don't have the facility to solder it back in, which is what it looked like. I've not bought a new one, and a new ADSB dongle too, but I'm still not seeing any ADSB traffic. I've tried the new aerial with two dongles (which I've tested separately and they do work to pick up traffic with a Windows application on my laptop). Is it possible that I damaged the bridge running PA with the broken aerial? I've posted my log below with the Mac address obscured - is there something here that explains why my ADSB no longer works? How can I test the bridge to see if there's something wrong with that?

=======
Use of uninitialized value $eth0_ip in concatenation (.) or string at htdocs/index.cgi line 152.
Use of uninitialized value $eth0_ip in concatenation (.) or string at htdocs/index.cgi line 152.
Use of uninitialized value $eth0_ip in concatenation (.) or string at htdocs/index.cgi line 152.
Use of uninitialized value $eth0_ip in concatenation (.) or string at htdocs/index.cgi line 152.
(17:26:28) NAV-UDP   : LEASE: (Expire 2018-01-13 17:26:27) 1515864387 34:12:98:XX:XX:XX 192.168.1.20 XXXX 01:34:12:98:XX:XX:XX (note I’ve changed the MAC address)
(17:26:28) NAV-UDP   : /var/lib/misc/dnsmasq.leases Lease file updated
(17:24:51) NAV-UDP   : /var/lib/misc/dnsmasq.leases Lease file updated
'
(17:24:49) NAV-TCP   : NAV_LOGGING Message='
(17:24:49) NAV-TCP   : Device Table End
(17:24:49) NAV-TCP   :     Device 11 = NAV_LOGGING
(17:24:49) NAV-TCP   : Device Table Start
(17:24:49) NAV-TCP   : Device Add 11 NAV_LOGGING
(17:24:46) TFC-USB   : Startup
(17:24:46) MAIN      : Radio OK
(17:24:46) MAIN      : Await Radio Startup
(17:24:45) MAIN      : Await Radio Startup
(17:24:44) MAIN      : Await Radio Startup
(17:24:43) MAIN      : Await Radio Startup
(17:24:42) MAIN      : Await Radio Startup
(17:24:41) MAIN      : Await Radio Startup
(17:24:41) BMP-I2C   : HW_OK
(17:24:41) FILESYS   : Mount RO
(17:24:41) FILESYS   : Mount RW
=======

[exfirepro]

Hi Francois,

I don't see anything obvious in your log to explain the symptoms you are reporting.

The SDR Dongle and thinner 1090 antenna (which you say you 'broke' are designed to receive the normally very strong ADSB signals (+ Mode C and S if Mode C/S reception has been selected in the PilotAware Configure Screen - it is 'OFF' by default). The internally mounted PAW 'Bridge and its 'thicker / longer' antenna are used for transmit and receive of the PilotAware P3i side. These two functions are completely separate, so if as you say you only pulled the cable out of the thin antenna base, that will have had no effect whatsoever on the Bridge.

The easy way to check if the Bridge is transmitting is to log into the PAW WiFi with your phone or tablet then bring up the PAW Home Screen via the URL 192.168.1.1. It should be showing 5 green 'lights' down the left hand side of the table, (or 4 if the SDR Dongle has been disconnected). You can see the Bridge performance from the TRX (RX/TX) line, as the 'TX' figure will be increasing each time the Bridge transmits - NOTE: the Bridge will ONLY Transmit if the unit has a solid GPS fix and the GPS 'light' is green as it can't transmit its position unless it knows where it is.

Ideally take a screen grab of the Home Screen and post it here so we can see what is going on. A screengrab of the 'Configure' Screen would also be useful so I can check your settings.

Regards

Peter

[Admin]

Hi francois
Can you post a screenshot of the following pages
- Home
- Traffic

Thx
Lee

[francoisvl]

So I went to park today to try out the two dongles I have. The original still gives me a red to show not working, and the new one gives me a green, but very little traffic (park in central London, usually tens of aircraft). Also, no aircraft showing in traffic when the ADSB is showing red on home (obviously). I've attached the images to the post. 

[exfirepro]

Hi again Francois,

The screen images above certainly bear out what you are reporting,  - i.e. the first two certainly show no ADSB traffic, but confirm that the SDR Dongle IS connected, with a good GPS fix and all other functions showing green 'lights', but the PilotAware unit had only been running for 8 minutes when you took the screengrabs, [UPTIME: 0 days  00:08 (minutes)], - OK you were in the centre of London - so there may well have been aircraft about, but your receiver was on the ground, so the aircraft could fairly easily be screened out by tall buildings. You would need to leave the unit running far longer for the test to be conclusive.

The second set of images clearly show 5 green 'lights', so in this case SDR Dongle is connected and working, with the Traffic screen showing a single ADSB equipped aircraft, but in this case the unit had only been running for 2 minutes, so again inconclusive.

The Bridge is definitely transmitting (as shown by the increasing TX figure on the TRX (RXTX) line)

Both sets of images show that the unit is clearly 'working', but that there is either just not a lot of aircraft 'in range', or that your antenna is still faulty (which would seem very unlikely). From the results shown, I also suspect that 'Mode C/S Select' is still on the default ' OFF' setting.

We really need to see a shot of the 'Configure' screen to see what settings you have selected and you need to run the test for much longer out in a clear area.

Regards

Peter

[francoisvl]

Hi Peter - thanks for that. I can confirm my Mode C/S select is on, as it has always been. The unit is not behaving as it has all along before the aerial issue - I've had it for over a year. The screen captures were in an open park where I do go to test it as it's clear of any obstructions. Usually in the garden I can see planes lining up on final at Heathrow - now I get one or two aircraft or best. The helicopters going over just now did not even register. Something is definitely not working.
How can I order another dongle and aerial identical to the ones that came with my original kit? If the bridge was not damaged, then there is definitely still something wrong with the reception I'm getting with the new aerial.
Cheers for taking the time to look at this.
Kind regards
Francois

Ps I've attached a copy of the settings tab

[exfirepro]

Hi Francois,

OK on the Mode C/S settings, etc. and the proximity to Heathrow. Everything looks fine in your ‘Configure’ settings. That being the case you should certainly be seeing a lot more commercial ADSB traffic and I would also expect you to be seeing some CAT Mode S (which shows as CS in the Traffic Table) as well as entries for Mode C analysis. So it does look like there is an issue with the 1090MHz receive side of your PAW.

Looking again at your earlier screenshots, the ‘Home Screen’ shots both show a connected ADSB dongle, and even if there is a problem with the 1090MHz antenna, you should be able to receive 1090MHz signals on the metaphorical piece of wet string - as ADSB signals especially are VERY strong at close range. To eliminate the antenna/cable, you could try making up a temporary antenna from a straightened paper clip - seriously! Bend it into an L shape and carefully push the short leg of the L into the centre of the MCX connector on the 1090MHz dongle making sure it’s only touching the centre connection. Alternatively a length of thin wire will do the same job (no need to remove any insulation except to make the connection). Either option should work well enough to test for local ADSB traffic at close range.

Whilst looking back over the screenshots I did notice one thing I hadn’t expected. The SDR dongle in the first Home Screen image is reporting its ‘chip’ as ‘Realtek RTL2838UH1DIR’ (near the bottom of the table), while in the other Home Screen image (the one with the 5 ‘greens’), the dongle is reporting as a ‘Stratux LowPowerV2’, which is not a standard dongle for PilotAware, though provided it is the standard 1090MHz version it should still work. Stratux, however, also sell dongles pre-configured to operate on 978MHz, so this could be an issue, depending on where you got it from. Can you advise please - in particular did it come as a ‘single’ dongle or as one of a pre-tuned ‘pair’?

Regards

Peter

[francoisvl]

Thanks Peter - I did buy the new dongle online based on a blog indicating that someone in the UK had got one and it worked.. It came only as one unit, with no indication of what it is tuned to so I've sent an email to ask, but it may well be the wrong frequency.
I did some more testing this morning and I think it may be the new aerial that is the problem as I can pick up one or two aircraft with the original dongle that came with my unit, and did pick up an aircraft flying overhead (see attached) even when the home page was showing red for ADSB - still no traffic showing on SkyDemon though. Also I could pick up one or two aircraft, but they would come and go - ie they would not show for very long. I couldn't get a paperclip into the dongle - it looks too fat. I'll hunt for a thinner paperclip and try that too.
Cheers for the detailed responses you are making.
Kind regards
Francois

[exfirepro]

Hi again Francois,

That's a Mode S aircraft in your Traffic Table, so a good spot and proves the 'system' IS actually working, even if extremely 'deaf'. Let's get this problem sorted first and then we can look at what's going on with SkyDemon.

You may be correct about your new antenna being defective, though that would be very unusual. If a paperclip won't fit as a temporary antenna you could use pretty much any length of thin wire or cable that you can find which will fit in. The length isn't in any way critical for what we are trying to do here. All we are trying to do is determine whether the problem is with the antenna or the dongle.

The Stratux dongles 'should' work - my concern was that Stratux was designed primarily for the American market where they use 1090MHz for ADSB and 978MHz for an additional UAT weather/Flight Information rebroadcast system, so they sell matched 'pairs' of dongles pre-programmed for the two specific frequencies. If you bought yours as a single dongle, however, I would expect it to be either pre-tuned for 1090MHz or with the tuning left up to the software (though I could be wrong).

Regards

Peter

[Paul_Sengupta]

Do you have a link to the SDR dongle which you have?

I've got one such dongle which looks exactly like the dongles which comes with the PilotAware units, but it actually has an E4000 tuner in it rather than a R820T. It's very deaf when it comes to 1090MHz. The E4000 is much sought after and the tuning range goes higher than the R820T, but at 1090MHz it is quite deaf, only bringing in a short range here in Guildford.

[francoisvl]

Hi there - this is the dongle - https://www.rtl-sdr.com/tag/low-power/ the description looks like it says the signal is decoded on the Pi so probably a software thing?

I cut off the old aerial and created one from the remaining cable. I then used the dongle that came with the unit originally. When I do this, within a minute I see a couple of aircraft as per the attached. Looks like the dongle and unit are okay, and it's the aerial that I bought that seems faulty. If I can find a soldering iron, I will fix the one I broke properly but I'm away for a couple of weeks so I'll need to see about it when I get back.

When I plug the new aerial in, the number of planes drops and they 'come and go', switching back to my bodged aerial leads to an increase back to what you see attached.

Does this look right to you? Thanks very much for all the help!
Cheers
Francois