Author Topic: Tuning the DVB Antenna for 1090MHz Specific reception  (Read 31036 times)

GarethHorne

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #15 on: June 10, 2016, 05:42:54 pm »
Thanks Peter, yes, it was cut to the 69mm total length (19mm base + 50mm top) as Vic suggested so should be ok. I'm just waiting for my tuned dipole antenna for the bridge to try and work out an acceptable method of mounting them both with a clear view forward in a metal aeroplane without a permanent external aerial.

Vic

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #16 on: June 12, 2016, 05:43:26 pm »
Interestingly (and very timely) these two videos have appeared on Youtube looking at the supplied DVB-T antennas..

https://www.youtube.com/watch?v=Rb_GzhvVTQ4  ..for the techies amongst us. Good though there is resonance at around 540MHz so also at 1090! the cable probably is quite lossy then though.

https://www.youtube.com/watch?v=3RsazRx4cxE  ..shows a teardown of the antennas much as I did earlier in the thread.

Richard

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #17 on: June 12, 2016, 06:32:23 pm »
He doesn't rate them much!!!!
Richard.
Europa XS

AllanBirt

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #18 on: December 04, 2016, 10:00:33 am »

So, my tip is to unscrew the top whip of the DVB antenna and cut it to a total of 50mm in length. Hope someone finds this useful!



Morning Vic, just to make sure I have understood the total length of the top whip antenna, when cutting this down to 50mm, is this including the thread section that screws into the base, or is it just the pole section only. I hope I have made myself clear  ;D ;D ;D

exfirepro

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #19 on: December 04, 2016, 10:13:57 am »
Hi Alan,

We met yesterday on the stand at the show. Not sure if Vic is about at the moment. The 'optimum' length overall IIRC is 69mm from point where the inner coax connects to the radiating element inside the bottom of the antenna. As this is a receive only antenna, however, and we are working with fairly strong transmitters at this 'end' of the unit, the exact length is not critical. If anything though, beware of cutting it too short as this might reduce the strength of received signals, which has a direct knock-on effect on triggering of the alert systems.

Regards

Peter
« Last Edit: December 04, 2016, 10:16:18 am by exfirepro »

AllanBirt

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #20 on: December 05, 2016, 09:06:00 am »


This is what I have done, but I'm not sure if this is correct  8) 8)

Any assistance on this would be much appreciated, I've also shortened the length of the cable and re-soldered, even the  earth plate, as recommended by Peter after seeing him at the show  ;) ;)

Regards

Allan
« Last Edit: December 05, 2016, 09:48:50 am by AllanBirt »

exfirepro

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #21 on: December 05, 2016, 10:35:26 am »
Good Morning Alan,

I have just re-read the whole of this thread and now see where the confusion arises. In his original post, Vic mentioned that the short section of exposed coax inner inside the base ..'is itself an antenna of about 19mm', but it's not clear whether he then included this as part of his 69mm total antenna length. If so, the '50mm' vertical part would need to include the vertical section inside the base cone from the point where the coax is soldered on, though that would make the antenna much shorter overall than it looks in Vic's pictures. I suspect therefore that when he says 'cut the top whip to a total of 50mm', he means from the bottom of the screw connector on the left in your photo. This would make the overall length of the vertical part (excluding the horizontal coax, but including the vertical part inside the base) about right. I may however be wrong, so have dropped Vic a PM to ask him to clarify.

As I have said before, this antenna is 'receive only' so its length is far from critical - as long as you don't make it so short that you start to attenuate the received signals as this will have a directly negative effect on the triggering of warnings for 'bearingless' Mode C/S targets.

Watch this space

Regards

Peter
« Last Edit: December 05, 2016, 10:45:45 am by exfirepro »

AllanBirt

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #22 on: December 05, 2016, 11:28:41 am »
Thanks Peter,

The overall length of this antenna including the thread section is about 65mm and this is picking up aircraft almost 300km away when in flight, so I'll probably leave as is  :) :), note this does not include the base section in this measurement  :) ;)

Like you said best to leave as is rather than making it to short  ;D ;D

Regards

Allan

Vic

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #23 on: December 05, 2016, 01:00:57 pm »
Hi Allan, sorry for the delay in getting back.

Yes, the whole antenna starts from where the braiding of the Coaxial cable stops covering the inner conductor. Everything from there onwards forms part of the resonant length of the antenna. Think of it as blowing across the top of a bottle and adding water to get a note you want only we are doing it with radio waves.

However, the perfect antenna relies on a clear area of space around it in all directions and we'll never get that anyway inside a light aircraft. You will  perfectly fine with what you have there and may, from experience, even have to adjust the sensitivity down in the PAW settings.

Probably more important than all this is to solder the braiding down to the base disc of the antenna. ;)

exfirepro

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #24 on: December 05, 2016, 01:40:22 pm »
Thanks Vic,

Hopefully we have now cleared that point up and Alan now has a more effective antenna installation (with the braid now soldered to the base disc as well).

Regards to all

Peter

AllanBirt

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #25 on: December 06, 2016, 11:55:33 am »
Thanks Vic & Peter for your assistance on this.

This is what mine looks like  ;D  ;D  ;D



All wires soldered, even the earth plate  8)  8)  8)

Regards

Allan

exfirepro

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #26 on: December 06, 2016, 12:39:27 pm »
Well done Allan,

Have fun and fly safe.

Regards

Peter

mmcp42

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #27 on: June 26, 2017, 11:31:41 am »
made the same mod to a pigtail, added a couple of layers of heat shrink - works a treat!

exfirepro

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #28 on: June 26, 2017, 02:58:32 pm »
Nice Mod,

Should work well, though you might find it starts to slip round on the MRX plug eventually away from the vertical if the plug ever starts to work loose on the dongle. A tiny dab of silicone or hot glue (carefully applied) will prevent this.

Regards

Peter

mmcp42

Re: Tuning the DVB Antenna for 1090MHz Specific reception
« Reply #29 on: June 27, 2017, 10:16:25 am »
Nice Mod,

Should work well, though you might find it starts to slip round on the MRX plug eventually away from the vertical if the plug ever starts to work loose on the dongle. A tiny dab of silicone or hot glue (carefully applied) will prevent this.

Regards

Peter
aha good thought :)