ADS-B and VHF Air on Same Mast


#1

Hi all,

I recently upgraded my setup to an outdoor antenna (A3 made by jetvision), and so far am very impressed by the performance. I have however mounted it, very close to a VHF antenna (Diamond D-777) at the top of a telescopic mast. Whilst the ADS-B performance (constantly over 1000 messages/sec at daytime) is very promising, I’m noticing a lot of interference on VHF: it seems the two antenna’s are disrupting each other.

Here is a picture of my setup:

https://dl.dropboxusercontent.com/u/44440768/mast.jpg

Does anyone have any ideas how I could mount the antennas to stop them interfering with each other? So far I have considered two options:

a) Raise the telescopic mast another 50 cm and mount the ADS-B antenna directly below the VHF one. In this scenario however, the ADS-B antenna is no longer at the top of the mast, but its top would coincide with the top of the mast (possible 180 degree blockage?).

b) try and implement some sort of mast side-arm to horizontally separate the antennas by 30-40 cm. This however could cause stability issues due to the changed Centre of Gravity given the weight of the antennas at the top of a 5 meter pole.

The above picture is taken from the ground, the telescopic mast is already extended approx 5 meters, this is necessary to clear the UHF TV antenna. This is about as high as I felt would be safe in windy conditions.

If anyone has any ideas, I’d much appreciate it! :smiley:

Many thanks

olivermbs


#2

If you do A) consider making the top part of the mast out of PVC or something else nonconductive. C) add another mast some distance away from the current one.


#3

The photo below is an example of a 2-meter band (144-148 MHz) J-Pole and 1090 Mhz Franklin on same mast.

This was built by Flightradar24 forum member “lutorm” (FR24 forum “best antenna”, post # 993).

The big one is a 2 meter band J-Pole made of Copper pipe,
The small one (on horizontal arm right of J-Pole) is a 1090 MHz Franklin Collinear made of thick wire. The Line amplifier is near the start of the horizontal arm:


#4

Hi gents,

many thanks for your replies. The solution of putting the ADSB antenna on an “arm” seems to be the best way forward as I am unfortunately unable to put up another mast. Does anyone know what the minimum distance offset (arm length) requirement for such an arm would be? I have read in various sites that it should be a minimum of 1/4 wave length from the lowest frequency antenna, so at 108 Mhz that would be 70 centimeters (~ 27 inches) if I’m not mistaken?

Many thanks!

olivermbs


#5

In fact they do not interact really.


#6

You say that, but your image shows a different scenario. Specifically, the distance between antennas compared to the wavelength of the signal being picked up. It seems there will be a stronger interaction the closer the distance is to the wavelength of the signal (or 1/2, etc.).


#7

I’m now looking at spacing them horizontally by 80cm, but having them vertically at the same height using this: http://wimo.de/bilder/23071a.gif. As 80cm is more than a 1/4 wavelength of 118 Mhz (=63 cm), would this provide adequate spacing to avoid interference?

Thanks,

olivermbs


#8

Does anyone know a source for a ROHN TB5125BA Double Bend U-Bolt Assembly or something equivalent?

http://ecx.images-amazon.com/images/I/41wDbnze0TL.SX355.jpg

I’m trying to attach a side-arm to my current mast.

TIA!


#9

Try Google?
I got:
amazon.com/ROHN-TB5125BA-Dou … B013IRMZI6
but it’s out of stock without an eta.


#10

randl.com/shop/catalog/produ … s_id=31040


#11

Thanks!

I’ll give them a try.


#12

… they have lots of antenna mounting stuff: http://www.theantennafarm.com/catalog/diamond-s1-7293.html


#13

This looks like it would secure the cross arm a lot better than the double bend U-bolt.

Thanks!


#14

… perfect :slight_smile:


#15

Worked like a champ!

Thanks again for the referral!!

theantennafarm.com/catalog/d … -7293.html


#16

no big deal … have a good one :slight_smile:

tom