Correct way to run lead from Antenna.


#1

Hi Guys, I am a newbie here so please be gentle :slight_smile:

My setup is currently a borrowed Rasberry Pi with PiAware and a DVB-T dongle and wireless connection to the router. I started using the little aerial that came with the dongle and mounted it in a window facing NW. I am in Auckland, New Zealand and traffic is not high by comparison to many other cities around the world but with the stock aerial I was getting around 5000-6000 reports each day. Not surprisingly the traffic was mostly gathered from a NW direction.

With respect to Auckland, air traffic to and from international airports and domestically within New Zealand is mainly in the S-W, W-N and N-E quadrants with very little in the way of ADS-B equipped aircraft travelling in the E-S quadrant except the occasional LAN Chile flights going to South America. So, my coverage was a little underwhelming especially since I am at 600 feet elevation but was to be expected with an indoor aerial. Nevertheless, while the azimuth coverage was limited to the NW, the little stock aerial was happy detecting flights out to 200nm. After reading somewhere that a coffee tin placed under the aerial can help, I found I was getting 210-220nm ranges with a 235nm being the record for that arrangement. I calculated that was pretty close to the radio horizon. However, daily report stats were still low and coverage in other areas was either poor or non-existant so I decided to experiment with a homemade collinear aerial.

I used one of the many good tutorials on the net and made an eight element colliner with RG6 and a velocity factor of .83 which calculated out at 11.5 cm segments. This was taped to the NW facing window and connected to a BNC to MCX pigtail to access the Dongle receiver. Improvement was immediate. Coverage was now from North through West to South, reports are up to 25,000 per day and my record range is now 242nm.

Of course this is still not helping coverage of the N-E sector which is most likely due to the number of walls and bricks the signals have to pass through to get to the aerial. So my next step is to get the aerial outside and above the roofline.

To do this I have decided to place the 8 segment collinear and a bit of lead in a PVC pipe attached to a 2 metre aluminium mast stood off from and placed behind the existing satellite dish and mast. The lead will run down the aluminium tube before exiting at the sat dish mast, following it down under the eaves and then entering the roof. The COAX lead will be no longer than 5 metres and in the ceiling space it will be attached to the Pi as before with the BNC to MCX pigtail lead and a wireless connection to the router.

Hopefully the description above gives all the background. Now to my question. Is it acceptable to run the lead from the aerial down inside two metres of aluminium pipe (ie the mast)? Will this create interference, noise, extraneous RF, dB loss, shielding or other unwanted outcomes? If so, how else would you get the lead down? Would you take it on the outside of the metal tube and cable tie it to the tube? In which case would a wooden mast be a better option? I thought about a PVC mast but the lack of rigidity poses an issue. I am 600 feet up on a ridge line in a very high wind zone and PVC mast would whip and bend like crazy. In fact, it quite likely that no matter what the mast is made of it will not last the winter since at some point wind gusts exceeding 80-90 kph are most likely. Repairing damage after storms is just part of the norm where we live. But a PVC mast is just too flimsy, that’s why I went for metal.

I will try to keep the Satellite antenna and the ADS-B aerial leads away from each other since I understand they can interfere with each other if run or conduited together. But what about the 2 metre metal mast placed behind the satellite dish? The closest point the mast will come to the dish is about 400mm as the top of the dish inclines into the intended path of the new mast. Is this going to cause reflections or other interference to either satellite or ADS-B reception? The placement of the ADS-B mast and aerial is driven by the need to keep things on the N-W-S side of the house where the main air traffic flows are, to keep the leads short and still have everything in good wireless reach of the router, to leverage off the existing satellite dish mast which is tri-braced and to keep all aerials out of site of our entrance gate to avoid the place looking like a government spy headquarters LOL.

If you read this far then thanks in advance for any assistance/advise you can provide.

Cheers

Terry

PS. Couldn’t work out how to post pics. Used the IMG brackets but not sure what had to happen after that.


#2

If the bottom halfwave segment of the collinear is well (say at least 10cm or so) above the top of the metal mast you should be fine. There is no problem running the coax through the metal mast, in fact it will help protecting it. Just be aware that your antenna now might be exposed to other strong signals around and your RTL could become saturated.
Many of us around here have experienced a well working indoor setup with disappointing results after getting it up on the roof. Search for “filter” to read the many posts on how to cure this.
Your location is great! 210-220 nm range is really impressive for an indoor antenna!
Enjoy!
/paul


#3

Thanks Paul.

  • " Many of us around here have experienced a well working indoor setup with disappointing results after getting it up on the roof. "*

Never a truer word said. Finished manufacturing, mounting and connecting my antenna on the roof today and eagerly looked at my stats. They are worse than ever. :frowning:

I am in a pretty isolated spot with no nearby cell towers so before I worry about filters, I’ll take the aerial down, open it up and make sure I haven’t botched something. I also noted when I was cutting the ‘PVC’ pipe that there there was a black layer in cross section. I have never seen that in PVC pipe before. Did I get the wrong stuff maybe? Perhaps it is attenuating the signal somehow? Anyway, I’ll open it up and tape the aerial to a fiberglass stick and see if that makes a difference. Otherwise the whole thing went together well and there has been no noticeable problem with the satellite dish reception.

Thanks for your quick response Paul and I’ll let you know how I get on.

Cheers

Terry