Trial Run Results for Three Types of Whip Antennas

AnirbanSen

Member
If you have installed Planefinder, it also provides a map like dump1090 provides. Go to following address in your browser:

IP-of-Pi:30053

.
Been using that :)
The 3D Polar View is fascinating and makes the case why the camera should be on the rooftop.
Haven't been convinced of any one antenna yet, but may use a LMR 400 wire which may just eliminate the need for additional hardware, except the filter.
 
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AnirbanSen

Member
Also, I briefly received Mode AC packets which then stopped completely. I received about 10-12KBps in Received bandwidth when I set this up. But the last bit of wire squeezes into the room through an iron frame window and may be some signal is lost there. I have to keep it closed because of my cat who has been very curious with the spider antenna.
Set at RECEIVER_OPTIONS="--device-index 0 --gain 49 --ppm 0 --net-bo-port 30005" Reading set to past hour. From 13:35hrs onwards.

2844
 

wiedehopf

New Member
Might be one of those cases where the optimum would likely be between AGC an 49.6 (there are discrete values, the software chooses the closest value)

You'll have to find yourself which setting suites you best.

Mode AC packets are a feature that is normally disabled as most aircraft have Mode S transponders.
You can enable Mode AC:
--modeac Enable decoding of SSR Modes 3/A & 3/C
(from dump1090-fa --help)

You can just add this option to the RECEIVER_OPTIONS.
 

AnirbanSen

Member
Yes, with 30m cable definitely an LNA is required.

The requirement of filter depends on the strength of mobile/cell signal at your location.
There's a lot of GSM chatter at even 946 MHz. I'm having trouble selecting a good LNA. I came across this article: https://19max63.wordpress.com/2019/04/14/low-cost-lna-tested/ but that LNA required power to be fed at the antenna. I'm trying to see if that would work with a Bias T feeding 5V from the USB of the Pi into the coax.

I am wondering if the 950-2150Mhz tested by ab cd would work better. That needs a Bias T?

Also, point to note, the radial wires on the spider antenna is 64mm (my mistake) and not 69mm. The lead wire is 64mm. How much difference does this make in theory?
 
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wiedehopf

New Member
You could buy 2 bias-T and use one to put 5V into the coax and the other one to retrieve 5V from the coax.
But that drives up the price somewhat, especially when the bias-T has SMA connectors and you need adapters.

But if you can use coax to bridge distance, couldn't you bridge that distance with ethernet cable?
I'm not quite clear yet where you want to put the RPi and where the antenna.

To be honest if you don't need too long of a feed line you don't need an LNA.
(Most of the reason i suggest an LNA is the good filtering and system design of the rtl-sdr LNA, if you use a cheap LNA it might not be worth it but maybe that 2$ LNA can actually improve things, i don't know :) )
Without good filtering an LNA can introduce frequency separation problems, the receiver frontend gets overloaded with noise.
 

AnirbanSen

Member
I'll buy some cheap stuff for testing. Its quite a bother when you order in mid-May and don't get all the parts till end June (sometimes).

I'm using a Pi 0 Wireless. so the Pi needs to be within Wireless range. I'm assuming you mean the ethernet to network and power the Pi. Otherwise, I am generally averse to using both a coax and a CAT5.

The building consists of 7 floors. I am on the 4th floor. The 8th floor is the public terrace. On top of the public terrace are the elevator shafts and water tanks. On top of the elevator shaft, the view is 360 till almost 6-8Km with a few tall buildings here and there. I intend on placing the antenna here.
2848

See picture.
I took a picture of my building few months ago intending on setting up a weather station. It might give you a better idea of the set up.

For placing the Pi, my 1st choice is next to my window on the 4th floor. (Allows to easy removal and updates in case wlan0 goes down). From here, the roof of the elevator shaft where the antenna is to be placed is about 25m up (could be 30m). Quite possibly, a good cable will carry the signal down just fine. But a filter and/or LNA may be a good idea to increase the range. Right now, the antenna is on an external staircase half way up. I get some signal in the 100-150 range but not more.

2nd choice for placing the Pi is the outer wall of public terrace in a IP66 box. Still within wireless range of my 4th floor router. I can send up power in just a twin cable of 15m length with 12V DC. Step it down to 5V at the IP66 box before the Pi. From here another 10m up is the roof. In this arrangement, the signal loss is minimal, but I'd still want to ensure a further range than now.
 
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AnirbanSen

Member
The Satellite amplifier (950 ~2050 Mhz) does need a bias-t and a12v~15v dc power supply.


Setup of Satellite amplifier and bias-t

https://forum.planefinder.net/threads/ads-b-diy-antenna.23/post-210


DIY bias-t

https://forum.planefinder.net/threads/ads-b-diy-antenna.23/post-5093

Should be a fun make if I can get the parts.
Went to the local electronics market the order day and was informed by most shops that they only sell in bulk. I had to buy 10 SO-239s or none at all. Finally convinced a shop to sell me 2 pieces and 3x their unit price in bulk. 20 years ago, they would give all parts and tick off your list.
 

wiedehopf

New Member
Network cable is generally cheaper than coax and you can run power on it as well.

But having the pi accessible is nice so if you can get coax then by all means go for it.
Advantage of the satellite amplifiers is that they are waterproof and you only need to make sure water doesn't get into the cable at the connectors.
Without an LNA the coax quality is very important, with an LNA you can get away with 10 dB coax loss no problem :)

If you can get the filtered LNA it is going to improve the range but no doubt the satellite amplifier described should work as well.
 

AnirbanSen

Member
Some stuff has been ordered in Aliexpress. Have to be patient till it gets there. I think I'll wait and watch next couple of weeks and get a baseline of flight activity and timings in my area.

There might a supposedly good coax (LMR 400) coming up on sale on Amazon sometime next month. May check that out and see how it responds with a spectrum scan and 1090 SnR levels. Lots of trial and error ahead for sure.

Still undecided if the permanent antenna on the roof should be a coax spider. Whether it will last the weather and possible tampering.
 

wiedehopf

New Member
With an LNA well shielded RG6 satellite cable is just fine and should be cheaper.

In regards to the antenna i'm curious what tampering you mean? :) Birds?
Anyway if the location is easily accesible then fixing a coax spider is easy as well.

You should seal the cable entry with silicone or hot clue so not water gets into the coax.
 

AnirbanSen

Member
Birds, possibly. More like ill intentioned or callous humans.‍ Perhaps I'll put a small sticker with Danger 440V AC.. About 1 metre of coax has to be kept on reserve coiled up.

Have got the epoxy sealant. But would need a mounting L that raises the spider about a foot above the wall periphery. Let's see if some dish TV mount bracket can be salvaged.
 
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AnirbanSen

Member
I've already ordered this:

This can be sealed inside a PVC tube, with or without LNA and/or BPF filter and sealed off with a silicone self-fusing tape and PVC cap.

But I will have to also determine if the Spider is superior. Perhaps I can use both antennas, PCB and the Spider, with the demux ABCD had shown in Pic 2 at https://forum.planefinder.net/threads/ads-b-diy-antenna.23/#post-210
Not sure if I can make the home made coil forming an air inductor though. (Funnily, I've worked a lot earlier with resistors and capacitors, but never with inductors.)

Have to first measure the required wire length.
 

wiedehopf

New Member
I wouldn't try muxing two antennas for the same frequency. (In the setup mentioned two different freqencies are combined)

That would mean the signals need to be in phase. So you would effectively be building a colinear antenna.
For such things you need antenna test gear to measure phase.
 

AnirbanSen

Member
I wonder if I can borrow some equipment from friends. Where I live, it is difficult. In my hometown, should be easier. The Univ physics lab is sure to have a few.
 

wiedehopf

New Member
What i'm saying is: Don't bother muxing two antennas, what abcd did was aimed at coupling in VHF airband into the same coax so he can switch what to receive with the dongle.

If you want to build a colinear antenna from coax, you can try these instructions:
https://www.balarad.net

Having to guess the propagation velocity of the coax makes it complicated though.
You could still try two 4 element ones with 2mm different length for each element and check which works better.
 

AnirbanSen

Member
What i'm saying is: Don't bother muxing two antennas, what abcd did was aimed at coupling in VHF airband into the same coax so he can switch what to receive with the dongle.

If you want to build a colinear antenna from coax, you can try these instructions:
https://www.balarad.net

Having to guess the propagation velocity of the coax makes it complicated though.
You could still try two 4 element ones with 2mm different length for each element and check which works better.
I've heard the colinear antenna may not necessarily good results and depends a lot on the construction. Is that true? Or the difference between a spider and a colinear may not be that much. The construction is worth a try.
What do you mean 2mm different length for each element? Each element is 1/2 wave x VF, right?

First, I'm thinking of building a spider with the SO239 and then using it first where the existing spider is and test it efficiency, and then test it on the roof. At least I'll know whether the coax spider or so239 spider is better. Also, one advantage of using the SO239 would be - I can dismantle it from the connector and use different type of antennas, insert a filter and LNA.

Just measured using an old CAT5 lying around - about 25m of wire should be sufficient length of wire to the roof with about 1-2m spare.
Contacted a vendor online and attached are the details of a coax he is willing to provide. Approx. 16EUR equivalent. What do you think?
 

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wiedehopf

New Member
Also, one advantage of using the SO239 would be - I can dismantle it from the connector and use different type of antennas, insert a filter and LNA.
If you have push on connectors you can do that with the quick spider as well. Just cut the coax and place two connectors.

What do you mean 2mm different length for each element? Each element is 1/2 wave x VF, right?
I meant if you don't know the VF of your coax, you could make 2 antennas with slightly different measurements :)
 
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