Height of antenna or short cable best?

[sas945]

Hi all

I have been using a homemade antenna for about a year but this week I bought my first real radar antenna. It is a big difference in amount of planes tracked at the same time and range is also better.

Since I got it I have only been trying it indoors. Today I connected 25 meter RG6T low loss cable (still indoors) to see how it would perform outdoors with a long cable. I get a little less range with the longer cable run but I have to turn DOWN the gain with the longer cable and not up as I thought I would have to...

It looks like the longer cable hear more noise as I have to turn the gain down but I am sure the signals from the aircrafts get stronger if I get the antenna outside.

So my question to the experts is, should I keep it indoors with a very short (5 meter) cable run or should I use the 25 meter cable run and put it up as high as possible?

Best regards!

[Oblivian]

Depends on the cable loss.

AS you point out, longer cable to a higher antenna may yield the same results if the signal is lost through the cable. RG6 is not designed for the band range ADSB is using, so the loss is greater than something more chunky.

And yes, if using an amp. If noise is present the amp will also boost that.

[peterhr]

You will receive stronger signals if you place your antenna high enough to be clear of all obstructions. Obstructions include the material your house is made of as well as what ever surrounds it (trees, neighbours houses and so on). so:
* You need to put it as high as is practically possible - higher than the top of the roof and if it's attached to a chimney - higher than the chimney, so you collect as much signal as possible.
* you want to get as much of that signal as possible into the receiver - don't use just any old cheap coax, read about what you're buying to get a reasonable quality ... That doesn't mean it's got to be expensive it just means you carefully select what you use and there is a balance.
* don't put any sharp bends in the coax.

By the way, you don't say (roughly) where yo are or what the antenna is. On mine I use a low cost satellite LNB amplifier (wrapped in self amalgamating tape) fixed between the antenna and the down lead - this runs on 15v DC that is inserted onto the coax by an voltage injector at the receiver end of the cable. This is all low cost stuff and added 10-15% to the range (to 400km + in un-obstructed directions) and increased reliability of reception of distant planes (check te links in my sig)

[sas945]

Thank you very much Oblivian and Peter!

I live in the middle of Sweden.

Right now I get 220nm with my antenna indoors so I am mixed if to put it outside or not. I asked at my local TV-store what cable is best for 1000 mHz and they said RG6T so I bought it.

If I put it outside I will gain 5 meters in height but 25 meter of cable to get there.

The amplifier I use is a normal TV-amplifier. When I tried with long cable I had 25 meter from the antenna to the amplifier and then 5 meter from the amplifier to the dongle, and thats when I got higher noise. Probably because the amp make noise stronger too.

[Mike]

You should use as short cable to get as good view as possible. Once you have a good view adding one extra meter altitude/cable does not make any change in coverage but you can loose signal in the cable.

[sas945]

Thank you very much Mike!

Then I will leave it indoors, I doubt 5 meters in height will do a big difference in coverage after reading your answer, especially with the extra 25 meter cable I need.

[peterhr]

How portable is your setup.
Could you temporarily try the antenna in a high position = a good view, - the signals are easily blocked by water (trees with leaves) and minerals (walls of brick built houses)

see what difference it makes - then decide what to do.

[Mike]

Leaving it indoors is for sure not a good solution as you have no view from inside. The coverage is basically what you can see from the point where the antenna is located. I'm sure you will get 5-10 times more coverage if you put the antenna on the roof instead of inside. But you will probably not get any extra coverage if you put it 1 or 2 meters above the roof, unless you will get above some objects nearby.

[sas945]

Thank you very much for all replies!

Now I have the answer to my question. I got the antenna over the roof two hours ago and it is difference like night and day. I have +180nm in each direction after the first two hours and the message rate is just unbelievable for a friday evening.

So all I can do is agree with what I have read here earlier, height is king for ADS-B.

[expertdecisions]

Thank you very much Oblivian and Peter!

I live in the middle of Sweden.

Right now I get 220nm with my antenna indoors so I am mixed if to put it outside or not. I asked at my local TV-store what cable is best for 1000 mHz and they said RG6T so I bought it.
...

If you want good cable do not ask in a TV shop. Instead go to a radio amateur store.
BTW if you don't care about cable thickness you should use RH200INT

At 1000 MHz:
Your cable RG6t has a loss of signal of about 24 dB every 100 m.
RH200INT has a loss of 13,2 dB every 100 m.

Also care about matching impedances. Most ADSB antennas have 50 Ohm and TV/Satellite cables, like your RG6T, are 75 Ohms... And impedance mismatches equals signal loss.

Personally I use a USB RTL2832U/R820T stick connected to the antenna via a very short cable (10 cm) then the stick is connected to my computer via an USB/Ethernet cable extender so there is no transmission loss.
Initially I placed the complete set (Raspberry Pi + RTL2832U/R820T + D-Link PoE splitter) in the base of the antenna, powered with a D-Link PoE injector, but as I had to go to my roof several times to replace the SD card due to data corruption, my choice was finally to leave only the stick in the base of the antenna.

[SamInTexas]

Feedline and amplifiers

For optimum results, you should consider installing a preamplifier that is designed for the ADS-B frequency of 1090 MHz. A standard TV pre-amplifier will not be adequate and will add noise to the system. For best results, the pre-amplifier will need to be located as close to the antenna as possible. The preamplifier will require power.

I don't have a recommendation for a preamplifier however. Maybe someone else can provide advice.

Here is a link to another forum that provides some good advice.

http://www.airnavsystems.com/forum/i...p?topic=6844.0

Regards,
Sam

Thank you very much Oblivian and Peter!

I live in the middle of Sweden.

Right now I get 220nm with my antenna indoors so I am mixed if to put it outside or not. I asked at my local TV-store what cable is best for 1000 mHz and they said RG6T so I bought it.

If I put it outside I will gain 5 meters in height but 25 meter of cable to get there.

The amplifier I use is a normal TV-amplifier. When I tried with long cable I had 25 meter from the antenna to the amplifier and then 5 meter from the amplifier to the dongle, and thats when I got higher noise. Probably because the amp make noise stronger too.

[peterhr]

In your first post you said range 220nm - was that the diameter of the circle?

I'm getting 240nm in the best direction with my antenna + satellite amp + dongle. The other directions are not as good because of rising ground, hills, trees and so on.

[sas945]

Hi

Thanks for all the replies again, interesting to read all advice!

220nm is to the east which is my best direction. West give only about 100nm at its best.

[expertdecisions]

For optimum results, you should consider installing a preamplifier that is designed for the ADS-B frequency of 1090 MHz. A standard TV pre-amplifier will not be adequate and will add noise to the system. For best results, the pre-amplifier will need to be located as close to the antenna as possible. The preamplifier will require power.

I don't have a recommendation for a preamplifier however. Maybe someone else can provide advice.

Sam

If you have a reasonable cable length, low loss type, and a good antenna, the amplifier could be unnecessary.
In order to achieve the best signal noise ratio when using a sideband amplifier (like those used in satellite TV) a good idea is to place a 1090 MHz filter between the antena and the amp.
The filter can be home made but its adjustment to optimum is a ninja task...
In this link you can see how to made a coaxial cavity filter.