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Help with splitting antenna for a noob

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Help with splitting antenna for a noob

Postby thommo17 » Thu Sep 28, 2017 2:58 pm

G'day fellas,

Someone mentioned you guys in a Reddit thread and I thought you might be able to help me planning a little project to upload a good Melbourne traffic feed to liveatc.net.

I already have an antenna set up which can't be changed which comes down to an F type connector which is currently plugged into an ancient base station which we use for our company frequency.

What I want to do is take that F type out and plug it into a 3 way splitter so I can run 2 RTL dongles on a Raspberry Pi to get 135.7 and maybe 132.0 or 129.4 for arr/dep.

Now, I don't want to affect the current setup too much as the boss might get pissy so should I get an amp before the splitter so I don't have too much loss? Also will a splitter affect the transmitting?

I am very new to this so any advice will be helpful and any improvements to my plan are welcome

Also if you need more info just ask and I will try to answer as much as possible

Thanks!
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Re: Help with splitting antenna for a noob

Postby Phantom » Fri Sep 29, 2017 6:56 am

You are wanting to use the same line (antenna and coax) that you TX on now and wish to RX on for this project? I assume you are transmitting on your company frequency?
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Re: Help with splitting antenna for a noob

Postby alinco21 » Fri Sep 29, 2017 7:28 am

A little confused - but I would assume the company freq would be pushing 10, 25 or 50 watts out of the radio up the coax.
you want to split the line and Rx the said freq. Not sure on what the company freq would be but if they would Tx that would come across and back down all 3 split lines. Small filters would possibly not take out the band splatter not to mention the possible loss of Tx power from the radio.

Advise leave the company radio alone, if you cause interference or loss of reception when it is needed most you might be liable for any thing that would happen.

Do your own setup in the end and ask the Boss for permission. it will come down to Yes or No in the end.
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Re: Help with splitting antenna for a noob

Postby Vkfour » Fri Sep 29, 2017 8:06 am

I agree with Alinco21. Using one antenna as both transmit and receive is not an easy job. Even repeaters using the one antenna but with the TX and RX frequencies separated by up to 10 MHz need quality filters.
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Re: Help with splitting antenna for a noob

Postby Blake » Fri Sep 29, 2017 9:55 am

G'Day Thommo,
Yeah, that was me mate, welcome aboard.
While I can't help directly with you question, I can recommend listening to these blokes, they're extremely knowledgeable.
Have fun, and I'll see you around.
VESARS


"cognitio vincit tenebras"
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Re: Help with splitting antenna for a noob

Postby thommo17 » Fri Sep 29, 2017 11:00 am

Phantom wrote:You are wanting to use the same line (antenna and coax) that you TX on now and wish to RX on for this project? I assume you are transmitting on your company frequency?


Yeah, we TX and RX at the moment with an old base station on the company freq. I was hoping I could just split it and listen on another frequency with the same antenna.

alinco21 wrote:A little confused - but I would assume the company freq would be pushing 10, 25 or 50 watts out of the radio up the coax.
you want to split the line and Rx the said freq. Not sure on what the company freq would be but if they would Tx that would come across and back down all 3 split lines. Small filters would possibly not take out the band splatter not to mention the possible loss of Tx power from the radio.

Advise leave the company radio alone, if you cause interference or loss of reception when it is needed most you might be liable for any thing that would happen.

Do your own setup in the end and ask the Boss for permission. it will come down to Yes or No in the end.


Ok so since we TX from the base station and it uses say 50 watts it would bleed into all the other frequencies and lines connected? I guess I was hoping that the splitter was one way like a check valve I guess where the TX would just go up to the splitter somehow only go directly to the the antenna and not down the other lines.

If he did give me the go ahead what would you recommend the best approach would be to minimise loss of functionality of the current setup?

Vkfour wrote:I agree with Alinco21. Using one antenna as both transmit and receive is not an easy job. Even repeaters using the one antenna but with the TX and RX frequencies separated by up to 10 MHz need quality filters.


Hmmm, I was really hoping it would be a simple thing to do with a few splitters, amps and maybe a filter here or there.
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Help with splitting antenna for a noob

Postby Phantom » Fri Sep 29, 2017 11:38 am

Best way, leave the existing setup alone. If it ain't broke - don't fix. Mucking with the existing setup could invalidate the licensing for that frequency?

For the RX, get an antenna that is best tuned to the band you wish to listen to. In your case, get one that covers the aeronautical band.

If you wish to then split that feedline, that would be ok as it's only for RX. You could use a splitter and a small amp if needed to amplify the incoming signal into the receivers.

As for the internet feed, that is a different area and depends on your budget/equipment etc

You simply don't want to throw 10-50W straight into the input of a receiver at close range (read same coax) as not only will it overdrive the receiver but could cause some damage.

Would you turn the fire hydrant on and point it straight up the kitchen drain whilst trying to empty it at the same time? Crude analogy but I hope it makes sense?

If you are wanting to create a feed, best to keep it simple and isolated (from existing transmission stations). This will produce better results as well as help to isolate any problems should they arise.
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Re: Help with splitting antenna for a noob

Postby thommo17 » Fri Sep 29, 2017 6:21 pm

Phantom wrote:Best way, leave the existing setup alone. If it ain't broke - don't fix. Mucking with the existing setup could invalidate the licensing for that frequency?

For the RX, get an antenna that is best tuned to the band you wish to listen to. In your case, get one that covers the aeronautical band.

If you wish to then split that feedline, that would be ok as it's only for RX. You could use a splitter and a small amp if needed to amplify the incoming signal into the receivers.

As for the internet feed, that is a different area and depends on your budget/equipment etc

You simply don't want to throw 10-50W straight into the input of a receiver at close range (read same coax) as not only will it overdrive the receiver but could cause some damage.

Would you turn the fire hydrant on and point it straight up the kitchen drain whilst trying to empty it at the same time? Crude analogy but I hope it makes sense?

If you are wanting to create a feed, best to keep it simple and isolated (from existing transmission stations). This will produce better results as well as help to isolate any problems should they arise.


Yeah that definitely makes sense. It is a lot of power.

I might just need to do the listening at home which is too bad because I won't be able to get much from ATC just from pilots I'd say due to my position. It'd be the only way of using my own antenna because I'd have to contact linfox to get another antenna on Essendon airports roof. Slim chance of that I think.

For the internet it should be ok when it's all set up as it will just run from a raspberry pi as a server.
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