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two repeaters one house

repeaters antenna spacing

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#1 wqzw301

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Posted 17 June 2019 - 10:46 AM

I have a repeater, Motorola 50 watt, cellwave 6 cavity band pass notch duplexer - 38 watt output after duplexer.

 

My brother now has a repeater 50 watt Motorola with vertex standard 6 cavity notch duplexer.

 

Our frequencies will be about 14mhz apart.    mine - 462's  and his - 448's

I use dx 400 max coax with a slim jim

He will use lmr 400 not sure about antenna???

 

Looking for some opinions about antenna spacing???

I have a vertical 20' pole mount on the 20' roof

 

Should we flip a coin and see who will be low man on a vertical split totem pole???? and how far apart?

 

or can we go horizontal with another mount???

 

I've heard of two repeaters sharing an antenna... but commercial repeaters set ups by bridgecom...

 

Any recommendations???

thank you

301

 

 

 

 



#2 berkinet

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Posted 17 June 2019 - 11:21 AM

...

He will use lmr 400 not sure about antenna???

...Any recommendations???

 

 

I'd go with vertical separation with as much distance between the two antennas as your mast will allow. The higher mounted antenna should be for the repeater you want the greatest range on.

 

And... DO NOT USE LMR-400

 

From repeater-builder.com

 

 

In duplex service you want to avoid any coax that has dissimilar metals rubbing against each other (such as Belden 9913) or any LMR-(any 3-digit or 4-digit number) cable since both use an aluminum foil shield rubbing against a copper braid (and they are not the only ones with that type of construction). In a coax cable any dissimilar metals in contact with each other are bad news. Aluminum oxide is formed when raw aluminum is in contact with oxygen, and the chemical reaction that converts the top few molecules of the exposed surface of aluminum into aluminum oxide is almost instantaneous. Aluminum oxide makes a dandy diode. All those millions of contact points between the copper braid and the aluminum oxide layer on the aluminum foil become millions of little tiny diodes. In the presence of high RF power levels all those little diodes cause RF noise. The amount of noise energy on any one frequency (such as on your repeater input frequency) is a low level, but when you have the noise source inside the same feedline that feeds a sensitive receiver it doesn't take much level to be audible.

I repeat - any cable that has dissimilar metals pressed together, even inside a jacket, will sooner or later create wideband noise (sometimes called duplex grunge) when hit with RF power. Even something as simple as a 1-foot-long jumper between the feedline and the antenna at the top of the tower can cause major desense problems (and for a long time the major antenna manufacturers were shipping 9913 jumpers with their antennas). 9913 is usable in an indoor simplex environment, but you will find that 9913 or any dissimilar metals cable, especially LMR-(any 3-digit or 4-digit number), is a disaster just waiting to happen on a duplex system.


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#3 Corey

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Posted 17 June 2019 - 12:09 PM

I have a repeater, Motorola 50 watt, cellwave 6 cavity band pass notch duplexer - 38 watt output after duplexer.

 

My brother now has a repeater 50 watt Motorola with vertex standard 6 cavity notch duplexer.

 

Our frequencies will be about 14mhz apart.    mine - 462's  and his - 448's

I use dx 400 max coax with a slim jim

He will use lmr 400 not sure about antenna???

 

Looking for some opinions about antenna spacing???

I have a vertical 20' pole mount on the 20' roof

 

Should we flip a coin and see who will be low man on a vertical split totem pole???? and how far apart?

 

or can we go horizontal with another mount???

 

I've heard of two repeaters sharing an antenna... but commercial repeaters set ups by bridgecom...

 

Any recommendations???

thank you

301

 

You will not have any issues at all, i have commercial pairs way closer then that and combining TX.


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Just My $.02

 

Corey

 

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https://mwgmrs.com


#4 WRAK968

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Posted 17 June 2019 - 03:35 PM

I have a repeater, Motorola 50 watt, cellwave 6 cavity band pass notch duplexer - 38 watt output after duplexer.

 

My brother now has a repeater 50 watt Motorola with vertex standard 6 cavity notch duplexer.

 

Our frequencies will be about 14mhz apart.    mine - 462's  and his - 448's

I use dx 400 max coax with a slim jim

He will use lmr 400 not sure about antenna???

 

Looking for some opinions about antenna spacing???

I have a vertical 20' pole mount on the 20' roof

 

Should we flip a coin and see who will be low man on a vertical split totem pole???? and how far apart?

 

or can we go horizontal with another mount???

 

I've heard of two repeaters sharing an antenna... but commercial repeaters set ups by bridgecom...

 

Any recommendations???

thank you

301

I don't believe you'll have many issues, Personally I use LMR400 right now and I dont have the issues Berkinet has, though my LMR400 is Aluminum on Aluminum, so perhaps this was an old issue the manufacture has since fixed.

One thing you'll want to do is make sure any jumpers you use are shielded well from RF wherever the radios live, And you'll want to label each repeater with a callsign just in-case one causes an issue with interference and is hunted back to your place, you can show that both are being operated legally under their own license. Lastly, while you shouldn't need to go super far with separating the antennas It is wise to put about a 10 foot gap from the top of the first antenna to the bottom of the second to avoid signal distortion when both radios are transmitting. I remember having to do that with the FD antennas when they upgraded from 33mHz to 480. lowering one antenna 10 feet below the other stopped the distortion when PD and FD talked at the same time. :)


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#5 wqzw301

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Posted 17 June 2019 - 04:57 PM

Thanks for the info and knowledge guys

Yes, both repeaters have a Morse id call sign . I believe I have all jumpers extra shielded.

I think I will go with the 10ft vertical separation.

I'll do some experimenting, break out the field strength meter...I have some Palomar mix 61 ferrites to try.....

Thank You!



#6 WRAK968

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Posted 17 June 2019 - 05:14 PM

I want to note, I meant a physical label, not morse ID. Its something commonly done in multi-transmitter environments. This allows the FCC, should a complaint arise, to easily tell which radio is the true offender and what license it falls under. (Sometimes the morse ID is hard to decode, especially with todays lazier governments employees)







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