probably a stupid question, but i'm not very well versed on duplexers and the intricate details of an antenna system...
like the subject says, can an entire trunked system share 1 antenna for TX and RX? if i were to have 5 MTR2000's in the 450-470 range, could they all be duplexed (multiplexed?) to a single antenna? the best transmit site i have is on the roof of the courthouse and space is at a premium. i don't think it would be possible to put up 4 more antennas so i was hoping one could be shared. possible? ...or is it a desense nightmare?
trunked system share 1 antenna?
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trunked system share 1 antenna?
"In the beginning of a change, the patriot is a scarce and brave man, hated and scorned. When his cause succeeds however, the timid join him, for then it costs nothing to be a patriot." - Mark Twain
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Dan562
- Posts: 533
- Joined: Mon Aug 23, 2004 7:30 pm
- What radios do you own?: Kenwood, Yaesu, ICOM, Motorola
eboe,
This can be accomplished but there are trade off with the XMTR / RCVR system performance on a Combiner plus Duplexer and one Anteena. Since you would be using 1 Control Channel and 4 Voice Channels. I would not recommend a greater than 1 MHz Frequency Spread between F1 Tx through F5 Tx because of the Duplexers degradation on Transmit and Receive signals and RF equipment losses.
The 5 Channel RF Combiner/Circulators will have -3.5 dB, the Duplexers will have -2.0 dB and the Feedlines Heliax 1/2" -1.5 dB/100' or 7/8" -1 dB/100' totaling between -6.5 & -7.0 dB Losses or between 20 & 25 RF Watts at the base of the +6 dB or +9 dB Gain Antenna. This does not include other Signal Path Losses such Buildings, Hills, Foliage (Trees) and Subscriber units (Portables/Mobiles).
The Frequency Tx to Tx Spread would be as an example: F1 Tx 461.000 MHz, F2 Tx 461.200 MHz, F3 461.400 MHz, F4 461.600 MHz & F5 Tx 461.800 MHz. It's all about Path Losses, if you're able to accept the degradation with the signal losses.
This can be accomplished but there are trade off with the XMTR / RCVR system performance on a Combiner plus Duplexer and one Anteena. Since you would be using 1 Control Channel and 4 Voice Channels. I would not recommend a greater than 1 MHz Frequency Spread between F1 Tx through F5 Tx because of the Duplexers degradation on Transmit and Receive signals and RF equipment losses.
The 5 Channel RF Combiner/Circulators will have -3.5 dB, the Duplexers will have -2.0 dB and the Feedlines Heliax 1/2" -1.5 dB/100' or 7/8" -1 dB/100' totaling between -6.5 & -7.0 dB Losses or between 20 & 25 RF Watts at the base of the +6 dB or +9 dB Gain Antenna. This does not include other Signal Path Losses such Buildings, Hills, Foliage (Trees) and Subscriber units (Portables/Mobiles).
The Frequency Tx to Tx Spread would be as an example: F1 Tx 461.000 MHz, F2 Tx 461.200 MHz, F3 461.400 MHz, F4 461.600 MHz & F5 Tx 461.800 MHz. It's all about Path Losses, if you're able to accept the degradation with the signal losses.
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MSS-Dave
- Posts: 770
- Joined: Mon Jun 30, 2003 6:02 pm
- What radios do you own?: Harris XL200M. XPR7550E, NX300
I'm doing this exact thing with a UHF LTR trunking MTR2K system. 4 channels into dB Spectra TX combiner (old DB Products..), RX multicoupler with window filter and a TX/RX trunking duplexer. The window is 1 MHz wide on the duplexer. You should put all of your freqs within 2 MHz max, TX/RX can supply that but narrower the better due to the need for spacing between highest RX freq and lowest TX freq. Mine are currently less than 1 MHz space for the 4 channels. Key is to space the TX out to get the max output from the combiner, mine are about 350 Khz apart now. 100 watts in gives me around 30-35 out per channel.
Dan is right on about the degradation with path loss. Optimize where you can, duplex multiple channels as a last resort. My system is portable in 3 cases and I didn't want to use 2 antennas. I don't have issues with path loss usually because the system is a "on site" design.
Good luck with it. If you need info on the duplexer, I'll gladly post up the model number and the specs as supplied, I don't have it right now to post though....
Dave
Dan is right on about the degradation with path loss. Optimize where you can, duplex multiple channels as a last resort. My system is portable in 3 cases and I didn't want to use 2 antennas. I don't have issues with path loss usually because the system is a "on site" design.
Good luck with it. If you need info on the duplexer, I'll gladly post up the model number and the specs as supplied, I don't have it right now to post though....
Dave
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Dan562
- Posts: 533
- Joined: Mon Aug 23, 2004 7:30 pm
- What radios do you own?: Kenwood, Yaesu, ICOM, Motorola
eboe,
I just thought of a previous post on this Forum regarding your present system having talk-in problems from the out lying sites. As you've stated your current radio site is centrally located on a Court House in a metropolitan area. I don't recall the Height of that Building or the present antenna gain, model or manufacture that you're using on the top of the building.
It worries me if you're already using a +9 dB Gain antenna because if you decide to use a UHF (450-470 MHz) RF Combiner / Circulator / Duplexer system and incurr more RF Path Losses, the Outbound Tx Signal may not be heard or penetrate those remote building sites. Losing an additional 3~4 dB of Tx signal will reduce your Tx coverage radius by 25 to 28% in air miles.
One method to determine if the reduction of Tx signal will be affected is to adjust the RF Output of your current 100 Watt XMTR down to 30 to 35 Watts Output and then go out in the field to check and record the RF signal coverage at those remote locations. You will want to have a balanced RF system for Tx & Rx coverage. It's all about Path Losses versus RF Signal Coverage, if you're able to accept the degradation with the RF Signal Losses then the system should work okay.
In MSS-Dave's case, he's got a Portable system to move around to different sites and mostly worry about signal penetration for the InBound and Outbound signals within the one local site.
An ounce of prevention is worth ten pounds of cure.
Dan
You've got to look out for # 1 but Don't step in # 2 while looking out for #1!
I just thought of a previous post on this Forum regarding your present system having talk-in problems from the out lying sites. As you've stated your current radio site is centrally located on a Court House in a metropolitan area. I don't recall the Height of that Building or the present antenna gain, model or manufacture that you're using on the top of the building.
It worries me if you're already using a +9 dB Gain antenna because if you decide to use a UHF (450-470 MHz) RF Combiner / Circulator / Duplexer system and incurr more RF Path Losses, the Outbound Tx Signal may not be heard or penetrate those remote building sites. Losing an additional 3~4 dB of Tx signal will reduce your Tx coverage radius by 25 to 28% in air miles.
One method to determine if the reduction of Tx signal will be affected is to adjust the RF Output of your current 100 Watt XMTR down to 30 to 35 Watts Output and then go out in the field to check and record the RF signal coverage at those remote locations. You will want to have a balanced RF system for Tx & Rx coverage. It's all about Path Losses versus RF Signal Coverage, if you're able to accept the degradation with the RF Signal Losses then the system should work okay.
In MSS-Dave's case, he's got a Portable system to move around to different sites and mostly worry about signal penetration for the InBound and Outbound signals within the one local site.
An ounce of prevention is worth ten pounds of cure.
Dan
You've got to look out for # 1 but Don't step in # 2 while looking out for #1!
As Dan and Dave have pointed out, this is a fairly common configuration for trunking systems. It's a whole lot easier to do at 800MHz, but is do-able for UHF as well.
The smaller the frequency spacing between channels, the more loss you will have in the TX combiner circuit. For example, channels 50KHz apart would likely incur losses of greater than 7dB through the combiners, where channels about 200KHz or more might be half that or better. As they said, you don't really want to go more than 1MHz between your highest & lowest frequencies...so with 5 channels you're looking at a maximum spacing of 200KHz between channels. There are duplexers available which can allow up to 2MHz, but there is fairly significant "roll-off" at both ends...so your high & low channels may not cover as well as your middle channels.
It's not such a big deal on the RX side. There are many types of RX multicouplers available which will accomodate 5 (or more) receivers. Most are available with a built-in low noise pre-amp to compensate for multicoupling loss. You can generally order them with anywhere from 2 to 10 dB gain.
I've heard good things about TX/RX Systems, and they will also do the engineering for you if you buy the products from them. Otherwise, Sinclair & Celwave also are good choices in my experience.
Todd
The smaller the frequency spacing between channels, the more loss you will have in the TX combiner circuit. For example, channels 50KHz apart would likely incur losses of greater than 7dB through the combiners, where channels about 200KHz or more might be half that or better. As they said, you don't really want to go more than 1MHz between your highest & lowest frequencies...so with 5 channels you're looking at a maximum spacing of 200KHz between channels. There are duplexers available which can allow up to 2MHz, but there is fairly significant "roll-off" at both ends...so your high & low channels may not cover as well as your middle channels.
It's not such a big deal on the RX side. There are many types of RX multicouplers available which will accomodate 5 (or more) receivers. Most are available with a built-in low noise pre-amp to compensate for multicoupling loss. You can generally order them with anywhere from 2 to 10 dB gain.
I've heard good things about TX/RX Systems, and they will also do the engineering for you if you buy the products from them. Otherwise, Sinclair & Celwave also are good choices in my experience.
Todd
No trees were harmed in the posting of this message...however an extraordinarily large number of electrons were horribly inconvenienced.
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thanks guys, good info.
dan, good memory on my current system. the courthouse is listed as 72.0m w/o appurtenances but i think they were conservative on that for the coordination. (EFD has it listed as 62.0m on their license) current antenna is a DB404-B exposed dipole which is advertised as 3.8dBd/5.9dBi. the whole antenna system is pretty old. feedline and connections are of questionable condition.
talk-in IS a problem in some fringe areas if you're in a basement or other highly shielded area. talk-out is only a problem to one small section of town. the antennas are mounted on a perimeter type railing around, and slightly below, the peak of the courthouse. the peak is like concrete stadium seating with a big honking metal chimney stack of some sort up through the middle. having my antenna lower than that can't be good! it just so happens that the talk-out problem area is exactly OPPOSITE the chimney stack. go figure.
i'm getting a new antenna pretty soon. going with a DB408-B which is advertised as 6.6dBd/8.7dBi. almost 3dB gain. it has 8 elements instead of 4 so it's about twice as tall and it's going on a taller mast to get it clear of the roof peak from all directions with new feed-line if needed. the new stuff should fix any path-loss problems that may already exist. further plans to implement a voting system will make talk-in problems a thing of the past so i think i can get away with [some] path loss from the combiner/multi-coupler and still be better than what it is right now. the voting system will be in place long before i even decide if trunking is necessary.
i was asking about this whole antenna-sharing thing because my only other alternative would be to have a voted/trunked system with 5 transmitters at different locations. i'm not sure how much of a fluster-cluck it would be to network 5 trunk controllers with 5 comparators and let's say approx 3 voting sites per channel. gettin kinda hairy with that one, eh?
i think i'd rather deal with a few db of loss than to have a networking nightmare like that.
basic plan:
1) new antenna system on courthouse
2) voting system for courthouse repeater
3) voting system for other repeaters
4) migrate to trunking
1 thru 3 are easy. i'm just trying to plan ahead for #4 so i know what to expect. if the transmitters will all be moved to the courthouse or not is one question. and i also want to make sure i get the right type of voting equipment to be able to use it if/when i go trunked.
sorry to bombard you guys with so much info. lol
i'm going to try TX/RX and see what they say about the channel spacing and losses. i appreciate the tip!
dan, good memory on my current system. the courthouse is listed as 72.0m w/o appurtenances but i think they were conservative on that for the coordination. (EFD has it listed as 62.0m on their license) current antenna is a DB404-B exposed dipole which is advertised as 3.8dBd/5.9dBi. the whole antenna system is pretty old. feedline and connections are of questionable condition.
talk-in IS a problem in some fringe areas if you're in a basement or other highly shielded area. talk-out is only a problem to one small section of town. the antennas are mounted on a perimeter type railing around, and slightly below, the peak of the courthouse. the peak is like concrete stadium seating with a big honking metal chimney stack of some sort up through the middle. having my antenna lower than that can't be good! it just so happens that the talk-out problem area is exactly OPPOSITE the chimney stack. go figure.
i'm getting a new antenna pretty soon. going with a DB408-B which is advertised as 6.6dBd/8.7dBi. almost 3dB gain. it has 8 elements instead of 4 so it's about twice as tall and it's going on a taller mast to get it clear of the roof peak from all directions with new feed-line if needed. the new stuff should fix any path-loss problems that may already exist. further plans to implement a voting system will make talk-in problems a thing of the past so i think i can get away with [some] path loss from the combiner/multi-coupler and still be better than what it is right now. the voting system will be in place long before i even decide if trunking is necessary.
i was asking about this whole antenna-sharing thing because my only other alternative would be to have a voted/trunked system with 5 transmitters at different locations. i'm not sure how much of a fluster-cluck it would be to network 5 trunk controllers with 5 comparators and let's say approx 3 voting sites per channel. gettin kinda hairy with that one, eh?
i think i'd rather deal with a few db of loss than to have a networking nightmare like that.
basic plan:
1) new antenna system on courthouse
2) voting system for courthouse repeater
3) voting system for other repeaters
4) migrate to trunking
1 thru 3 are easy. i'm just trying to plan ahead for #4 so i know what to expect. if the transmitters will all be moved to the courthouse or not is one question. and i also want to make sure i get the right type of voting equipment to be able to use it if/when i go trunked.
sorry to bombard you guys with so much info. lol
i'm going to try TX/RX and see what they say about the channel spacing and losses. i appreciate the tip!
"In the beginning of a change, the patriot is a scarce and brave man, hated and scorned. When his cause succeeds however, the timid join him, for then it costs nothing to be a patriot." - Mark Twain