Microwave Systems and Remotes Links

ltginrage

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Hello,
I have a few answers that google wasn't as clear about, hoping you guys would know more on these topics.
What is a microwave system (as in a microwave public safety license)? Are they monitorable?
And what is a remote link?
Thanks
 

ProScan

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Hello,
I have a few answers that google wasn't as clear about, hoping you guys would know more on these topics.
What is a microwave system (as in a microwave public safety license)? Are they monitorable?
And what is a remote link?
Thanks
A Microwave system is made up of Microwave links or paths. They are like pipes. They carry DS-3 traffic(28 T-1's multiplexed) and the newer systems carry IP traffic. They are not monitorable. They are up in the GHz range somewhere from 2 GHz and above. If they were monitorable, you would need to be in the direct path which wouldn't be likely considering the dish may be located on a high rise roof, tower, or tower on a mountain top. The T-1's are multiplexed from 24 channels and each channel could be a voice or data channel.
 

K4EET

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These would be in the GHz frequencies and are generally high speed data transmissions so basically, no, they can not be monitored.

Besides, the beamwidth is fairly narrow so you would have to be right on the path to receive the signal and if you blocked the beam, you would be in a heap of trouble. When I was doing path studies, we had a shot going over a coal mining company where the coal pile would increase in height over time. A company not to be named did the first study and shot the path when the coal pile was at a minimum height. The microwave system was installed per their design. The system went down like clockwork for 2 days every 4 weeks. We re-shot the path on paper and in the field and found the offending coal pile. Needless to say, the dishes at each end had to be raised so the narrow beam would clear the maximum height of the coal pile! :ROFLMAO: :ROFLMAO: :ROFLMAO:
 

ofd8001

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Many large radio systems have multiple sites. There may be a dispatch center, one or more transmitter sites, some satellite receiver sites, etc. It is the microwave system that "connects" these sites together. Back in real old days these sites may have been connected using leased telephone lines.

Leased telephone lines are expensive and have the occasional malfunction. So microwave systems/paths were created to overcome those issues. They are radio (big dish antennas) but as noted above, very narrow in their waves, as in one point to another. They are licensed by the FCC in the MW (for microwave) service. With a little bit of research, you can see the microwave paths in licensing information.
 

ProScan

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These would be in the GHz frequencies and are generally high speed data transmissions so basically, no, they can not be monitored.

Besides, the beamwidth is fairly narrow so you would have to be right on the path to receive the signal and if you blocked the beam, you would be in a heap of trouble. When I was doing path studies, we had a shot going over a coal mining company where the coal pile would increase in height over time. A company not to be named did the first study and shot the path when the coal pile was at a minimum height. The microwave system was installed per their design. The system went down like clockwork for 2 days every 4 weeks. We re-shot the path on paper and in the field and found the offending coal pile. Needless to say, the dishes at each end had to be raised so the narrow beam would clear the maximum height of the coal pile! :ROFLMAO: :ROFLMAO: :ROFLMAO:
Where I retired from, we had a path go down at the same time each day. We found a crane had moved in the path. We've also had a path go down when a building under construction added a new floor. Another time, a over grown tree was blocking the path of a OC-3 radio.
 

K4EET

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Where I retired from, we had a path go down at the same time each day. We found a crane had moved in the path. We've also had a path go down when a building under construction added a new floor. Another time, a over grown tree was blocking the path of a OC-3 radio.
Hate it when that happens... :ROFLMAO:
 

mmckenna

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Another time, a over grown tree was blocking the path of a OC-3 radio.
Been there, done that, been out in the storm with a tree crew to take the top off it.


Remote links are connections to other radio sites. As stated, many radio systems might have multiple receivers all connected back to a voter. The voter will pick the receiver that has the highest signal to noise ratio and use that to feed the repeater(s). Multiple transmit sites may exist also.
And while I'm old, I'm not that old and am still running leased telco lines to some of my sites. Some is on our own cable, some is from the local exchange carrier. All will eventually be transitioned to IP over the next few years. Microwave, conditioned telephone lines, optical, and IP links may be used to connect the remote sites together.
 

bb911

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Not microwave, but the US Forest Service uses UHF links on some Nat Forests. Around 409 - 411 MHz. I'm not quite sure exactly how they work, but it's not unusual to receive them better then their repeaters. Also, for many years the State of California - Office of Emergency Services (OES) has had a statewide microwave system. Last year Nokia was selected by OES to "upgrade the statewide microwave network to support first responder communications."
Press Release
 

mmckenna

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Not microwave, but the US Forest Service uses UHF links on some Nat Forests. Around 409 - 411 MHz. I'm not quite sure exactly how they work, but it's not unusual to receive them better then their repeaters. Also, for many years the State of California - Office of Emergency Services (OES) has had a statewide microwave system. Last year Nokia was selected by OES to "upgrade the statewide microwave network to support first responder communications."
Press Release
NOAA uses some 400MHz links to some of their transmitters around me. I can usually pick them up.
 
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Been there, done that, been out in the storm with a tree crew to take the top off it.


Remote links are connections to other radio sites. As stated, many radio systems might have multiple receivers all connected back to a voter. The voter will pick the receiver that has the highest signal to noise ratio and use that to feed the repeater(s). Multiple transmit sites may exist also.
And while I'm old, I'm not that old and am still running leased telco lines to some of my sites. Some is on our own cable, some is from the local exchange carrier. All will eventually be transitioned to IP over the next few years. Microwave, conditioned telephone lines, optical, and IP links may be used to connect the remote sites together.
When the winds from Harvey hit Austin...I got a call from one of the rural county EMC's stating three of his sites were going in and out of site trunking every minute or two. The wind was moving the dishes making the short path back to CoA's core unstable. I ended up unplugging the PTP800's network cable to force the long path because I didn't want to take the hours needed to figure out how to add cost on the GGM8000's. The real take away from that day...when you have your microwave radios in the same layer 2 network (in this case a /24 broadcast domain) it can take up to 40 seconds for OSPF to recalculate a route.

I had a construction crew build a tank battery in 100 ft from a 50ft tower that back-hauled all of the SCADA data for that field. It was good...until they put the last 10 ft up.
 

12dbsinad

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There are still many UHF remote links in service out in the country in my neck of the woods. Many are used for voter links back to the comparator. These are referred to as "poor mans microwave" or "poor mans voter links". But hey, they do work and you can do a difficult shot!
 

ltginrage

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Remote links are connections to other radio sites. As stated, many radio systems might have multiple receivers all connected back to a voter. The voter will pick the receiver that has the highest signal to noise ratio and use that to feed the repeater(s). Multiple transmit sites may exist also.
And while I'm old, I'm not that old and am still running leased telco lines to some of my sites. Some is on our own cable, some is from the local exchange carrier. All will eventually be transitioned to IP over the next few years. Microwave, conditioned telephone lines, optical, and IP links may be used to connect the remote sites together.
Must have missed that when scrolling through. So there basically extra towers for mutual aid or something like that?
 

mmckenna

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Must have missed that when scrolling through. So there basically extra towers for mutual aid or something like that?
No, mutual aid and remote links are different things.

A radio system does not have to be restricted to a single tower or radio site.
There are a couple of other ways of doing things:
Remote receivers that link back to a central site. This puts receivers out closer to the lower power hand held or mobile radios. They put the 'ears' closer to the source. Those remote receivers (often called satellite receivers, but not space type satellites, just others out away from the main tower) are often linked back via radio, microwave, fiber optic cable, T-1 circuits, conditioned telephone circuits, etc.
Multiple transmitters, the simulcast that you may hear referred to on this site is where a radio system may have multiple transmitters located at different sites all transmitting the same signal on the same frequency at the same time, again, radio link, microwave, fiber, telephone, T-1, etc.
Multiple transmitters at different sites transmitting the same thing on different frequencies (multicast).

I've got a system here at work that has one main repeater site that handles the transmitting, plus about 5 different remote receivers scattered around the area that help with portable radio coverage. I'm in the process of designing/building a new system that will have simulcast sites and remote receivers to improve portable coverage.
 

ofd8001

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Back in the dark ages, as in the late 1970s, the Kentucky State Police was on VHF low band. The base stations (or posts) transmitted on 44.62 and the mobiles were on another frequency. This was all across the state.

There were some locations that were just too far away for the troopers to hear the base stations. So they set up links where the post would transmit on a third frequency that was received by a remote location, which was then repeated on the post frequency.

The call signs for these remote links was different, 3 letters and 2 numbers versus 3 letters and 3 numbers.
 

ab3a

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Decades ago, microwave was used for transmitting voice channel trunks and leased line circuits from place to place. I used to work for a water utility and we had LOTS of microwave --mostly 6 GHz industrial band equipment. The original stuff was actually a very wide band FM transmission on 6 GHz. The channel was 10 MHz wide and the modulation would carry voice in the form of a single sideband signal from 60 kHz to about 2600 kHz. Each channel was 4 kHz wide. There was a pilot signal that would be sent to keep everything in phase from station to station. The baseband would be relayed around a loop of about a dozen stations, mostly located on water towers.

The thing is, our license was very restrictive. We had to have 8 foot diameter dishes to be able to meet the requirements for a 1.3 degree half-power beamwidth. You could theoretically receive the signal off the dish, but we also ran very low power. Many transmitters put out only 10 milliwatts of power. So intercepting the signal with a microwave receiver would have been quite difficult and unless you were outside the first fresnel zone you'd just get a lot of distorted, noisy junk on the baseband of your receiver.

BTW, in those days the radios would fill an entire rack. But surprisingly, the system worked.

These days, you're more likely to find 45 MBPS DS3 speed radios on those channels. If you happened to have an LNB with a decent sized dish, you might be able to pick up a side lobe with a Software Defined Radio. But you'd need a lot of patience and the dish would have to be line of sight from you. And you'd need a pretty decent SDR to be able to detect the QAM signal reliably. And then you'd need to know the coding methods used for the constellation. Those are not published either.

So, if you were REALLY determined, you might be able to build something. And then you too could listen to all sorts of mundane traffic like telephone trunks, Two way radio traffic, lots of IT network traffic filled with mundane things like work-orders, purchase orders, and dull stuff like that, and some really dull SCADA telemetry. And good luck figuring out what is what. By the time you could begin to parse that stuff, they'd probably update something and everything you thought you knew will be garbage.
 
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