Greetings to all,
Working on a system design issue that I was wondering if anyone has every attempted or designed before.
We basically want to do a situation similar to that if you are traveling between two cities and listening to a radio station in city A but as you get closer to city B, which has a radio station on the same freq., the station in city B is picked up by your radio as the station in city A fades away. With that:
We are planning on putting up 2 VHF amateur repeaters. Repeater # 1 will be in Town A which the top of the building we are trying to get on is about 2 ft HAAT. Repeater # 2 will be in Town B where the location of the antenna will be about 150ft HAAT. (Sadly we can not get any higher then the site we are on for Town A without having to pay $$$$ for site rent.)
Due to VHF repeater pairs being in short supply (thank you paper repeaters) we will be using the same freq with different PL's per site, however we want to link the two repeaters and this will be via UHF simplex. We want to do this becasue Town A is about 15 air miles from Town B and someone in Town A can not hit Town B with a portable if they are inside a building and vice a versa.
In essence we want someone to key-up on Rptr A and get repeated out on Rptr A & Rptr B at the same time. This way if someone in Town A wants to talk to someone in Town B they can do so by just using the local repeaters. In addition we want to use the rptr in Town A to provide good Rx and Tx coverage for Town A only. Town B will be the main site and for good coverage if it is needed. (We all feel that if this will be used for emergency or priority communications we need to make sure that a portable has the best possible coverage on street level as well as the best possible interior coverage, hence the set-up.)
Now of course the 100% way to do this would be to use simulcasting equipment at each site. However, we do not have about $1,000.00 per site to sink into this project. In addition we can not find a repeater site between the two towns to do a good transmitter site and install remote receive sites with a comparator at each town. Also we do not have any phone or interent connections at either site so we will have to do the linking on UHF. Maybe in the future but not now!
Now since the two sities will not be synch'd for simulcasting even though they are on the same freq we are planning on running a different PL for Encode & Decode per site. Now using the Radio Mobile software and entering all the information we have found that if we adjust the power output, antenna direction, antenna gain, etc.. we will have very low overlap in coverage and in the areas that we do have overlap in coverage one signal will be higher in dBm then the other thus making one repeater stronger to the radio then the other, and the PL's will also help with the radio.
So has anyone ever done a set-up like this and if so what has been the issues you have seen with it? We are some what concerned that we might have some echoing if a person is in the overlap coverage even with the PL???
Thanks in advance!
simulcasting w/o simulcasting equipment
Moderator: Queue Moderator
simulcasting w/o simulcasting equipment
" ah the fatman made a funny!" - Stewie from the family guy.
I went to the doctor and all he did was just suck blood. Never go to Dr Acula - M. Hedberg
I went to the doctor and all he did was just suck blood. Never go to Dr Acula - M. Hedberg
Re: simulcasting w/o simulcasting equipment
Just using the different PL DECODE on the subscriber radios in the field will only help a small amount.
With both TX's on at the same time, the distortion in the overlap area will likely cause the subscriber
Radios to PL mute then unmute, then mute, then unmute, and the overlap audio will be very distorted due
To both TX carrier difference, and audio (voice) phase difference. And overlap areas at VHF are large.
You would really have to get the coverage areas to be "mutually exclusive" and then ya' wind up with an area
of no coverage.
Your linking via UHF should work.
As you say, true simulcast is pretty expensive.
If it were me, I would try to get a very low coverage repeater pair for the city that needs the least coverage.
Maybe make an arrangement with a repeater operator a way off and use different tones.
Use BOTH an RX for pair A and pair B in the low coverage town.
That gets repeated local at low power and linked to the other city like a remote receiver.
One local low coverage repeater, one remote receiver for the high coverage repeater, and the second
high coverage repeater.
Talk on one, talk on all.
With both TX's on at the same time, the distortion in the overlap area will likely cause the subscriber
Radios to PL mute then unmute, then mute, then unmute, and the overlap audio will be very distorted due
To both TX carrier difference, and audio (voice) phase difference. And overlap areas at VHF are large.
You would really have to get the coverage areas to be "mutually exclusive" and then ya' wind up with an area
of no coverage.
Your linking via UHF should work.
As you say, true simulcast is pretty expensive.
If it were me, I would try to get a very low coverage repeater pair for the city that needs the least coverage.
Maybe make an arrangement with a repeater operator a way off and use different tones.
Use BOTH an RX for pair A and pair B in the low coverage town.
That gets repeated local at low power and linked to the other city like a remote receiver.
One local low coverage repeater, one remote receiver for the high coverage repeater, and the second
high coverage repeater.
Talk on one, talk on all.
Re: simulcasting w/o simulcasting equipment
I understand your position and reasons for taking the stand your trying to take. However and I mean
this with great concern, it is not a good move. I have spent well over 40 years in the two way and
public safety areas over the years. Been a ham radio geek for even longer. Worked for a company that
did multi site paging for about 15 years. So what I am trying to pass along is not off the top of my
head.
In a number of cities that I have traveled through and also been a part of the ham repeaters over
the years, the subject of linking of two or more ham repeaters always comes up. As the other
person has already mentioned, there is always an overlap area of coverage of multiple sites. It
is hard, even with the correct hardware to make both sites play well together in the no mans
land of the overlap area. Hate to say this, but the solution is not to do it.
You will be much better off putting your tail between your leg's and go begging to the repeater
coordinator for a second pair of channels. Keep your idea of tone in and out on the channels.
The advantage with different channels is that the users can switch between the locations and
use the best of signal.
Jim
this with great concern, it is not a good move. I have spent well over 40 years in the two way and
public safety areas over the years. Been a ham radio geek for even longer. Worked for a company that
did multi site paging for about 15 years. So what I am trying to pass along is not off the top of my
head.
In a number of cities that I have traveled through and also been a part of the ham repeaters over
the years, the subject of linking of two or more ham repeaters always comes up. As the other
person has already mentioned, there is always an overlap area of coverage of multiple sites. It
is hard, even with the correct hardware to make both sites play well together in the no mans
land of the overlap area. Hate to say this, but the solution is not to do it.
You will be much better off putting your tail between your leg's and go begging to the repeater
coordinator for a second pair of channels. Keep your idea of tone in and out on the channels.
The advantage with different channels is that the users can switch between the locations and
use the best of signal.
Jim
n9upc wrote:Greetings to all,
Working on a system design issue that I was wondering if anyone has every attempted or designed before.
We basically want to do a situation similar to that if you are traveling between two cities and listening to a radio station in city A but as you get closer to city B, which has a radio station on the same freq., the station in city B is picked up by your radio as the station in city A fades away. With that:
We are planning on putting up 2 VHF amateur repeaters. Repeater # 1 will be in Town A which the top of the building we are trying to get on is about 2 ft HAAT. Repeater # 2 will be in Town B where the location of the antenna will be about 150ft HAAT. (Sadly we can not get any higher then the site we are on for Town A without having to pay $$$$ for site rent.)
Due to VHF repeater pairs being in short supply (thank you paper repeaters) we will be using the same freq with different PL's per site, however we want to link the two repeaters and this will be via UHF simplex. We want to do this becasue Town A is about 15 air miles from Town B and someone in Town A can not hit Town B with a portable if they are inside a building and vice a versa.
In essence we want someone to key-up on Rptr A and get repeated out on Rptr A & Rptr B at the same time. This way if someone in Town A wants to talk to someone in Town B they can do so by just using the local repeaters. In addition we want to use the rptr in Town A to provide good Rx and Tx coverage for Town A only. Town B will be the main site and for good coverage if it is needed. (We all feel that if this will be used for emergency or priority communications we need to make sure that a portable has the best possible coverage on street level as well as the best possible interior coverage, hence the set-up.)
Now of course the 100% way to do this would be to use simulcasting equipment at each site. However, we do not have about $1,000.00 per site to sink into this project. In addition we can not find a repeater site between the two towns to do a good transmitter site and install remote receive sites with a comparator at each town. Also we do not have any phone or interent connections at either site so we will have to do the linking on UHF. Maybe in the future but not now!
Now since the two sities will not be synch'd for simulcasting even though they are on the same freq we are planning on running a different PL for Encode & Decode per site. Now using the Radio Mobile software and entering all the information we have found that if we adjust the power output, antenna direction, antenna gain, etc.. we will have very low overlap in coverage and in the areas that we do have overlap in coverage one signal will be higher in dBm then the other thus making one repeater stronger to the radio then the other, and the PL's will also help with the radio.
So has anyone ever done a set-up like this and if so what has been the issues you have seen with it? We are some what concerned that we might have some echoing if a person is in the overlap coverage even with the PL???
Thanks in advance!
-
chartofmaryland
- Batboard $upporter
- Posts: 411
- Joined: Sat Dec 28, 2002 11:25 pm
- What radios do you own?: Alot
Re: simulcasting w/o simulcasting equipment
You are wading in new waters it appears,
I would first do a search on google for information on this as there is alot to learn from your brain storming.
Second, this is possible, and without the multi PL and what not. There will be an area in between your systems where conversations will be unintelligible with the distortion.
This is NOT for public safety use so you can experiment if you have the time and resources, since that is what the hobby is about.
You will have to check with your coordination council and make sure your coordinated transmitter and your non coordinated transmitter can function in their set locations without hate and discontent to other co and adjacent users.
The main deal is to setup your link and get that perfect aka transparent for the audio, then pass audio from a voter to your transmit line at both sites.
Setup three people one at each site then one in the middle, key the system and have the people at both sites adjust the output power between the transmitters until you can understand the conversation in the middle of the two sites. This is not easy which is why it is not done often and people would rather go out and buy simulcasting products instead.
That is one way of doing it and it does leave much to be desired unless you have a good distance between site A and B say past 60 miles or so you can add some audio delay to your phasing.
The next thing to try is depending on your controller if equipped with an audio delay board you can control phasing with those settings until you can understand the audio in the middle of the two sites.
Again, these are all real hokey ways of completing your request, its poor mans simulcasting, and let me tell you it is done more than it should be on commercial systems people pay to use, now that's SICK.
So, DO NOT rely on this for Sky Warn Nets and anything else that may be deemed a threat to life or property and then go out and try it and see where you get.
CoM
I would first do a search on google for information on this as there is alot to learn from your brain storming.
Second, this is possible, and without the multi PL and what not. There will be an area in between your systems where conversations will be unintelligible with the distortion.
This is NOT for public safety use so you can experiment if you have the time and resources, since that is what the hobby is about.
You will have to check with your coordination council and make sure your coordinated transmitter and your non coordinated transmitter can function in their set locations without hate and discontent to other co and adjacent users.
The main deal is to setup your link and get that perfect aka transparent for the audio, then pass audio from a voter to your transmit line at both sites.
Setup three people one at each site then one in the middle, key the system and have the people at both sites adjust the output power between the transmitters until you can understand the conversation in the middle of the two sites. This is not easy which is why it is not done often and people would rather go out and buy simulcasting products instead.
That is one way of doing it and it does leave much to be desired unless you have a good distance between site A and B say past 60 miles or so you can add some audio delay to your phasing.
The next thing to try is depending on your controller if equipped with an audio delay board you can control phasing with those settings until you can understand the audio in the middle of the two sites.
Again, these are all real hokey ways of completing your request, its poor mans simulcasting, and let me tell you it is done more than it should be on commercial systems people pay to use, now that's SICK.
So, DO NOT rely on this for Sky Warn Nets and anything else that may be deemed a threat to life or property and then go out and try it and see where you get.
CoM
If the lights are out when you leave the station and then come on the second you key up, you know you have enough power.
Re: simulcasting w/o simulcasting equipment
With the decline of the paging business, simulcast capable paging transmitters and delay devices might be found on the surplus market dirt cheap - thus allowing you to make the system work pretty well at low cost.
Re: simulcasting w/o simulcasting equipment
What none of us techies have not mentioned so far is much of this depends on the two transmitters
being on the exact same frequency. They can't drift plus or minus in frequency at all. The only way
you can make this happen is with a high stability frequency source. You don't get that in any ham
transmitter of even the normal Motorola base stations. It requires a special stabilized oscillator. You
only will find these in paging transmitters. Reason being is just why this thread is going on.
In some cases, the 2 transmitters are off set just a few Hz from each other. This way you do get
a slight slow rumble, but the paging traffic works better. Problem is using a stable enough frequency
counter to set the transmitters with. Most average service monitors do not have the needed
stability to set the frequencies.
Just my added 2 cents.
Jim
being on the exact same frequency. They can't drift plus or minus in frequency at all. The only way
you can make this happen is with a high stability frequency source. You don't get that in any ham
transmitter of even the normal Motorola base stations. It requires a special stabilized oscillator. You
only will find these in paging transmitters. Reason being is just why this thread is going on.
In some cases, the 2 transmitters are off set just a few Hz from each other. This way you do get
a slight slow rumble, but the paging traffic works better. Problem is using a stable enough frequency
counter to set the transmitters with. Most average service monitors do not have the needed
stability to set the frequencies.
Just my added 2 cents.
Jim
Re: simulcasting w/o simulcasting equipment
Would the portables in the desired coverage area be able to adequately hear the repeater with the best location? If so, why not just set up the repeater on the best site and add a remote receiver at the lesser site that's UHF linked to the better site? You would have to use a controller that can handle a second receiver and vote it, but that seems basic to the knowledge you seem to already have.
curmudgeon.....and I like it.
-
motorola_otaku
- Posts: 1854
- Joined: Tue Jan 13, 2004 7:03 am
Re: simulcasting w/o simulcasting equipment
Actually, I thought of that too, and the thought of using MSF5000s pulled from trunking systems and set up for external frequency reference came to mind.. but then, if he were on 900 MHz I doubt coordination would be a problem.Jim202 wrote:What none of us techies have not mentioned so far is much of this depends on the two transmitters
being on the exact same frequency. They can't drift plus or minus in frequency at all. The only way
you can make this happen is with a high stability frequency source. You don't get that in any ham
transmitter of even the normal Motorola base stations. It requires a special stabilized oscillator. You
only will find these in paging transmitters. Reason being is just why this thread is going on.
First and foremost, remember that repeater coordination is voluntary and is in no way, shape, form, or fashion required by law. All it does is grant you the upper hand with the FCC in an interference complaint. Personally, as far as I'm concerned, if you send two or three certified letters to a paper repeater owner and don't get a reply, and you've verified that no actual repeater is on the air then that dude's pair is up for grabs. And if the dude starts squawking about interference as soon as you put your equipment on the air, you have your certified letter receipts to show to the repeater council and FCC showing that you unsuccessfully tried to make contact prior.
Anywho, if it were me I'd do this: make Town A's repeater your "master site" and make Town B's repeater a slave site with TX and RX audio relayed full-duplex back to the master site using UHF or 900 MHz links (I always thought DARCOM 9000 radios would be great for this purpose, but not knowing a whole lot about them I won't make a 100% recommendation.) Town A's master site operates on your coordinated pair and Town B's site operates on a verified-vacant pair, non-standard pair, or whatever else is deemed to be suitable. Remember, this is hammy work.. you have a lot of flexibility in regards to frequency usage that the Part 90 guys don't have.
Re: simulcasting w/o simulcasting equipment
three things come to mind:
1) high power transmitter on hill/tower between two towns, using remote receivers (no local RX at TX site) backhauled to the transmitter site via UHF. You could even put the two remote transmitters on the same frequency, causing the capture effect to dictate which of the two local receivers have priority.
2) two repeaters, linked via simplex link. KC0ONR's link system does this, and he provides a lot of documentation as to how the systems are built. When the first repeater is keyed up, it keys up a 222MHz link radio, which the other repeater groups hear and repeat. However, if there is a collision, then the local repeat audio is retransmitted, and the inactive repeaters repeat the resulting zero-beating signal as remote audio
3) cross-band hub. each local repeater is actually a full-duplex cross-band repeater, where the local RX connects to a UHF transmitter which is recieved and repeated on a 440MHz repeater between the two sites. The audio from the 440MHz repeater is then repeated out the transmitter at each RX site.
Several of these combinations require extraordinary frequency stability with respect to the transmitter's carrier, as well as minute delays in the microseconds to compensate for the speed-of-light delay between sites.
I think that #1 and/or #2 would be your best bet. #1 eliminates the requirement for duplexers, and #2 is the most practical.
1) high power transmitter on hill/tower between two towns, using remote receivers (no local RX at TX site) backhauled to the transmitter site via UHF. You could even put the two remote transmitters on the same frequency, causing the capture effect to dictate which of the two local receivers have priority.
2) two repeaters, linked via simplex link. KC0ONR's link system does this, and he provides a lot of documentation as to how the systems are built. When the first repeater is keyed up, it keys up a 222MHz link radio, which the other repeater groups hear and repeat. However, if there is a collision, then the local repeat audio is retransmitted, and the inactive repeaters repeat the resulting zero-beating signal as remote audio
3) cross-band hub. each local repeater is actually a full-duplex cross-band repeater, where the local RX connects to a UHF transmitter which is recieved and repeated on a 440MHz repeater between the two sites. The audio from the 440MHz repeater is then repeated out the transmitter at each RX site.
Several of these combinations require extraordinary frequency stability with respect to the transmitter's carrier, as well as minute delays in the microseconds to compensate for the speed-of-light delay between sites.
I think that #1 and/or #2 would be your best bet. #1 eliminates the requirement for duplexers, and #2 is the most practical.
-
psapengineer
- Posts: 175
- Joined: Thu Oct 07, 2004 10:00 am
We call it: SLOPPY-CAST
[size=85](and, just because we use the word sloppy ii isn't meant in a derrogatory manor)[/size]
This would be a fun project..............
I would consider doing this with 3 PL codes for the Portable/Mobile side.
One CTCSS to bring Both Transmitters on the air
One CTCSS to bring Town A only on the air
One CTCSS to bring Town B only on the air
Here are some thoughts regarding the overlap zone:
Since we don't know the terrain inbetween the two towns this is admittitedly speculative. But, that said, the math regarding path loss to any one point in the overlap zone from Town A and Town B is consistant regardless of power level. So, reducing power equally on both ends only creates poor outbound coverage in the overlap area. Now, if there is some higher terrain in between the two towns where you can create an RF curtian by adjusting the power levels such that they are equal for a reciever at the crest of the terrain you're lucky. Even in an overlap zone with stronger signals fixed stations can use a directional antenna with a high front to back ratio to descriminate reception to the best site.
Is there a point half way in between the two sites where you could put a third site? Here's why, if you're using identical systems on each end, using a Link Tx site (with Omni antenna) excactly half way in between,to transmitt the outbound audio to the two Town transmitters' would work. You don't need delay lines in this specific case. Then the remaining challenge is to align the reference oscillators in the Town transmitters to minimize the hetrodyne that will be heard since the are not diciplined to a common reference. Also, if you're inclined to try this, what about putting an Rx voter at this site which votes audio delivered from RXs that use the CTCSS for "both" sites?
Good Luck on your project; sounds fun,
Bob
This would be a fun project..............
I would consider doing this with 3 PL codes for the Portable/Mobile side.
One CTCSS to bring Both Transmitters on the air
One CTCSS to bring Town A only on the air
One CTCSS to bring Town B only on the air
Here are some thoughts regarding the overlap zone:
Since we don't know the terrain inbetween the two towns this is admittitedly speculative. But, that said, the math regarding path loss to any one point in the overlap zone from Town A and Town B is consistant regardless of power level. So, reducing power equally on both ends only creates poor outbound coverage in the overlap area. Now, if there is some higher terrain in between the two towns where you can create an RF curtian by adjusting the power levels such that they are equal for a reciever at the crest of the terrain you're lucky. Even in an overlap zone with stronger signals fixed stations can use a directional antenna with a high front to back ratio to descriminate reception to the best site.
Is there a point half way in between the two sites where you could put a third site? Here's why, if you're using identical systems on each end, using a Link Tx site (with Omni antenna) excactly half way in between,to transmitt the outbound audio to the two Town transmitters' would work. You don't need delay lines in this specific case. Then the remaining challenge is to align the reference oscillators in the Town transmitters to minimize the hetrodyne that will be heard since the are not diciplined to a common reference. Also, if you're inclined to try this, what about putting an Rx voter at this site which votes audio delivered from RXs that use the CTCSS for "both" sites?
Good Luck on your project; sounds fun,
Bob
Re: simulcasting w/o simulcasting equipment
Thanks for the input so far from everyone and I would like to answer a few questions that some people have or need to know!
1.) We looked high, hard, and far to try and find a location between the two cities to find a site for transmit. While yes we did find a few sites most are either commercial or cellular companies that all they heard was $$$ and without paying them a handsome rental fee/month we have NO way of getting on these towers/locations.
2.) We do not have money for simulcast, nor do we have money for voting! We have two VHF repeaters and two UHF repeaters.
3.) We plan on using the VHF repeater at each site and then connecting the UHF repeater to each VHF repeater. The UHF will be modified so that radio will operate in a simplex link and the input to each UHF repeater will be used for future expansion (remote input sites for future usage).
4.) Due to town A's antenna height only being at about 2ft HAAT we wanted that repeater to focus directly within town A to make sure the area was able to have good in-bldg Tx & Rx. (We do not expect town A to have great coverage, hence why we have the site in town B planned for extended coverage.)
5.) The lay of the land = town A is pretty much in a hole with the highest structure of the town (4 stories) being right at about average terrain. Town B is a little more flat with the average height of the city at about avg terrain. We have also decided that the antenna on top of site B will omni but positioned on the north facing side of the tower. For town A the antenna will be omni but south facing. (The location in Town A is on the northern part of town and the town is expanding southward!)
6.) The air distance between the two towns is approx 15 miles, but taking a look at terrain goes uphill from town A towards town B.
Once again thank you for all the input and if you have anymore questions please feel free to contact me!
1.) We looked high, hard, and far to try and find a location between the two cities to find a site for transmit. While yes we did find a few sites most are either commercial or cellular companies that all they heard was $$$ and without paying them a handsome rental fee/month we have NO way of getting on these towers/locations.
2.) We do not have money for simulcast, nor do we have money for voting! We have two VHF repeaters and two UHF repeaters.
3.) We plan on using the VHF repeater at each site and then connecting the UHF repeater to each VHF repeater. The UHF will be modified so that radio will operate in a simplex link and the input to each UHF repeater will be used for future expansion (remote input sites for future usage).
4.) Due to town A's antenna height only being at about 2ft HAAT we wanted that repeater to focus directly within town A to make sure the area was able to have good in-bldg Tx & Rx. (We do not expect town A to have great coverage, hence why we have the site in town B planned for extended coverage.)
5.) The lay of the land = town A is pretty much in a hole with the highest structure of the town (4 stories) being right at about average terrain. Town B is a little more flat with the average height of the city at about avg terrain. We have also decided that the antenna on top of site B will omni but positioned on the north facing side of the tower. For town A the antenna will be omni but south facing. (The location in Town A is on the northern part of town and the town is expanding southward!)
6.) The air distance between the two towns is approx 15 miles, but taking a look at terrain goes uphill from town A towards town B.
Once again thank you for all the input and if you have anymore questions please feel free to contact me!
" ah the fatman made a funny!" - Stewie from the family guy.
I went to the doctor and all he did was just suck blood. Never go to Dr Acula - M. Hedberg
I went to the doctor and all he did was just suck blood. Never go to Dr Acula - M. Hedberg
Re: simulcasting w/o simulcasting equipment
Try lower power and lower antenna at town A , just to get into the buildings you are need in town.
More power and higher antenna at town B and no Tx PL tones on the repeaters.
As someone posted before overlap area can cause PL to mute radios ,mobiles will see this more if they use PL RX option.
Remember, even in a paging system the reciever only needs a few millseconds of good rx and you will be talking a lot longer than that.
( and I will timeout your repeater if I rag chew )
Sounds like good summer time club project .
Good Luck
More power and higher antenna at town B and no Tx PL tones on the repeaters.
As someone posted before overlap area can cause PL to mute radios ,mobiles will see this more if they use PL RX option.
Remember, even in a paging system the reciever only needs a few millseconds of good rx and you will be talking a lot longer than that.
( and I will timeout your repeater if I rag chew
)Sounds like good summer time club project .
Good Luck
ab
still lurking here
still lurking here