POCSAG Paging

[RadioGuy3007]

Hello,
I need more ideas as I've been brainstorming for a long time. I am working on a project for a hospital that uses VHF Pocsag Paging. We just upgraded their paging system from a Motorola Nucleus with Zetron Terminals to a new ISC 250watt transmitter with a virtual terminal and the antenna is on a 250ft tower on the north side of town. The hospital currently has a paging booster that grabs the pages via over the air from an antenna on top of their building and then comes into an old motorola radio with some small pre-amps and then back out through the building. The building has BNC Motorla antennas every 10ft or so on most of the floors.

They are having issues in the entire basement area and we suggested that they purchase the other 250watt transmitter so we can simulcast the transmitters together for better coverage. They are not able to do that right now and are wanting us to replace the paging booster.

What would you suggest for a new paging booster? I'd rather replace the current booster and add lines in the basement area. If you want to chat more about this. Send me a message and I can share some more info.

 

[WB5UOM]

Id be interested to know WHO decided a hospital paging transmitter needed to be located ANYWHERE but at the hospital.

 

[GTR8000]

Having the transmitter on-site is not always ideal, especially if it's up on the roof, due to the umbrella effect. Sometimes a nearby site can provide better in-building penetration/coverage. Of course if that site is a few miles away, that kind of defeats the purpose. 🤦‍♂️

 

[WB5UOM]

Yup, a nearby site with the explicit intention of getting signal in to a particular building...but I think that may be mainly for 900mhz paging more so than VHF.
..I am aware of a hospital that teed off the VHF antenna port for the roof antenba ,and ran heliax down to the basement to a ground plane antenna.

 

[WB5UOM]

But, if the transmitter can not be moved to the hospital...it might be possible that a Zetron 55D paging repeater might work..

 

[RadioGuy3007]

Id be interested to know WHO decided a hospital paging transmitter needed to be located ANYWHERE but at the hospital.

First of all we live in a smaller city and have a lot of Doctors/Clinics in the area up north. We planned to put the antenna onto that tower because of it being on a hill as well as the coverage it would provide. We have a backup transmitter on the roof of our building.

 

[RadioGuy3007]

Having the transmitter on-site is not always ideal, especially if it's up on the roof, due to the umbrella effect. Sometimes a nearby site can provide better in-building penetration/coverage. Of course if that site is a few miles away, that kind of defeats the purpose. 🤦‍♂️

It's not a few miles away. It's on a large hill, 250ft in the air to provide coverage around the 3 surrounding cities and areas where doctors live. We looked at several difftent coverage options and having it on the tower made more sense. Prior to the tower site, we were on a building that was 84ft tall. We are now at 250ft and we have great coverage everywhere else except our basement where a lot of the radiology areas are such as interventional radiology, mammography, X-Ray/CT, cath lab and nuclear imaging.

 

[GTR8000]

Easy, fella, I was speaking in general terms based on what I've seen in real life, not taking a shot at your situation.

 

[speedway_navigator]

Have you measured the signal strength in the basement and each floor without the internal transmitter on?
My cousin made a passive repeater with half inch hardline into a hospital basement and it did the trick.

Does the internal xmtr have a 50Ω antenna distribution system? I can see a few antennas per floor if it's a big building but not dozens.
Did you measure power at the furthest antennas? Does it match the number of 3 dB loss splitters from the xmtr?

My first step would be feed the basement only with the booster.

 

[RadioGuy3007]

Have you measured the signal strength in the basement and each floor without the internal transmitter on?
My cousin made a passive repeater with half inch hardline into a hospital basement and it did the trick.

Does the internal xmtr have a 50Ω antenna distribution system? I can see a few antennas per floor if it's a big building but not dozens.
Did you measure power at the furthest antennas? Does it match the number of 3 dB loss splitters from the xmtr?

My first step would be feed the basement only with the booster.

Yes we have did what you suggested.

With the repeater off we are getting -70

With the repeater on in the radiology area we are getting -65

In my office which is also in the basement we are getting -49

 

[RadioGuy3007]

Easy, fella, I was speaking in general terms based on what I've seen in real life, not taking a shot at your situation.

Your good man. I didn't mean anything negative on my end either

 

[speedway_navigator]

Those numbers look pretty good. Can you generate a page from the roof backup xmtr only to see if that works? I wonder if there is a time of arrival delay between the main site and your internal xmtr.

 

[RadioGuy3007]

Those numbers look pretty good. Can you generate a page from the roof backup xmtr only to see if that works? I wonder if there is a time of arrival delay between the main site and your internal xmtr.

Yes, it does work. However the backup transmitter we have is a 100watt Nucleus. The hospital did not want to purchase another ISC 250watt transmitter with GPS antenna for simulcasting. So when we use the backup transmitter, if you are not specifically in the transmitter range you get garbled pages. I'm really pushing for the upgrade to the other 250watt transmitter because of being able to simulcast as well as automatic fail over. Right now the Nucleus is a manual transfer.

We use Zetron 6600s for the paging controllers.

 

[speedway_navigator]

Sounds like they need to bite the bullet, simulcast would give them the backup they need.

 

[WB5UOM]

With the signal levels you say you are getting...something else is at play.
How far in miles is the main transmitter from the hospital?
if you are 'repeating' the signal then audio delay comes into play, as does modulation.
And what speed is the paging? 512,1200,2400...
higher the speed, the more need for audio delay in multi-site paging and more attention to modulation, not to mention all xmtrs should be carbon copies.

 

[techsender]

One thing to keep in mind in the radiology area is the extensive shielding in place which works both ways. Having the booster transmitter feed a piece of radiax that goes down those hallways and ending up with an antenna not too far from your most difficult area to cover in the hospital basement might be a strategy. Each situation is different. Radiax comes with different levels of "leakage" but is pretty cool stuff I have used it to solve some interesting problems. The other advantage to this approach may be to minimize signal interference issues as they are not synchronized, so the receiver gets to use FM capture effect.

 

[speedway_navigator]

Our county does not have simulcast so we key 2 xmtrs that are far enough from each other there is no overlap, then key the 3rd. I wonder if that might help in the basement.

An engineer friend was called in to fix a radio coverage problem in a subway tunnel. They installed a DAS but used 75Ω coax and 50Ω antennas.
They put baluns on each antenna hoping that would help, but it didn't.
A major electronics equipment and parts supplier sold them Fieldfoxes to find bad baluns using DTF.

 

[WB5UOM]

simulcast is not hard...you dont 'have' to have gps timing at least at 512..(remember, pocsag was here long before gps timing)
if they are already using Zetron model 66 controllers, there is an option board for audio delay ...that would leave only the modulation issue between the different xmtrs and even then, if they were close, at 512, might not be much of an issue.

 

[speedway_navigator]

simulcast is not hard...you dont 'have' to have gps timing at least at 512

Change GPS to the high dollar term PNT and I'll give you a thumbs up...

 

[WB5UOM]

And it goes quiet.....