Local Fire Department Repeater (Range Problem)

[dean83]

Hello Everyone,

We have recently installed a 'repeater' of types. This repeater was designed and installed by a local company and was supposedly approved by 'designers'.

We have been having some decreased range and reception issues.

This repeater consists of:

• AYA-1503 YAGI ANTENNA
  OMNI OFFSET ANTENNA TRAM1487
  2 PM400 VHF
  Cabinet

The antennas are mounted approximately 40 and 50 feet high on a local tower that also supplies internet to the area.

The radios transmit to the main tower approximately 35kms away, the transmit/receive to this tower is working fine.

We are recently having problems with the transmit/receive from the local tower on the local frequency. The recent average temperatures have been around -7C to -10C. The enclosure is vented and not heated.

The terrain is average with no significant hills however there may not be direct line of sight to the tower.

The portables transmitting to the tower are Motorola HT1250 on high power.

The variables that we may be able to change are:

Heat in the cabinet (easy with a lightbulb, heat pad, etc)
Height of the local rx/tx antenna on the tower (may be able to go another 10 feet higher. Yes, obvious gain with the height, however the current location is where the tower owner approved it's installation and any higher may interfere with the towers designed use).
Local repeater Radio tx wattage - unsure of the program settings on the PM400 - possible to change program settings
Position of the antenna on the tower. Currently the local antenna is on the east side of the tower. I am unsure if the tower itself would cause any interference or decrease range.



Any suggestions are appreciated. I can take pictures of the tower and radio setup if it helps.

Thanks in advance.

[dean83]

In addition the ranges we are having problems with are between 5-10 kms, give or take 3-4 miles.

I am curious as to if the HT1250's may be the problem. We are bringing down a kenwood tk-2180 to test.

[wavetar]

It's a little unclear from your post, so two questions:

1) Did the system give the desired coverage to begin with, and then deteriorate? If so, was it gradual, or sudden?

2) Is this a 'fleet wide' issue? If all radios are affected, it's likely an issue with the repeater. Could be as simple as moisture in a cable due to a poor weather-tape job. I say 'likely' because it only takes a few bad portables to make it appear the entire system is bad.

[Bill_G]

It's a little unclear from your post, so two questions:

1) Did the system give the desired coverage to begin with, and then deteriorate? If so, was it gradual, or sudden?

2) Is this a 'fleet wide' issue? If all radios are affected, it's likely an issue with the repeater. Could be as simple as moisture in a cable due to a poor weather-tape job. I say 'likely' because it only takes a few bad portables to make it appear the entire system is bad.

+1

Yes - the cold can do odd things, and a simple lightbulb is sometimes the answer. As Todd pointed out, moisture and ice could have crept damaging a connector and/or the antenna. Who is servicing it, or has it become your baby to feed and care for?

[Wowbagger]

So, this site is a link to the main site? It accepts input in VHF, and retransmits it to the remote site - on what band? Also VHF?

If so, then you should have a duplexer in the equation to prevent the link from desensing the input - could the tuning have drifted due to cold?

[dean83]

Thanks for your replies. It seems I need to get more information to help troubleshoot this.

I will take some photos of the system and antennas.

I will also do some radio checks with our kenwood tk-2180 (no tests with that portable to date) and see if it makes any difference.

It does seem that the reception has decreased over time. Initially we did radio checks and the reception was good out to 4-5 miles with a portable. At the time, the big difference was simply the radios being inside or outside of a vehicle - even through glass.

The radios are VHF. The Main repeater tx is 172.xxxx and rx is 169.xxxx. The new repeater consists of 2 radios and a rick. one radio transmits to the main on 169.xxx and the other radio transmits and recieves on 158.xxxx. (Photos to follow tonight, and the xxxx'es are because I dont have the exact #'s handy.).

Thanks. Sorry for not posting complete info off the start!

[dean83]

A quick reply with a link to some pictures of our tower:

http://i179.photobucket.com/albums/w301 ... photo3.jpg

There are two photos.

The higher antenna is located on the east side of the tower approximately 18 inches from the tower itself on 2 steel angle iron beams.

The lower antenna is the one that transmits to the main repeater 35km north of this tower.

Pictures of the setup will be added tonight along with some kenwood portable radio check results.

[Jim202]

My first question is did this work good before the cold weather?

Are there any duplexer cans or filters in this contraption? Trying to use an in band repeater is not the best idea. You haven't been exactly clear on what the frequency use is on this. I am trying to figure if the 158 frequency is a simplex or if you have a pair of frequencies in the 158 MHz range. Either way, when the 169 MHz transmitter comes up, it will cause problems for any receiver on 158. We need much more specific details to understand the problem.

Is there any indication of what it sounds like on the 158 MHz side? Are you getting a hiss or scratchy noise or wired sounds? Is the sound the same coming out of the main repeater?

[Astro Spectra]

I would look at an immediate fix by dropping the power (if that hasn't been done already) of the PM400 radios. You probably don't need much power to reliably hit the distant repeater and since the gadget is talking to portables there is no point running 45W. In any case those radios won’t last long running much power in repeater duty cycle.

[dean83]

Hi and thanks for the continued replies.

I dont believe there are any duplexers or anything on this. All That is in the box are 2 Pm400, a power supply, and a motorola 'repeater interface'. I couldnt get a part number due to the mount but I was able to get a picture.

http://s179.photobucket.com/albums/w301/Dean830/

I have also included a picture of the repeater setup and the included frequencies for clairity.

The main repeater works fine, no problems. Our portables communicating to the local repeater and vice versa is the problem. I wouldn't say there is a hiss or other continual background noise, just very poor reception. Orignally the reception was decient (with some variation between portables (ht750 vs ht1000)) but over the past month or so it has decreased significantly.

We are testing the kenwood tonight and I will post back with the results. Unfortunately I do not have any service software or hardware to test portable radio power output.

Example the other night. In the tanker on a CDM we could barely hear the portable communicating. The reception was very scratchy and broken. However dispatch did hear although I am unsure on how clear the transmission was that dispatch heard.

This may then be a problem with the repeater transmitting back out locally? It may be the primary issue.

Thanks.

[kb4mdz]

Based on what I see in the picture of the tape wraps of the coax going out of the box, (which, IMNTBHO, SUCKS MONKEY-TOES!!), you likely have something similar at the antenna end. Just saying. Poor workmanship tends to be 'if it is evident in one spot, esp. if it's evident in two, then it's likely all over the place'.

That, combined with the in-band repeat, with no duplexer (that I can see...), even tho the freqs are 10 MHz apart, ehhh, so some professional designed this, eh? Bet he also has a case of *ss against hams, too.

Lemme go back & reread your descriptions; I'll be back in a minute.

[kb4mdz]

OK, couple thoughts. And it sometimes helps to think of 'talk-in' or 'inbound' and 'talk-out' or 'outbound'; then you break your troubleshooting into subsections.

How is the outbound of the main site? Good/Bad? We'll assume (for now) that it's good, because you don't know of any complaints elsewhere in the system.

And in your picture #5, the 169.93750 TX, is that also RX on 171.36250? I'm also willing to guess that the Yagi goes to that radio;

If so, and does that radio have a front panel speaker? How does the audio from the main site sound?

[Bill_G]

Thanks for the photos Dean. They help. This is a simplex repeater using a VHF link. I think the system drawing is incomplete. It does not show the main system on the left, and the freq list is missing the rx for the link on the right. The design is depending on the vertical separation of the yagi and the omni on the side arm to keep desense down. There are no filters or duplexers. It is what it is, and probably works okay.

However, if I had to guess based on what you have said, and on the bill of materials, I'd say the Tram 1487 omni is broken. It is probably the casualty of ice inside the fiberglass breaking the elements. It is a low cost antenna, and the high price reflects the combined cost of the sidearm. I'd suggest a better antenna, but I doubt the tower could take the loading on the sidearm. The Tram is only two pounds. A better antenna would weigh significantly more, and could put the tower into failure under high wind and ice conditions. So, you are limited to light antennas. An engineering study would tell you for sure how much thrust you can put on that model of tower at that elevation.

As pointed out already, it could be the weatherproofing on the connectors at the antennas has failed. It looks like silicon tape in the photo, but it may just be electrical tape. I definitely don't see a buffalo wrap of butyl tape over the connectors under the outdoor cabinet. But, the contractor may have been depending on the cabinet to shield weather from the bottom connectors, and applied better weatherproofing at the antennas.

The bill of materials lists 100ft of coaxial cable for $1. Obviously they used low cost cable with that token price, and obviously the install used more than 100ft of line. It looks like LMR400 in the picture. Normally that would be acceptable for a ten year project. But, the crimp on connectors can be problematic. They may not have been applied well, and have already broken at one end or the other, or the center pin has recessed breaking the connection.

Honestly, I'd have the contractor review the system, and give you an opinion. But, any trained tech should be able to give you an analysis fairly quickly.

[mike m]

Also take a close look at photo 3 where the coax cables are going into the cabinet, it looks like some type of corrosion has dripped down the cable just below the wraps?


It doesn't look like tape or sealant residue, it looks almost like leaky battery acid residue, What is it ?


Mike

[Bill_G]

Ice crystals. What little condensation is in the air forms on the surface of everything. Bring your chapstick, and stay away from lemon drinks.

[Will]

Cheep coax and questionable antenna. Real engineers spec hard line.

How does the reception sound when listing to the return from the repeater on it's output frequency?

[Bill_G]

I would say the solution was driven by the bottom line. A lot of agencies just don't have the money. You do what you gotta do.

[Jim202]

Bill made mention of using LMR type cable. This may or may not be the type of coax cable your using. Before you go spending a bunch of time trying different attacks on the problem, on your next trip to the site, try to verify just which type of coax cable your using.

A real brief history on using LMR type coax for duplex operation, it has been well documented that it will cause problems over time. It seems that the junction between the foil shield and the braided shield cause intermod and noise in repeater operation. The more moisture that migrates into the under jacket region of the coax, the more this problem will show itself. Many repeater owners have fought with strange noise problems that only ended when the LMR coax was replaced with a heliax type coax cable. The more the cable flexes in the wind, the greater the problem shows itself.

As Bill has suggested, replacement of the antenna is a good start.

Jim

[psapengineer]

Watch out………….

I'm not familiar with the AYA-1503 yagi model but, if it’s similar to the old Maxrad MYA-1503 series, which is an unbalanced feed:

Yagi antennas that use a single-end/unbalanced feed will nearly "reverse" their directionality when they are coated with ice or hoar frost beginning with as little as maybe 1.5mm of coating. This affect, can in the UHF band, be on the order of 20 to 30 db of loss, I don’t have stasts for VHF.

This comes from a manufacturer's technical support engineer some years back when we were suffering a problem during icing conditions. I'm told that balanced feed yagi antennas, do not suffer from this problem.

In frosty ice prone environments, in my opinion, log periodic antennas such as the SCALA CL7-150URM series are a good choice for public safety systems. We've made the commitment not to use yagi antennas in this environment and have successfully been using the log periodic for years now without any complaints.

Comment: If falling ice is a hazard and you need an Ice Shield for the LogP, let me know and I can send along the design we used (Microflect 3’ Standoff Mount and a support assembly holding a piece of entry ice bridge).

Regards, Bob





just under

[dean83]

Thanks for the replies! We still havn't gotten around to some more testing but we will soon possibly tomorrow or tuesday.

OK, couple thoughts. And it sometimes helps to think of 'talk-in' or 'inbound' and 'talk-out' or 'outbound'; then you break your troubleshooting into subsections.

How is the outbound of the main site? Good/Bad? We'll assume (for now) that it's good, because you don't know of any complaints elsewhere in the system.

And in your picture #5, the 169.93750 TX, is that also RX on 171.36250? I'm also willing to guess that the Yagi goes to that radio;

If so, and does that radio have a front panel speaker? How does the audio from the main site sound?

The main tower is on a cell tower 25-30 km north of us. Within 20-25kms of that tower reception is clear without any issues. Mobiles are OK from that tower even in our area.

The front panel speakers appear to be disabled, no sound comes from either.

Honestly, I'd have the contractor review the system, and give you an opinion. But, any trained tech should be able to give you an analysis fairly quickly.

Yes I would only assume that the RX on the repeater is 171.36250 from the main.

We are going to have the contractor check this out again and utilizing some of this information maybe get him on the right path.

I would say the solution was driven by the bottom line. A lot of agencies just don't have the money. You do what you gotta do.

Bottom line, not sure. While we are a little tight up top in the budget side of things, I think the contractor speced' this to make the sale cost effectiveThere was no RFP or specs put out, they replied to our request with this design. A couple more grand here or there for a better antenna, higher quality cable, etc probably wouldn't have broke the deal.

Bill made mention of using LMR type cable. This may or may not be the type of coax cable your using. Before you go spending a bunch of time trying different attacks on the problem, on your next trip to the site, try to verify just which type of coax cable your using.

A real brief history on using LMR type coax for duplex operation, it has been well documented that it will cause problems over time. It seems that the junction between the foil shield and the braided shield cause intermod and noise in repeater operation. The more moisture that migrates into the under jacket region of the coax, the more this problem will show itself. Many repeater owners have fought with strange noise problems that only ended when the LMR coax was replaced with a heliax type coax cable. The more the cable flexes in the wind, the greater the problem shows itself.

As Bill has suggested, replacement of the antenna is a good start.

Jim

.

I will check to see if I can identify the cable type tomorrow.

Watch out………….

I'm not familiar with the AYA-1503 yagi model but, if it’s similar to the old Maxrad MYA-1503 series, which is an unbalanced feed:

Yagi antennas that use a single-end/unbalanced feed will nearly "reverse" their directionality when they are coated with ice or hoar frost beginning with as little as maybe 1.5mm of coating. This affect, can in the UHF band, be on the order of 20 to 30 db of loss, I don’t have stasts for VHF.

This comes from a manufacturer's technical support engineer some years back when we were suffering a problem during icing conditions. I'm told that balanced feed yagi antennas, do not suffer from this problem.

In frosty ice prone environments, in my opinion, log periodic antennas such as the SCALA CL7-150URM series are a good choice for public safety systems. We've made the commitment not to use yagi antennas in this environment and have successfully been using the log periodic for years now without any complaints.

Comment: If falling ice is a hazard and you need an Ice Shield for the LogP, let me know and I can send along the design we used (Microflect 3’ Standoff Mount and a support assembly holding a piece of entry ice bridge).

Regards, Bob

While there is frost occasionally, increased amounts when it is foggy, I could not estimate the quantity.

I will check with the tower owner to see what the maximum weight of antenna we could place on this tower, they have the full engineering design for the tower and could probably provide this.

----------------

I will post back in the next couple of days with the radio check results - it's warmer out the last couple of days and reception has been slightly better.

Thanks

[Bill_G]

Honestly, I'd have the contractor review the system, and give you an opinion. But, any trained tech should be able to give you an analysis fairly quickly.

Yes I would only assume that the RX on the repeater is 171.36250 from the main.

We are going to have the contractor check this out again and utilizing some of this information maybe get him on the right path.

I would say the solution was driven by the bottom line. A lot of agencies just don't have the money. You do what you gotta do.

Bottom line, not sure. While we are a little tight up top in the budget side of things, I think the contractor speced' this to make the sale cost effectiveThere was no RFP or specs put out, they replied to our request with this design. A couple more grand here or there for a better antenna, higher quality cable, etc probably wouldn't have broke the deal.

I will check with the tower owner to see what the maximum weight of antenna we could place on this tower, they have the full engineering design for the tower and could probably provide this.

----------------

I will post back in the next couple of days with the radio check results - it's warmer out the last couple of days and reception has been slightly better.

Good morning Dean -

This suggests the contractor has already looked at it once and given it a passing grade. Then it warms up a little and you get better reception on your portables. You said earlier the problem occurs 5-10km away give or take 3-4 miles which really isn't that far. Depending on terrain, I would have expected a solid 10 mile radius around that tower. Something isn't right. I lean towards the Tram antenna or the connectors gone bad.

They need to do the following -
VSWR check with a wattmeter
Return loss check with an Anritsu or similar
Freq check with a service monitor
Direct and effective (desense) sensitivity check with a service monitor

No offense, but this is a very low cost solution. This is something you would put in the trunk of every commander to improve fire ground comm back and forth with dispatch. It will do nothing to improve coverage on the scene. He turns it on when he arrives, everyone switches to that direct channel, and dispatch can hear what's going on. He turns it off when he terminates command, and everyone switches back to the main channel as they head back to the barn. Because you have five or twelve of these things in select vehicles, you want to keep the costs down.

But, you don't put something like this on a tower in a non-environmentally controlled enclosure as a main system extender if you can afford it. If you had a lot of mountainous valleys, and solar power with batteries were your only option, this would be the way to go. Otherwise, you want something a little more robust to give you primary coverage in poorly served areas.

[psapengineer]

FYI,

When I mentioned Balanced vs Unbalanced feed I wasn't referring to the cable. Unbalanced 50ohm line is fine.

It's the feed to the driven element that's at issue.

Google a picture of the MYA-1503, its a single feed tapping the driven element at one place, a gamma match.

You're looking for a balanced driven element of some sort like on the SY203-SF4SNM(E) or as a mentioned, the log periodic, described in the earlier e-mail.

[dean83]

Thanks again for the replies.

The silly thing is, this repeater is less than 6 months old.

I have placed a call to the company to set up a service appointment.

Is there any way to 'add' to this (besides a change in antenna), to improve it or make it more of a long term solution. Considering the factors being a small cabinet, no heat source.

Thanks,

Dean

[dean83]

Radio Checks completed today with a Motorola HT750 and a Kenwood TK-2130.

One important note here (and it may have been obvious to you already), is that when transmitting with a portable only the dispatch could hear the transmission, then on the dispatch reply to the rado check, everyone could hear the transmission.

At 5 miles to the east (very flat terrain) the reception was 4x5 with the kenwood, slightly more than the motorola.

At 5 miles to the west with moderate terrain, just before going down a moderate hill the reception was 4x5 with both.

At 6 miles to the west just after the moderate hill (enough to drop out of line of sight) there was very minimal reception with only a mic click that the repeater was activated.

At 6 miles back up on the hill but within questionable line of sight the recption was improved but still very staticy 3x3 at best.

What do we need to make this repeater so portables can talk to eachother via repeater on the local channel 158.75500? (yes i believe it removes the 'simplex' aspect of it.) Another frequency? Duplexer?

What would you expect the 'low end' cost of a GOOD repeater would be? We have it in writing that they garuntee this to work so they may be required to upgrade at a parts only cost to us.

Regardless thanks for ALL of the very technical and informative replies. I believe we have something to go on here and I will keep you informed what develops.

[dean83]

To clarify the portables when transmitting were not being relayed locally by the repeater.

[Bill_G]

Dean - what you have is not really a repeater in the classic sense that most people think of. It is an extender - it extends the main system coverage into poorly served areas. It does nothing to improve portable to portable, or mobile to mobile coverage within that extended area as a classic repeater would.

If your goal was to improve unit to unit coverage as well as extend the main system coverage, then you need a repeater with a link to the main system. At the minimum you will need a second licensed freq, a duplexer, and a repeater station.

The best way, but the most expensive way to accomplish this is with simulcasting. One channel covers as large an area as you have towers to serve them. Users never have to change channel on their radios in the footprint. The expense comes from building out the synchronized links between the towers and the processing to make it function correctly.

The next method is multicasting. You tie several towers together, but have to manually change channels as you move through the service area to reach the best tower. You can use lower cost stations, lower cost links, and lower cost processing.

[desperado]

Another option that might be considered is the spacing of the antenna's on the tower. you said that they are 10 feet apart, that is pushing it for the radiation patterns crossing and causing desense. What that means is because you are transmitting and receiving on VHF, the transmitter is getting into the receiver radio and causing it to not receive as well. A simple test for this is to have someone go out with a portable into an area that has poor coverage, then turn off the transmitter radio and listen to see if the receiver hears better without the transmitter on. You indicated that the speakers were disabled on the radios so you might need to get that dealt with first somehow. If nothing else get a speaker wired up to the radio connector where the RICK is connected, take a mike and key the transmitter radio with it and see what if it is causing the received signal to get weak.

Personal opinion is that the transmitter link should have been on UHF and not VHF but that make not have been possible.
See what happens with this test, and then if you see that is a problem, move the beam antenna further down the tower and / or have the radio people reduce the transmit power out on the link transmitter.